FINAL REPORT DATA TRANSMISSION STUDY

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80B00829A000600020001-0
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 123
• Document Creation Date: November 17, 2016
• Document Release Date: August 11, 2000
• Sequence Number: 1
• Publication Date: December 15, 1975
• Content Type: REPORT

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FINAL REPORT
DATA TRANSMISSION STUDY
25X1A
15 DECEMBER 1975
PREPARED FOR
ROME AIR DEVELOPMENT CENTER
GRIFFISS AIR FORCE BASE
ROME, NEW YORK
25X1A
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FINAL REPORT
DATA TRANSMISSION STUDY
HARRIS ELECTRONIC SYSTEMS DIVISION
15 DECEMBER 1975
PREPARED FOR
ROME AIR DEVELOPMENT CENTER
GRIFFISS AIR FORCE BASE
ROME, NEW YORK
UNDER
CONTRACT F30602-76-C-0081
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?
Paragraph
TABLE OF CONTENTS
Title
Page
1.0
INTRODUCTION ................................
2
2.0
REQUIREMENTS AND SYSTEM CONSTRAINTS .............
4
2.1
System Definitions and Assumptions .....................
4
2.2
Terminal Interaction ..............................
9
2.3
Throughput Considerations ...........................
13
3.0
TECHNICAL EVALUATION ..........................
18
3.1
Image Recording and Scanning ........................
18
3.1.1
Image Quality Factors .............................
19
3.1.2
Speed Considerations ..............................
25
3.1.3
Scan Density Selection .............................
34
3.1.4
Recording Media Considerations .......................
37
3.2
Recorder/Scanner Candidates ........................
43
3.2.1
Laser-Galvanometer Recorder/Scanner ...................
43
3.2.2
Cathode Ray Tube (CRT) Recorder/Scanner
46
3.2.3
Drum Recorder/Scanners . . ..........................
47
3.2.4
Laser Beam Recorder/Scanners ........................
50
3.2.5
Terminal Recorder/Scanner Recommendations ...............
52
3.3
Terminal Input and Output Consideration .................
53
3.3.1
Operational Concepts
53
3.3.2
Store and Forward Operation .........................
55
3.4
Terminal Intercompatibility ..........................
59
3.5
Terminal Modularity ...............................
63
3.6
Security Considerations .............................
66
3.7
Communication Interface Considerations ..................
68
3.8
Data Compression ................................
70
3.9
Data Processing Options ............................
75
4.0
TERMINAL CONFIGURATIONS .......................
82
4.1
The "D" Terminal ................................
82
4.2
" Terminal ..............................
The "D
85
4.3
5
The "C Terminal ................................
85
4.4
The "B" Terminal ................................
88
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TABLE OF CONTENTS (Continued)
Paragraph
Title
Page
5.0
PROGRAM CONSIDERATIONS ....................... 92
5.1
Technical Considerations
92
5.2
Cost and Schedule Considerations
94
Appendix Al ...................................
97
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Figure
Title
Page
2.1
Image Quality and Terminal Operating Ranges for Scan Density ..
6
2.2
General Block Diagram of Terminal ....................
9
2.3
Image Transmission Setup ..........................
11
2.4
Image Throughput Versus Link Bit Rate For Link Limited
Operation (No Overhead) ....... .. .. ..... 14
~
2.5
As A Function of Step-Coding
Throughput Versus Link Range
Reduction ................................... 16
3.1
Image Spatial Frequency and MTF .....................
20
3.2
Image Scanning Input/Output Responses .................
22
3.3
Recorder/Scanner Scan Rate Versus Scan Density ............
26
3.4
Film Transport Limitations ..........................
29
3.5
Laser-Galvanometer and CRT Performance Limitation.........
30
3.6
Drum and LBR Performance Limitations ..................
32
3.7
Scan Density Selection Options ......................
35
3.8
Application Range for Recording Data ..................
40
3.9
Recorder Laser Power Requirements ....................
42
3.10
Laser-Galvanometer Recorder/Scanner Components ..........
44
3.11
Improved Laser-Galvanometer Implementation .............
45
3.12
Acousto-Optically Controlled Down Recorder/Scanner........ 49
3.13
Terminal Automation Options ........................
54
3.14
Terminal Multidrop Arrangement ......................
60
3.15
Basic Data Processing Function Diagram .................
64
3.16
EICS and Laserfax TEMPEST Tests .....................
66
3.17
Terminal Interface Through MIL-STD-188C ...............
68
3.18
REARCS and Zoom Capability ........................
73
3.19
General Data Processing Trade-Offs ...................
77
3.20
Data Compression Processing Limitations .................
78
4.1
"D" Terminal Block Diagram ........................
83
4.2
"D" Terminal Artist's Conception .....................
83
4.3
"DRO" Terminal Block Diagram ......................
86
4.4
"C" Terminal Block Diagram ........................
86
4.5
"B" Terminal Artist's Conception ......................
87
4.6
"B" Terminal Block Diagram .........................
88
4.7
"B" Terminal for Photointerpretable Imagery Over
High-Speed Communication Links .................... 89
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Table
Title
Page
3.1
Recorder/Scanner Cost Dependent Factors . ......... . . . .
52
3.2
Level Change Statistics and Coding ................ . .
71
3.3
MOS and Bipolar Microprocessor Comparison .... . .......
76
5.1
First Unit Costs ($000) ........................
95
5.2
Unit Costs in Lots of Ten ($000) ... ............. . ..
95
5.3
Program Costs ($000) ...........................
96
Al
European AUTOVON Sites
99
A2
European AUTODIN Sites ? ...........
100
A3
European AUTOSEVOCOM AN/FTC-31 Switch Sites.......
100
A4
Transmission Facilities - Europe ...... . ..... . .. . . . . .
102
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SECTION 1.0
INTRODUCTION
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1.0 INTRODUCTION
This final report summarizes the results of a study performed for Rome Air
Development Center by HARRIS Electronic Systems Division (Harris ESD) for analysis and
definition of image terminals and configurations required to meet anticipated Department
of Defense requirements. The report is divided into four major sections and an Appendix.
Section 2.0 reviews the basic study requirements and system constraints and contains a
brief review of some system considerations for image terminal interaction and throughput.
It is shown that some form of data compression is required to achieve the desired throughput.
Section 3.0 is the major technical section in which evaluation of various technologies,
equipment, and operability conditions is performed. The specific recorder/scanner candi-
dates include laser-galvanometer, cathode ray tube, drum and laser beam types. It is
concluded that terminal configurations should be based on drum and laser-galvanometer
recorder/scanner technology, depending upon the type of imagery which is to be processed
by the terminal. Section 4.0 briefly describes the main features and performance param-
eters of four terminal types. The terminal configurations are comprised of modular compo-
nents which, beginning with the least complex version, can be upgraded by adding higher
performance recorder/scanners and more processing capability. Section 5.0 describes
advanced development projects which are recommended to be performed in conjunction
with the program and also summarizes the cost estimates for several potential network
implementation scenarios. The final section is an appendix which discusses the current
and anticipated military communications environment in Europe.
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SECTION 2.0
REQUIREMENTS AND SYSTEM CONSTRAINTS
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2.0 ' REQUIREMENTS AND SYSTEM CONSTRAINTS
2.1 System Definitions and Assumptions
The primary technical requirement of this study is to produce general speci-
fications, operational analyses and cost data for several different image terminals. The
image terminals, which are points of interface with an imagery transmission system, are
devices used for the receipt and/or transmission of electrically transmitted imagery. The
four different types of terminals evaluated are classified according to their ability to
receive and/or transmit a range of image scanning densities. The "B" terminal has the
capability of transmitting and receiving images with the highest resolution, i.e., with
scanning density of 2000 lines/inch and lower. The "C" terminal receives and transmits
imagery at scanning densities of between 800 and 1000 lines/inch and lower. The "D"
terminal receives and transmits between 300 and 500 lines/inch and lower whereas the
"E" terminal, which we will refer to hereafter as the DRO ("D" Read Only) terminal,
receives 300 to 500 lines/inch and lower imagery. For purposes of this study, it is
assumed that imagery received from, or transmitted to, terminals with a scan density
lower than 300 to 500 lines per inch will be consistent with the operating parameters
of the Tactical Digital Facsimile (TDF) equipment.
Four image quality groups have been defined so that a generalized image
quality performance characteristic can be identified and associated with an image
product.
? Low Readability (LR): A level of image quality that is suitable for
briefing aids and similar products as defined by individual users. This
quality level, chosen to be less than 3 line pairs per millimeter, is
established to provide a quality descriptor for transmitted materials
which can fulfill an operational requirement even at this relatively
low resolution. Briefing quality materials would be suitable for trans-
mission by a system which operates at less than 220 lines per inch.
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? Medium Readability (MR): An image quality range of 3-6 line pairs
per millimeter viewed at a distance of 18 inches with average lighting
and contrast (physiological limit of the average eye). An image of
quality greater than medium readability could be optically magnified
to obtain more information. An image of less than medium readability
quality, if optically magnified, would not provide additional informa-
tion. This quality is resolvable by a scanning system operating
between 220 and 430 lines per inch.
? High Readability (HR): An image quality range of 6-20 lines per milli-
meter. This quality is resolvable by a scanning system operating at
430 to 1400 lines per inch.
PI Quality: PI quality is defined as an image quality range varying
from the upper bound of the "High Readability Quality" range to the
quality of the sensing system that created the original image. Actual
transmitted qualities may vary throughout this range depending upon
format and magnification factors; however, the information content of
the sensing system shall be retained as closely as possible.
Figure 2.1 compares the terminal scan density range with the image quality
ranges defined above. A terminal of a given scan density range also includes the ability
to receive and/or transmit at lower scan densities.
Evaluation Factors
Factors used as a basis for technical evaluation of the terminal are sum,
marized below:
? Resolution: A factor which covers a broad range from about 3-30
cycles per millimeter. The principle aim of the study is to configure
the terminal to provide a capabity for transmitting all types of imagery
and graphics at the minimum acceptable quality level to assure the
most timely dissemination of the product.
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LOW READABILITY
220
1
430
I
1400
1
PHOTOINTERPRETABLE
300
1
"D" AND "DRO"
500 800
1
C
-- -- ---------~.,B"
Figure 2.1 . Image Quality and Terminal Operating Ranges for Scan Density
500 1000 1500 2000
I I I I I I 1 1 1 1 I 1 1 1 1 I 1 1 1
SCAN DENSITY (LINES/INCH)
1000 2000
o I
L I
? Shades of Grey: A Factor Expressed in Bits Per Pixel - The upper limit
for the number of grey shades discerned and reproduced by the equip-
ment is specified at 6 bits/pixel or 64 shades per pixel in all areas of
the image that are not degraded by data reduction schemes. For docu-
ment transmission only two shades of grey are considered.
? Data Compression/Reduction: The baseline approach uses the Redun-
dant Area Coding (REARC) scheme which has produced data reductions
on the order of 20:1 and greater on the Experimental Image Compres-
sion System (EICS). The REARC concept is explained in Paragraph
3.3.
I
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? Input/Output Factors: Each terminal will be capable of recording
and scanning opaque or transparent material and be able to record
positive or negative images. The maximum image format size is 9
inches by 13 inches. Terminals "B" and "C" shall have the capa-
bility to scan selective portions within this format.
? Recording Media: Both silver halide film and dry si Iver paper and
film should be considered as options.
? Automatic Operation: Automated operation of the terminal should be
considered to the maximum practicable extent without compromising
reliability or producing inordinately complex or costly implementation.
? Digital Interface and Temporary Storage: A factor which permits
digital input to the system processor and bulk storage of digitized
imagery for a store and forward mode of operation.
? Security: A factor which assures that the terminal is compatible with
existing communications security (COMSEC) equipment and meets alI
applicable TEMPEST requirements.
? Militarization: A factor to which consideration shall be given for
ruggedization of the equipment. Most terminals are assumed to be
installed in office type environments. Field deployable terminals may
be used in tactical shelters and other transportable military containers.
The cost impact of full military specification ruggedization is to be
determined.
? Intercompatibility: A factor which requires that each terminal type be
able to communicate with any other terminal. Scale and format changes
changes should be considered.
? Modularity: A factor which requires that the terminals be configured
for easy upgrading to higher capability by adding either improved or
additional modules.
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? Communications Interface: A factor requiring easy interface to a
variety of communication links including wire line, microwave, tropo-
spheric scatter and/or satellite communications.
? Data Rate: A factor which applies to the communication network and
the internal terminal data rate. The terminals, scanning, digitizing,
and recording rate should not be the limiting factor affecting trans-
mission time for data rates up to 32 kb/s, including data compression.
The "B" terminal will be configured to supply data at 1 .5 mb/s but,
in this case only, without data compression.
? Broadcast Mode: A factor which requires certain terminals to simulta-
neously transmit to more than one terminal.
? Maintenance: Terminals are to be configured for easy maintainability
by field service personnel.
? Data Processing: Several data processing techniques will be examined
and, if appropriate, the hardware will be selected from a list of stan-
dard DOD processors.
Although the factors listed above are adequate to perform a top level evalu-
ation of the terminal performance, a detailed in-depth evaluation required information
on communication loading and time-critical demands which were not available during
the course of the study effort. Consequently, the conclusions reached and the resulting
recommendations are based on certain assumptions, most of which are taken as worst-
case situations. The effect of these assumptions may be to place more severe constraints
on the hardware than is actually required. For example, it has been assumed that the
average data rate which must be sustained by al I terminals is equivalent to operating
over a 32 kb/s link with data compression factors up to 20X. This produces an average
data rate of 640 kb/s with instantaneous rates several times higher, thereby placing
greater demands on the processing and recording equipment than may be actually
required. The price for greater capability is usually higher cost. Detailed examination
of alI system aspects will be required to determine if the conclusions reached in this
study are consistent with anticipated terminal usage.
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2.2 Terminal Interaction
The image terminals which are evaluated in this report are configured on
the basis of certain assumptions regarding the method which may be used to initiate,
maintain, and modify transmission of the image. The terminal is assumed to be connected
to a fixed rate communication link; the bit rate over the link being determined by a
local oscillator located at the transmission site. A block diagram of the general termi-
nal components is shown in Figure 2.2. The general steps for transmitting one scan line
of data to a recorder are identified below.
I OPERATOR 1/0 DIGITAL
DEVICE STORAGE
I RECORDER
I AND/OR
CONTROL
PROCESSOR
`TERMINAL J COMMUNICATION LINK
Figure 2.2. General Block Diagram of Terminal
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? The terminal data processor commands the scanner to scan a line,
encodes the data in an output buffer from which data is clocked at
link bit rate to the COMSEC equipment.
? The COMSEC equipment encrypts the encoded data and passes the
encrypted data to the modem if the transmission is to be made over an
analog link.
? The modem converts the digital data into a form which is suitable for
transmission over the analog link. For a digital link, the encrypted
data is connected directly to the link.
? The encrypted data is transmitted over the link and reconverted to its
original encrypted digital form, if required, at the receiver.
? The digital data is transmitted through the COMSEC equipment which
converts it to the form of the original encoded data.
? The data is decoded and placed into an output buffer one line at a
time by the data processor in the receiving terminal.
? The image recorder is commanded to step one line when the output
buffer is full.
? The output buffer is emptied by transferring its contents to the image
recorder which exposes one line of imagery.
Transmission is started by synchronizing the COMSEC equipment. When the
transmitter is manually commanded to transmit, four setup words, such as shown in Figure
2.3, are transmitted at 512 bit intervals. The receiver detects the sync code and compares
adjacent words until two are found that are identical. This multiple setup word trans-
mission is used to reduce the probability of either missing the start of picture or obtaining
the wrong setup data when burst errors are encountered. The setup information includes
the scan density at which the data is to be transmitted, areas of the picture which are to
be step coded, the number of bits into which the density function is quantized, and a
flag bit identifying that the coding has been bypassed for this transmission. The data
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processor in the receiver uses this information to select which recorder type (if more
than one option is available) is to be used and to select the line and pixel deletion or
repetition ratio. The receiving terminal would normally produce images with the same
scale factor as on the original. The receiving terminal alters the recording resolution
to maintain the same scale factor; manual intervention is required to effect a scale change.
Redundant
SYNC
Transmitter
area select
Quantized
REARCS Coding Bypassed
32 bits
2 bits
117 bits
1 bit
1 bit
Transmitter Setup Data Frame
? Transmitted 4 times at intervals of 512 bits
? Two adjacent frames must be received which compare at receiver
for acceptance
? Elements are:
Sync a fixed Barker word sync to allow
detection of start of message by receiver.
Transmitter Identifies transmitting terminal scan density.
Redundant Area Identifies in unitary code by 1-inch square areas
Select the redundant area.
Quantized Identifies the level of quantization of the
Coding Bypass Identifies the following message as being
REARCS coded or not.
Figure 2.3. Image Transmission Setup
On completion of transmission of the last setup word, the transmitter sends
three consecutive 30-bit sync words which identify the state of data. The 30-bit sync
word is transmitted once more with no intervening interval to identify start of the first
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data block. If the data of this first line contains both step and Huffman coded data,
the 30-bit sync word is inverted and repeated once again. The data is broken every
256 samples for the insertion of 11-bit step coding parity check word or a 13-bit parity
word for Huffman coding. End of line code is not provided. For the situation where the
scanner or data processor cannot provide data at a rate which is fast enough to fill the
link, fill bits are inserted until the next line is ready. Each line has the 30-bit sync
pattern repeated once for lines which contain single codes or twice, with inversion of
the second repetition, for lines which have mixed codes. The first line of each 1-inch
block of copy is preceded by two consecutive transmissions of the complement of the
30-bit sync pattern. The end of picture is signalled by a repetition of three consecutive
30'-bit sync patterns. After a delay of 512 bits, the end of picture message is repeated.
The receiver accepts the decrypted data and identifies the start-of-picture
code. The data which follows is decoded and checked for parity error. Upon completion
of the decoding operation, the line of data is transferred from the output buffer to the
recorder. At the same time, a second buffer is being filled as the data from the new line
is decoded. When the first buffer is empty, the recorder is commanded to step to the next
line and is then ready to record data from the second buffer. Pixel deletion, repetition
and line deletion is handled by the data processor before data is stored in the output
buffer. Line repetition is implemented by reading the buffer several times before switch-
ing to the next buffer.
Manual inputs are required to define scan resolution, tolerance for step
code, bypass condition, redundant areas and quantization. Scale change is achieved
by manual intervention of both transmitter and receiver operating personnel. Manual
override at the receiver may be used to cause the recorder to produce an image with a
two, four or eight times expansion of scale as indicated below:
Source Terminal Receiving Terminal Scale Change
Any it 2, 4, 8
Any 1, 2, 4
Any 1, 2
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Thus, the "B" terminal may obtain an 8X magnification of a subelement of the frame by
transmitting at say 1600 and recording at say 200 Ipi.
2.3 Throughput Considerations
The number of bits required to represent a scanned and digitized picture,
with no coding overhead or data reduction, is given by:
N = HWQSHSW
where N is the total number of bits
H is the image height
W is the image width
Q is the quantization level
SH is scan density in the image height direction
SW is the pixel density in the image width direction
For this discussion, SH and SW are assumed to be equal and will be referred to as S.
Consequently, the expression for bit capacity is
N = HWQS2
The number of images which can be transmitted per unit time is referred
to as the system throughput. Expressed in terms of images per hour, the throughput is given by:
3600 L
3600 L
T
=
N
HWQS2
where L is link bit rate in bits per second.
The S2 factor nonlinearly limits throughput. Doubling the sample density
doubles the resolution of the reconstructed picture, but reduces the number of pictures
which may be transmitted per unit time by a factor of four.
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The throughput rate (in pictures per hour) for various link bit rates,
quantizations, and image sizes are shown in Figure 2.4. Note that only 0.45 - 9 inches
x 9 inches images per hour can be transmitted over a 9.6 kb/s link when sampled at 400
lines and samples per inch and quantized to 6 bits. This corresponds to the case
DESIRED
MINIMUM
THROUGHPUT
RANGE
0.1
1K 2K 5K 10K 20K 50K 100K 200K 500K 1M
LINK BIT RATE (BITS/SEC)
Figure 2.4. Image Throughput Versus Link Bit Rate
For Link Limited Operation (No Overhead)
where two medium readability images are transmitted over conditioned telephone lines.
A minimum of 2 hours and 13 minutes would be required to transmit a single image. Using
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only Huffman DPCM coding on this image increases the average throughput to 1 .1
images per hour while a typical (10:1 compression) application of REARCS increases it
further to 4.5 images per hour.
It should be remembered that the amount of data compression which can be
achieved with any type of compression technique is not a constant but depends on many
factors. The actual amount of data compression is a function of:
? image size
? the size of the redundant area
? the quantization levels in the redundant and nonredundant areas
? the line and pixel deletion ratio in the redundant area
? the tolerance assignments in the step-coded region
? spatial and temporal scanning spot intensity distribution
? the density distribution in the image
The effect of these factors is'to cause the amount of data reduction to
appear as a random variable. The amount of data reduction using a REARCS approach
varies from 0.55 to 282 with a mean value of 10 to 12 for most grey shade imagery. The
amount of data reduction using only a Huffman encoded DPCM approach varies from
0.46 to 6 with a mean value of about 3. These estimates do not, however, include the
normal system overhead bits but refer only to data associated with the image. Figure
2.5 shows the range over which image throughput may be affected by different step-coding
reduction ratios. The image is assumed to be a 9 inch x 13 inch image scanned at
400 Ipi and quantized to 6 bits per sample.
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9" X 13" IMAGE
400 LPI SCAN DENSITY
400 SAMPLES/INCH SAMPLING DENSITY
6-BIT QUANTIZATION
1 K 2K 5K 10K 20K 50K 100K 200K 500K 1M
LINK BIT RATE (BITS/SEC)
0.1
Figure 2.5. Throughput Versus Link Range As A
Function of Step-Coding Reduction
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SECTION 3.0
TECHNICAL EVALUATION
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3.0 TECHNICAL EVALUATION
In this section, the technical requirements are evaluated in terms of current and
projected technology. In all cases, the emphasis has been placed on technology which
has been either proven in field service or which could be well developed and reliable by
the FY80 time frame. The frame of reference for evaluation is comprised of the system
definitions and assumptions summarized in Paragraph 2.1 above.
The primary emphasis in this section is the evaluation of technology and techni-
cal approaches which will meet the image scanning, transmission and recording require-
ments for the Theatre Dissemination System. Specifically, several image recording/
scanning techniques and associated input/output media are addressed in terms of their
applicability and cost-effectiveness. The role of the data processing function is discussed
along with the effect of processing speed on the selection of specific implementation
approaches. Although the primary discussion focuses on the image producing hardware,
it is also of use to evaluate the terminal technology in terms of key operability and func-
tional parameters such as intercompatibility and modularity. The evaluation of technical
factors leads to a general list of top-level terminal specifications which are discussed in
Section 4.0.
3.1 Image Recording and Scanning
This section reviews some of the basic concepts associated with image trans-
mission and examines the factors which limit the full exploitation of current image pro-
ducing technology. A complete examination of component technology associated with
image recording and scanning is beyond the scope of this study. Rather, the examination
is confined to technology or devices which in some way restricts or bounds the perfor-
mance of various recording and scanning equipment designs.
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3.1.1 Image Quality Factors
Many factors must be considered for a thorough evaluation of image quality and
a total discussion of this topic is clearly beyond the scope of this study. It is instructive,
however, to examine a few of the key image quality factors and terms and to relate these
to the somewhat arbitrary image quality ranges defined in Paragraph 2.1. The four major
characteristics of grey scale photographic imagery which enter into a description of
image quality are: 1) average density, 2) geometric fidelity, 3) resolution, and
4) contrast.
The first two factors are easily quantified in objective terms and will not be
discussed in detail here. Average density refers to the average brightness of the image
and is controlled by adjusting the overall exposure level and by selecting proper record-
ing media which will support the average and extreme values of exposure. It has been
shown that the eye has a limited range of average density which it perceives as an
appealing scene. Geometric fidelity refers to the absolute and relative location of any
point in the image. An image with high geometric fidelity corresponds very closely with
the geometry of the original object. For scanning systems, high scan density usually
correlates with high geometric fidelity. The recording and scanning factors which
primarily determine the degree of geometric fidelity are scale factor and two-
dimensional scanning linearity.
Resolution and contrast are considered together because they are interdepen-
dent; i.e., visual resolution is dependent upon the contrast. This relationship is
expressed in terms of the Modulation (contrast) Transfer Function (MTF) which is defined
as the contrast in the image produced by a sinusoidal intensity distribution in the object
plan. This number is a function of the spatial frequency, i.e., the number of cycles per
unit length of the sinusoidal object. Figure 3.1 shows a graphical representation of the
input object target and the image. The graphical representation of a typical MTF curve
is shown in Figure 3. 1 (c).
It should be noted that MTF is only strictly defined for sinusoidal objects and
linear systems. Frequently this restriction is violated which then requires careful
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'MAX (V) - 'MIN (V)
'MAX(V) - 'MIN (V)
O L ~- V 0 L
0 0
(c) MTF DIAGRAM
Figure 3. 1. Image Spatial Frequency and MTF
interpretation of "MTF" response. Despite this limitation, the concept of MTF can be
quite useful. The sinusoidal limitation is really not a limitation at all, since any object
can be represented as a linear combination of sinusoidal signals by Fourier composition.
Much additional information can be gained if the curve is examined in its entirety.
Consider, for example, the two curves plotted in Figure 3. 1 (d). Although curve A
represents a system with higher resolution than system B, the image from system B would
appear "sharper" and, therefore, better to most observers. This is because the eye
responds primarily to spatial frequencies in the lower range where the MTF is greater in
system B.
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In scanning systems where the recording material is usually nonlinear, a system
MTF is not rigorously defined; however, it is possible to specify the resulting modulation
on the output as a function of spatial frequency, even though this number is not linearly
related to the input function. Consequently, general classification ranges such as the
readability criteria used in this study may be useful guides which can be used to correlate
with measured performance values.
There is usually some confusion about the relationship between MTF, line scan
density, spot size, etc. This can be made clear by understanding how scan line density
and spot size affect the MTF curve. In general, the MTF of a scanning system is depen-
dent upon the scan direction: the along-scan and across-scan MTF are, in general, only
loosely coupled. For the along-scan direction, spot size and modulation bandwidth are
the major factors which affect MTF. It can be shown that the MTF in this direction is
given by the Fourier transform of the spot intensity distribution multiplied by the modu-
lation bandwidth (spatial frequency bandwidth) of the spot. For a given scanning system,
this MTF curve can be calculated exactly. In the specific case of a Gaussian spot inten-
sity profile, the Fourier transform of the spot is also Gaussian and this, multiplied by the
modulation bandwidth, is the system MTF. The along-scan MTF is therefore given by:
MTFA/S = B(f) exp [_(7Tvd0/2v(1o3)]2
[_v2ci02/1.23 B(Vv) exp (10-6)]
where
u = spatial frequency in cycles/mm
do = spot diameter in micrometers
B(f) = system electrical response in Hz
V = scanning spot velocity in mm/s
f = electrical frequency in Hz
In the cross scan direction the situation is more complex. The complexity
arises from the fact that the "resolution" depends upon the relative alignment of the
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object with respect to the scanned line. In Figure 3.2 (a) we show a square-wave object
signal which is oriented as shown and is to be scanned with a spot which we assume has a
CROSS-TRACK DIRECTION
UlLI9.'YO~i1~" YIl
CASE 1 1/2
na A
1
CASE II
1/2
AVERAGE
r -VALUE
DC
AVERAGE
_VALUE
OUTPUT FOR LOW
CYPfl IIRF V41 I IF
OUTPUT FOR HIGH
EXPOSURE LEVEL
1
CASE III 1/2 -- COMPROMISE
EXPOSURE LEVEL
0
Figure 3.2. Image Scanning Input/Output Responses
Gaussian intensity profile in the cross-track direction. In Case I, the scan lines exactly
coincide with the square-wave object period, thus, resulting in a strong cross modulation
signal. In Case II, the same situation occurs except that the location of the scanning
center line is shifted by one-quarter of the object period. Each spot intercepts the same
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average area of the square wave object resulting in no net modulation in the cross-track
direction. In between these two extremes are a continuous range of solutions, all of
which might be contained in any one image transmission. It is this dependence of the
resolution on phase of the scan structure that causes the familiar banding or moire effect
common to line scan imaging systems.
There is, however, a commonly used technique which eliminates this effect at
the expense of resolution. In the previous example, one should recognize that the max-
imum resolution (in cycles/mm) is equal to one-half the scan density (in lines/mm). If
as in Case I of Figure 3.2 (a) the spot size is increased so that the modulation is zero,
then the modulation will always be zero at that frequency, thus, eliminating the problem.
Of course, there is some residual effect for lower spatial frequencies, but once the scan
line density is about four times the spatial frequency of interest, the phase dependence
has been averaged out. The penalty for this is reduced resolution. The ratio of the
actual resolution to the maximum resolution (1/2 scan line density) is historically known
as the Kell factor. For Gaussian spot intensities the optimum Kell factor has been cal-
culated to be 1/Jor 0.707. In practice the value ranges from about 0.65 to 0.75.
The cross-scan MTF for Gaussian profile scanning systems is similar in form to
the expression previously given for along-scan MTF. It is given by:
v pK/21 (103)] 2~
MTFC/S = exp [17 J
= exp C-(vpK)2/1.23 (10-6 )1
where
p = scan line density in mm and
K = Kell factor
and is valid only for Kell factors which are less than 0.75. One should note that larger
spots also reduce the MTF in the along-scan direction. In some cases the spot is pur-
posely elongated to form an elliptical scanning spot but this generally leads to perfor-
mance in which horizontal and vertical resolutions are unequal.
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Up to this point, only linear systems have been considered, however, most
recording materials exhibit nonlinear behavior. While rigorous analyses of these effects
are possible, it is perhaps more instructive to look at what happens to a linear MTF when
it undergoes a nonlinear transformation. Film nonlinearities cannot increase the system
MTF: at best they leave it unchanged. This can be illustrated by considering what
happens to the modulation at different exposure levels as depicted in Figure 3.2 (b). For
low exposure (Case I), the exposure of the peak regions have been sacrificed to obtain
better definition in the low signal area. For a high exposure level (Case II) the opposite
effect occurs. In between these two examples is an exposure which is a compromise such
as shown in Case Ill. In many cases a means for purposely distorting or linearizing expo-
sure values is implemented to produce image enhancement.
Producing uniform grey fields may cause a different set of problems. As
previously explained, the Kell factor tends to smooth scan structure in the output image
which, assuming no other errors, would tend to produce a uniform grey field for unmodu-
lated input signals. For imaging from a digital source one has another potential source of
error called quantization noise. If the recording material has a useful dynamic range of
30 grey shades and 5 bit (32 steps) encoding is chosen, a nearly uniform grey area may
show structure due to the uncertainty in the least significant bit. This effect, called
false contouring, is common to all digital systems, but it is particularly distracting in
imagery work because of the human eye's ability to discriminate between two adjacent
areas of slightly different density. False contouring is minimized by using the maximum
grey shade capability of the system - in this study we assume that 6-bit quantization is
used, thereby minimizing the effects.
We have up to now been concerned primarily with the equipment used to
produce the image. In addition to many of the controlled nonlinear equipment effects,
the recording and scanned media also produces nonlinear effects. Careful attention must
be placed on the effects of dynamic range, substrate type, image tone and granularity.
The dynamic range is the maximum to minimum range of densities that can be supported
by the material. For most imagery work, the greater the dynamic range, the better.
Substrate type is important in high quality imagery applications because it is not
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uncommon for the substrate (film base or paper) to be of poorer surface quality than the
actual photosensitive emulsion. This is particularly true for paper base materials where
the fiber structure of the paper degrades the imagery. Image tone refers to the subjec-
tive "color" of the black areas on the material. Some are indeed black, while others
may be brown or dark blue. The subjective image quality depends somewhat on this tone,
with black being generally preferred. The last parameter, granularity, refers to the
actual grain structure of photographic emulsions. Similar in effect to paper fiber struc-
ture, these grains may degrade the image but this is usually apparent only under high
magnification.
In summary, many factors must be considered when analyzing and predicting
performance of image transmission equipment. The MTF concept is the most commonly
used measure of system "resolution" but for detailed evaluation, the effects of nonlinear
factors must be assessed. Concepts such as we have discussed in this section must be used
to accurately define and specify equipment and materials in detailed design exercises.
To avoid a complicated specification of image quality, it is common to group classes of
imagery into categories which bear some general relationship to the degree of image legi-
bility or "readability." In Paragraph 2.1 we defined four readability groups which will
be used only to aid us in our analyses of various terminal configurations.
3.1.2 Speed Considerations
The evaluation of image recording and scanning techniques requires an
understanding of the speed limitations which are imposed by the selection of specific
devices or subassemblies. The specification which determines the instantaneous operating
speed of the recorder/scanner is that the terminal scanning, digitizing and recording rate
not be limited by equipment considerations when operating over a 32 kb/s link with data
reduction. It is also desirable to configure the terminal such that PI quality information
can be transmitted over 1.5 Mb/s links without data compression.
The primary factor which limits the operating speed of most image recorder/
scanners is mechanical inertia. This is particularly true for asynchronous recorder/
scanners which operate by on-demand signaling for data recording and line advance. In
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the most general case, such equipments operate with a triggered asynchronous line
sweeping mechanism, e.g., CRT sweep or galvanometer, and an asynchronous Iine
advance mechanism such as a stepped film transport. Obviously, a variety of methods
could be used to overcome these limitations but they generally involve either more data
buffering capacity or more costly and complex mechanisms to compensate for the mecha-
nism shortcomings.
The operating speed of recording and scanning technology cannot be
evaluated without also considering the scanning density of the image to be transmitted.
Figure 3.3 displays operating speed on the ordinate axis in terms of scan lines per second
IMAGE SIZE - 9" X 9"
QUANTIZATION -6 BITS/SAMPLE
DUTY CYCLE - 80%
CURVE A - 32 kB/SEC (20:1 COMPRESSION)
CURVE B - 1.5 MB/SEC (NO COMPRESSION)
CURVE C - 1.5 MB/SEC (5.5:1 COMPRESSION)
200 500 1000 2000 5000
SCAN DENSITY (LINES PER INCH)
Figure 3.3. Recorder/Scanner Scan Rate Versus Scan Density
and scan density on the abscissa in pixels per inch. A "standard frame" measuring 9
inches by 9 inches and containing 64 grey shades per pixel has been used. In order
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to arrive at some value for limitations to be placed on the scanning and transport
mechanisms, a somewhat arbitrary 80 percent duty cycle has been assigned to the
recording/scanning process. This factor is included to account for all types of processing
inefficiencies including scanner flyback time (duty cycle effects), line and frame
synchronization, and all other types of overhead. The diagonal lines on the graph
represent the three data rates which we used to evaluate equipment performance limita-
tions. The equation used to plot the diagonal lines in Figure 3.3 is:
LC LC lines
R = (0.8)(6)(9) S - 0.023 S s
where
R is the scan rate in lines/s
S is the scan density in lines/inch
C is the data compression factor and
L is the data rate in b/s
Three link parameters are shown on the figure which is of interest in this
study. The lower line is the one of primary interest and represents a link operating at a
data rate of 32 kb/s with an average of 20:1 data compression on the image. (Note that
lower data compression values such as 10 or 12 to one would produce a line even lower on
the graph.) The middle line represents a data link operating at 1.5 Mb/s without data
compression. The top line is the some 1.5 Mb/s wideband link but operating with a
5.5:1 data compression factor.
It is instructive to overlay various image recording/scanning mechanisms on
this chart to determine if the technology can support the link requirements. Specifically,
we consider the limitations imposed by film transport mechanisms, galvanometer scanning
mirrors, drum and carriage recorders and finally the high performance recorders generally
referred to as "laser beam recorders" (LBR). The limits chosen for each technology should
not be considered as absolute values but rather as an attempt to set some practical limits
on the technology. In most cases, the limits which were set can be exceeded by either
more sophisticated design approaches or by adding complexity (and cost) to the data
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processing function. Consequently, the boundaries established should be considered
"soft" rather than "hard" and used as a guideline for pointing toward technology which
is most appropriate for the terminal requirements.
The first technology which is of interest is that associated with the move-
ment of the recording medium by means of a transport mechanism. The two primary con-
siderations are the precision and the step-and-settle time associated with the asynchronous
advance mechanism. It is assumed that a transport of this type would be used with a
cathode-ray tube, laser-galvanometer or high speed multifaceted mirror laser beam
recorder. Experience indicates that 9-inch wide film can be moved reliably and
repeatably by pulsed stepping motors and appropriate gear mechanisms at rates between
100 and 200 lines per second or between 5 and 10 milliseconds forstepping and settling.
The precision with which film can be stepped, assuming the use of a capstan prime mover
and recording on the capstan, is compatible with a scan density of about 2000 lines per
inch. This implies a placement accuracy which is some fraction of the 0.5 mil line separa-
tion distance. Figure 3.4 shows the two limits imposed by stepped mode Film transport
technology. As discussed in Paragraph 3.1.3, scan densities between 400 and 2000 lines
per inch for the three terminal configurations are of primary concern. Between these
bounds, current film transport technology will support the primary link requirements of
32 kb/s with 20:1 data compression and 1.5 Mb/s without data compression. At higher
system data rates (such as the upper curve of Figure 3.4), the film transport technology is
able to support the link rate only at scan densities of between 1000 and 2000 lines/inch.
But even in this region, the technology is being pushed to near practical limits. To avoid
operation near the edge of this technology requires a detailed trade-off analysis of the
cost of extra buffering, synchronous film motion or alternative optical scanning techniques
which is beyond both the requirements and scope of this study.
Figure 3.5 shows the limitations of current recording and scanning tech-
nology which uses a laser as the light source in conjunction with a scanning mirror driven
by a moving coil galvanometer. This technology has been recently developed for
military applications in the Tactical Digital Facsimile (TDF) and for commercial applica-
tions such as the Harris Laserfax and Associated Press Laserphoto equipment. This
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IMAGE SIZE - 9" X 9"
QUANTIZATION - 6 BITS/SAMPLE
DUTY CYCLE - 80%
CURVE A - 32 kR/SEC (20:1 COMPRESSION)
CURVE B - 1.5 MB/SEC (NO COMPRESSION)
CURVE C - 1.5 MB/SEC (5.5:1 COMPRESSION)
100 200 500 1000 2000 5000
SCAN DENSITY (LINES PER INCHI
A
FILM TRANSP
ORT
Figure 3.4. Film Transport Limitations
equipment commonly operates with 3M dry silver paper and film which is discussed in
Paragraph 3. 1.4. Experience with this type of equipment indicates that performance is
limited in both dimensions by galvanometer constraints. To some extent speed limit and
scan density limit are interdependent. The upper bound on galvanometer speed is set at
about 50 scan lines per second for mirror sizes which are large enough to support medium
readability imagery. The value of 50 scans per second assumes that a unidirectional scan
is used and that about two mil I iseconds are used forretrace and settling. An approach
using bidirectional scanning could improve the scan rate by a factor of two, but such an
approach complicates the data buffering and adds timing complexity by requiring line-
to-line phasing synchronization signals. The primary limitation on precision appears to
be along-scan and cross-scan jitter of the galvanometer scanner. This limitation is set
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IMAGE SIZE - 9" X 9"
QUANTIZATION - 6 BITS/SAMPLE
DUTY CYCLE - 80%
CURVE A - 32 kB/SEC (20:1 COMPRESSION)
CURVE B - 1.5 MB/SEC (NO COMPRESSION)
CURVE C - 1.5 MB/SEC (5.5:1 COMPRESSION)
200 500 1000 2000 5000
SCAN DENSITY (LINES PER INCH)
Figure 3.5. Laser-Galvanometer and CRT Performance Limitation
at about 500 scan lines per inch with selected galvanometers. The result of these two
limitations relegates the basic laser-galvanometer approach to a region containing
medium readability imagery. In low readability applications (say at 200 Ipi), the speed
limitation of the galvanometer scanner precludes filling a 32 kb/s link at 20:1 data
compression.
Although the inherent limitations of the galvanometer restrict its current
usage to medium readability imagery, evidence indicates that the scan density limitation
can be at least doubled by using supplementary optics to compensate for mechanical
uncertainties. In the along-scan direction, a precision ruling to clock data out from the
buffer on the basis of laser beam position could be used rather than galvo signal. In the
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cross direction, minor cross track corrections could be made using standard acousto-
optical beam deflectors. Obviously, such an approach adds complexity and cost to a
basically low cost device but it should be considered for future laser-galvanometer
investigation and extends operation into the HR region. At 400 lines per inch, the
scanning speed required is well within the physical limitation of the galvanometer so that
a 32 kb/s link can be filled at 20:1 compression.
The cathode-ray tube has been used as a standard image recording device
for many years and will continue to provide adequate performance in limited areas for the
foreseeable future. However, it appears that during the next 5 years, CRT technology
will give way to laser scanning techniques. In terms of resolution, the CRT is limited to
the medium and high readability groups. Although scan density on the CRT faceplate can
be increased by image demagnifications, this method is generally limited by the finite
time-bandwidth product of the CRT. Although new phosphor deposition techniques may
improve CRT image quality, only marginal gains may be anticipated. Experience with
several CRT image recorders indicates an upper limit for reliable trouble-free operation
of somewhat in excess of 5000 pixels across the tube face which, for a 9 inch image,
corresponds to about 600 pixels per inch. This places the CRT resolution limit at the low
end of the high readability group. The speed limitation for CRT recorders is a somewhat
complicated function which is dependent upon the recording medium, the brightness of the
CRT trace and the optical speed of the imaging optics. The actual sweep speed of the
CRT trace, typically measured in microseconds per line, for exceeds the inherent scanning
limitations of a laser-galvanometer approach for identical scan density. Figure 3.5 shows
the limitation for CRT performance.
A drum recorder/scanner approach is significantly different from the tech-
nology discussed previously. In place of moving film, a fixed recording frame attached
to a rotating drum is exposed by physically moving a light source carriage along the
length of the drum. Although a drum recorder/scanner generally offers some definite
cost/performance advantages,.it may require a compromise in operational flexibility.
Some methods for overcoming these constraints are indicated in Paragraph 3.2.3. Figure
3.6 shows the speed and resolution limitation for standard drum recorder/scanner
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IMAGE SIZE - 9" X 9"
QUANTIZATION - 6 BITS/SAMPLE
DUTY CYCLE - 80%
CURVE A - 32 kB/SEC (20:1 COMPRESSION)
CURVE B - 1.5 MB/SEC (NO COMPRESSION)
CURVE C - 1.5 MB/SEC (5.5:1 COMPRESSION)
200 500 1000 2000
SCAN DENSITY (LINES PER INCH)
Figure 3.6. Drum and LBR Performance Limitations
implementation. The resolution limit for a drum recorder/scanner is determined primarily
by the precision with which the mechanical components (e.g., lead screws, drum surface,
bearings) are fabricated and assembled. Resolution well up into the photointerpretable
region and approaching 10,000 scan lines are possible using the best technology avail-
able. For purposes of this study, it is clear that achieving 2000 scan line per inch
resolution is easily realizable for drum recorder/scanner technology. The speed limita-
tion for drum recorder/scanner technology is determined by two factors: the speed with
which the recording carriage can be stepped to the next line and the rotation rate of
the drum. The centrifugal force on the film is a function of the square of the drum
rotation rate which, at high speed, may require unusual techniques to keep the film on
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the drum surface. Although means are available for circumventing these problems, an
upper limit for drum rotation rate at6,000 r/min for a 9 inch circumference will be set,
which corresponds to 100 scan lines per second. Step and settle times associated with the
carriage are put at between 5 and 10 milliseconds which results in a total scan rate limi-
tation of typically 50 scan lines per second. These values are plotted in Figure 3.6 and
show that both the 32 kb/s and 1.5 Mb/s links can be filled using drum recorder techno-
logy. The most severe speed constraint would occur for a medium readability drum
recorder/scanner operating at 400 scan lines per inch. A lower rotation and stepping
rate is required for PI quality (2000 scan lines per inch) operating over a 1.5 Mb/s link
without compression than is required for MR imagery.
The high performance recording devices commonly referred to as laser beam
recorders generally consist of a laser, high-speed multi-faceted mirror spinner beam
deflector, focussing optics and a means for moving the recording medium. Two different
approaches are commonly used to implement the laser beam recorder: one which uses a
complex lens to produce 20,000 or more well resolved spots on a flat field platen
(capstan) and other which uses less complex optical componentry and records on a curved
platen. Resolution of these recorders is determined by optical and mechanical compo-
nents which can be readily configured to achieve 2000 scan line/inch PI quality and
greater. The speed of the multifaceted mirror spinner is determined by the precision of
the assembly. Speeds of 10,000 scan lines per second have been achieved in both ground
and airborne recorders. The speed limitation of these recorders, assuming asynchronous
operation,. is determined by the film transport mechanism.
'The speed and resolution limitations of the laser beam recorder are plotted
in Figure 3.6. This technology, which is expensive, clearly meets all of the link
requirements including the desire to support a 1.5 Mb/s link with 5.5:1 data reduction.
Laser beam recording technology is the most suitable technology only for applications
which require both high performance and high speed and where cost considerations are
less important than quality and image throughput.
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3.1.3 Scan Density Selection
In this section we examine several ways in which the scan density (lines per
inch) may be selected to meet the terminal readability and compatibility requirements.
The scan density ranges for readability groups and terminal configurations are:
Low Readability
Medium Readability
High Readability
Photo Interpretable
"B" Terminal
"C" Terminal
"D" Terminal
Less than 220 scan Iines per inch
220 to 430 scan Iines per inch
430 to 1400 scan lines per inch
More than 1400 scan lines per inch
2000 scan lines per inch and lower
800-1000 scan lines per inch and lower
300-500 scan lines per inch and lower
In addition, an unstated requirement exists to be compatible with TDF
equipment which operates at scanning densities of 100, 150, and 200 lines per inch;
thereby satisfying the requirement for handling low readability imagery.
The criteria used for selection of appropriate scan densities are highlighted
below:
0 Operate at a scan density of at least 2000 1 ines per inch when record-
ing or scanning PI quality imagery.
0 Select scan densities for the terminal equipment which are related by
factors of two. This approach facilitates compatibility between ter-
minals. By selecting the scan densities as integral multiples of the
next lowest scan density, the functions required of the data processing
module for magnification or demagnification are simplified. An image
scanned at a low scan density can be reproduced on a higher scan
density reproducer by repeating each sample the correct number of
times and repeating the resulting line the same numberof times. This
maintains a unity scale factor between the original and the reproduction.
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? Minimize the number of different scan densities required to meet the
terminal readability requirements. A single scan density for each
readability requirements. A single scan density for each readability
range will be considered to be adequate.
Figure 3.7 shows the scan density selections for two of the most likely
options. The first option is derived by using the highest scan density requirement
8
SCAN DENSITY (LPI)
500 1000 1500 2000
000 TDF EQUIPMENT
"D" TERMINAL
"C" TERMINAL
MF1 HR PI
Figure 3.7. Scan Density Selection Options
(2000 Ipi) and successively decreasing the value by two, thereby producing scan densities
of 1000, 500, and 250 Ipi. (Note that 1000 and 500 Ipi fall within bounds set for the
"C" and "D" terminal, respectively,.) Incompatibility arises at the lower end of the
readability spectrum because this selection is not consistent with any of the TDF scan
densities.
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The second option begins by selecting the highest TDF scan density
(200 Ipi) and successively increasing this by a factor of two; thereby producing 400, 800,
and 1600 Ipi scan densities which fall within the bounds set by the "D4," "C, " and "B"
terminals, respectively. To these scan densities we must add the capability to effect
transmission at 2000 Ipi. The effect is to make reception of 2000 Ipi imagery with unity
scale factor on equipment which operates at a basic scan density of either 800 or 1600 Ipi
a difficult task which places unrealistically severe requirements on the data processing
equipment. It is believed that the requirement for operating at 2000 lpi should be con-
strained to situations where communication is between "B" terminals only. When PI
quality imagery is to be transmitted to either C or D terminals, it can be scanned at
1600 Ipi over the 32 kb/s link. We believe the option which operates at 200, 400, 800,
1600 and 2000 Ipi is the best choice and meets all current readability requirements.
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3.1.4 Recording, Media Considerations
The two candidate recording materials which are currently being used for
image recording and will continue to be used in the FY 1980 time frame include con-
ventional wet processed silver halide film and 3M dry silver film and paper. Wet and
dry processed recording materials are commercially available in a wide variety of
characteristics to meet the requirements of many applications. The leading domestic
manufacturer of wet processed recording material, Eastman Kodak, supplies silver halide
material on both a transparent film base and an opaque paper base. The 3M Company,
the leading supplier of heat-processed recording media, similarly supplies sensitized film
and paper.
At the present time, silver halide wet processed transparent film holds an
unrivaled position in applications where the ultimate in imagery quality is desired. By
proper control of the recording and developing processes, exceptionally high resolution,
uniform response and long tonal range can be achieved. It is readily available in a
variety of formulations which cover a broad spectrum of performance characteristics. For
the terminals under evaluation silver halide film is not the limiting performance factor.
The price one pays for high quality is the inconvenience of handling and replenishing wet
chemicals and the costs for maintaining operational processing equipment.
Heat processed dry silver film is in the early stages of the development
cycle. Of the six commercially available films, two are specifically designed for image
recording: type 7859 for P-31 CRT exposure and type 7869 sensitized for peak response
corresponding to the helium-neon laser wavelength. Although the resolution ( >100 -/
mm) and maximum density (> 3. OD) are adequate to meet some requirements, this material
does not currently offer the same high degree of image uniformity, long scale range, and
archival keeping quality when compared to silver halide film. Dry silver film is currently
about 25 percent more expensive than the combination of silver halide film, wet chemistry
and chemistry mixing labor costs. These estimates are based on current GSA schedule
prices for 200-foot film rolls and do not account for higher silver halide processor main-
tenance costs, downtime due to chemical spillage and less troublesome operation. One of
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the most significant recent developments regarding dry silver film is progress on develop-
ing the so-called hard top coat or HTC films. The process has the primary advantage that
the film can now be processed in the same heat processor used to develop the dry silver
paper. Care must be taken to ensure exact control of the developing temperature to
produce uniformly processed images. Experience indicates that platen temperature must
be controlled to within ?0.50 C to achieve consistent results but that temperature can
be regulated to achieve results which may be considered compatible with the low end of
the high readability performance group but not uniform enough to record PI quality
imagery.
The situation with recording paper is somewhat different. In the past, a
silver halide based stabilization paper was used in most high quality photographic quality
recording applications. This paper produces high quality images but requires a two-step
wet chemistry process to produce the image. We have demonstrated that pictures of
equivalent quality can be produced at lower cost per image. This is due to the laser
techniques used to reproduce the image and in part due to recent dramatic improvements
in the recording media. Experience with facsimile equipment which operates at the low
end of the medium readability group indicates that the standard 7771 paper base material
may be limiting the resolution of the product. Furthermore, a significant improvement in
readability can be achieved by using a still experimental polyester base material. This
base material will be more costly but may provide the difference between useable and
unuseable medium readability paper products scanned at 400 lines per inch.
One of the primary limitations of dry silver film and paper is the greater
susceptibility of these products to environmental conditions - especially excessive
temperature. This appears to be a limitation only under extreme operational conditions
involving tactical missions. In this case, the care with which the recording material
must be stored is far outweighed by the operational convenience of a dry process. In
most situations, normal film handling procedures are adequate to preserve image quality.
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A detailed analysis of various wet and dry recording materials is beyond the
scope of this study and depends to a large extent on the specific design details of the
recorder. We can, however, make some general observations regarding the applicability
of these materials to specific terminal configurations. Firstly, experience indicates that
only silver halide film is currently capable of meeting the general requirements of PI
quality imagery. This condition is likely to remain so into the FY 1980 time frame.
High readability requirements recorded at 800 lines per inch can be satisfied
by both dry silver film and wet processed film. At the present time, the grey shade
reproduction of dry silver film is marginal for this readability group but we expect that
improvements will be made by the FY 1980 to improve the repeatability of the tonal scale.
The medium readability requirements of 400 scan lines per inch are currently satisfied by
dry silver film. I t appears that currently available dry silver paper and even the newer
polyester base opaque material is only marginally acceptable for medium readability
imagery. Even though no paper products are able to support the quality requirements,
they should be considered as an inexpensive means for obtaining minimally acceptable
opaque copy. Paper base copy is completely unacceptable for HR and PI quality applica-
tions. Figure 3.8 shows the practical resolution limits for the four types of imaging
media which may be considered applicable to each readability group.
Finally, it is instructive to examine the sensitivity of various recording
media to determine the amount of energy which is required to expose it. This evaluation
is aimed at estimating a rough order of magnitude for the required power so it will not be
rigorous. A plot of scan rate versus scan density is again a useful one with which to
compare results. A useful parameter for recording images is the instantaneous area scan
rate measured in area per unit time. When this is multiplied by recording medium sensi-
tivity and divided by optical efficiency, we arrive at value for laser power, i.e.,
P = (IASR) (et )
L 71
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8 ~8 8
0 500 1000
-;.~._4 SCAN DENSITY
1500 2000 (LINES/INCH)
I
HR-
DRY
SILVER PAPER (STANDARD BASE)
DRY SILVER PAPER (POLYESTER BASE)
DRY SILVER FILM
SILVER HALIDE FILM
Figure 3.8. Application Range for Recording Data
where PL is required laser power in watts
IASR is recording rate in in2/sec
,J is media sensitivity in watt-sec/in2, and
r1 is optical system efficiency.
If we restrict our discussion to a standard 9 inch by 9 inch frame, it is possible to express
IASR in terms of scan rate, R, and scan density, S, by:
IASR = 9 R/S
where R is the scan rate in lines per second and
S is the scan density in lines per inch.
Substituting for IASR and solving for R yields:
P b 77 S
R =
9,9
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Figure 3.9 shows this equation plotted for various values of laser power and 3M Brand
Type 7869 Dry Silver Film. We have used a sensitivity value of 300 ergs/cm2 or 1 .94
(10-4) watt-sec/in2 for Type 7869 which is the least sensitive recording material under
consideration. A helium-neon laser has been chosen because of its high reliability and
low-noise characteristics. An overall optical efficiency of 5 percent is assumed.
The primary observation regarding this calculation relates to the application
of dry silver film in the medium readability recorder which operates at 400 scan lines per
inch and at about 30 scan lines per second to fill the 32 kb/s link at 20:1 data compress-
ion. For these values, a laser power of only about 2 milliwatts is required - a value
which is readily obtainable from a number of small and reliable commercial lasers and is
typical of the laser power currently used in commercial facsimile equipment. The general
conclusion one reaches is that both recording media and laser power requirements are well
within the state of the art for all terminal requirements.
In summary, both 3M Brand dry silver products and conventional wet
processed films will find applications in the various terminal configurations. The 3M
Brand dry silver film is recommended for rapid access to medium readability imagery
recorded at 400 Ipi . We have showed that only low power lasers are required to expose
this material. To preserve the overall resolution and image quality of high readability
and PI quality imagery, we recommend the use of conventional wet processed film.
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IMAGE SIZE - 9" X 9"
QUANTIZATION - 6 BITS/SAMPLE
DUTY CYCLE - 80%
3M BRAND 7869 DRY SILVER FILM
HELIUM - NEON LASER
5% OPTICAL EFFICIENCY
CURVE A - 32 kB/SEC (20:1 COMPRESSION)
CURVE B - 1.5 MB/SEC NO COMPRESSION)
CURVE C - 1.6 MB/SEC (5.5:1 COMPRESSION)
wn
5000
2000
1000
-
-
500
._
B
200
100
50
20
10
100 200 500 1000 2000 5000
SCAN DENSITY (LINES PER INCH)
Figure 3.9. Recorder Laser Power Requirements
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3.2 Recorder/Scanner Candidates
The previous section discussed several technology factors associated with image
recording and scanning, and placed some bounds on the speed and resolution attainable with
the technology. Using this information, some specific schemes are now examined for imple-
menting the image recorder/scanner in terms of terminal requirements. Candidates include:
(1) laser-galvanometer types, (2) cathode ray tube (CRT) types, (3) drum recorder/scanners
and (4) laser beam recorders (LBR). It is believed that these four candidates, which now
dominate the medium and high quality imaging recorder/scanner market, will continue to
do so well beyond the FY 1980 time frame.
Specifically omitted are two candidate approaches which have either been
developed or are being developed for special applications. The first of these is electron
beam recorder (EBR) technology which is capable of exceptionally high quality and high
speed operation and actively competes with LBR technology. EBR has been omitted because
of the difficulty and cost associated with producing 9 inch by 13 inch images. Also,
the applications of LED or laser diode recorder/scanner have not been considered because
they do not currently provide any significant operational advantage over the other candidate
technology and will find application in the marketplace only after recording material
sensitivity is extended to longer wavelengths. It is expected that visible gas and ion
lasers will be the preferred Iight source well into the FY 1980 time frame.
It is beyond the scope of this study to provide a detailed second level design
analysis of the four candidate recorder/scanners. Rather, we evaluate top level design and
operational parameters and their impact on terminal performance.
3.2.1 Laser-Galvanometer Recorder/Scanner
In Paragraph 3.1.2 the laser-galvanometer (L/G) recorder/scanner approach
was categorized as one which is capable of supporting medium readability imagery. Sucess-
ful implementation and field service for commercial L/G technology has taken place over
the past few years by application to the Associated Press Laserphoto wire service. The
TDF equipment currently under development also uses this technology but in the low read-
ability region. The key elements of the L/G equipment are: (1) a laser, usually a low
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power helium-neon type; (2) a modulator to change the intensity of the light during the
recording process (e.g., an acousto-optic modulator); (3) a galvanometer-mounted mirror
used to sweep laser beam across the recording medium, (4) focussing optics to form a record-
ing spot and; (5) a mechanism for moving the recording medium past the scanned line.
Figure 3.10, as an example, shows the components which are used in the Harris ESD pro-
duct line of Laserfax equipment. This equipment is capable of operating in the lower
SCANNER PHOTODETECTOR (OPAQUES)
Figure 3.10. Laser-Galvanometer Recorder/Scanner Components
quality portion of the medium readability group and at scanning speeds near 50 scan lines
per second. For operation at 400 scan lines per second, the same general arrangement is
used but two additions are made to the system: 1) an auxiliary lens which flattens the field
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of the scanning spot and 2) a linear grating through which a portion of the beam is
directed to and subsequently detected to produce accurate timing for accessing the
data buffer. The major components required to implement this scheme are shown in
Figure 3.11.
ACOUSTO-OPTIC
MODULATOR
~p'gF
FEEDBACK
DETECTOR
GALVANOMETER
SCANNER
BEAM EXPANSION
OPTICS
minnun
RULING AND
DETECTOR
FIELD FLATTENING
LENS
Figure 3.11. Improved Laser-Galvanometer Implementation
Similar optical, mechanical and electrical components are required for
the L/G scanner. In this case, an unmodulated laser beam scans either an opaque paper
copy or transparent film. For paper scanning, the light reflected from the surface is
detected by either a single long detector or a series of individual segments connected
together electrically. For transparency scanning, the detector is mounted behind the
platen into which an aperture has been cut. The light which is detected has therefore
been modulated by the film density variations. Both scanning methods have been
successfully implemented on the L/G equipment.
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Although it is possible to configure a transceiver design for the L/G
equipment, separate transmitter and receiver implementation is favored. This approach
is particularly attractive for the case where only "DRO" terminals are required and
minimizes the cost of these terminals. The L/G approach can be designed to meet the
requirements of medium readability imagery and is the recommended image recorder/
scanner for medium readability applications.
In addition to the performance advantages of L/G technology, it offers
functional advantages over other medium readability image device technology.
Specifically, the transmitter and receiver modules are relatively small and light. The
size of the transmitter is typically 1.3 cubic feet and weighs about 40 pounds while the
receiver is about 7.8 cubic feet and weighs 120 pounds. Both are mounted on a tabletop
and are easily transportable.
3.2.2 Cathode Ray Tube (CRT) Recorder/Scanner
A CRT recorder/scanner approach would be applicable for medium
readability applications and is therefore competitive with the laser-galvanometer
approach. The laser, modulator and galvanometer deflector are replaced with a line
scan CRT. The line is imaged onto the recording medium by conventional optics or
fiber optics. The scanning function is performed by using an unmodulated CRT beam
and the reflected (or transmitted) light is detected in a manner similar to that described
for the L/G approach. The recording medium is stepped past the CRT scan line just
as it is for the L/G and LBR approach.
The primary equipment limitations that we identify for CRT recorders are
marginal performance when exposing dry silver recording material and a significantly
lower MTBF. Experience with CRT recorders indicate that image quality is to a large
extent dependent upon the quality of the phosphor and fiber optics. It is almost
impossible to produce defect-free CRT's and fiber-optic assemblies, the result of which
is a characteristic pattern noise which is difficult and costly to eliminate.
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The MTBF of a CRT is estimated at 3,000 hours. Assuming a replacement
cost of $5,000 for a commercial high quality CRT yields an operating cost of $1.67 per
hour. By comparison, the L/G laser head, with a 10,000 hour MTBF and a $1,000
replacement cost yields an estimated operating cost of $0. 10 per hour. The operational
cost of this factor alone on several hundred "D" terminal receivers and transmitters is
significant impact.
CRT recording technology is a mature one which has (and will continue to)
served well in both commercial and military applications. Although it is capable of
satisfying the performance requirements of medium readability imagery, it is not
recommended for new equipment design. Laser-galvanometer technology coupled with
dry silver recording material is already replacing CRT technology in medium readability
applications. By the FY 1980, L/G technology will be the dominant one for medium
readability and medium speed applications.
3.2.3 Drum Recorder/Scanners
The concept of using drum recorders and scanners for recording images
precedes most of the other technology which is discussed in this section. The rotation
of a drum, which is governed by accurate servo speed control, provides one of the
best and most reliable means for achieving linear scan velocity. To achieve cross
track motion of the recording spot, a carriage is usually moved along the drum axis -
either continuously or in asynchronous steps. The discussion of drum recorder/scanner
design principles in beyond the scope of this study. Rather, a few of the major factors
which influence the application of this technology to image transmission will be
highlighted. As indicated in Paragraph 3.1.2, the drum is capable of producing
image quality across the entire range of readability groups but is limited in speed to
practical limits of 50 scan lines per second. This corresponds to a drum rotation rate
of 3,000 r/min. Although some applications can exceed this value, it is clear that
higher rotation rates compound the problem of holding the recording material onto
the drum surface. In any case, the worst case drum speed required to meet the 1.5 Mb/s
link requirements is about 1,800 r/min. (It is assumed that the "C" terminal need not
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transmit 800 Ipi data over a 1.5 Mb/s link.) The requirements of the link would be
satisfied by the drum if the system were operating synchronously and the recording
carriage were translated down the drum axis and producing a helical trace. In practice
this is not possible so that one must provide for stepping the carriage to adjacent scan
lines. The limitation for the carriage step-and-settle time is similar to that for a film
transport mechanism; i.e., a few milliseconds for the cycle. To accommodate for this
motion, the drum diameter is usually increased to provide some additional dead time
around the circumference. This time decreases the duty cycle and increases the
instantaneous data rate requirement. The design tasks involved here usually require a
trade-off of these and other factors to arrive at compromise solutions.
The availability of efficient and reliable acousto-optic beam deflectors
now permits the implementation of a technique which does not require the use of carriage
step-and-settle mechanisms and thereby minimized drum diameter and decreases the
instantaneous data rate. The scheme for implementing this is shown in the sketch of
Figure 3.12. The acousto-optic beam deflector, which is mounted in the carriage
housing, is capable of deflecting the laser beam along the axis of drum depending upon
the frequency and modulation of the signal applied to the deflector. For discussion
purposes, assume that the drum is recording at 2,000 scan lines per inch or 0.0005 inch
between lines. The position of the beam along the drum axis is controlled by two
signals, one derived from a linear encoder which runs the length of the drum and is
commonly used on precision drum recorders and another signal derived from the
rotational drum encoder used to strobe out data onto the drum. The linear encoder defines
absolute carriage position while the drum rotation encoder supplies correction signals
depending on the angular position of the drum. The carriage rate is not dependent upon
drum rotation rate and in fact operates in a quasi-asynchronous manner.
The same principle of using acousto-optics to improve the operability of
drum recorder/scanners can be used to increase the flexibility. In selecting a scan
density for high readability and P1 quality imagery, 800 and 1,600 lpi were chosen
as multiples of the 200 Ipi TDF scan density. However, it was also required to provide
capability at 2,000 Ipi. These unrelated scanning densities can be recorded on a
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ACOUSTO-OPTIC
BEAM DEFLECTOR
Figure 3.12. Acousto-Optically Controlled Down Recorder/Scanner
single drum scanner without physically modifying the recorder. The acousto-optic beam
deflector is now used to "dither" the basic 2,000 Ipi recording spot along the axis of
the drum to achieve 800 and 1,600 Ipi recording and scanning resolutions. A high
frequency signal is applied to the acousto-optic deflector to achieve the dither effect.
Consequently, a versatile recording and scanning device is obtained which covers both
HR and PI quality imagery.
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The scanning function is relatively easy to implement on a drum
device. The detector, which can be of small size and high speed capability, is located
near the recording plane and intercepts the light reflected from the surface. The same
light source is used to illuminate the copy. For HR and PI quality imagery, film is the
only medium which will support the resolution and grey shade. Experience has shown that
film can be read in reflectance by supporting the base with a diffuse backing material.
This elimates the problem of using transparent drum cylinders for the scanning operation.
A word is in order regarding the degree of automation, especially regard-
ing unattended operation of the image recorder/scanner. It is possible to design an
automatic loading and unloading mechanism for the drum recorder. This mechanism
could load 9 inch x 13 inch sheets of film onto the drum prior to recording and unload
them into a catchbox upon completion of the recording operation. Such a mechanism
is useful only in applications where high throughput is of paramount importance. A
careful examination of the image loading should be made before this decision is made.
In order to maximize terminal reliability, automatic loading mechanisms should be
avoided unless all throughput traffic requirements indicated otherwise.
3.2.4 Laser Beam Recorder/Scanners
The key technology involved in laser beam recorders is contained in five
major components: the laser, the optical modulator, the beam deflector, the film
handling mechanisms and the recording media. The choice of laser is dictated primarily
by the power required to expose the recording medium, the desired signal-to-noise ratio
and, in some cases, the MTF of the recording system. Three types of lasers have been
successfully used to record high resolution imagery including the common helium-neon
type, the newer helium-cadmium type, which produces energy in the near ultra-violet,
and the argon-ion laser, capable of producing several watts of coherent radiation.
Two types of optical modulators are used in high performance laser
recorders: The electro-optic type, which modulates tight by an electronically-
controlled change in the refractive index of the active crystal, and the acousto-optic
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type, which produces a refractive index change that forms a microscopic phase grating
across the laser beam. Unless some special feature of the electro-optic process is
required, the acousto-optic modulator is generally superior in all but the most unusual
applications. Rise time less than 100 nanoseconds and extinction ratios in excess of
1500 are easily obtainable in off-the-shelf devices.
Current laser beam recorders which produce 20,000 spot resolution on
continuous copy roll film all use multifaceted rotating mirrors to achieve the scanning
motion across the film. Galvanometers are not capable of achieving 20,000 spot
resolution at the required scan rates. Acousto-optic beam deflectors are limited by
time-bandwidth product constraints to applications which require microsecond sweep
times but less than 2,000 spot resolution. The two basic multifaceted mirror spinner
configurations include scan-before-focus and focus-before-scan types. The scan-before-
focus approach is used in conjunction with a special F/9 lens which is designed to
produce a uniform scan on a flat field. The principal advantage of this approach is
that it leads to a less complex film transport and permits recording directly on the drive
capstan. The focus-before-scan apporach does not require special lens design because the
focussing lens always operates on-axis. A curved recording film platen is used to
compensate for large field curvature produced by this type of scanning. The curved
platen approach results in somewhat more complex film threading and film transport
mechanisms. Both approaches have been successfully employed in high resolution
scanners. The cost of a specially designed lens is usually offset by the cost of machining
curved platens resulting in comparable cost impacts.
The high performance laser beam recorder is not considered to be a
suitable candidate for producing PI quality imagery because of high cost. Its use would
be recommended only if the link requirements were significantly higher than specified.
For example, an LBR is a likely choice if PI quality (2,000 Ipi) imagery, and lower were
to be transmitted over 1.5 Mb/s links with 5.5:1 data compression.
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3.2.5 Terminal Recorder/Scanner Recommendations
Several recorder/scanner technologies have been discussed in the four
preceding paragraphs on the basis of technical performance factors. Table 3.1
summarizes the relative rankings of these technologies when viewed in terms of initial
and operating costs for typical implementations.
Table 3.1.
Recorder/Scanner Cost Dependent Factors
Type
Initial
Cost
Operating
Cost
MTBF
Laser-Galvo
low
low
long
CRT
med.
low/med.
med.
Drum
med./high
low
long
LBR
high
med./high
med./short
The evaluation of recorder/scanner technology leads to some obvious
recommendations for configuring the four terminals. The recommendation for MR
imagery is separate laser galvanometer transmitters and receivers operating at a scan
density of 400 lines per inch with dry silver paper and film. This is the only image
device required for the "D" and "DRO" terminal. To handle PI quality imagery a
drum recorder/scanner (transceiver) is recommended which operates at 800, 1,600
and 2,000 Ipi. The "B" terminal will therefore contain both a 400 lpi L/G recorder
and scanner but also a drum transceiver. The "C" terminal will similarly contain a
L/G recorder and scanner but a drum which is capable of handling only 800 lpi imagery.
Only minor modifications would be required to be made to this drum configuration for
upgrading to "B" terminal capability. The hardware description and performance
parameters for the individual terminals is discussed in Section 4.0.
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3.3 Terminal Input and Output Consideration
The three primary aspects of terminal input and output products and func-
? The recorder/scanner recording media
? The degree of automated unattended operation which should be
implemented
? The feasibility of providing a store and forward capability within the
terminal
Paragraph 3.1 .4 discussed various recording media options in relationship
to the requirements for image terminal readability. Consequently, the evaluation in this
section will be confined to the latter two points listed above.
3.3.1 Operational Concepts
Figure 3.13 gives a relatively complete top level summary of the possible
levels of automation within the transmitter and receiver, but neglects the remainder of
the system including the communication link. As shown, both receiver and transmitter
can be viewed as being comprised of several functions which may be implemented with
varying levels of automation. In general, the level of automation of each of these
functions may be independently selected. However, system constraints, such as a require-
ment for human judgment in selecting the material to be transmitted, the quality of trans-
mission, the destination, and a second requirement for transmission to multiple receivers,
serve to limit the degree of automation of several of the transmitter functions. Receiver
function automation is not similarly limited. The receiver function automation levels
depicted have been refined for several of the functions by distinguishing between levels
of automation which are feasible under local control and those which are feasible under
remote control . For example, it is feasible to provide completely automatic selection of
the reproduction parameters of a receiver by remote control from the transmitter, but not
by local control, due to the variability of the parameters and the lack of information
available in the receiver system regarding the values for the present transmission.
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NONREDUNDANT
L AREA SELECT
SEMIAUTO L-SEMIAUTO
AUTO
I MEDIUM
LOAD
MANUAL
AUTO
NONREDUNDANT
AREA SELECT
LOCAL
MANUAL
SEMI
~-- REMOTE
SEMI
AUTO
CODE PARAMETER
SELECT
DESTINATION
SELECT
SCAN PARAMETER
SELECT
CODE PARAMETER
SELECT
REPRO PARAMETER
SELECT
MEDIUM
PROCESSING
f-- LOCAL
MANUAL
SEMI
LOCAL
MANUAL
SEMI
REMOTE ~-- REMOTE
SEMI SEMI
AUTO AUTO
Figure 3.13. Terminal Automation Options
MANUAL
AUTO
In order to determine the most suitable level of automation for a terminal
in the receiver mode of operation, it has been assumed that unattended operation of the
receiver is required. The assumption eliminates the choices requiring manual or semi-
automatic implementations. The resulting fully automatic receiver mode appears to be
well within the state of the art for the medium resolution range. The high resolution and
photointerpretable ranges however would require the development of specialized and
expensive capabilities as discussed in Paragraph 3.2. For this reason, a slightly less auto-
mated approach appears to be more cost-effective. In this approach, the medium resolu-
tion portion of all terminals is capable of fully automatic reception. The remaining
54
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portion, if any, of all terminals is capable of fully automatic reception with the excep-
-tionthat manual loading and removal of film is required. The "B" and "C" terminals are
thus capable of receiving one picture at high resolution and many at medium resolution
without manual intervention.
The most suitable level of automation for the transmitter may be determined
in a similar manner. In this case, the proper choice is much less well defined. In the
absence of statistical data on the expected values for the various parameters, use of
fixed preprogrammed parameter value tables is not required. The choice falls between
completely manual selection and some form of semiautomatic selection in which a single
selection input controls all parameters that are uniquely determined by that selection.
An example of the latter is selection of both line-to-line spacing and along-scan sample
spacing for a system in which it is desirable to maintain equal resolution in both dimen-
sions by means of a single selection input. Simplicity of operation requires that the
latter approach be taken. Copy loading, for the reasons discussed above, should be
manual for the high resolution portion of the "B" and "C" terminals and automatic for
the medium resolution portion of all terminals.
On a systems level, it is apparent that the functions of synchronization and
fill character insertion and removal must be automated to achieve the desired performance.
This area is described in more detail in Paragraph 2.2. The basic point of interest is that
the reproducer has a fixed line length so that it will accept the data following a line
sync word up to the maximum Iine length or next line sync word for reproduction. A
line sync word starts each line. If line sync words are further apart than the maximum
number of samples in a line, all excess samples are treated as fill words and deleted.
3.3.2 Store and Forward Operation
Addition of image storage capability to the basic terminal provides certain
advantages which are listed below:
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Terminal Mode Recorded Data Advantages/Disadvantages
? Receive Clear Unencoded Multiple copies with different
scales from one transmission.
Transmitter of this terminal free to
transmit. Reproduction may be
done off line.
? Receive Clear Encoded Picture start may be delayed.
or Secure Multiple copies with different
scales from one transmission.
Decoding may be done off line.
Reduced storage.
? Transmit Secure Picture start may be delayed.
Encoding may be done off line.
Receiver free to receive. Trans-
mitter free to transmit. Reduced
storage .
? Transmit Clear Encoded Picture start may be delayed.
Encoding may be done off line.
Reduced storage.
? Transmit Clear Unencoded Picture start may be delayed.
Scanning may be done off line.
Only one COMSEC equipment and one encoder per terminal has been assumed. There
may be some advantage in using temporary storage, but only if dedicated communication
I inks are not used.
Communications security requirements prevent a single controller and data
recorder from being used in all of the modes mentioned above. The data recorder may be
either clear or secure, but not both. For this reason the data recorder should interface
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to the data processing equipment and be used in the clear modes, avoiding the necessity
for a complex controller and an additional data recorder while still yielding most of the
advantages listed.
The expression for the bit capacity of a digitized image is given in
Section 2.0. An image with 6 bit quantization measuring 9 X 9 inches and scanned
at 400 Ipi contains 7.8 (107) bits. Candidate storage devices should be capable of
storing several equivalent images. The current technology which is applicable is:
? Digital Magnetic Tape - has a capacity of 3.7 (108) bits (about
5 images per reel) with read/write speeds at selectable fixed rates
of up to 5.8 (105) bits/sec.
? Analog Magnetic Tape (Linear Scan) - has a capacity of 7.2 (109)
bits (about 90 images) with read/write speeds up to 3.2 (107) bits/sec.
? Helical Scan Digital Tape - has capacity of 7.5 (1010) bits (almost
1000 images) with average read/write speed of 6.3 (106) bits/sec
and maximum fixed speed of 8.1 (106) bits/sec.
? Disk - has capacity of 0.7 (109) bits (about nine images) with fixed
read/write speed of 6.4 (106) bits/sec.
The various types of magnetic tape units exhibit a major disadvantage in
this type of system configuration because of the variable access rate. When used as the
transmitter data source, the tape must provide a line of data on demand from the data
processor input buffer or operate only with the encoded data. When used as the receiver
data source, the tape must provide a line of data on demand from the data processor
input buffer or the reproducer output buffer. The tape transports currently available are
not well suited to this type of operation - including the analog magnetic tape and helical
scan digital tape. Start/stop times for these two types are on the order of seconds result-
ing in long interrecord gaps. To utilize these techniques efficiently, the data processor
buffer size must be increased to handle several seconds of data. This represents an
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increase of several orders of magnitude over standard requirements so it is not an attrac-
tive solution. Digital magnetic tape transport stop or start in milliseconds, but the
capacity of the tape is not very high.
The magnetic disk memory, however, suffers from none of these problems.
No buffer size increase is required because the access time is no more than 20 milli-
seconds per line. The storage capacity is sufficiently large for three disks to be used for
high scan density image storage.
Other technologies showing considerable promise for this application by the
1980 time frame are charge coupled device (CCD) memories and magnetic bubble mem-
ories. Presently these devices are experimental in nature, with indications that the cost
and performance may eventually be competitive with the magnetic disk. One CCD
memory device has been commercially introduced at a cost of 0.15 cents per bit with
further reductions expected. This compares with a cost of 0.003 cent per bit for the disk
subsystem discussed above. The CCD or magnetic bubble memory lends itself to rugged-
ization more readily than the disk. Since these technologies are immature at present,
the prediction of precise cost trends is much more difficult than for the magnetic tape or
disk.
The additional capabilities offered by the addition of picture storage to
the terminal must be evaluated by the user on the basis of cost-effectiveness. The cost
of a nonruggedized disk subsystem is approximately $70 thousand. The option of store-
and-forward operation is technically feasible and implementable with currently available
hardware. We consider it to be an exercisable option but have not included it in the
terminal configurations.
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3.4 Terminal Intercompatibility
Terminal intercompatibility is one of the key requirements to ensure flexible
system response to dynamic situations. A high degree of flexibility is required to respond
rapidly to changing military and political situations. Several advantages may be realized
if the network system and the terminals are configured so that every terminal type be
capable of communicating with every other terminal type. For "B" and "C" terminals,
an intercompatibility configuration in which transmit or receive portions of the equipment
are used tends to increase the availability of the network.
Transmission capability from a low level ("D" or "DRO ") terminal to a high
level terminal ("B" or "C") is a basic requirement of this approach. Upwards compat-
ibility is realized by including the capability within each terminal to receive trans-
missions from lower level terminals. This may be accomplished by providing an image
recorder of the type used in the "D" terminal as part of the "B" and "C" terminal. The
volume of incoming data can be increased or decreased, if required, by the data
processor.
The overall impact of intercompatibility is to allow the system to be recon-
figured in a variety of ways subject only to the communication system constraints and the
basic terminal parameters. Depending on the availability of suitable communication
links and the operational situation, networks may be merged, increased or decreased in
size, and added or deleted.
Terminal types "B,'l 11C," and "D" can easily be configured to allow auto-
matic arbitration of image recorder type, recorder spot size, image quantization, and
pixel/line deletion or repetition so that any terminal can transmit to any mix of receiving
terminals either simultaneously or one at a time. The configuration of a typical multidrop
system is shown in Figure 3.14. If terminal "B" is to transmit to "C" and "D" terminals in
the net, manual inputs to the "B" terminal cause data to be scanned and transmitted at
800 lines and pixels per inch. The resulution of the transmitted data is signalled to the
receiving terminals in the set-up word as indicated in Section 2.0. The "C" terminal
receives the data and utilizes it without modifying the resolution. The "D" terminal
deletes alternate lines and pixels of data to convert the received data to a compatible
resolution.
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1. SWITCHING IS IN COMM SYSTEM.
2. FIRST WORD OVER LINK IS A
SETUP WORD DEFINING RESOLU-
TION, QUANTIZATION, AND
TERMINAL ADDRESS OF
TRANSMITTER AND RECEIVERS.
3. LINK DATA RATE RESTRICTED
TO THAT OF SLOWEST TERMINAL.
4. COMM LINKS ASSUMED COMPATIBLE
WITH CONNECTION SHOWN - MUST
BE EVALUATED FOR SPECIFIC CASE.
5. TYPICAL CONNECTION SHOWN.
Figure 3.14 Terminal Multidrop Arrangement
In general, the data is scanned and transmitted at a resolution equal to the
highest resolution which is reproducible by any single receiving terminal. Other receiv-
ing terminals would then convert the received data into a suitable resolution by line and
pixel deletion. For those instances where the original data does not require high resolu-
tion reproduction, where time is an overriding factor, or where the transmitter does not
have the capacity to transmit at any higher resolution, the receiving terminals utilize
the proper reproducer to ensure compatibility. Note that line and pixel repetition is
never required in a unity scale factor reproduction. For example, if the "D" terminal is
the transmitter in Figure 3.14, the data is transmitted at 400 lines and pixels per inch.
The "B" and "C" terminals would use the laser/galvo recorder contained in the terminal
and reproduce the data as transmitted, without modification of the resolution. The
reproducer is chosen by the receiving terminal on the basis of the set up word received.
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Unattended operation, except for replenishment of paper, maintenance and
repair, is thus permissible between any levels of terminals as long as the data is trans-
mitted and received at 200 or 400 lines and pixels per inch. High resolution transmissions
use a drum scanner and reproducer which require manual loading and unloading at both
transmitter and receivers. Operation with other than unity scale factor also requires
manual intervention at transmitter and/or receivers. Note that the discussion in this
section relegates the link switching, if any, and the crypto synchronization to the com-
munication system.
If a portion of an image or an image of less than 9 by 13 inches in size is
to be transmitted, the transmitter must be informed which portion of the image is to be
transmitted or the size of the image. This information is manually entered from the image
area designator device.
This device allows designation of image areas 1 inch square for utilization
in defining image size and redundant areas to the data processing module. The present
concept of this device uses an overlay on the image with 1 inch grid lines, indexed to
the upper right corner of the image. A group of pushbuttons provides the means for
designating individual 1 inch square areas and the type of compression algorithms used in
the redundant areas. The transmitter scans the entire 9 by 13 inch area but transmits only
the designated information. Scanning will cease when the remaining portion of the
picture contains no additional area designated for transmittal. This approach permits
smaller formats to be handled more efficiently.
The same feature is used to transmit a magnified version of a small image.
Magnification is accomplished by scanning at one scan density and recording at another.
For example, a 2 inch square portion of the image could be scanned by a "B" terminal at
1600 1pi by reception as a "B," "C," or "D" terminal. This would be accomplished by
selecting the area to be scanned by the image area designator and causing the transmitter
data processing module to identify the 16001pi data as 400 1pi data to the receiver. The
effect would be to cause the linear dimensions of objects in the magnified image to be
four times larger than in the original image scanned. Similarly 2X magnification is
accomplished by scanning at twice the scan density of the reproduction. It should be
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noted that the results of the magnification process described above are effectively
identical to employing optical magnification of the corresponding value (2X or 4X) on a
2 inch square image scanned and reproduced at 1600 lpi. Objects slightly above the
limit of detection in the 1600 lpi reproduction appear correspondingly larger, but still
only slightly above the Iimit of detection in the 400 1pi reproduction.
Magnification is also possible by scanning and reproducing at the same scan
density, with each data sample and each line repeated twice for 2X magnification. This
is called "empty magnification" because the objects in the image appear twice as large,
but do not contain more information. Empty magnification could be employed to
achieve magnification between terminals with the same scan density.
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3.5 Terminal Modularity
A natural method of upgrading terminal performance is by exchanging a
portion of the terminal for higher performance hardware or by adding equipment to an
existing configuration to improve terminal capability. The primary advantage of
modular design is that it affords a means for upgrading terminal performance with
minimal cost impact. The two major subsystems considered for modular implementation
are the recorder/scanner subsystem and the data processing subsystem.
The recorder/scanner subsystem modularity concept must be considered in
terms of its application in the various terminal configurations. The lowest performance
configuration is one using only the laser-galvanometer recorder for reception of 400 Ipi
imagery in the "DRO" terminal . The image recorder receives data at 400 Ipi but is
capable of recording at two spot sizes - one which is consistent with 400 Ipi resolution
and another which has twice the spot size but still scans at 400 Ipi. This latter approach
tends to produce a more uniformly pleasing image than one produced by merely dropping
pixels and lines for 200 Ipi operation. The laser-galvanometer recorder records on
either 3 M brand dry silver paper or film from continuous 200 foot rolls. Image sizes of
up to 9 inches by 13 inches can be easily accommodated. The recording medium is
processed automatically after completion of the recording sequence.
The image recording and scanning capability of the "DRQ"" terminal may
be upgraded to "D" terminal status by adding a laser-galvometer scanner module. It
too is designed to operate at 400 Ipi but has the capability of scanning with two different
spot sizes.
For performance beyond medium readability capability, a drum recorder/
scanner is added. The initial step to "C" terminal status requires the addition of one
capable of operating at 800 Ipi. For "B" terminal capability, this drum is further
modified to provide both 1600 and 2000 Ipi recording and scanning capability. Input
and output media for use with the drum equipment is restricted to film which is manually
loaded and unloaded from the device.
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Six data processing module options are recommended to cover the full
range of terminal requirements. The first of these is the basic "D" terminal Data Pro-
cessor, a bipolar microprocessor based device that performs the functions of setup,
encoding, decoding and data buffering. This function is illustrated by Figure 3.15.
FROM
SCANNER o-
TO SCANNER, RECORDER
STEP, CUT, PROCESS/
MANUAL LINK/MODEM
INPUTS
SOL
Figure 3.15. Basic Data Processing Function Diagram
The basic buffer size is 3600 words. The second module provides additional memory to
extend the buffers to a 7200 word length which is required for the "C" terminal. The
third module provides yet more extension memory for a total of up to 18.0K words which
is required for the "B" terminal.
The fourth module is an optional high speed Huffman encoder/decoder which
provides an average 2.4 x increase in picture transmission speed. This module is capable
of operating at the 1 .5Mb/s link rate expected on high bit rate links and provides a
measure of data reduction at rates above those for which conventional general purpose
serial data processors are feasible. Input buffering is provided in the module.
RECORDER/SCANNER CLOCK CLOCK
-_~ FROM
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The fifth module is a high speed buffer/link interface. This unit allows the
drum scanner/reproducer to interface to the 1 .5 Mb/s link, either directly or through the
Huffman code module described above. All buffering necessary for direct interface, as
well as sync code insertion is provided by this module. The code output is buffered to
the link when used in conjunction with the Huffman encoder/decoder module.
The sixth and final module is the store and forward module. This module
provides a magnetic disk and interface to operate as described in Paragraph 3.3.2.
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3.6 Security Considerations
The two aspects of security which are sufficiently important to require
special attention are:
1. Conformity to TEMPEST requirements
2. Compatibility with COMSEC equipment
The elimination of compromising emanations from the RED terminal equip-
ment must be a goal which is addressed early in the detailed design phase. Experience
with the ICS equipment indicates that it is a difficult task to eliminate compromising
emanations after the equipment has already been designed and built. As shown in
Figure 3.16, the original EICS equipment did not meet the imposed TEMPEST require-
ments and even after extensive modifications, it was judged to be only marginally
conforming.
10 kHz 20 50 100 kHz 200 500 1 MHz 2 5
Figure 3.16. EICS and Laserfax TEMPEST Tests
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Indications are that the laser-galvanometer equipment will also be difficult
to modify to conform to NACSEM 5100 requirements.
Power line filters, located as for as possible from the terminal, should
reduce conducted RFI/EMI to an acceptable level. AC power should be conducted to the
terminal from the filter through semirigid conduit. The COMSEC equipment should also
be located as far as possible from the terminal with shielded cables and optical isolators
provided for the RED data interface to the COMSEC equipment. The basic EMI strategy
for the terminal is one of containment with EMI cabinets to be used throughout the
terminal. Special attention must be paid to the EMI design of the acousto-optic
modulator and driving circuitry to reduce emanations from this source. If careful
attention is given to the EMI/RFI and TEMPEST aspects of the design the terminal will
conform to NACSEM 5100 and MIL-STD-461.
The terminal should be compatible with the applicable COMSEC equipment
since it will be compatible with MIL-STD-188C for low level interface. Encryption and
decryption devices are normally required to have MIL-STD-188C compatible interfaces.
Provision for clock and data input/output lines are common to all COMSEC devices.
Other lines for initiation of sync, alarms, and power control are usually persent but may
vary from one type to the next. Local control should be provided for these functions.
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3.7 Communication Interface Considerations
Most communication links in use today are basically analog in nature,
even though portions of the link may be digital. Digital signals are transmitted over
analog lines by the use of modems at both ends of the link. The modems (modulator-
demodulator) convert the digital signal into an analog form suitable for transmission
over the analog line at the transmitter and convert the analog form back into digital
form at the receiver. Compensation is usually applied to the received analog signal
which allows distortion, frequency shift, phase shift noise, and band limiting to occur
without disrupting the link. The upper portion of Figure 3.17 illustrates this type of
operation and shows a standard MIL-STD-188C low level interface between the terminal
and the modem.
FROM/TO ANALOG
MODEM L - LINK INTERFACE
EQUIPMENT
MIL-STD 188C LOW LEVEL
FROM/TO DIGITAL LINK
INTERFACE EQUIPMENT
MIL-STD 188C LOW LEVEL
Figure 3.17. Terminal Interface Through MIL-STD-188C
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A second type of interface is shown in the lower half of the figure. In
this case the communication link interface is digital. The communication link may be
totally digital over the entire length or digital over only a portion of the length. Few
links today are wholly analog or digital - most are a composite of analog and digital
portions. The effect is that there is little difference between the two types of links
except for the actual location of the modem which can be either inside or outside of
the link.
Another consideration for communication interface is the source of the
timing for data transmission. Modems and digital link interfaces may operate either
synchronously or asynchronously. At lower speeds, modems are often asynchronous, i.e.,
operated at a variable bit defined by the data source to the transmitter. At high speeds
modems are almost always synchronous or operated at fixed bit rates defined by
precision timing sources located most commonly within the transmitting modem but some-
times external to the modem in the transmitter. Timing for the receiver is derived from
the transmitted data. Similarly, digital link interfaces may be either synchronous or
asynchronous. Often digital input data at lower rates are multiplexed digitally, perhaps
through several stages, to form a single higher bit rate stream for transmission over a
high bit rate link. In this case, timing must be phase locked to the multiplexer rate in
order to ensure usable data. At the receiver, the data stream is used to regenerate
timing for control of the demultiplexing process. Demultiplexing requires phase-locked
timing through the lowest stage.
Accordingly, the terminal operating as a transmitter must be capable of
generating the timing signals sent to the modem or link interface, and alternately of
accepting the timing signals from the modem or link interface. In the receiving mode,
the terminal must be capable of accepting the timing signals from or generating the
timing signals for the modem or link interface. Provision for a precision timing source
internal to the terminal and selection circuitry for the timing source is a standard design
technique.
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3.8 Data Compression
During the course of this study, the RADC-developed Redundant Area
Coding Scheme (REARCS)1' 2 is employed as the baseline approach for achieving high
data compression factors. The data compression technique has been successfully imple-
mented and evaluated on an Experimental Image Compression Subsystem (EICS)3 under
several RADC-sponsored contracts with HARRIS Electronic Systems Division (Harris
ESD). In this section, the basic operating principles of REARCSare reviewed.
The purpose of the Redundant Area Coding Scheme (REARCS) is to reduce
data content in a picture so it may be transmitted in minimal time over a communication
link. Since not all areas of normal reconnaissance imagery carry the same level of
interest, only the areas of high information need to be transmitted exactly. The low-
information (redundant) areas are used primarily for orientation, so they can be coded
for transmission at the maximum data reduction rate and still be effective. Based on
these facts, the REARCS approach applies different coding techniques to the two types
of areas. In the nonredundant area, a statistical coding is used to preserve all of the
data by coding the data exactly as it is digitized. In the redundant areas, an inter-
polative step technique is used that can be combined with lower resolution scanning to
obtain data compression.
The redundant and nonredundant areas of the picture and the coding tech-
niques in the boundary areas are selected by the operator using a grid matrix. A con-
venient grid of, say, 1 inch x 1 inch spacing is usually chosen.
In the nonreaundant area we use an entropy-preserving statistical
code. Starting with the value of one pixel, statistical coding is used to encode the
changes in grey levels between adjacent pixels. The frequency of occurence of
U.S. Patent No. 3743765, Redundant Area Coding System, U.S. Air Force;
4 March 1970.
3"Redundant Area Coding Study," RADC-TR-71-192 September 1972.
"Experimental Image Compression Subsystem (EICS)," RADC-TR-74-191 January 1975.
70
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different difference values follows a definite statistical pattern; no-change and
single-level changes occur most frequently, while two- and three-level changes occur
less often. Table 3. 2 is a list of the statistics of level changes which were determined
by measuring many different types of reconnaissance images. Only minor changes
occur in the statistics of complicated images compared to uncomplicated images.
Table 3.2.
Level Change Statistics and Coding
Huffman
Code
Statistical
Occurrence
(In Percent)
No change
68.0
One-level change +
01
12.1
One-level change -
001
12.1
Two-level change +
00011
Two-level change -
00001
2.0
Three-level change +
0000101
1.2
Three-level change -
000100
1.2
Four-level change +
0000011
0.4
Four-level change -
0000001
0.4
Remainder code
0000010 (followed
by a 6-bit data
value)
0.6
In order to assign a unique code to each event, a Huffman coding
approach is used. The most likely events are assigned the shortest codes. All changes
of more than four levels are assigned a new reference by assigning a special code
with the absolute 6-bit value of the sample sent right after the code. This form of
coding yields 2.0 to 2.4:1 data reductions depending upon the activity of the picture
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data. The outstanding characteristic of this code is that it is non interpolative or
entropy-preserving. Thus, if no link errors are introduced, the decoded data will be
exactly like the input.
In the redundant areas, an entropy-reducing step coding technique is
used. The step coding algorithm is a zero order reduction interpolative technique. The
code fixes a reference point with the "next sample" and establishes a tolerance around
this point. The subsequent samples are examined to determine if they lie within this
tolerance. All consecutive values within the tolerance are transmitted as a single
sample with the assigned value of the center of the tolerance range. The count of the
samples falling within the tolerance is transmitted as a run length. When a sample falls
outside the tolerance, a new "next sample" reference is established using this sample
and subsequent samples are tested against this newly established tolerance. The
operator can select various tolerances and numbers of lines and samples to be dropped -
depending upon the quality he desires to transmit in the nonredundant. The transmission
time is, of course, affected by the coding; a scheme that perserves more of the original
data will take longer to transmit.
Another feature that has been incorporated in the system is the zoom tech-
nique. By using this technique, a small area of the original photograph can be scanned
at higher resolution and reproduced on the receiving end in an expanded form at lower
resolution. For example it is possible to:
? Scan a 4 inch x 4 inch area at 400 lines/inch and reproduce on the
receive end as an 8 inch x 8 inch copy at 200 lines/inch for a X2
expansion.
? Scan a 2 inch x 2 inch area of the original photograph at 800 lines/
inch and reproduce on the receive end an 8 inch x 8 inch photo-
graph at 200 lines for a X4 expansion. This capability allows the
operator the option of transmitting the whole copy at 200 lines/
inch as the first picture in the set, and then zoom in to transmit the
small 2 inch square of the picture at an effective 800 lines/inch.
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The REARCS technique can be applied to the zoom pictures in the same
manner that it was applied to the 1:1 picture. For instance, a 2 inch x 2 inch pic-
ture scanned at 800 lines/inch would be divided into 8 x 8 grid squares. Each grid
square in this case would be 1/4 inch square. Thus, the operator can select very small
areas within the zoom picture to be transmitted at high resolution and the remainder of
the area in the zoom picture will be at a lower resolution, depending upon the number
of lines and samples dropped. Figure 3.18 illustrates the zoom and the Redundant Area
Coding features which can be implemented.
4X EXPANSION
SCANNED AT 800 LPI
REPRODUCED AT 200 LPI
rMTI
1 i .1 11
Li _J
E
REDUNDANT
LOW RES AREA
NONREDUNDANT
HIGH RES AREA
2X EXPANSION
SCANNED AT 400 LPI
REPRODUCED AT 200 LPI
2X EXPANSION
LOW RES AREA
HIGH RES AREA
_.-4X EXPANSION
HIGH RES
Figure 3.18. REARCS and Zoom Capability
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The zoom technique, combined with REARCS has proved to be an
extremely effective technique for transmitting intelligence and reconnaissance picture
data. The reaction thus far to the use of the two-coding technique and the zoom tech-
nique has been very favorable. The EICS testing has shown that the coding combination
described is very effective and that the lower resolution in the redundant areas does not
affect the usability of the received information. This testing has shown that, on the
average, between 5 and 10 boxes are all that are required to designate most of the
target areas in any one picture. The system is flexible, however, such that the
operator could, if he desired, select all of the boxes as target areas and transmit the
entire picture at the highest resolution possible. Tests have shown that a data com-
pression factor of between 10 and 15 is easily achieved and under some conditions, it
is possible to obtain 20:1 reduction on reconnaissance imagery.
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3.9 Data Processing Options
Several different technologies for implementing the data processing func-
tions are considered in this section. The four types of implementation approaches
considered are:
1. Hardwired logic
2. Minicomputers
3. MOS microprocessors
4. Bipolar microprocessors
The hardwired logic approach is the convential one which uses individual
MSI logic elements in a parallel organization to perform the buffering, encoding and
decoding, and interface functions. The logic design is specifically tailored to the
stored program coding algorithm which is to be used. This approach is relatively inflex-
ible but offers the highest speed capability of any of the methods of implementation
considered. Minor changes to the coding algorithm may not be implemented without
expensive redesign and replacement or rework of the hardware. Although no software
cost is incurred using this approach, the hardware cost is high; consequently, the overall
cost is the highest of the approaches considered. The size of the control memory is
dependent upon the specific stored program algorithm but it is usually smaller than for
other implementation technologies.
The minicomputer approach generally offers the system designer a rapid
implementation cycle and a relatively low level of design and programming effort. The
primary advantages of a minicomputer approach include availability of ruggedized models
as well as a wide range of software packages and peripheral equipment all of which are
supported by systems oriented customer service. The disadvantages include limited operat-
ing speed, size and long delivery schedules.
The microprocessor approach utilizes LSI techniques to provide a word-
parallel central processor using very few integrated circuits. Although no basic difference
exists between minicomputers and microcomputers, a few trends can be identified.
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Minicomputers are usually purchased as complete systems including power supplies and
memory whereas microcomputers are purchased as either complete systems or sets of
integrated circuits without power supplies, memory, or mounting hardware. Although
present minicomputers are being fabricated with TTL and MSI circuitry, the trend is
toward implementing minicomputers with LSI microprocessor chips.
The microprocessor is most often used in a dedicated application instead of
as a general purpose machine; consequently, relatively little system support software is
available for most microprocessors when compared with minicomputers. The minicomputer
architecture is generally more easy to implement than the microprocessor because of the
pin-out constraints on the LSI packages.
The two most common microprocessors available today are based on either
MOS or bipolar technology. The MOS technology yields more complex and versatile
chips but bipolar circuitry is much faster. The table below compares several key
parameters.
Table 3.3. MOS and Bipolar Microprocessor Comparison
MOS Bipolar
Word Sizes (Bits) 4,8,16 2,4
Speed Ranges 2-60ps .5-2ps
(Macro Instruction Time)
Architecture Types
Monolithic
Functional Slice
Bit Slice
Languages Macro
Micro
Bit Slice
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Table 3.3. MOS and Bipolar Microprocessor Comparison (Continued)
Software Aids
Hardware Aids
MOS Bipolar
(X) Assemblers 1-X Assembler
Editors For Micro-Code
Loaders
1-Higher Level Language
Simulators
Real-Time Development None
Systems
The general cost, speed and flexibility trade-offs are compared for the four
data processing technologies in the Figure 3.19. The bipolar microprocessor offers greater
ARAMETER
P
COST
SPEED
FLEXIBILITY
PROCESSOR
HARDWIRED
HIGHEST
FASTEST
LOWEST
LOGIC
MINICOMPUTER
MODERATE
MODERATE
HIGHEST
MOS
LOWEST
SLOWEST
MODERATE
MICROPROCESSOR
BIPOLAR
MODERATELY
MODERATELY
MODERATELY
HIGH
MICROPROCESSOR
HIGH
FAST
Figure 3.19. General Data Processing Trade-Offs
speed than the minicomputer at similar flexibility and cost levels. The hardware cost
for the bipolar microprocessor includes firmware to perform the required coding algorithm.
Firmware changes can be easily accomplished by card replacement to permit changes in
the coding algorithm. Ruggedization of the bipolar microprocessor is easily accomplished.
The minicomputer approach offers very high flexibility; accomplished by changes to the
software. This approach does not offer the speed of the bipolar microprocessor and is
quite expensive if ruggedization is required. Additional peripherals are required to
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achieve full flexibility. The MOS microprocessor offers the lowest cost approach but
is also the slowest. The operation of a MOS microprocessor may be changed by modify-
ing the firmware.
The speed of operation of the four processing technologies is superimposed
on a graph of computer operations versus data compression ratio as shown in Figure 3.20.
loots
5oM
20M
COMPUTER
OPERATIONS 2M
PER SECOND
0.2M
0.1M
50K
STEP
CODING LIMIT
7
,
P i
HUFFMAN
1
CODING
LIMIT
b\s
~
9~O ?b\ti -
a~
veti`
~0.
HARDWIRED
TTL
BIPOLAR MICROPROCESSOR
MINI
Figure 3.20. Data Compression Processing Limitations
The operating speed of the data processor is determined by the data compression factor
and the bit rate which must be attained to fill the communications link. The data pro-
cessing module must operate at a sufficiently high speed to be capable of supplying data
to fill the link regardless of the data compression presently occurring.
The number of samples per second which must be processed can be calcu-
lated asa function of the bit rate and data compression factor and is given by:
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Z = HWS2 = LC
T Q + (OH) CHWS
where (OH) is the total number of overhead bits C is the compression factor and the
other quantities are as defined in Paragraph 2.3. Twenty operations per sample is
estimated for implementing the coding algorithm for both the Huffman DPCM and step-
coding modes. These operations are simple arithmetic and register-to-register operations
which are compatible with microprocessor capabilities.
The calculation made above and plotted in Figure 3.20 for various link
rates shows that high speed processing is required to achieve the desired goal of filling
a 32 kb/s link at a 20X compression ratio. For this requirement, hardwired TTL logic
can be used but a bipolar microprocessor would be marginally usable. Hardwired TTL
is also required to meet the speed requirements of a 1 .5Mb/s link without compression
and with 5.5X compression.
79/80
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SECTION 4.0
TERMINAL CONFIGURATIONS
81
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4.0 TERMINAL CONFIGURATIONS
Many of the technical factors which influence the general form, perform
once and functional features of a terminal are evaluated in Section 3.0. On the basis
of these cost-dependent factors, it is possible to synthesize an implementation approach
which meets the basic guidelines and objectives of the study. A summary of the
recommended configurations and terminal features is presented in this section.
4.1 The "D" Terminal
The "D" terminal forms one of the basic building blocks of any image
transmission system which would be constructed using the technology discussed above.
This terminal is the one which is most likely to be implemented in large quantities in any
practical network arrangement. This terminal transmits (and receives) medium readability
imagery (and lower) to (and from) all other types of terminals. A block diagram of the
"D" terminal configuration, shown in Figure 4.1, consists of a separate medium
readability receiver and transmitter, data processing module with memory buffer and
REARCS coder. Communication security and modem equipment are also included In
the block diagram but have been treated as part of the communication link. The medium
readability receiver is a loser -gaIvan ometer recorder which is capable of recording on
either dry silver paper or film. The medium readability transceiver is a laser-galva-
nometer scanner which can scan either opaque or transparent products. An artist's
concept of a commercial grade "D" terminal configuration is shown in Figure 4.2.
The laser-galvanometer recorder is located in the center and the smaller scanner unit
is shown to the right. The REARCS coding selector grid and associated push button
selector switches are located on the top surface of the console. The console, as
depicted, contains the data processing, commsec and modem equipment. In practice,
the latter two devices may be required to be physically located away from the terminal
equipment to meet communication security requirements.
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MEDIUM
READABILITY
RECEIVER
MEMORY
BUFFER
REARCS
CODER
MEDIUM
READABILITY
TRANSMITTER
OPERATOR
CONSOLE
32 kb/s
AND LESS
COMM
LINK
Figure 4.1. "D" Terminal Block Diagram
MEDIUM READABILITY
RECEIVER AND
TRANSCEIVER
MICROPROCESSOR
MODEM
COMSEC EQUIPMENT
Figure 4.2. "D" Terminal Artist's Conception
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The principal top level "D" terminal characteristics and performance
parameters are highlighted below:
Laser -Go Ivanometer Scanner (Transmitter)
? Dual Scan Density: 400 and 200 Ipi
? Average scan rate of approximately 30 Ips
? Quantization at 6 bits/sample
? Paper opaque or film transparency input medium
? Nine inch wide by 13 inch long image size
Laser-Ga Ivanometer Recorder (Receiver)
? Dual Scan Density: 400 and 200 Ipi
? 30 lps average scan rate
? Quantization at 6 bits/sample (5 bits/sample preserved on film)
? Recording medium: 200-footrolls of 3M Brand Dry Silver Paper or Film
? Nine inch wide by 13 inch long image size
? Positive or negative recording polarity
Data Compression
? Operator Selectable REARCS with Huffman DPCM Coding
? Three operator-selectable tolerance or deletion modes
Communication Interface
? Digital or Analog Communications Links
? MIL-STD-188C Compatible
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? Compatible with 2.4, 4.8, 9.6, 16 and 32 kb/s modems
? Compatible with most COMSEC equipment
The primary features of the "D" terminal are:
? Unattended receiver operation
? Dry processed recording materials
? Compatible with all other terminals
? Microprocessor controlled coding and terminal control
? Upward compatibility (modularity)
? Up to 32 kb/s transmission rate
? REARCS compression
? Low-cost laser-galvanometer recorder/scanner
4.2 The "DRO" Terminal
The "DRO" terminal is a descoped version of the "D" terminal and
represents the minimum terminal configuration. This terminal is capable of only
receiving medium readability imagery (and lower). Consequently, it need not contain
all of the equipment required for image scanning and REARCS area selection. This
configuration is the one which is most readily adapted to mobile deployable field use.
A block diagram of the "DRO" terminal is shown in Figure 4.3. The performance
parameters and features are identical to those listed for the recording aspects of the
"D" terminal listed in Paragraph 4.1 and are not repeated here.
4.3 The "C" Terminal
The "C" terminal, which is capable of recording and scanning high
readability imagery, is configured as shown in the block diagram of Figure 4.4.
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MEMORY
BU
PROCESSING
MODULE
32 kb/s
AND LESS
COMM
LINK
MEDIUM
READABILITY
RECEIVER
Figure 4.3. I'DRO" Terminal Block Diagram
COMSEC
EQUIPMENT
FILM
PROCESSOR
HIGH
READABILITY
TRANSCEIVER
INTERFACE
EXTENSION
MEMORY
EXTENSION
MEDIUM
READABILITY
RECEIVER
MEDIUM
READABILITY
TRANSMITTER
MEMORY
BUFFER
DATA
PROCESSING
MODULE
COMSEC
EQUIPMENT
REARCS
CODER
OPERATOR
CONSOLE
Figure 4.4. "C" Terminal Block Diagram
32 kb/s
AND LESS
COMM
LINK
The major differences between the "C" terminal and the "D" terminal are the addition of
a drum recorder/scanner (transceiver) which is used only for high readability imagery,
the extension to the memory buffer and interface, and a film processor for the film.
The approach taken to achieve terminal modularity is evident by comparing the block
diagram of the "D" terminal to the "C" terminal. The equipment characteristics are
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EIIT
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identical to those described for the "D" terminal with the exception of those factors
which relate to the high readability transceiver. This equipment consists of a laser
drum recorder/scanner which has the following characteristics:
Single scan density at 800 Ipi
to the
? Single rotation rate at 2,000 r/min
? Six bit quantization preserved
? Scan and record on wet processed silver halide film
? Nine inch wide by 13 inch long copy size
The physical appearance of the "C" terminal equipment is nearly identical
terminal equipment shown as an artist's concept in Figure 4.5.
MEDIUM
REARCS CODING READABILITY
SELECTOR PANEL /RECEIVER
MEDIUM
PHOTO INTERPRETABLE READABILITY
TRANSCEIVER /TRANSMITTER
MICROPROCESSOR(S)
MEMORY EXTENSION
MODEM
COMSEC EQUIPMENT
Figure 4.5. "B" Terminal Artist's Conception
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4.4 The "B" Terminal
The "B" terminal configuration, which is capable of recording and scanning
photo interpretable images, is the most sophisticated and costly of the terminal types.
It is implemented by adding capability to the "C" terminal described in the previous
section. Figure 4.6 shows a block diagram of the basic "B" terminal components.
In this case, the photo interpretable transceiver is an upgraded version of the "C"
terminal drum transceiver and operates at three scan densities; 800, 1,600 and 2,000
lpi. The data processing memory extension is greater than required for the "C" terminal.
The normal interconnection path to other terminals is through the 32 kb/s
link shown at the bottom of the block diagram. This link is used when the data has been
scanned at 400, 800, 1,600 Ipi. A high speed channel (1.5 Mb/s) is shown at the top
of the diagram for use only when 2,000 lpi imagery is to be transmitted to other "B"
terminals. The communication over this link may be made secure and may include
FILM
PROCESSOR
PHOTO-
INTERPRETABLE
TRANSCEIVER
MEDIUM
READABILITY
RECEIVER
MEDIUM
READABILITY
TRANSMITTER
INTERFACE
AND
SWITCH
DATA
PROCESSING
MODULE
COMSEC
EQUIPMENT
32 kb/s
AND LESS
COMM
LINK
Figure 4.6. "B" Terminal Block Diagram
88
MAXIMUM
1.5 Mb/s
COMM
LINK
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some form of simple data compression such as Huffman encoded DPCM. Figure 4.7
shows a block diagram of the major blocks required to configure a special channel from
the PI quality transceiver over a 1.5 Mb/s communication link.
FILM
PROCESSOR
PHOTO-
INTERPRETABLE
TRANSCEIVER
HARDWIRED CPU
BUFFER ENCODER AND
FORMATTER
Figure 4.7. "B" Terminal for Photointerpretable Imagery Over
High-Speed Communication Links
HARDWIRED
BUFFER
700 kb/s
OR
1.5 Mb/s
LINK
The principal features of the "B" terminal are listed below:
? Minimum operator intervention in receiver mode
? Low risk drum technology for PI quality
? Up to 32 kb/s transmission plus 1.5 Mb/s option
? REARCS compression at 32 kb/s
? Two-device recorder/scanner
? Operates at 2,000 Ipi between "B" terminals
? Operates at 1,600 Ipi for backup over lower rate link
? Compatible with all terminals
The ultimate "B" terminal configuration is one which is capable of
transmitting and receiving PI quality imagery over 1.5 Mb/s lines with data compression
in excess of 5:1. This requirement represents a significant departure from those which
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are evaluated in the previous sections. As shown in Paragraph 3.1.2 and 3.9, such a
requirement leads one to a terminal configuration requiring an expensive high speed laser
beam recorder/scanner and special high speed coding and decoding logic.
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SECTION 5.0
PROGRAM CONSIDERATIONS
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5.0 PROGRAM CONSIDERATIONS
This section is devoted to a brief discussion of some program related factors
which are derived from the analyses made and the conclusions reached in the previous
sections. The identified program related factors include recommendations for continued
technical evaluation and testing plus cost estimates which are based on the terminal
configurations discussed in Section 4.0.
5.1 Technical Considerations
During the course of this study several technical questions arose which,
because of the severe time constraints, were not addressed to the depth that is required
for a program of this type. Accordingly, the following list is submitted as a recommen-
dation for consideration as advanced development for the program:
1 . A detailed trade-off analysis of the different source encoding algo-
rithms for application to the nonredundant areas of the REARCS
algorithm is recommended. Analysis of this problem is complicated by
several interrelated factors including technical, operational and data
origination. The technical factor is primarily related to the perform-
ance of the algorithm compared to the complexity of implementing
the algorithm. The emphasis should be placed primarily on a compari-
son of transform codings versus various DPCM entropy-coded
approaches. The operational considerations involve both interface
compatibility between terminals (i.e., should a common algorithm be
used for all terminals?) and the degree of availability of data which
may be available only in Fourier-transformed forms. Thirdly, it is
possible that data which undergoes cascaded source encoding processes
from DPCM through transform encoding may suffer in quality due to
the compounding effects of successive operations. An approach to a
solution requires that the operational questions be addressed first at
the proper clearance level so that the proper framework for technical
analysis and simulation can be established.
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2. A project to determine a practical "filter" which would reduce the
bandwidth requirements of the imagery but still retain adequate infor-
mation for tactical exploitation is recommended. Throughout this study
it has been assumed that a very simple decision process is employed
when high quality imagery is transmitted to less sophisticated and
lower quality terminals. For example, consider the situation of having
2,000 Ipi imagery and a communication bandwidth link to a user which
only allows for 800 Ipi point rastering. One method, and the simplest,
is to transmit one of the pixels in every 2.5 x 2.5 pixel array.
Another approach, and one requiring more storage, is to transmit
one pixel which represents the average value of the pixels in the
2.5 x 2.5 array. This is termed uniform averaging. A more general
approach provides for weighted averaging by transmitting one pixel
which is the weighted average over one or more arrays of 2.5 x 2.5
pixels each.
The analysis of this problem requires a trade-off between implementa-
tion complexity and the potential for improved image quality from
more complex filtering.' The trade-off should be made on the basis of
impact on the "B" and "D" terminal hardware and software performance
and cost. A facility which has the capability for experimentally
altering the filtering operations should be used with standard tactical
reconnaissance photography to evaluate the effects on image quality.
3. It is recommended that the "specifications" for the MTF amplitude, and
phase response for the "B" and "D" terminals be formulated. This
specification should include both amplitude and phase factors extend-
ing from dc to twice the sampling density. The approach recom-
mended is one involving three phases. The first is a detailed analysis
of the terminal recorder/scanner transfer functions including the
effects of spot profile, modulator bandwidth, recording media
limitations, etc., over the operating ranges of the equipment. The
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second is an evaluation of the MTF and phase rolloff sensitivity for
standard tactical reconnaisance imagery which can be determined
largely by experimental techniques. Finally, a detailed second-
level design of the "B" and "D" terminals is recommended which
would include appropriate filtering concepts to achieve the best
performance versus implementation trade-off. The second-level
design effort should also include a careful analysis (and experimental
verification) of the acousto-optic cross-track dither concept and a
thorough characterization of dry silver film and paper for MR and HR
image applications.
5.2 Cost and Schedule Considerations
Previous sections dealt with the application of measurable scientific
principles. This section will deal with the rather subjective areas of cost and schedule.
These parameters could vary significantly depending upon who performs the measurement.
The estimates included here are based upon knowledge of typical imagery and data
processing equipment development and production costs. Both commercial and military
types of equipment will be addressed.
Nonrecurring Activities
Nonrecurring activities are those necessary to take existing equipment,
implement new technology and update the designs to provide prototype terminals meet-
ing the requirements presented earlier. Table 5.1 shows estimates of the costs to the
Government associated with obtaining the first unit. It should be noted that the esti-
mates are in "1976" dollars.
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Table 5.1, First Unit Costs ($000)
Commercial Military
Terminal Type Specifications Specifications
545
1,120
265
560
The nonrecurring cost for the "D" terminal is also
included in the cost for the "B" terminal .
In regard to schedule, the first commercial prototype could be delivered
12 months after go-ahead. The military model would probably take 15 months.
Recurring Activities
Estimates of recurring costs for small (510) lots of terminals in terms of
1976" dollars are shown in Table 5.2.
Table 5.2. Unit Costs in Lots of Ten ($000)
Commercial Military
Terminal Type Specifications Specifications
240
300
100
180
Program Costs
Three theoretical programs have been investigated in regard to costs and
funding requirements. These programs are defined as:
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European Test Net - This program would deploy four "B" and 12 "D"
terminals at selected sites in Europe by the beginning of 1977 for
evaluation under conditions of actual use. The terminals would be
built to commercial specifications.
2. Solid Shield 1978 - This program would deploy five "B" and five "D"
commercially specified terminals within the United States by the end
of 1977 for use in the Solid Shield 1978 exercise. Again, evaluation
would occur as a result of actual use.
3. Normal Preproduction Production Program - This program would be the
normal military hardware procurement program with definition, proto-
type, qualification test, operational evaluation, preproduction and
production phases.
For estimating purposes, four prototypes of each terminal types have
been included with 27 production "B" terminals and 131 production
"D" terminals.
'Table 5.3 shows cost estimates applied by calendar year. Factors were
included for economies in producing quantities and for the effects of inflation. Costs
include nonrecurring efforts and contractor O&M support.
Table 5.3 . Program Costs ($000)
1976 1977 1978 1979 1980 1981 1982 Tota I
European Test Net 2,500 300 2,800
Solid Shield '78 1,300 800 100 2,200
Test Net and Solid Shield 3,500 1,200 100 4,800
Preproduction/Production 1,000 1,500 1,000 6,500 11,000 8,500 3,000 32,500
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APPENDIX Al
EUROPEAN COMMUNICATION NETWORK
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NETWORK CONSIDERATIONS - EUROPE
A look was taken at the assets available for communicating in the European
theater of operation during the 1976/1977 time period and beyond. The available assets
and means in which they might be utilized has been reported. Recommendations as to
what the ground rules might be for establishing an imagery dissemination test in Europe
are discussed. Overall evolutionary trends of the DCS and other interfacing communica-
tions assets are described herein.
It is understood that a demonstration will be established in the 76/77 time
frame in the European theater involving 4 "B" and 12 "D" terminals. No attempt will be
made to select the sites since this is the Government's responsibility, but ground rules
which could affect the successful outcome of the overall experimental test program and
the site selection will be discussed. The flexibility in providing various data rates in
addition to the 2400 b/s test system rate will also be covered. DCA-EUR will allocate
any circuits required in the DCS assets in the European theater. Rules for describing the
needs for the experiment can be derived from the material presented here.
A2.0 EUROPEAN COMMUNICATIONS ASSETS
The current DCS is predominantly analog in nature i .e., the 4 kHz (3 kHz
on some undersea cable and HF radio) frequency-division multiplex (FDM) voice channel
is the carrier of most of the information transferred over the DCS.
The switched voice network commonly known as AUTOVON is a network of
voice channels switched on a space division basis. Data transferred over this network is
converted to quasi-analog signals and synchronization between terminals is on an end-to-
end basis in the form of both bit time recovered from the received signal and frame or
block timing based on specific data stream format. This system is the DCS equivalent of
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the commercial telephone system that we all use at home. In addition to the normal func-
tions of the commercial system such functions as preemption, conferencing, survivability,
and precedence call initiation are provided. In Europe, the primary AUTOVON switch-
ing centers are located in Germany, Italy, England, Greece and Spain as listed in
Table Al .
Table Al . European AUTOVON Sites
Feldberg, FROG Mt. Vergine, Italy
Langerkopf, FROG Martlesham Heath, UK
Donnersberg, FROG Hillingdon, UK
Schoenfeld, FROG Mt. Pateras, Greece
Coltano, Italy Humosa, Spain
An interconnecting network has been assembled between these circuit switch-
ing sites. It is possible to dial anyone in the world who is connected to the AUTOVON
telecommunications network and if the dialing party has the correct level of precedence
and the other party is available a connection can be accomplished. Any terminal inter-
facing with AUTOVON which utilizes the correct addressing scheme as spelled out in the
AUTOVON standards can communicate with another like terminal.
A2.2 AUTODIN
The switched data network is a message store-and-forward switched network.
Data in AUTODIN is transferred over 4 kHz voice channels in a quasi-analog form and
synchronization and encryption is on a link-to-link basis; i.e., from user-to-switch,
switch-to-switch and switch-to-user. It is a master-slave relationship in that AUTODIN
switching centers contain highly accurate clocks and synchronous terminals are configured
to be slaved to the timing recovered from data streams received from the switch. Frame
and block timing is also obtained through the rigid format and protocol used.
In Europe, there are four AUTODIN store-and-forward message switching
centers. These are located in Germany, Italy, and England as shown in Table A2 below.
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Table A2. European AUTODIN Sites
Pirmasens, FROG Coltano, Italy
Augsberg, FROG Croughton, UK
The AUTODIN Switching Center accepts properly formatted data from sub-
scriber terminals. A hierarchical next level subscriber interface point is the Digital Sub-
scriber Terminal Equipment (DSTE). A terminal requiring digital transfer of information to
another terminal may interface either through the DSTE or directly with the AUTODIN
Center once it has been ensured that the proper format and blocking is being used. The
AUTODIN standards specify the proper manner in which terminals may interface this store-
and-forward message switching network.
A2.3 AUTOSEVOCOM
The current secure voice network is switched on a space-division basis over
a combination of 4 kHz voice channels and special 50 kb/s conditioned circuits. Depend-
ing on the specific circuit setup, synchronization is either on an end-to-end basis or on a
user-to-switch-to-user basis or the switch would regenerate the signal .
There are four AUTOSEVOCOM wideband AN/FTC-31 switch sites located
in Europe. These are located as shown in Table A3.
Table A3. European AUTOSEVOCOM AN/FTC-31 Switch Sites
London, UK Heidelberg, FROG
Weisbaden, FROG Stuttgart, FROG
The current application of this system is to interconnect localized subscribers
(those within 20-30 kilometers of each other via a special 50 kb/s wideband service
which is automatically switched through the FTC-31 switches), If a long-houl intercon-
nection is required, there is an operator-controlled switchboard called the SEVAC associ-
ated with each FTC-31 that allows narrowband 2.4 kb/s to 9.6 kb/s interswitch connection.
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Thus, a 50 kb/s subscriber in the London area can be connected to a similar sub-
scriber via the narrowband trunk in the Heidelberg area. The system could be modified to
transfer digital data in the immediate areas of each switch at 50 kb/s, or through an aug-
mented store-and-forward method send the data long distance through the narrowband
trunks. This could be considered as an optional secure communications capability if prop-
erly modified for an experiment. The need for mentioning this possibility here is coupled
with the knowledge that the DOD secure voice capability will be changed in the future
such that the current AUTOSEVOCOM system is no longer required.
A2.4 DCS Transmission Facilities
There is a significant network of transmission facilities interconnecting the
DCS in the European theater of activity. The media includes microwave, cable, tropo-
scatter communication, HF radio and commercial PTT facilities.
Since many of these transmission media interface at relay nodal points, it is
not necessary to access the system solely at AUTODIN or AUTOVON switching centers.
If a given relay point, let's say, for a microwave connection between two switches has
what is called drops, it is possible to enter at this point. In other words, at a given nodal
point very often (as can be seen by the attached representative diagram of a subsector of
the European theater) the groups of voice grade channels or trunk subsets are split and
sent to more than one switching center. Based on the fact that FDM multiplex schemes are
currently used, it is possible to enter the system not only at a voice grade level (4 kHz
channel) but at the group or supergroup level or, indeed, through proper priority at the
microwave level itself. Thus, high data rate modems operating at 48 kb/s upward could
be utilized if properly interfaced with either the multiplex banks at relay nodes or at the
switching centers themselves.
There is currently one satellite ground station terminal associated with the
DCS that is located at Landstuhl . This terminal among other destinations can connect
with Ft. Dix in CONUS.
A summary of the transmission facilities that are utilized in the European
theater is shown in Table A4.
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Table A4. Transmission Facilities - Europe
Microwave
Tropo
Other
FRC-37
FRC-75
Cable
MW-508D
MRC-80
HF TRC-24
MW-509E
FRC-96
TELPACK
LC-8
FRC-136
SATCOM Terminal
74A2
MRC-98
HM-510/560
MRC-121
TRC-180
TRC-66
TRC-150
FRC-56A
FRC-109
FRC-39
LC-4
FM-120
FRC-80
FRC-147
EM-12/400
MW-503
FRC-84
A3.0 TEST RECOMMENDATIONS
The factors that will have an impact on the design of an experimental imag-
ery dissemination effort in the European theater of operation are discussed in the following
paragraphs. Of particular interest are comments on the rules that should be adopted in the
planning of a successful experiment for the dissemination of secure imagery through auto-
matic or manual means.
A3.1 Nodal Adjacency
It is very important that the tail connections to nodes or switching centers be
minimized in length. The longer the tail, the more corrupt it becomes from the standpoint
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 [
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of noise or other external influences. These factors become more important when rates in
excess of 2.4 kb/s are contemplated. The AUTOVON system was fundamentally designed
as an analog voice switching and transmission network. Therefore, its main distribution
frames and tech control facilities are subject to digital crosstalk based on the fact that
they were not designed to attenuate this sort of disturbing factor. Also, if terminal site
locations are adjacent to major nodes, facilities are more likely to be available.
The AUTODIN sites are RED from a TEMPEST standpoint. Therefore, if
terminal equipment is to be housed within their environs (should there be any space avail-
able), it must fully meet the TEMPEST requirements. On the other hand, the AUTOVON
and nodal locations are BLACK in nature.
It is possible to enter the system through any number of means but primarily
the multiplex plan affords the flexibility of possibilities in the voice grade bandwidth
area. The sort of diagram as attached hereto is available for the entire European theater
of activity and can be used in order to plan a basic interconnection of the imagery termi-
nals to the overall system for communications purposes.
A3.2 Data Rate,Considerat ions
The fundamental rates of AUTOVON and AUTODIN are at 2.4 kb/s with
upgrade contemplated to 4.8 kb/s in the future. It is possible to utilize specially designed
modems which can interface directly at the group, supergroup or multi-supergroup level at
the FDM multiplex bays. In this manner, it is possible to achieve rates up to and including
48 kb/s, 240 kb/s and 960 kb/s (for four supergroups). The FTC-31 wideband secure
voice switch could be modified to provide local area 50 kb/s digital interconnection on an
automatic basis. The FKV interconnect system will have the ability of providing 1.5 Mb/s
at the trunking level . Also, it is possible to directly enter the radio systems and achieve
very high rate digital interconnections but at the expense of interrupting the normal tele-
phone network interconnection. This very likely would not be possible for an experimental
program.
When the initial TRI-TAC switches are introduced into the European field,
it will be possible to obtain trunk capability between 1 and 20 Mb/s and tail capability
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LANGENDAMM
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at 16 or 32 kb/s. An 8/16 kb/s wire line modem is being developed by Harris ESD under
the auspices of RADC. This modem in its early development form may be available in
several copies during the time frame of the planned experiment. The 16 kb/s rate is only
adequate when utilized with CVSD voice analog-to-digital conversion since it essentially
will have a BER on the order of 10-2. The eight kb/s mode will have a 10-5 BER which
will be adequate for the imagery interconnection. This development should be kept in
mind in the experimental planning. There are quite a few modems available that could
serve each and every of the data rates mentioned above. Therefore, they are generally
not considered a problem unless it is necessary to squeeze into a rather narrow channel
bandwidth such as a voice grade four kHz bandwidth with eight kb/s of data. Harris ESD
is also developing a two bits/Hz modem to be utilized for digital trunking applications
and also is being developed under the auspices of RADC. The considerations relating to
KG's are detailed later in Paragraph A3.7.
A3.3 Dial-Up Considerations
It will be possible to conduct automatic dial access to desired imagery ter-
minals connected to the AUTOVON System through conventional pushbutton matrix ini-
tiation. The matrix is conventional from the standpoint of AUTOVON since it has addi-
tional pushbuttons relating to the levels of precedence invoked in that system.
It will be possible to either use a telephone subset in conjunction with the
imagery terminal or to build in this function as desired.
A3.4 Dedicated Interconnections
It is possible to provide a strictly preassigned interconnection system on
either a point-to-point or multiline point-to-point basis. The dedicated system would
allow intercommunication between any two terminals at one given time through the selec-
tion of the proper dedicated channel by the terminal operators.
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A3.5 Operator Intervention
It is possible to provide a manual interconnection for purposes of conducting
the imagery dissemination experiment through tech control patching at the nodal or cir-
cuit switching centers. This could be operationally adequate for the experiment but would
not be amenable to long-term implementation of the theater dissemination system. If the
AUTOSEVOCOM is modified and the SEVAC is used, an operator intervention is normally
provided for the 50 kb/s interconnections should the terminal operators desire such assis-
tance. This only applies to the case where long-haul narrowband trunking is associated
with the 50 kb/s to local service.
In the case of manual PBX operation, an operator can be employed to con-
duct the interconnection on a requested basis.
A3.6 Certified Facilities/Clearances
Since it is expected that real intelligence imagery will be transferred
during the experimental tests in Europe, it wi I I be necessary to have RED facilities from
the TEMPEST standpoint. This also implies the use of crypto equipment for protection of
intersite connections.
It is essential that any special clearances required for contractor personnel
to obtain access to the sites where the terminals are to be utilized must be acquired in
plenty of time in order that delays in entry do not disturb the overall experimental test
program. We have recently participated in the conduct of tests of the EICS system devel-
oped by Harris ESD at Ramstein and Schierstein in the FROG. Careful planning was
required in order to ensure the smooth running of those tests.
A3.7 COMSEC Considerations
The AUTOVON System can provide digital interconnection when used
with 2.4 kb/s modems. There are a number of contemporary cryptographic equipments
that can satisfy this need. Examples are the members of the KG-30 series, the anti-
quated KG-13, the new KG-81 or KG-82, the KG-28, etc. If there is a system need to go
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to data rates in excess of 1 Mb/s with the KG-30 series, the HN-74 phasing unit is
required. This allows secure operation in excess of the 1 .5 Mb/s contemplated for the
imagery dissemination terminals.
If the FTC-31 switches are used for local 50 kb/s routing, the same KG's
as above could be used after one deletes the KY-3 units from the system. Interswttch
narrowband trunking via SEVAC could be accomplished directly with the current KG-13
units operating at 2.4 kb/s.
When the TRI-TAC System is employed in the field, operation will be con-
ducted at 32 or 16 kb/s using the LKG. The TED is generally planned for trunking at
either a trunk level or submultiplex level between TRI-TAC switches. However, these
units (LKG and TED) could be utilized in other non-TRI-TAC related applications. The
TRI-TAC use could only be employed if the experiment was delayed by some time. A
ruthless preemption could be employed in that case and up to 20 Mb/s trunks could be
utilized if the imagery data were important enough. A current system for interconnecting
the U. and S. CINCS is currently employed which utilizes ruthless preemption at 50
kb/s for secure voice conferencing.
A4.0 COMMUNICATIONS TRENDS IMPACTING EUROPE
The evolving communications technology and plans that will affect the
dissemination of imagery in the European theater (and elsewhere) are now discussed. Since
the actual deployment is a function of the budgetary and political policies of several
future administrations, actual dates have no real significance in depicting the evolution.
In their place the time periods have been called near future, digital growth explosion and
future integrated digital network. A guess for the three periods would be the present to
1985, 1978 to 1995 and 1985 to 2015.
A4.1 DCS-Near Future
This period in the DCS evolution consists of two major thrusts; that is, con-
version of transmission paths to digital operation and conversion of switching to time
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division techniques. implementation of the transmission path conversion is currently
in progress on a relatively small scale test bed basis and will continue throughout the
conversion process. Implementation of the switching hierarchy conversion will start in
the near future.
A4.1.1 The FKV Project
This project is being implemented. In involves conversion of selected line-
of-sight microwave links in Germany from FDM/FM operation to PCM/TDM/FM operation.
The paths connect Frankfurt, Koenigstuhl and Vaihingen, thus FKV. It utilizes both
commercial and military versions of the Bell System PCM/TDM hierarchy. All analog
signals (voice, quasi-analog, data signals, signalling tones, facsimile, etc. are converted
to digital signals in a two-step process; i.e., amplitude sampling of the analog signal at
an 8 kilosamples per second rate, and quantizing of these samples into 256 levels using an
8-bit word. The eighth bit is also shared as a signalling channel for supervisory signals
(on/off hook, etc.). The individual quantized signals are time division multiplexed into
a composite signal of 1.544 Mb/s representing the equivalent of 24 voice channels.
Data stream users in digital format can also be accommodated in later configurations of
this first-level TDM; i.e., digital I/O cards can be substituted for voice channel cards
on a one-for-one basis to provide 0-50 kb/s and 56 kb/s asynchronous ports, and 56 and
64 kb/s synchronous ports. The asynchronous ports are accommodated through buffering,
bit stuffing and encoding techniques while the synchronous ports are clocked by the TDM.
The second level TDM accepts from two to eight of the first level streams on
an asynchronous basis, i.e., each first-level TDM uses an independent internal clock at
a nominal 1.544 Mb/s rate. Second level synchronization is accomplished through a
combination of buffering and bit stuffing. The composite stream is then converted to a
three-level partial response signal and applied to the FM modem of an analog oriented
LOS path on a link-to-link basis through conventional receive time recovery techniques.
First-level TDM synchronization is via the buffer/bit stuff/unstuff processing. Quasi-
analog data users via the PCM voice channel maintains synchronization on an end-to-end
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basis; data users, via the digital ports, maintain synchronization through the buffer/bit
stuff/encoding processing in the first-level TDM for asynchronous users, and on a master-
slave basis for synchronous users with the user slaved to the first level TDM as master.
The beauty of this scheme is that while it permits conversion of transmission
links to digital operation with its inherent improvement in performance for both voice
and data users it also permits retention of all existing analog voice channel space-division
switching and data message store-and-forward switching.
A4.1 .2 Project DEB
The next step in transmission path conversion if Project DEB which is a
series of phased tasks for further conversion of the European LOS links to digital operation.
Although at the time of this writing a final decision has not been made, it appears that
early phases will be a refinement of the FKV project. Additional LOS links will be con-
verted to digital operation utilizing the three-level partial response modulation scheme
over the FM LOS radio path. However, a Digital Applique Unit (DAU) is being devel-
oped which adds considerable capability to the subsystem. In FKV, the binary-to-partial
response signal conversion is accomplished as a function of the second-level TDM as is
recovery of bit timing interval in the TDM receiver. Radio path diversity combining/
switching and hot standby switching are still performed on an analog parameter detection
basis at the IF frequency or at the FM baseband. The DAU concept combines the three-
level partial response modem, a local clock, diversity switching/combining, receive bit
time recovery circuitry, a means of pseudoerror performance monitoring, insertion/
removal of digital order wire channels, hot standby switching control, a message stream
randomizer and other digital functions in a common facility. It is arranged to be either
synchronous on a link-to-link basis with the DAU clock and receive time recovery clock
providing timing to the TDM hierarchy, or to operate as a slave to a station master clock
which can be an independent clock or a nodal clock in a timing/synchronization subsystem.
The TDM hierarchy will also be refined in order to provide 8,000 n bits per
second I/O ports for compatibility with the new 8,000 n bits per second standard data
rate users; the TDM will also be arranged to be convertible from the asynchronous bit
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stuff mode to a synchronous nonbit stuff mode TDM. These innovations represent good
planning in that provisions are made for introduction of synchronous operation at any
time period.
Later phases of the DEB project wi II probably introduce a new digital radio;
i.e., one which eliminates the FM modem and substitutes a digital modem at an IF inter-
face. This is known as the DRAMA terminal and includes the multiplex and radio functions.
This radio can be operated on a link-to-link synchronous basis or as a slave to an external
clock. From the network timing point of view, the new digital radio is similar to the
DAU concept except for greater bit rates and some potential improvement in performance
in terms of average BER, availability in terms of average BER, and in mean-to-loss of
bit count integrity during deep fades. The latter is extremely important in the case of
maintaining cryptographic synchronization.
Harris ESD is directly involved in these efforts by our participation with
RADC to develop a 70 MHz IF interface digital modem having a 2-bit/Hz bit density at
RF, our internal R&D program to develop the DAU, our contract with RADC to develop
the concepts and initial units of an 8 kb/s/16 kb/s wire line modem, and our participation
with DCA and the Army in developing specifications for the digital radio and conducting
a study of the precise time and time interval requirements for the evolving DCS.
A4.1 .3 Digital Tropo
Another ongoing project is the development of a digital modem for use
with tropospheric scatter radio links. This modem will interface with the same multiplex
hierarchy as will the LOS links and be configured to be synchronous on a link-to-link
basis or be slaved to an external clock. The primary difference of the digital TROPO
link will be the lower grade of performance in terms of bit error rate, bit count integrity,
availability due to the more frequent deep, rapid, and dispersive fades and a wider
variation in path length due to these fades.
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A4.1.4 Bulk Encryption
Another significant change during these efforts is the introduction of bulk
encryption; i.e., at various levels in the TDM hierarchy as opposed to encryption on an
individual user channel basis. Encryption will also take place on a user channel basis,
where required, but all information traversing the digital transmission link will be
encrypted on a bulk basis. These bulk cryrptodevices will be arranged to receive timing
from the modem/TDM hierarchy or from an external clock source. The actual devices
devised for this application are the Trunk Encryption Devices (TSEC/KG-81).
A4.1.5 DSCS
The DSCS will also undergo an evolution to synchronous digital link opera-
tion. Although the present DSCS links primarily serve unique users requiring wide band-
widths and access to remote areas, the future DCS concept envisions a more extensive
utilization of satellite links for internodal trunks and conversely the terrestrial DCS will
provide extensive extension of the satellite channels to users remote from the earth
terminal.
The DSCS conversion, in most respects, parallels that of the terrestrial
LOS links; i.e., some link conversion on the basis of PCM,TDM/FM and most on the
basis of single channel per carrier digital modems. Harris ESD is participating in these
efforts with SATCOMA by having developed the PSK and QPSK modems being used in
the DSCS terminals. The digital DSCS terminals will also contain a timing distribution
capability. On the receive end of a link, buffers will be utilized to accommodate the
Doppler effects and path length variations caused by the cyclic satellite pattern. A
portion of the satellite transponder will be arranged to provide a frequency or timing
beacon, receivable by all earth terminals and traceable to universal time. At the earth
terminals, this signal will be used to slave modem and multiplex clocks.
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A4.1 .6 Introduction of Time-Division Swtiching
Introduction of time-division switching which is a combination of temporal
and spatial switching in conjunction with a supporting time-division multiplex hierarchy
forces the issue of synchronous nodes.
In a time-division multiplex/switching environment with bit streams arriving
from many diverse sources with varying degrees of connectivity, each incoming bit must
be available to enter its assigned timeslot at the specified instant it is required. An
ideal system of course with exact time at every node and fixed delays between nodes
could easily accommodate this requirement. However, in the real-world environment,
these conditions do not exist and there are variations in both time and path delay between
nodes and between users and nodes.
Two major DCS programs and one major technical program force this decision;
i.e., DCS Secure Voice II, DCS AUTODIN II, and TRI-TAC.
Secure Voice II
Secure Voice II envisions conversion of CONUS users to 8 kb/s operation
using voice channel modems for transmission and AUTOVON space division switching
modified to accommodate the 8 kb/s quasi-analog signals. However, in overseas locations,
during the same period, 16 kb/s secure voice will be introduced in conjunction with a
DCS digital time-division switch (this switch may or may not be a configuration of the
TRI-TAC switch).
Interface between the CONUS and overseas subsystem wi I I be at a
MAROON interface. Somewhat later some of the CONUS AUTOVON switches wi II be
modified to switch the 8 kb/s users on a time-division basis. Also during this period,
lower level time-division oriented facilities will appear; e.g., digital PABX and digital
access exchange (DAX).
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AUTODIN II
AUTODIN II plans not only to provide for computer teleprocessing and
record communications for common users but also must provide for absorbing certain
dedicated networks such as WWMCCS and SATIN IV. In the initial stages, the CONUS
switches will be modified to provide packet switching for several hundred terminals and
processors while continuing to provide message store and forward switching to the bulk of
its users. Later during this period, time-division circuit switching and multiplexing and
lower level time-division oriented concentrators or communications access processors will
be introduced in the CONUS AUTODIN II complex. Overseas the conversion plan is
similar except for a later schedule and Military ownership versus leased facilities in
CONUS.
Another significant change introduced by AUTODIN II is the provision for
end user-to-end user encryption through the seitched netwoek as opposed to the current
user-to-switch, switch-to-switch and switch-to-user encryption. This is significant
because the existing synchronization in AUTODIN follows the link-to-link encryption
scheme and must also follow the AUTODIN II end-to-end encryption concept.
TRI-TAC
TRI-TAC is the joint Military tactical communication system and, as such,
is not part of the DCS. However, the TRI-TAC transmission plan depends on the use of
DCS trunks to interconnect some of the TRI-TAC switching, multiplex nodes. The TRI-
TAC switch is being designed as a multifunction switch; i.e., it will handle analog voice,
digital voice, and data traffic. It is a secure system and utilizes 16/32 kb/s rates for
the secure voice. It will provide time-division circuit switching for voice and data and
message store and forward switching for record communications. There is no switching
hierarchy; i.e., all TRI-TAC switching centers (AN/TTC-39 switches) operate on a
lateral basis. However, when connected to a DCS node for transmission trunking, they
will appear as a minor node with unique characteristics.
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The TRI-TAC switch subsystem consists'of subscribers, digital switchboards,
encryption devices and the switch, all of which are interconnected via a time-division
multiplex hierarchy and, in turn, trunking between switches is via a time-division multi-
plex family. All of the devices and links within a single switch subsystem are synchro-
nized on the master-slave basis to an atomic standard clock.
The first few TRI-TAC switches will be introduced during the same general
period as the limited introduction of Secure Voice II and AUTODIN II time-division
switching.
A4.2 The DCS-Digital Growth Explosion
This period consists of all the time between the limited introduction of time-
division switching and up to the time at which the DCS is a totally integrated digital
switch network. AUTODIN II, Secure Voice II and TRI-TAC time-division switches
will be widespread and the great bulk of transmission links will be digital links. Digital
subscribers will number in the 30-50,000's and switching nodes will number in the 20-30
range. The switching centers will be well established in a tandem and regional switch
hierarchy.
This hierarchy is based on the concept of the tandem switch being a trunking
switch serving AUTODIN II regional switches, Secure Voice II digital switches and TRI-
TAC switches; i.e., users would not normally home on a tandem switch. The concept
also envisions that a tandem switch would always be colocated with a regional switch
and include the functions of a major Secure Voice II switch.
The tandem switch thus becomes the DCS major node in that it is the major
interface between the backbone trunking subsystem and the time-division centers pro-
viding access to that trunking for all users via their respective lower level switching
center.
The regional switch center, Secure Voice II switch and TRI-TAC switch
then become minor nodes in that they are the interface between the tandem switch (via
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digital links of a few feet to many miles) and the next lower level which can consist of
users, digital PABX's, DAX, unit level switches (ULS), communications access proces-
sors and independent user susbystems. Minor node switches wi II normally home on two
tandem switches to provide link redundancy.
From the present period through this growth period and on into the final
period, other digital system conversion efforts may be implemented by others and must
be considered since the DCS interfaces with these systems and, indeed, in some cases is
highly dependent on them. These systems are, of course, the commercial carrier systems,
foreign and domestic, and military systems, other than TRI-TAC, including NATO and
other allied forces. Foreign common carriers are embarking on digital conversionplans
similar to that of the U.S.carriers although somewhat delayed in implementation schedule.
INTELSAT is moving toward construction of PCM/TDM/QPSK/TDMA links
at bit rates of 50-150 Mb/s. These satellite links wi l l operate in a burst mode with pre -
cise on-off carrier control at the transmitter. Receivers will have very rapid carrier and
timing interval acquisition capabilities and all earth terminal input/output port users
must be synchronous with directly related data clocks by a master-slave relationship with
the earth terminal.
NATO and Allied Forces interfaces are well documented in the final report
of the DOD Committee on Interoperability and much of the specific data is classified.
However, in general, these systems are adopting the 8,000 nb/s structure and 16/32
kb/s rates for digital voice; the NATO satellite trunks, now FDM/FM, appear to be
headed toward an 8,000 nb/s digital structure upgrade.
This period is truly one of the digital explosion; not only in terms of the
DCS but also including all military and commercial systems. The "wired city" concept
will appear on military installations as well as in the cities. New local area distri-
bution transmission links, such as optical waveguide, fiber optics, millimeter wave-
guide and LOS radio will enter the various subsystems.
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A4.3 The DCS-Future Integrated Digital Network
This period is conceived to provide a switching, trunking and user access
network to provide access for any type of subscriber or subsystem for communications of
all types of information within bandwidth constraints to other subscribers or subsystems,
within the same community of interest or between communities of interest, on an end-to-
end secure basis; the JMTTS Concept.
This period would seem to be easier to accommodate than the previous
explosion period. Most, if not all, of the analog facilities will have been converted to
digital operation, the myriad of interface problems will have been solved, and growth
will have slowed to a more reasonable rate. All of this would be true, if technology
would stand still. However, it will not and so the problems presented by, this period
and those following are predominantly those of future technology and its potential
demands and impact on the DCS.
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