Document text
(KASA-CE-151584) EVAiaATICW OF S'-BAND Fm" ■ - * ^78-15330
DIRECT IIITK SIGHAl 'AND SISTEH' DESIGN ‘ Final
Report .(Axiomatix, ■ Marina del Eey, Calif,.)
111 p HC A06/HF A01 ■ . CSCI^ 17B. - ' '' Unclas'
G3/32" 59491
Marina del Rey » California
EVALUATION OF S-BAND FM DIRECT LINK
SIGNAL AND SYSTEM DESIGN
CONTRACT NO. NAS 9-14870
FINAL REPORT -
■ „ ■ PREPARED TOR
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
LYNDON B. JOHNSON SPACE CENTER
■ .... HOUSTON, TEXAS 77058
' * ' . *
PREPARED BY
AXIOMATIX
13900 PANAY WAY, SUITE llOM
MARINA DEL REY, CALIFORNIA 90291
Axiomatix Report No. R7609-3
September 27, 1976
TABLE OF CONTENTS
original ®JS
OP POOR OUALrofi
Page
LIST OF TABLES ' iii
LIST OF FIGURES : . 1v
1.0 INTRODUCTION ' 1
2.0 DESCRIPTION OF CURRENT (BASELINE) S-BAND FM LINK DESIGN 2
2.1 Functional Requirements - NASA Missions 2
■ 2.2 Functional Requirements - DoD Missions 5
2.3 Performance Requirements -5
2.4 Signal Characteristics : 5
2.5 Orbiter Signal Design Parameters (Modulation
Characteristics) 6
2.6 Orbiter RF Parameters • 12
2.7 Orbiter Antenna Characteristics ■. . . . 14
2.8 Ground Station Characteristics 21
3.0 PERFORMANCE PREDICTIONS - ■ ' 23
3.1 Mathematical Models 23
3.2 Circuit Margins Using Nominal (+1 dB) Antenna Gains
and Orbital Slant Range 30
3.2.1 Link Geometry . /. . . 30
3.2.2 Television Circuit Margins , .■ .. : ... 30
3.2.3 Main Engine Data Circuit Margins 34
3.2.4 'Real-Time Attached Payload Data Circuit Margins ... 34
3.2.5- Playback Data Circuit Margins 39
3.3 Performance During Ascent ' .42
3.3.1 Ascent Geometry 42
3.3.2 Ground Station Availability 47
3’.3.3 Ascent Signal Strength Calculations 49
4.0 ASSESSMENT OF ADEQUACY OF S-BAND FM LINK TO SAFETY
. REQUIREMENTS '59
5.0 RECOMMENDATIONS ' ’ 60
APPENDIX A. LOW DATA RATE FM LINK TEST REPORT 62
APPENDIX B. SHUTTLE FSK DATA LINK. OPTIMIZATION TEST REPORT 72
APPENDIX C. DEVELOPMENT FLIGHT INSTRUMENTATION (DFI) LINK 96
APPENDIX D. APPROACH AND LANDING TEST (ALT) TELEMETRY LINK 101
ii
Table
LIST OF TABLES
Page
1. Television Baseband Parameters 9
2. G-STDN S-Band Parameters . . . ; 22
3. SCF S-Band Parameters -22
4. Circuit Margin Calculation Summary Sheet - Orbiter-to-
G-STDN S-Band FM Downlink Television Channel (30-foot
station, OFT Orbiter configuration) 32
5. Circuit Margin Calculation Summary Sheet - Orbiter-to- •
G-STDN S-Band FM Downlink Main Engine Data Channels,
576 kHz Subcarrier (30-foot station, OFT Orbiter
Configuration) ‘ 35
6. Circuit Margin Calculation Summary Sheet - Orbiter-to-
G-STDN S-Band FM Dov/nlink Main Engine Data Channels, .
768 kHz Subcarrier (30-foot station, OFT Orbiter
Configuration) 36
7. Circuit Margin Calculation Summary Sheet - Orbiter-to-
G-STDN S-Band FM Downlink Main Engine Data Channels,
1024 kHz Subcarrier (30-foot station, OFT Orbiter
Configuration) , • 37
8. Circuit Margin Calculation Summary Sheet.- Orbiter-to-
G-STDN S-Band FM Downlink Real-Time Attached Payload
Analog Data (4 MHz) 38
9. Circuit Margin Calculation Summary Sheet - Orbiter-to-
6-STDN Operational S-Band FM Downlink Real-Time Attached
Payload Digital Data (5 Mbps) '40
10. Circuit Margin Calculation Summary Sheet - Orbiter-to-SCF
S-Band FM Downlink Payload Data Channel (256 kbps) 41
11. Circuit Margin Calculation Summary Sheet - Orbiter-to-
G-STDN S-Band. FM Downlink Playback of Recorded 01 or
' MSS Data (1024 kbps) - 43
12. C-ircuit Margin Calculation Summary Sheet - Orbiter-to-SCF
S-Band FM Downlink Playback of 01 or MSS Data (960 kbps) .... 44
m
LIST OF FIGURES
Figure Page
1. S-Band FM Direct Downlink Functional Configuration
(Orbiter-to-G-STDN) . . . . ' . 4
2. Main Engine Data Block Structure 7
3. Television Composite Video Waveform 8
4. Playback 01 Telemetry Frame Format (High Data Rate Mode) ... 10
5. Baseband TDM Frame Format for the Return and Direct
Downlinks (High Data Rate Mode) - 11
6. Interconnection Diagram - S-Band FM System Coaxial
Cables and Antennas 13
7. S-Band Flush-Mounted Antenna Locations . . 15
8. Expected and Desired, Gain Contours for Hemi Antennas 16
9. Sketches Indicating General Nature of Pattern Measure-
ments for Orbiter Hemi Antennas (Orbiter/ET/SRB
Configuration) ' 17
10. Composite Radiation Distribution Pattern for Shuttle
■ S-Band Hemi Antennas (Orbiter Only) .... 18
IT. Composite Radiation Distribution Pattern for Shuttle •
S-Band Hemi Antennas (Orbiter/ET) . . .' ' 19
12. Composite Radiation- Distribution Pattern for Shuttle
S-Band Hemi Antennas (Orbiter/SRB/ET) . . . i • 20-
13. Link Geometry for S-Band FM Downlink '31
14. Shuttle Launch Pad/Ground Station Locations for KSC 45
15. Shuttle Ascent Trajectories ' . . . 46
16. . Potential Ground Station Coverage for Shuttle Ascent 48
17. Signal Strength Measurements for Reference Mission 1
(Due East) at MIL 50
18. Signal Strength Measurements for Reference Mission 1
(Due East) at VAN '. . . . 51
19. Signal Strength Measurements for Reference 'Mi ssi.on 1
(Due East) at BDA 52
iv
Figure ■ Page
20'. Signal Strength Measurements for Reference Mission 1
(Due East) at ROS 53’
21. Signal Strength Measurements for Reference Mission 2
(37.88 Azimuth) at MIL . . . 54
22. Signal Strength Measurements for Reference Mission 2
(37.88 Azimuth) at VAN 55
23. Signal Strength Measurements for Reference Mission 2
(37.88 Azimuth) at BDA 56
24. Signal Strength Measurements for Reference Mission 2
(37.88 Azimuth) at ROS 57
1
1.0 INTRODUCTION
The' Shuttle Orbiter will have several communications links, depending
on the particular type of mission involved and depending on the mission
phase. The primary support network for NASA missions wi.lT be the Space
Tracking and Data Network (STDN), which will include the Tracking and Data
Relay SatelTi-te System (TDRSS')' and a few (ultimately 3 to 5) ground stations
(G-STDN). The primary support network for DoD missions will probably also
be the NASA STDN, although there is a definite requirement for direct com-
munications with the USAF Satellite Control .Facility (SCF). The Shuttle
communications links and services may be categorized as shown below:
A. S-Band Direct Links (G-STDN or SCF) ■
e PM Uplink (voice, commands and ranging)
*' PM Downlink (voice, telemetry, and ranging)
e FM Downlink- (television, recorder playback, main engine data,
and payload. -data)'
B. S-Band Relay. Links (TDRSS)
• -PM Uplink (voice and commands)
e PM Downlink (vdice and telemetry)
C. S-Band Payload Links
9 Orbiter-to-Payload (commands)
'• Payload-to-Orbiter (telemetry)
D. KU-Band Relay Links (TDRSS)
Uplink (voice., commands, and text/graphics)
® Downlink (voice, telemetry, television, payload data, and
recorder playback)
E. UHF Direct Links
« ATC voice
r EVA voice/ telemetry.
2
The purpose of this report is to assess the adequacy of the S-Band
FM Downlink to satisfy all known requirements during all mission phases.
Some potential performance problems are described in subsequent sections
of the report and corrective actions are recommended when appropriate.
■2.0 DESCRIPTION OF CURRENT (BASELINE) S-BAND FM LINK DESIGN
2.1 Functional Requirements - NASA Missions
A general requirement for Shuttle RF communications is that services
be required as specified during the following mission phases: ■
• Prelaunch'
• Liftoff (SSO/ET/SRB mated ascent)
.’9 Ascent (SSO/ET)
t' On-Orbit Operations
« Reentry
■® Landing
• Post-Landing . . ■
The specific functional requirements which have been imposed on the
*
S-Band FM direct downlink for NASA missions (whenever direct Orbiter-to-
G-STDN line-of-sight exists) are for transmission of one Cat a time) of the
following :
t
9 Three independent 60 kbps digital real-time main engine
data channels
9 Real-time television composite video
e Real-time attached payload data (analog up to' 4 MHz or
digital up to 5 Mbps)
e Playback digital data from the Operational Instrumentation
(01) recorder, consisting of one at a time of the following:
(1), Playback, of any one recorded 60 kbps main engine data
channel at any one of four playback data bit rates from
60 kbps (1:1 playback) to 960 kbps (16:1 playback) as
3
60 kbps (1:1 playback) to 960 kbps (16:1 playback) as
established prior to each mission.*
(2) Playback of recorded 128-kbps PCM telemetry data at any
one of three playback data bit rates from 128 kbps (1:1
playback) to 1024 kbps (8:1 playback) as established
prior to each mission.*
(3) Playback of recorded 192-kbps timetdivision-multiplexed
(TOM) data (128-kbps PCM telemetry plus two 32-kbps .
-digital voice channels) at any one of two playback data
bit rates— 192 kbps (1:1 playback) and 960 kbps (5:1
playback) — as established prior to each mission.*
• Playback digital data from the’Mission Specialist Station (MSS)
recorder at a playback data bit rate up to 1024 kbps.
Figure 1 shows the functional interface configuration for this link.
In the Orbiter FM. signal processor, the three real-time main engine data
channels (at 60 kbps each) phase- shift-key (PSK) three subcarriers at
576 kHz, 768 kHz, and 1024 kHz, respectively, which are then frequency-
division-mul tiplexed into a single analog main engine data signal. The FM ‘
signal processor accepts. one of its input analog or digital data signals
or the FDM main engine data signal to frequency modulate (FM) the link
carrier (2250.0 MHz). At the ground station, the carrier modulating signal
is recovered^' by an FM wideband receiver and demodulator. The ground station
signal processor routes the postdetection signal as required.
★
Each of the three 60-kbps main engine data channels is recorded by
one of the two Orbiter recorders, and either the 128-kbps PCM telemetry
data or the 192-kbps TDM data (one at a time) is recorded by either of
the two Orbiter. recorders. The playback data bit rate is the real-time
data bit rate multiplied by the ratio of the playback to the recording
tape speed. Each recorder has four selectable tape speeds during a mission
which are pre-mission wired from 14 possible tape speeds. The possible
tape speeds for recording 60-kbps main engine data are 15, 19, 24, and
30 inches/second, and for recording 192-kbps TDM data are 24, 30, or 38
inches/second. The other possible tape speeds are 6, 48, 60, 76, 96, and
• 120 inches/second.
o o
8 §
**To be removed after OFT Flights (1-7)
Figure 1 .
S-Band FM Direct Downlink Functional Configuration (Orbiter-to-G-STDN)
5
2.2 Functional Requirements - DoD Missions
For DoD missions, the S-Band FM downlink functional requirements are
generally the same as for NASA missions, with the exception of a- lack of
requirement for television and that the maximum playback data bit rate of
recorded data is 960 kbps. At this stage of the Shuttle program, however,
plans for operation of DoD missions have not been firmly established, and
it is very possible tha1: requirements for other services (such as the main
engine data channels) may disappear.
2.3 Performance Requirements
The maximum received information bit error probability at the STDN
ground stations for any of the digital data channels described previously -
will be 10~^ for NASA missions and 10“^ for DoD missions in. which data
encryption is employed. The minimum received peak-to-peak television com-
posite video signal to RMS noise ratio at the STDN ground stations will be
35 dB in a 3.0 MHz postdetection filter noise bandwidth. When the. television
composite video signal is replaced by a sinewave signal of the same peak-
*
to-peak voltage and a frequency between 30 Hz and 3.0 MHz, the RMS sinewave
signal to RMS noise ratio at the STDN ground stations will be 26 dB in a
3.0 MHz postdetection filter noise bandwidth.
2.4 Signal Characteristics
The characteristics of each of the required signals to be transmitted
are detailed in this section.
• Main Engine Data . Each of the three 60 kbps main engine (ME)
data channels consists of successive Data Blocks separated by
fill bits. A Data Block contains 132 16-bit words, the time
between Data Blocks contains 288 "0" bits, and‘ the data rate
ORIGINAI- ®
OF ?OOR ftUALlK
6
is 25 Data Blocks/second. Figure 2 indicates the frame structure
of a main engine Data Block.
• Tel evision . Figure 3 shows the television composite video wave-
form. The peak-to-peak composite video signal is the voltage
difference between the synchronization pulse and the reference
white levels as indicated by (a+3).. Table 1 lists pertinent
parameters. Color is provided by sequential fields- of red,
green, and blue picture video. The composite video signal is
•■'OC coupled to the FM transmitter modulator.
• Real-Time Attached Payload Data . Analog data up to 4 MHz or
digital data up to 5 Mbps with formats are yet to be defined.
i Playback Data -01 . Playback main engine data, telemetry data,
or TDM data will be structured' the same as in real-time as
shown by Figures 2,. 4, and 5, respectively. Playback data
rates are as described in Section 2.I.-
f Playback Data' - MSS . * Any bit rate up to 1024 kbps. - The frame
structures are yet to be defined.
2.5 Qrbiter Signal Design Parameters (Modulation Characteristics)
In FM, the instantaneous RF carrier frequency deviation from the
j
nominal center frequency is proportional to the instantaneous modulating
signal voltage. All FM {except TV) is symmetric about the nominal center
frequency and is specified by the peak frequency deviation. At the G-STDN,
or SCF ground stations, a wideband FM demodulator will be used to recover
the modulating signal.
• Main Engine Data . Each of the three main engine data subcarriers
(576 kHz, 768 kHz, and 1024 kHz) frequency modulates the RF car-
rier at a peak frequency deviation of 635 ± 15 percent kHz.
ORIGINAL
OF POOR QUALII^y
7
DATA BLOCK
132 WORDS
2112 BITS
- IDENTIFI-
MAIN ENGINE
BITE
PARITY
CATION
CONTROLLER DATA
2 WORDS
128 WORDS
1 WORD
1 WORD
32 BITS
2048 BITS
16 BITS
16 BITS
BIT TIME jl
«T
0
4
5
6
7
9
icjljjl2
15
14
F
F]
WORD 1 ^
J.
1
1
1
0
i
0
0
0
1
3
WORD 2
WORD 131
WORD 132
E
E
I
•
E
0
ojo
1
1
1
1
r
0
1
1
1
.
I
1
1
1
1
1 II
1
1
“ 1
MIA
CIA
PWH 1
0
iT
TBS
. COLUMN RARITY (ODD)
STATUS KlODH
DUMP MODF.
A
*M1A - multiplex interface .
assembly flags
CIA - controller interface
assembly flags
PWR - power flags
S - secondar}' flag -
T - twice flag
TBS - spare bits
Figure 2. Main Engine Data Block Structure
OHfGINAL PAGE S
OF POOR QUAIAT^
NOTES:
1. B - 0.714 tO.l volts (100 IKE Units).
2. a - 0.286 (40 IRE Units) nominal.
3. Sync to total signal ratio (j^) “ (28.6 tS)l. .
4. Blanking • 7.5 jS IRC Units (2.5*. to 12.51 of 8).
5. Iloritontal Rise times npa.surcd from 101 to 901
amplitudes shall be less than 0,3 psec.
6. Overshoot on horiio.ntal bl.inking signal shall not
exceed 0.020 at beginning of front porch. and
0,050 at end of back porch.
7. Overshoot on sync signal shall not exceed 0.050.
8. Tq - start of vertical sync pulse,
9. Tj^ ■ start of vertical blanking.
11; A - vertical sync pulse," ISO tSO iisec measured between 901
amplitude points. i
IZ; Rise and fall times of vertical blanking and vertical sync pulse,
measured from 101 to 901 amplitudes, shall be less than 5 psec.
13. Tilt on vertical sync pulse shall be less than 0.1a,
14. If horizontal information is provided during the vertical sync
C ulse it must bo at 2H rate and as shown in the optional vertical
lanking interval waveform.
15, B - vertical serration • 4.5 tO.S psec measured between the 901
amplitude points. Rise times measured from 101 to 901 amplitudes
shall be loss than 0.3 psec. •
16. If equalizing pulses are use! in the vertical blanking interval
waveform they shall be 6 in number preceding the vertical sync
pulse and be at 2H rate.
Figure 3. Television Composite, Video Waveform
03
Table 1. Television Baseband Parameters
l
Frame
Rate
Lines
per Frame
Aspect-
Ratio
Color
Field
Sequence
Horizontal
Scanning
Frequency
Vertical
Scanning
Frequency
Video
Bandwidth
E9. 97/sec ,
525
Interlaced
4/3 •
R-G-B
15,734.624 Hz
Horizontal
Frequency
262.5
S-Band:
3.0 MHz
Ku-Band:
4.5 MHz
4 5
FRAME F0RMA1
■COUNT ID0
* SYNC PATTERN 76 57 1440 j
@ FRAME 1 ONLY
FRAME 100
L I FRAME.-3 1 ■
FRAME 2' /
1 y MAJOi
t I I FRAME 1
128 KBPS ■
8 BITS/WORD
160 WORDS/MINOR FRANE
100 MINOR FRA^1ES/MAJ0R FRAKE
1 MAJOR FRAAE/SECOND
FRANfl
Figure 4. Playback 01 Telemetry Frame Format (High Data Rate Mode)
BOOK GUAUlJt
24 Bits
8
8
8-
32 Bits
8
8
24 Bits
Sync
Frame
'^1
Voice .
h
Telemetry
Vi
■ V2
~ —
Sync
Pattern
Count
Voice
Data
Voice
Voice
Pattern
1 Byte -
(48- Bits)
39 Bytes
1 Frame
(40 Bytes)
(1920 Bits)
1920 Bits/Frame
100 Frames/Second
192 kbps
Sync Pattern: 76571 440g
Figure 5. Baseband TDM Frame Format for the Return and Direct Downlinks (High Data Rate Mode)
12
• Television . The TV composite video signal frequency modulates
the RF carrier at a peak frequency deviation of 4.5 ±15 percent
MHz such that the instantaneous carrier frequency at each video
synchronization pulse is 4.5 MHz less than the center frequency,
regardless of the picture video between synchronization pulses,
and is 4.5 MHz greater than the center frequency whenever the
picture video reaches reference white.
«■ Real-Time Attached Payload Data . Real-time attached payload
analog or digital data signals frequency modulate the RF carrier
at a peak frequency deviation of 2 ± 15 percent MHz. For an
analog modulating signal, the modulation sense is positive with
respect to the payload source and 'the ground user sink, i.e., an
increase in the payload output signal voltage causes an increase
in the instantaneous RF carrier frequency and an increase- in the
receiver postdetection output signal voltage.
• Playback Data - 01 or MSS . The playback digital data {main, engine,
attached payload, PCM telemetry, or TDM) at any playback data bit
rate from 60 kbps to 1024 kbps, frequency modulates the RF carrier
at a peak frequency deviation of 635 ±15 percent kHz.
2.6 Orbiter RF Parameters
The Orbiter FM transmitter power output is specified as 10 watts mini-
mum at a carrier frequency of 2250.0 MHz ± 0.004%, but system losses are
such that the power which is available at the antenna terminals is consider-
ably less. Figure 6, which illustrates detailed cable runs and connectors,
indicates a total transmit system loss of -10.6 dB for the OFT configuration
(Flights 1-7, when the DFI multiplexer is used) and a total of -7.2 dB for
the operational configuration (Flight 8 and all subsequent flights). The
OF POOR QUAUax
Figure 6. Interconnection Diagram - S-Baind FM System Coaxial Cables and Antennas
■<
in
S
o
(/I
i/)
cn
CL
D3
14
OFT value is of primary significance, since the S-band FM link provides the
only means of obtaining television for the early Shuttle flights (the Ku-
band .link is not scheduled to be available until Flight 4).
2.7 Orbi.ter Antenna Characteristics
Because the S-band FM direct link will be required during ascent and
reentry (when it will not be possible to deploy steerable antennas) and
because it will be desirable to achieve nearly spherical coverage about the
Orbiter, a switched -element array of two 'right-circularly-polarized (RCP),
flush-mounted, omnidirectional antenna elements (referred to as the hemi
antennas) has been baselined for the Orbiter. Locations for these antennas
are depicted in Figure 7. A set of. desired gain contours^ -for these elements
is shown in Figure 8. It is desired that each hemi provide a gain of +1 dB
over approximately a 145° cone, which would correspond to about 70% of total
spherical coverage. . Unfortunately, as the hemi antenna development progresses,
it appears that the desired gain characteristics will not.be provided, result-
ing in somewhat. less coverage. Figure 8 also illustrates the expected gain
contours for the hemi antennas-. ' The upper hemi antenna provides a gain of
1.5 dB over an area 120“ by 100°, while the lower hemi antenna provides a
gain of 1 dB over a 140“ cone. Thus, the hemi antennas provide a gain of
at least 1 dB over approximately 54% of total spherical overage.
Additional considerations which limit available hemi antenna gain
during ascent are the blockage and multipath effects due to the external
tank and solid rocket boosters during the various phases of ascent. Figures
9 through 12 show the results of antenna pattern measurements made at the
Lyndon B. Johnson Space Center using 1/10 scale models of the Orbiter,
external tank, and solid rocket boosters, and using early models of the
Figure 7. S-Band Flush-Mounted Antenna Locations
tn
Coverage Contour for Upper Hem1 Antenna
^ +1 dB gain
(expected)
'/'yy / / / ^ / y'y y y 'y'/y'/y /,'/ / / y y y y y /'////// /y'/ / y y'y y'77/^,
y^ /L: y-yyyiyyyyy. X2; y^y yL,' y^y^ y^ /S/ jL y^y/J. C/ ^y^y yLy''^/^ 'L.y^yyj!y^j.y!Zyj.
'^/''////yy
^ +1 dB gain
^ (desired)
< +1 dB gain
Coverage Contour for Lower Hemi Antenna
£+1 dB gain‘d
(expected)
Figure 8, Expected and Desired Gain Contours for Hemi Antennas
17
X-Y Plane Cut
Y-Z Plane Cut
(a) Upper Hemi Antenna
(b). Lower Hemi Antenna
X-Z Plane Cut
OF POOR
X-Z Plane Cut
Figure 9. Sketches Indicating General Nature' of Pattern
Measurements for Orbiter Hemi Antennas
(Orbiter/ET/SRB Configuration)
EZ] > ’•“«
i -2 ®
OBIGiNAt, PAGE IS
OE Pooh QUAtny
(degrees)
Figure 12. Composite Radiation Distribution ‘Pattern for Shuttle S-Bahd Hemi, Antennas ,(Orbiter/SRB/ET)
ro
o
21
Orbiter hemi antennas. The results of these measurements indicate roughly
that reflections and masking by the external tank and solid rocket boosters
result, in highly irregular patterns for the mated phases of ascent, even
at aspect angles generally considered favorable. The patterns are particu-
larly irregular along the tail of the Orbiter, with nulls as deep as about
30 dB. The absolute gain values along the Orbiter tail vary from about 0 dB
to -30 dB. How severe these gain values and fluctuations. are, of course,
depends on the aspect angle to the ground station- (and the corresponding -
antenna gain) versus the time from liftoff (and the corresponding slant -
range). If, at a particular time, the range is very short, then a very low
antenna gain may be tolerable. The actual effects of the antenna patterns-
depicted in Figures 9 through 12, then, cannot be fully determined until
signal strength calculations are performed versus time for various ascent,
trajectories. These calculations will be summarized in a subsequent section
of this report.
2.8 Ground Station Characteris'tics
The NASA 6-STDN presently consists of 12 stations, with antenna diam-
eters of 30. feet (one is 85 feet). The number of G-STDN stations is planned
to be reduced to 5 by OFT Flight 4 or 5, as the TDRSS becomes operational.
Table 2 details the G-STDN S-band parameters whichwill be provided for the
S-band FM downlink.
The USAF SCF consists of 9 stations at 6 different geographic locations
with antenna diameters of either 14 feet, 46 feet, or 60 feet. Table 3
details the applicable SCF S-band parameters.
22
Table 2. G-STDN S-Band Parameters .
30-Foot Antenna 85
l-Foot Antenna
Receive Frequency
2250 MHz
2250 MHz
Antenna Polarization
RCP
RCP
Receive Antenna Gain
43.5 dB
52,7 dB
Receive System Losses
(Included in Antenna Gain}
—
—
System Noise Temperature
140“K
*
140°K
Predetection Bandviidth
3 MHz
3 MHz
FM Discriminator Degradation
-1.0 dB
-1.0 dB
FM Threshold
10 dB
10 dB ■
Bit Synchronization Degradation
-2.0 dB
-2.0 dB
Table 1 ‘ SCF
S-Band Parameters
■■
14-Foot
Antenna
46-Foot
Antenna
60-Foot
Antenna
Receive Frequency
2250 MHz
2250 MH2
: 2250 MHz
Antenna Polarization
RCP
RCP
RCP
Receive Antenna Gain
33.5 dB
47.5 dB
48.2 dB
Receive System Losses
(Included in Antenna Gain)
—
—
—
System Noise Temperature
376°K
220° K
340°K
Predetection Bandwidth
5 MHz
5 MHz
5 MHz
FM Discriminator Degradation
-1.5 dB
-1..5 dB
-1.5 dB'
FM Threshold
10 dB
10 dB
10 dB
Bit Synchronization Degradation
-2.0 dB
-2.0 dB
-2.0 dB
23
3.0 PERFORMANCE PREDICTIONS
3.1 Mathematical Models
The end-to-end performance for any communications link can be expressed
in terms of a required SNR (signal -to-noise ratio in an appropriate bandwidth)
at some point in the receiving system. For an analog channel, this may be
the output SNR, or it may be the SNR at the demodulator input which is neces-
sary to provide the required output SNR. For a digital channel, the SNR (in
the bit rate bandwidth) at the bit detector input that is required for a
given bit error probability at the detector output is frequently used. For
either class of channel, a performance margin (or circuit margin) is the •
amount, in decibles (dB), by which the actual (or predicted) SNR exceeds the
required SNR at whatever reference point is chosen. Thus,
Circuit Margin = SNR -SNR (dB) .
actual (or
predicted) required,-
The required SNR can usually be -referred to a predetection point in
the receiving system where the noise has a constant power spectral density
in a known bandwidth or where the noise is a known system constant. Thus,
the performance margin may be expressed in terms of the received 'signal -to-
noise spectral density ratio
Circuit Margin = (dB) ,
‘^0 actual (or
predicted) required
or simply in terms of the received signal power.
Circuit Margin, = P . - P (dB) .
actual (or
predicted) required
24
Effective Isotropic Radiated Power
EIRP =
P^. + 4 + \ (dBW) , .
where
EIRP =
effective isotropic radiated power (dBW), a transmitting
system parameter
-
transmitter power (dBW)
4 =
transmit circuit losses (dB)
'
\ -
Space Loss
transmit antenna gain (dB).
ORIGINAL PAGE IS
. OF POOR QUALITY
= - (20 log f + 20 log R + 37.8) (dB)' ,
where
L = space loss (dB), range factor between transmitting and
^ ' receiving antennas
f = frequency (MHz)
R = range between transmitting and receiving antennas (nmi).
a
Atmospheric Loss
L = atmospheric loss (dB), attenuation of the signal power
® due to the propagation absorption of atmosphere oxygen
and water vapor (usually can be neglected for frequency
less than 10 GHz).
Polarization Loss
L =
P
2R-|R2
(1 +Ri^)(l +R2^)
+
(1-Rf)(l-R|)
n Q COS 2<|l.
2(1+Rf)(l+R2^)
10. log
1
2 +
(dB)
25
where
i = polarization loss (dB), reduction of the signal power due
P to the mismatch of the received signal polarization (usually
a design function of the transmitting antenna) with that of
the receiving antenna
R-, = axial ratio of ellipticallv polarized transmit antenna
[ellipticity = 10 log (1/R| ) dB]
■ R, = axial ratio of el lipticalli' polarized receive antenna
[ellipticity = 10 log (1/R2^) dB]
I* = alignment angle between two polarization' ellipses.
Antenna Pointing Loss
Lg = antenna pointing loss (dB), reduction of the received signal
power due to deviation of both transmitting and receiving
antenna maximum gain directions from the line-of-sight.
Receiving Net Gain (or Loss) Ratio
{^) ■= - 10 log (L) (dB) .
where
receiving net gain (or loss) ratio (dB) measured from the
antenna o.f the preamplifier inppt
- receive antenna, gain (dB) ' " '
L = receiving circuit loss ratio from antenna port to the
preamplifier input (.>1).
Total Received Power
P = total received power (dBW), which can be referred to the
receive antenna input, the antenna output terminal, or
the preamplifier input.
Referred to antenna input
EIRP + L + L + L + (dBW)
s a Ip o
26
Referred to antenna terminal ’
or
rec
ant
= EIRP +L +L +L +L +G (dBW)
s a p 0 r
Referred to preamplifier input
P
rec
pre
= EIRP + L. + L_ + L_ + L„ + (") (dBW)
= P,
rec
ant
s a p -0
- 10 log (L) . (dBW)
System' Thermal Noise Temperature
T = system thermal noise temperature (K), a receiving system
parameter which can be referred to the antenna terminal
or the preamplifier input.
Referred to antenna terminal
where
ant
= f3-+-(L-l)(290)“+ LT
pre
(K)
= antenna ngise temperature (K)-
T . = effective* noise temperature of the terminated pre-
^ amplifier (referred to the preamplifier input).
Referred to preamplifier input
pre.
-j^+ 0 -1)(290) t (K)
Receiver Noise Spectral Density
Ng = single-sided thermal noise spectral density (watts/Hz),
which can be referred to the antenna terminal or the
preamplifier input.
Referred to antenna terminal
No
ant
(watts/Hz)
27
where
or
where
or
or
where
k - Bo-1 tzmann ' s constant
Referred to preamplifier input
= 1.38x10”^^ (watts/K/Hz)
No
kT,
pre
(watts/Hz)
pre
Receiving Antenna Gain-to-System Thermal Noise Temperature Ratio
(S) = - 10 log
ant/
(dB/K)
- 10 log (L) - 10 log (T,
!pre)
(dB/K)
Gv =
(f)
antenna gain-to-system thermal noise temperature ratio
(dB/K), a receiving system parameter which is independent
of reference point.
Total Received Power-to~Noise Spectral Density Ratio
rec
No
= EIRP + L^' + -L^ + L + Lq + (I) - 10 log (k)‘ .(dB-Hz)‘
^rec
ant
- 10 log
("int)
= P
rec
(dB-Hz)
- 10 log /nq \ (dB-Hz)
pre V pre/
rec
N
= total received power-to-noise spectral density ratio
0 (dB-Hz), which is independent of reference point.
Signal -to-Noise Ratio at Demodulator Input
P
(?),
rec
1n %
- 10 log (B,^) (dB)
where
signal-to-no1se ratio at demodulator input (dB), a
quantity sometimes used in performance calculations
. = demodulator input bandwidth (Hz).
Bit Energy-to-Noise Spectral Density Ratio- at Demodulator Input
P
rec
- 10 log (R)
(dB)
bit energy-to-noise spectral density ratio at demodu-
lator input (dB), a quantity sometimes used in per-
formance calculations
R = information channel bit rate (bits/second)
Digital Data Bit Error Probability [For the S-band FM link, post-
detection signals are obtained by noncoherent carrier frequency
demodulation for both digital and analog modulating signals]
Pe =
0.5 exp [rO.5 YqY 5 (^b^f^O^in^
ORIGINAL PAGE' IS
OP POOR QUALiry
where *
Pe =
bit error probability
-
To '
degradation factor <1 for nonoptimum frequency shift
and/or predetection bandwidth for the given bit rate
Tb =
bit syncronization degradation factor
on equipment specifications
<1 , estimated based
ratio value of (E./N,.), .
b 0 ' 1 n
Postdetection Subcarrier Signal-to-Narrowband Noise Ratio (RMS/RMS)
[above FM threshold]
29
where
<V«)out
signal -to-noise ratio (RMS/RMS) at the output -of the
postdetection subcarrier bandpass filter (dB)
carrier peak frequency deviation by the subcarrier (Hz)
subcarrier frequency (Hz)
postdetection subcarrier filter noise bandwidth (Hz).
Conditions for the. above:
(S/N). llOdBl
in
B « f
S’ s
-Postdetection Analog Baseband Signal-to-Noise Ratio (peak-to-peak/RMS)
[above FM .threshold] !
<W">out = (S/N),„ + 10 log [3(4pp/B„„t)2(B,„/B„„t)] (dB)
where ‘ ■ ‘ ' " • .
■ (Spp/N)Qy.|- = signal -to-noise ratio (peak-to-peak/RMS) at the output
of the postdetection analog signal baseband filter (dB).
■A = carrier peak-to-peak frequency deviation by the analog
si.gnal (Hz)
' - %■ • *
B . . = postdetection baseband filter (lowpass filter) noise
bandwidth (Hz).
Condition for above:
(S/N)..^ >, 10 dB’
Postdetection Analog Baseband Siqnal-to-Noise Ratio (RMS/RMS)
[above threshold]
<WN)out = (S/N),„ + 10 log h
where
(dB)
(S /N) ^
rms 'out
signal-to-noise ratio (RMS/RMS) at the output of the
postdetection analog signal baseband filter (dB)
30
A = carrier peak frequency deviation by the analog
P signal (Hz)
F = analog signal peak-to-RMS voltage ratio.
Condition for the above:
(S/N). >10dB
in
3.2 Circuit Margins Using Nominal (+1 dB) Antenna Gains
and Orbital Slant -Range
3.2.1 Link Geometry
As illustrated in Figure 13, it is assumed that the Orbiter is in
a 270-nmi orbit with a maximum slant range of approximately 1122 nmi (5®
elevation angle) to the ground station. This maximumslant range will be ‘
used in the subsequent performance margin calculations, along with a nominal
(+l-dB) hemi antenna gain. It should be recognized that, the nominal values
thus, obtained are valid only when the Orbiter attitudes are such that nominal
(or better) antenna gains are available. As noted previously, for the on-
orbit ( unmated configuration), this condition is true for approximately 9%
* 1
of all possible Orbiter attitudes for low altitude orbit of 100 nmi and approx-
imately 25% for an orbit of 250 nmi with 12G-STDN stations..
3.2.2 Television Circuit Margins '
Using the mathematical models summarized in Section 3.1, and using
the Orbiter and G-STDN parameters detailed in Sections 2.5, 2.6, and 2.8,
it is a straightforward procedure to determine the performance margins for
television transmission. Since television transmission to the SCF is not
a requirement for DoD missions, then margin calculations are not performed
for SCF stations. Table 4 presents the OFT (Flights 1-7 for OV-102) margin
calculations for the case of a 30-foot G-STDN station. It can be seen that.
- ■ - 32
Table 4. Circuit Margin Calculation Summary Sheet — Orbi ter-to-G-STDN S-Band FM Oov;nlink
Television Channel {30-foot station, OFT Orbiter configuration)
Parameter
Value
Source
V
(1) S50 transmit power, dBW
10,0
i.-
10 W
(2) SSO transmit circuit loss, dB
-10.6
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54% of coverage
sphere ‘
(4) SSO EIRP, dBW
0.4
Sum (1) through (3), ICD 2-OD004
(5) Space Loss, dB
-1.65.8
f = 2250 MHz, R = 1120 nmi (maximum
slant range for 5° elevation and
270 nmi orbit)
(6) Pointing loss, dB
-0.5
Estimate
(7) Polarization loss, dB
-0.5
Estimate
(8) STDN receive antenna gain, dB
43.5
GSFC estimate (30-foot)
(9) STDN receive circuit loss, dB
—
Included in STDN antenna gain
(10) Total received power, dBW
-122.9
Sum (4) through (9)
(11) STDN system noise temperature, dBK
' 21.5
140 K (GSFC estimate)
(12) Boltzmann’s constant, dB (W/K/Hz)
-228.6
- 1.38x10-23 w/K/Hz
(13) STDN noise spectral density, dB (W/Hz)
, -207.1
Sum (11) and (12)
‘(14) STDN G/T, dS/K
22.0
(8) minus (11), ICD 2-00004
(15) Total received- power/noise spectral
density (P^ec/^o)’ dB-Hz
84.2
(10) minus (13) or sum (4) through
(7) minus- (12) plus (T4X
(16) Predetection .bandwidth (B^j^), dB-Hz
71.2
13.2 MHz, .ICD 2-00004
(17) Signal -to-noise ratio- (S/N)^-i^ at FH
discriminator input, dB
• 13.0
(15) minus (16)
(18) FM threshold, dB
10.0
ICD 2-0D004 . •
(19) FM threshold margin, dB
3.0
(17) minus (18)
(20) Signal-to-noise ratio (Spp/N)out (peak-
to-peak/RMS) at output or postdetection
lowpass filter, dB
33.7
App = 9.0 MHz, Bqp^ = 3.0 MHz,
ICD 2-0D004
(21) Required output signal-to-noise ratio,
dB
.35.0
ICD 2-0D004
, (22) Discriminator degradation, dB
-1.0
Estimate
(23) Required (Spp/N)out’
36.0
(21) minus (22)
(24) Required P^ec/No* dB-Hz
86.5
(23) plus (17) minus (20) plus
(16), ICD 2-0D004
(25) TV margin (postdetection), dB
-2.3
(20) minus (23) or (15) minus (24)
(26) Circuit margin, dB
-2.3
(25) less than (19)
33
if a 13.2 MHz predetection bandwidth is used, along with a 3.0 MHz post-
detection bandwidth, the margin above an assumed FM threshold of 10 dB is
3.0 dB, while the post-detection margin (above a 35 dB peak- to- peak/RMS SNR
requirement) is -2.3 dB. Although the threshold margin coiild undoubtedly
be improved by use of an extended threshold FM demodulator, the postdetec-
tion, margin could not be improved. The postdetection margin can only be
improved (assuming a constant ground station configuration) by increasing
Orbiter antenna gain or transmitter power, by decreasing Orbiter transmit
circuit loss, by reducing range, or by reducing the required output SNR.
It should be noted that use of an 85-foot G-STDN station would provide an
increase of 9.2 dB in antenna gain, thereby increasing the television post-
detection margin to. 6.9 dB, However, only one 85-foot G-STON station will
• be available, while 10 locations will have 30-foot stations and one location
will have a 40-foot station. Thus, the margin for 30-foot stations is of
the utmost concern.
For the operational configuration (Flight 8 and subsequent flights),
deletion of the DFI multiplexer reduces the Orbiter transmit circuit loss
to -7.2 dB, thereby increasing the television threshold margin to 6.4 dB
and the postdetection margin to 1.1 dB for the 30-foot 6-STDN stations.
Use of an 85-foot station would increase these margins to 15.6 and 10.3 dB,
respectively. ' ■
The negative postdetection margin for the Orbiter OFT configuration
is of real concern,, since it is during early OFT that the S-band FM downlink
will provide the only means of obtaining television. The marginal (+1.1 dB)
performance for the Orbiter operational configuration is not nearly of as
much concern. Section 5.0 of this report proposes, a signal design change
(increased Af for television) that should alleviate the concern in this area.
34
3.2.3 Main Engine Data Circuit Margins
Using the appropriate mathematical models described in previous sec-
tions, together with the Orbiter and G-STDN parameters, the performance
margins shown in Tables 5 through 7 were obtained for the worst case of
interest {30-foot G-STDN station, Orbiter OFT configuration). As shown in
the tables, the threshold margin is 9.4 dB, while the postdetection data
margin (based on bit error rate of 10"^) are 22.8 dB, 20.3 dB, and 17.8 dB, .
for the 576 kHz, 768 kHz, and 1024 kHz subcarrier channels, respectively.
These margins all improve by 9.2 dB if transmission is to an 85-foot station.
It is, doubtful that there will be a requirement for real-time trans-
mission of main engine data to an SCF station, but should the need arise, the
case of interest would be for the 14-foot station and the Orbiter OFT configu-
ration. For these conditions, the ground station antenna gain is lower' by.
10.0 dB and the ground station receiver system temperature is higher by.3.9;dB,
thereby resulting in a net reduction of 13.9 dB in all circuit margins for the
main engine data channels. If .a. 46-foot or- 60-foot SCF is utilized, the 6-STDN
margins would increase by 2.1 dB and 0.9 dB, respectively.
3.2.4 Real-Time Attached Payload Data Circuit Margins
3. 2.4.1 Analog Data (Up to 4 MHz)
Table 8 summarizes the circuit margin calculations for the (worst)
case of real-time transmission of 4 MHz of attached payload data to a 30-foot
G-STDN site (Orbiter OFT configuration), with an output SNR requirement of
SNRout in a 4 MHz postdetection bandwidth. The IF bandwidth assumed is the
Carson's rule bandwidth:
Bjp = 2{Af + fj^) = 2(2MHz+4MHz) =
12 MHz .
Table 5. Ci'rcuit Margin Calculation Summary Sheet ~ Orbiter-to-G-STDN S-Band FM Downlink
Main Engine Data Channels, 576 kHz Subcarrier (30-foot station, OFT Orbiter
Configuration) • •
Parameter
Value
Source
(1) SSO transmit power, dBW
10.0
10 W
(2) SSO transmit circuit loss, dB
-10.6
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54 ^ of coverage
sphere
(4) SSO EIRP, dBW
0.4
Sum (1) through (3), ICD 2-00004
(5) Space loss, dB
-165.8
f = 2250 MHz, R=1122 nmi (maximum
slant range for 5° elevation and
270 nmi orbit)
(6) Pointing loss, dB
1-0.5
Estimate
{7) Polarization loss, dB
-0.5
Estimate
(8) STON receive antenna gain, dB .
43.5
GSFC estimate t 30-foot)
(9) S’TDN receive circuit loss, dB
—
Included in STDN antenna gain
(10) Total received power, dBW
-122.9
Sura (4) through (9)
(11) STDN system noise temperature, dBK
21.5
140 K (GSFC estimate)
(12) Boltzmann's constant, dB (W/K/Hz)
-228.6
l,38x,10~^^ W/K/Hz
(13) STDN -noise spectral density, dB (W/Hz)
-207.1
Sura (11) and (12) •
(14) STDN G/T, dB/K '
22.0
(8) minus (11)
(15) Total received power/noise spectral
density (Ppec/No), dB-Hz • ’
84.2
(10) rainus-(13) or sum (4) through
(7) minus (12) plus (14)
.{16} Predetection bandwidth (Bin), dB-Hz
64.8
3 MHz, ICD 2-00004
(17) S fgnal -to-noise ratio (S/N)in at FH
• discriminator input, dB
19,4
(15) minus (16)
(18) FH threshold, dB
10.0
ICD 2-0D004
(19) FH threshold margin, dB
9.4
(17) minus (18)
(20) Postdetection subcarricr power/noise
spectral density (Psc/^), dB
82.0
f-c = 576 kHz, af = 635 kHz,
ICD 2-0D004
(21) Bit rate bandwidth, dB-Hz
47.8
60 kbps
(22) SNR in bit rate bandwidth (Ejj/nsd), dB
34.2
(20) minus (21)
(23) Theoretical required Ej^/nsd, dB
8.4
For 10-^ BEP
(24) FH discriminator degradation, dB
-1.0
Estimate
(25) Bit synchronization degradation, dB
-2.0
Estimate (including band! imi ting
effect)
(26) Required E^/nsd (postdetection), dB
11.4
(23) minus (24) minus (25)
(27) Data margin, (postdetection), dB
22‘.8
(22) minus (26)
(28) Required Ppec^*^ » dB-Hz
74.8
(16) plus (18), ICD 2-00004
(29) CIRCUIT MARGIN, dB
9.4
(15) minus (28), constrained by
FH threshold margin
36
Table 6. Circuit Margin Calculation Sunmtary Sheet - Orbiter-to-G-STDN S-Band FM Dovmlink
Main Engine. Data Channels, 768 kHz Subcarrier {30-foot station, OFT Orbiter
Configuration)
Parameter
Value
Source
(1) SSO transmit power, dBW
10.0
10 W
(2) SSO transmit circuit loss, dB
-10.6
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54% of coverage
sphere
(4) SSO EIRP, dBW
0.4
Sum (1) through (3), ICD 2-0D004 '
(5) Space loss, dB
-165.8
f= 2250 MHz, R=1122 nmi (maximum
slant range for 5° elevation and
270 nmi orbit)
(6) Pointing loss, dB
_-0.5
Estimate
(7) Polarization loss, dB
-0.5
Estimate
(8) STDN receive antenna gain, dB
43.5
GSFC estimate (30-foot)
(9) STON receive circuit loss, dB
—
Included in STDN antenna gain
(10). Total received pov/er, dBW
-122.9
Sum (4) .'through (9)
(n) STDN system noise temperature, dBK
21 -.5
140 K (GSFC estimate)
(12) Boltzmann's constant, dB (W/K/Hz)
-228.6
l;38x 10'23 w/K/Hz
(13) STDN noise spectral density, dBW/Hz
-207.1
Sun (11) and (12)
(14) STDN G/T, dB/K V
22.0
' (8) minus (11). ICD 2-0D004
(15) Total received power/noise spectral
density (Pf-ec/flo}> dB-Hz - '•
84.2
(10) minus (13) or sum (4) through
, (12) plus (14)
(16) Predetection ba.ndv/idth (B,-^), dB-Hz
64.8
3 HHz, ICD 2-OD004
(17) Signal -to-noise ratio (S/N).Jp at FM
19.4
(15) minus (16)
(18) FM threshold, dB
10. 0‘
ICD 2-OD004 , .
(19) -FM threshold margin, dB
9.4
(17) minus (18)
(20) Postdetection subcarrier power/noise
spectral density (Psc/N), dB
79.5
fc(. = 768 kHz, Af= 635 kHz,
■ ICD 2-00004'
(21) Bit rate bandwidth, dB-Hz
47.8
60 kbps
(■22)- SNR in bit rate bandwidth (E|^/nsd), dB
.31.7
(20) minus (21)
(23) Theoretical required Ej^/nsd, dB
8.4
For 10-4 BEP
(24) FM discriminator degradation, dB
-1.0
Estimate -
(25) Bit synchronization degradation, dB
-2.0
Estimate (including bandlimiting
effect)
(26) Required E^/nsd (postdetection), dB
11.4
(23) minus (24) minus (25)
(27) Data margin (postdetection), dB
20.3
(22) minus (26)
(28) Required Prec/^^O’ <^B-Hz
74.8
(16) plus (18), ICD 2-OD004
(29) CIRCUIT MARGIN, dB
9.4
(15) minus (28), constrained by
FM threshold margin
ORIGINAL PAGE k
OP POOR QUALITY
Table 7. Circuit Margin Calculation Summary Sheet - Orbiter-to-G-STDN S-Band FH Downlink
Main Engine Data Channels, 1024 kHz Subcarrier (30-foot station, OFT Orbiter
Configuration)
Parameter
Value
Source
(1) SSO transmit power, dBW
10.0
10. W-
(2) SSO transmit loss, dB
-10.6
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54% of coverage
sphere
{4} SSO EIRP, dBW
0.4
Sum (1) through (3), ICO 2-OD004 ’
(5) Space loss, dB
-165.8
f = 2250 MHz, R=1122 nmi (maximum
slant range for 5“ elevation and
270 nmi orbit)
(6) Pointing loss,’ dB
-0.5
Estimate
(7) Polarization loss, dB
' -0.5
Estimate
(8) STDN receive antenna gain, dB
43.5
GSFC estimate (30-foot)
(9) STDN receive circuit loss. dB
—
Included in STDN antenna gain
(10) Total received power, dBW
-122.9
Sum (4) through (?)
(11) STDN system noise temperature, dBK
21.5
140 K (GSFC' estimate)
(12) Boltzmann's constant, dB (W/K/Hz)
-228.6
1.33x10-23 w/K/Hz
(13) STDN noise spectral density, dB (W/Hz)
-207.1
Sum (11) and (12)
(14)' STDN G/T, dB/K • .
22.0
(8) minus (11), ICD 2-OD004
' (15) -Total received pov;er/noise spectral
density (Pfec/f^o)> <SB-Hz
84.2
(10) minus (13) or sum (4) through
(7) minus (12) plus (14)
(16) Predetection bandwidth (B-j^), dB-Hz
64.8
3 MHz., ICD 2-00004
(17) Signal-to-noise ratio (S/N)-jp at FM
discriminator input, dB
19.4
(15) minus (16)
(18) FH threshold, dB
' 10.0
ICD 2-0D004
(19) FH threshold margin, dB
9.4
(17) minus (18)
(20) Postdetection subcarrier power/noise .
spectral density (Pjc/N), dB
77.0
fsc= 1024 kHz, Af=635 kHz,
ICD 2-0D004
(21) Bit rate bandv/idth, dB-Hz
47.8
60 kbps
(22) SNR in bit rate bandwidth {Ej^/nsd), dB
29.2
(20) minus (21)
(23) Theoretical required Ej^/nsd, dB
8.4
For 10-'^ BEP
(24) FH discriminator degradation, dB
-1.0
Estimate
«
(25) Bit synchronization degradation, dB
-2.0 '
Estimate ’{-including bandlimiting
effect)
(26) Required Ejj/nsd (postdetection), dB
11.4
(23) minus (24) minus (25)
(27) Data margin (postdetection), dB
17.8
(22) minus (26)
(28) Required Prec/«0» ^^'^z
74.8
(16) plus (18), ICO 2-0D004
(29) CIRCUIT MARGIN, dB
9.4
(15) minus (28), constrained by
FH. threshold margin
33
Table 8. Circuit Margin Calculation Sumnsary Sheet - Orbiter-to-G-STDM S-Band FM Downlink
Real-Time Attached Payload Analog Data (4 MHz)
OEIGINAL PAGE IS
OP POOR QUALITY
As can be seen from Table 8, the threshold margin is 3.4 dB and post-
detection margin is given by
10 log [M^il - 1 - (jm)
L J \ N /Qut,req
where F = analog signal peak-to-RMS voltage ratio
(S _/N) t y.pQ ” required signal-to-noise ratfo (RMS/RMS) at the
’ ^ output of the postdetection lowpass filter.
3. 2. 4. 2 Digital Data (Up to 5 Mbps)
■ Table 9 summarizes the circuit margin calculation for the (worst)
case of transmission of 5 Mbps of real-time attached payload data to a 30-
foot G-STDN site (Orbiter operational configuration)'. A bit error rate
requirement of 10"^ is assumed. The signal parameters are optimized using ■
the results from Appendixes A and B that present tests performed on the
digital data on an FM link. For 5 Mbps NRZ data, the optimum IF bandwidth
is 7.2 MHz with frequency deviation ratio of 0.36. With a frequency deviation
Af = 2 'MHz as defined in ICD 2-OD004, the frequency deviation .ratio is 0.4,.
which causes a 0.3 dB degradation from the optimum .performance.
3. 2.4. 3 AFSCF Digital Data (256 kbps)
Table 10 summarizes the calculation for the case of 256 kbps trans- '
mission to an SCF station for either 14-foot or 46-foot with the Orbiter
operational configuration. The circuit margin for a 60-foot antenna site
is 1.2 dB less than the margin for the 46-foot antenna site. A bit error,
rate requirement of 10“^ is assumed.
3.2.5 Playback Data Circuit Margins
As discussed in Section 2.1, for playback of either main engine data,
01 telemetry data, TDM data, or payload data, the maximum playback rate for
NASA missions using the G-STDN is 1024 kbps, while that for DoD missions
40
Table 9. Circuit Margin Calculation Summary Sheet - Orbiter-to-G-STDN Operational S-Band
FM Downlink Real-Time Attached Payload Digital Data (5 Mbps)
Parameter
(1) SSO transmit power, dBW
(2) SSO transmit circuit loss, dB
(3) SSO transmit antenna gain, dB
(4) SSO EIRP, dBW
(5) Space loss, dB
(6) Pointing loss, dB
■(7) Polarization loss, dB
(8) STDN receive antenna gain, dB
(9) STDN receive circuit loss, dB
(10) Total received power, dBW
(11) STDN system noise temperature, dBK
(12) Boltzmann's constant, dB (W/K/Hz)
(13) STDN noise spectral density, dB (W/Hz)
(14) STDN G/T, dB/K .■ •
♦ * * *
(15) Total received power/noise spectral
density (P{-ec/f^o)> dB-Hz
(16) Predetection bandwidth (B^^), dB-Hz
(17) Signal-to-noise ratio (S/N)^j^ at FM
discriminator input, dB
(18) Bit rate bandwidth, dB-Hz
(19) SNR in bit rate bandwidth (Eb^^O^in’
(20) Required (Ej^/N^)^^, dB
(21) Discriminator degradation, dB
(22) Bit synchronization degradation, dB
(23) Required (Ejj/Nq)^.^^ (postdetection), dB -
(24) Required Pf.gc/^^0’ dB-Hz
(25) CIRCUIT MARGIN, dB
Value . Source
10.0 10 W
-7.2 Rockwell estimate
1.0 Specified over 54% of coverage
sphere
3.8 Sum (1) through (3), ICD 2-0D0O4
-165.8 f= 2250 MHz, R = 1122 nmi (maximum
slant range for 5°elevation and
270 nmi orbit) .
-0.5 Estimate
-0.5 Estimate
43.5 GSFC estimate (30-foot)
— Included in STDN antenna gain
-119.5 Sum. (4) through (9)
21.5 140 K (GSFC estimate)
-228.6 1.38x 10~23- W/K/Hz ■
-207-.1 Sum (11) and (12)
■ .22.0 (a) minus (11)', ICD 2-0D004
87.6 (10) minus (13) or sum (4) through
(7) minus (12) plus (14)
68.6 7.2 MHz, Appendix' B
19.0 (15) minus (16)
67.0 5 ,Mbps
20.6 (15) minus (18)
11.7 For 10"^ BEP, Af = 2 MHz,
ICD 2-0D004
-1.0 Estimate
-2.0 Estimate
14.7 (20) minus (21) minus (22)
81.7 (23) plus (18), ICO 2-OD004
(19-) minus (23) or (15) minus (24)
5.9
41
ORIGINAL PAGE Ib
. OR POOR QUALPIY
Table 10. Circuit Margin Calculation Summary Sheet - Orbiter-to-SCF S-8and -FH Downlink
Payload Data Channel (256 kbps)
Parameter
Value
Source
(1) SSO transmit power, dBW
10.0
10 W
(2) SSO transmit circuit loss, dB
-7.2
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54S of coverage
sphere
(4) SSO EIRP, dBW
3.8
Sum (1) through (3), ICD 2-00003
(5) Space loss, dB
-164.5
f = 2250 MHz, R = 966 nmi (maximum
slant range for 5° elevation and ^
225 nmi orbit)
(6) Pointing loss, dB
— .
Included in receive antenna gain
(7) Polarization loss, dB
—
Included in receive antenna gain
(8) AFSCF receive antenna gain, dB
47.5
33.5
AFSCF specification (46-foot)
14-foot site
{ 9 ) AFSCF receive circuit loss, dB
—
Included in AFSCF antenna gain
(.10) Total received power, dBW
-113.2
*-127. 2
Sum (4) through (9)
.(11) AFSCF system noise temperature, dBK
■ 23.4-
*25.8
220 K for 46-foot site; 376 K for
14 -foot site
(12) Boltzmann's constant, dB (W/K/Hz)
-228.6
1.38x 10-23 W/K/Hz
(13) AFSCF noise spectral density, dB (W/Hz)
-205.2
*-202.5
Sum (11) and" (12) ‘
(14) AFSCF G/T, dB/K
24.1
* 7.7
(8) minus (11), ICD 2-OD003
(15) Total received pov;er/noise spectral
density (Prec/Mo)» dB-Hz
92.0
*75.7
(10)_ minus (13) or sum (4) through
(7) minus (12) plus (14)
(16) Predetection bandwidth (B^p), dB-Hz
67.0
5.0 HHz, ICD 2-OD003
(17) Signal -to-noise ratio (S/N)-|p at FM
discriminator input, dB
25.0
* 8.7
(15) minus (16)
1
(18) Bit rate bandwidth, dB-Hz
54.1
256 kbps
(19) SMR in bit rate bandwidth dB
37.9
*21.6
(15) minus (,18)
(20) Required (Ejj/Ng)-^, dB
17.3
For lO'S BEP, Af= 635 kHz,
= 5 MHz
(21) FH discriminator degradation, dB
-1.5
Estimate
(22) Bit sychronization degradation, dB
-2.0
AFSCF estimate
(23) Required (E 5 /Nq)^p (postcietection) , dB
20.8
(20) minus (21) minus (22)
(24) Required Pf-gc/^O’
74.9
(23) plus (18), ICO 2-OD003
(25) CIRCUIT MARGIN, dB
17.1
* 0.8
(19) minus (23) or (15) minus (24)
*For 14-foot site
42
using the SCF is 960 kbps; consequently, the performance margin calculations
are summarized .in Tables 11 and 12 for transmission to a 30-foot G-STDN
station and to a 14-foot or 46-foot SCF station, respectively. Note that
the’ circuit margin for the 60-foot SCF station is 1.2 dB less than for the
46-foot station.
3.3 Performance During. Ascent
This section analyzes the performance of the FM downlink during ascent'
from Kennedy Space Center (KSC). Launches from Vandenberg Air Force Base
(VAFB) are not considered here because of lack of trajectory data for these
launches.
3.3.1 Ascent Geometry
■ For launches from KSC, Figure 14 indicates that the Shuttle, when on
the launch pad, will be located 8.3 nautical .miles to the northeast of the
STDN station (MIL) at MILA. When on the pad, the Shuttle will be oriented
such that the vertical stabilizer of the Orbiter is pointed“south.. Immedi-
ately after liftoff and tower clearance, the Shuttle goes through a roll
maneuver whith aligns the vertical stabilizer of the Orbiter with the launch
azimuth plane, such that the Orbiter is in a heads-down orientation as it '
begins to pitch over in the ascent trajectory.
\
Figure 15 illustrates the Shuttle ascent trajectories for the two
reference missions considered in this report. For reference mission 1, the
launch azimuth is 90° (due east), and the orbital inclination is 28.5°. For
reference mission 2, the launch azimuth is approximately 38°, with a resulting
orbital inclination of 55°. For either of these reference missions, the solid
rocket boosters (SRB) fire from liftoff until approximately 125 seconds (cor-
responding to an altitude of 23 nmi and a range of 24 nmi from MIL), After
SRB separation, the Orbiter and external tank remain mated until approximately
ORIGINAL PAGE IS
OF POOR QUAim
Table 11. Circuit Margin Calculation Summary Sheet - Orbiter-to-6-STON S-Band FM Downlink
Playback of Recorded 01 or MSS Data (1024 kbps)
Parameter
Value
Source
(1) SSO transmit power, dBW
10.0
10 H
(2) SSO transmit circuit loss, dB
Rockwell estimate
(3) SSO transmit antenna gain, dB
Specified over 54% of coverage
sphere
(4) SSO EIRP. dBW
3.8
*0.4
Sum (1) through (3), ICO 2-OD004
(5) Space loss, dB
-165.8
f= 2250 MHz, R = 1122 nmi (maximum
slant range for 5° elevation and
270 nmi orbit)
(6) Pointing loss, dB
-0.5
Estimate
(7) Polarization loss, dB
-0.5
Estimate
(8) STDN receive antenna gain, dB
43.5
GSFC estimate (30-foot)
(9) STDN receive circuit loss, dB
—
Included in STDN antenna gain
(10} Total received power, dBW
-119.5
*-122.9
Sum (4) through (9)
(11) STDN system noise temperature, dBK •
21.5
140 K (GSFC estimate)
(12) Boltzmann's constant,' dB (W/K/Hz)
-2'28.6
1.3Bx10"23 W/K/Hz - • ■ .
.(13) STDN noise spectral density, dB (W/Hz)‘
-207.1
Sum (-11) and (12)
(14) STDN G/T, d3/K
22,0
(8) minus (11), ICD 2-OD004
(15) Total received power/noise spectral
density (Pj-ec^^o)* dB-Hz
87.6
*84.2
(10) .minus (13) or sum (4) through
(7) minus (12) plus (14)
(16) Predetection bandwidth (Bj^), dB-Hz
64,8
■
3 MHz, ICD 2-OD004
(17) Signal -to-noise ratio (S/N)jp at FM
discriminator input, dB
22.8
*19.4
(15) minus (16)
(18) Bit rate bandwidth, dB-Hz
60.1
1024 kbps-
(19) SNR in bit rate bandwidth (Ejj/Ng)^-^, dB
. 27.5
*24.1
(15) minus (18)
(20) Required (Ejj/Nq dB
12,0
For IQ-"^ BEP, 4f= 635 kHz,
Bin = 3HHz
(21) Discriminator degradation, dB
-1.0
Estimate
(22) Bit synchronization degradation, dB
-2.0
Estimate.
(23) Required (E[j/Nq)^.^ (postdetection), dB
15.0
(20) minus (21) minus (22)
(24) Required Prec/*^0» tJB-Hz
75.1
(23) plus (18), ICD 2-00004
(25) CIRCUIT MARGIN, dB
12.5
* 9.1
(19) minus' (23) or (15) minus (24)
’•OFT only
Table 12. Circuit Margin Calculation Suianary Sheet - Orbiter-to-SCF S-Band FM Downlink
Playback of 01 or MSS Data (960 kbps)
Parameter
Value
Source
(1) SSO transmit power, dBH
10.0
10 W .
(2) SSO transmit circuit loss, d8
-7.2
Rockwell estimate
(3) SSO transmit antenna gain, dB
1.0
Specified over 54% of coverage
sphere
(4) SSO EIRP, dBW
3.8
Sum (1) through (3), ICD 2-0D003
(5) Space loss, dB
-164.5
f= 2250 MHz, R= 966 nrai (maximum
slant range for 5“ elevation and
225 nmi orbit)
(6) Pointing loss, dB
—
Included in receive antenna gain
(7) Polarization loss, dB
—
Included in receive antenna gain
(8) AFSCF receive antenna gain, dB
47.5
*33.5
AFSCF specification (46-foot)
(9) AFSCF receive circuit loss, dB
—
Included in AFSCF antenna gain
(10) Total received pov;er, dBW
-113.2
*-127.2
Sum (4) through (9)
(11) AFSCF system noise temperature, dBK
• 23.4
*25.8
220 K for 46-foot site; 376 K
for 14- foot site
(12) Boltzmann's constant, dB (W/K/Hz)
-228,6
1.38x10-23 W/K/.Hz .
(13) AFSCF. noise spectral density, dB (W/Hz)
-205.2
-202.9’
.’Sum (11) and (12),'
(14) AFSCF G/T, dB/K
’ /
24.1
* 7.7
(8) minus (11), ICD’2-0D003
(15) Total received pov;er/noise spectral
density (P^ec'^^O^*
92.0
*75.7
(10) minus (13) or sum (4) through
( 7 ) minus (12) plus (14)
(16) Predetection bandwidth (B^p,), dB-Hz
67.0
5.0 MHz, ICD 2-0D003
(17) Signal -to-noise ratio (S/N)^-p, at FH
discriminator input, dB
25.0
* 8.7
(15) minus (16)
(18) Bit rate bandwidth, dB-Hz
. 59.8
960 kbps
(19) SNR in bit rate bandwidth (Et,/No)j„, dB
32.2
*15.9
(15) minus (18)
(20) Required (E(j/Nq)-^. dB
14,1
For 10-5 BEP, if = 635 kHz,
Bin = 5 MHz
(21) FH discriminator degradation, dB
-1,5
Estimate
(22) Bit synchronization degradation, dB
-2.0
AFSCF estimate
(23) Required (Eb/%^in (postdetection), dB
17.6
(20) minus (21) minus (22)
(24) Required Prec/^O’
77.4'
(23) plus (18), ICD 2-OD003
(25) CIRCUIT MARGIN, dB
14,6
*-1.7
(19) minus (23) or (15) minus (24)
*For 14-foot site
4 ^
CTi
Figure 15. Shuttle Ascent Trajectories
47
520 seconds, which corresponds to an altitude of 60 rniii and a downrange dis-
tance of 800 nmi. Orbital insertion occurs at approximately 620 seconds,
corresponding to an altitude of 63 nmi and a downrange distance of 1200 nmi.
3.3.2 Ground Station Availability
■ During early OFT (for an undetermined number of flights), the 6-STDN
stations at Mila (MIL) and Bermuda (BOA) will be available for communication
support of the- Shuttle during ascent. In addition, the Vanguard (VAN) track-
ing ship will be available. There is also a 6-STDN station (ROS) at Rosman,
North Carolina, which also could potentially provide some ascent coverage.
The GBM station used for Apollo support has already been closed down and will
not be available during the Shuttle time frame.
As illustrated in Figure 16, the Shuttle during ascent is within sight
of MIL until approximately 450 seconds, corresponding to an altitude of 57 nmi
and a downrange distance of -600 nmi. Also, Bermuda (BDA) could provide coverage
from approximately 300 seconds through insertion for reference mission 1 and
from about 426 seconds to 528 seconds for reference mission 2. • ROS could
provide about one minute of additional coverage over that using only MIL when
the Shuttle launch azimuth is'in'a northerly direction, such as for reference- •
mission 2. No additional coverage would be afforded for easterly launches.'
Present planning does not commit ROS for Shuttle support.
The Tracking and Data Relay Satellite System (TDRSS), according to
current plans, will be an operational element of the STDN in time to support
the fourth or fifth vertical flight of the Shuttle. The TDRSS will consist
of two satellites (one over the Pacific Ocean at 171.37°W, the other over
the Atlantic Ocean at 41.37“W) and one dedicated ground station at White
Sands, New Mexico. Current planning is for the TDRSS to become fully opera-
tional by the fourth or fifth vertical flight of the Shuttle, and for most
Figure 16. Potenti.al Grgund Station Coverage for Shuttle Ascent
49
of the G-STDN stations (including BOA and VAN) to be phased out of service.
Thus, the S-band FM coverage available during ascent will be limited to that
afforded by MIL since the TDRSS links are far too weak to support uncoded
FM transmissions,
3.3.3 Ascent Signal Strength Calculations
Using the antenna pattern measurements described in Section 2.7, a set
of signal strength calculations has been made for FM downlink communications.
The results of the signal' strength calculations are plotted versus time from
liftoff in Figures 17 through 24, using MIL, VAN, BDA, and ROS as ground
stations. VAN is assumed to be positioned at 28°N and 79°W to fill the
period that the SRB plume blocks transmission to MIL, so Figures 17 through
24 do not consider the performance degradation due to the plume.
The main engine data circuit margins for MIL and BDA are shown in
Figures 17 and 19 to vary from 57 dB to -3 dB for reference mission 1. The
minimum margin is at 6 minutes from reference where BDA'is not visible and
MIL is at its minimum’ signal strength,. For. this case, there is' a break -in
FM coverage for .about 1 minute.. The use. of VAN at its present position does
not help to improve this break in coverage. (If ROS should be configured
for support of the FM link, however, then Figure 20 shows there is a minimum
of 3 dB margin during the time MIL is approaching its minimum signal strength.)
For reference mission 2, the main engine data circuit margins for MIL
and BDA are' shown in Figures 21 and 23 to- vary from 57 dB to 9 dB. The mini-
mum margin is at 7 minutes from reference where BDA is not visible and MIL is
at its minimum signal strength. Therefore,, there is excellent coverage during
ascent for this mission, except possibly during the plume period.
The problem of predicting the effects of rocket exhaust plumes on
propagation of communications signals is a very difficult one. The problem
0 : 0 :
Or 0:
: ’0 0 : 0 :
TIME FPCiM REF < DflY: HR : M I M >
. Signal Strength Measurements for Reference
(Due East) at MIL
flemi Comp
Hemi Comp
Hem.i; Comp
TIHE FROM REF < DflV: HR-- M I N >-
Figure 20. Signal Strength Measurements for Reference Mission 1
{Due East) at ROS
Hemi Comp
ORIGINAL PAGE IS
^ POOR qualm
Terrain Terrain
TIME FROM REF k DflV: HR: M IN )
Figure 23. Signal Strength Measurements for Reference Mission 2
(37.88 Azimuth) at BOA
Hemi Comp
58
has d’. Targe number of variables-; for example, signal attenuation turns out
to be- very sens-itive to such things as minute variations of certain types of
impurities in the propellant mixture. Many attempts at predicting plume
'attenuation effects by analysis for Tiquid-fuel rockets have been made-
most have failed or have provided only crudely approximate results. The
Shuttle case is much more difficult than the classical cases which have been
studied, because:
1. There are two plumes to contend with (plus the main engine
exhaust,, which we, are ignoring)-, rather than 'a single orie-.
2. The SRB engines use solid propellants and the resultant exhaust
contains quantities of ‘ionized metallic particles (sodium, potassium, and'
aluminum), which are byproducts of alkaline impurities inherent in the pro-
pellant mixture.
Even what should have been a relatively simple task, that of calculating
the size of the SRB exhaust plume as a function of altitude-, is extremely
difficult due to the dependence on exact propellant' composition. Therefore.,
some uncertainty exists as to when the line-of-sight from, the various Orbiter
antennas to MIL actually begin to pass through the SRBs 'pTum'es .
From analysis of measured data for other .programs. utilizing, sol id
rockets, signal attenuation of the order of 25 to 40 dB can- be expected due
to the plume. The main engine data circuit margin varies between 57 dB and
33’ dB' at MIL for reference mission 1 and between 47 dB and' 35 dB for mission 2
durinq the period of estimated plume blockage. Therefore, there will likely
be some FM communications for both missions 1 and 2 at MIL,, even with the
plume attenuation. While the. main engine data threshold is not known exactly-
for VAN, because it has not yet been configured, i.t is clear that there will
be- a large margin. Thus, if VAN is used, the problem of plume blockage is
comp.l etely el imi nated . ORIGINAL PAOS IS
OF POOE QUAL/i'^
59
4.0 ASSESSMENT OF ADEQUACY OF S-BAND FM LINK TO SAFETY REQUIREMENTS
The FM system design provides good margins in satisfying the link
requirements presented in Section 2.0, except for three cases: (a) tele-
vision, (b) the links to the SCF stations with 14-foot antenna diameters,
and (c) 6-STDN links during ascent.
The Orbiter-to-G-STDN S-band FM downlink television channel has a
-2.3 dB margin. Changes in the system design v/ill be required to improve-
this’margin^ Section 5.0 recommends a relatively' simple change'that pro-
vides a -^0.2 dB margin. While this margin is' not large, it is felt that -
the cable losses are very conservative and will be significantly reduced.
Also, the required output signal -to-noise ratio of 35 dB is conservative. ■
Therefore, it is recommended that a system design change be made to insure
a positive margin but a large positive margin is probably, not needed.
The high-rate payload data and the playback of 01 and MSS data- to ,
SCF stations with 14-foot antenna diameters have very small positive or
negative margins. It has been found, however, -that there is only one remain-
ing SCF 14-foot antenna and that is at the Greenland station. ‘ Note that the
recommended change to the system design to improve the television channel
will also adversely affect the margins for these data channels by about
0.8 dB. The circuit margins at the Greenland site can be made positive if
the IF bandwidth is optimized as described in Appendixes A and B.
S-band FM communications during ascent is predicted to be generally
good during early OFT for the cases examined (KSC launches with coverage
afforded by MIL, VAN, and BDA), with the exception of one short period
(-1 minute) during reference mission 1, which could possibly be covered
by repositioning VAN, if desired. For those later missions, in which the
number of G-STDN stations is reduced due to the phasing in of TDRSS, FM
60
coverage will be, limited, to that afforded by MIL. Performance using only MIL
will be affected by the SRB plume, but the plume effect may turn out to be
tolerable. In any event, the importance of FM communications during ascent
is felt to be greatly reduced for later KSC launches. For DoD missions
launched from Vandenberg AFB, the FM link may be required during ascent for
relay of payload data, and hence its importance may be somewhat greater.
■Although no trajectory data was available to perform coverage analyses for •
Vandenberg launches, it is' clear that some downrange station (or stations)
will be required if the link is required throughout the ascent phase. ’
5.0 RECOMMENDATIONS
As described in Section 4.0, only one potentially real problem asso-
ciated with the S-band FM link design is judged to warrant a system .design'
change. It is recommended that the FM transmitter' sensitivity (MHz/v) be.. -
increased such that the peak frequency deviation for television is ’changed'"
from 4.5 MHz to 6,0 MHz. This recommended change will 'provide, an increase
of 2.5 dB in output signal-to-noise ratio and will thus increase the circuit
margin from v2.3 dB to +0.2 dB. There will be a slight reduction {on the
order of 1.0 dB) in threshold margin for the TV channel, due to a resulting
increase in required predetection bandwidth, but this is considered acceptable
because of the relatively high (3.0 dB) threshold margin. There will also be
an effect for each of the other S-band FM services, due to the fact that the •
proposed increase in transmitter sensitivity will increase each of the other
peak frequency deviations by the same ratio (6/4.5 = 4/3). This effect will
be adverse for those channels which now have optimum Af ‘s, but will not dras-
tically affect performance (the margins for these channels are relatively high
and the adverse effect should only be on the order of 1,0 dB).
61
Although only the single system design change noted above is proposed,
the need for various activities has become apparent as a result of this study
effort. It is suggested that the following actions be taken by NASA:
(a) Additional RF coverage analyses need to be made for Vandenberg
AFB launches.
(b) If S-band FM coverage should potentially be required" for the
reentry/ landing phase, then RF coverage analyses need to be made for landings
at each of the various landing sites. - - - - ' .
(c) If a more accurate assessment of SRB plume effects -is desired
(perhaps to facilitate preflight planning, to firm up requirements for VAN
support, etc.), then plume loss measurements taken during one or more regularly
scheduled SRB static firings would be highly desirable. These measurements
could be used to provide a bound on the effects of the plume.
APPENDIX A
LOW DATA RATE FM LINK TEST REPORT
63
APPENDIX A
LOW DATA RATE FM LINK TEST REPORT*
1.0 INTRODUCTION
The Air Force has been assigned a data channel of the Shuttle FM Wide-
band Signal Processor which will operate in the 250 bps to 256 kbps range,
with a split-phase data format and a frequency deviation of +635 kHz. The
channel designated for NASA use will accommodate a range from 200 bps to -
5 Mbps, with split-phase data and a ±2.0 MHz frequency deviation. This
appendix provides results of laboratory tests conducted with various data
• - K r'
rates and frequency deviations using split-phase, .to aid in establishing
the ICD modulation specification.
Add-itional testing was performed for 1 Mbps NRZ data, in order to
determine the performance of an FM link at a frequency deviation of
± 2.36 MHz.
2.0 TEST PROCEDURES
The test configuration shown in Figure 1 was used to determine system
performance for the 200 bps split-phase FM link. The .specified frequency
deviations of + 2.0 MHz and ± 635 kHz were achieved by varying the modulation
voltage at the input to the FM transmitter. Predetection filtering was pro-
vided- by either a 2.7 MHz or a 6.25 MHz IF filter. For the first test of
the 200 bps link, a frequency deviation of ± 635 kHz and a 2.7 MHz IF filter
were employed. During the second test, the IF filter was held at 2.7’ MHz
and the frequency deviation was increased to i 2.0 MHz. Test 3 employed
the- 6-. 25 MHz IF filter and a frequency deviation of ± 2.0 MHz. System per-
formance was measured with the aid of the bit error detector and was recorded
as a function of total received power.
*This appendix is extracted from Report EE7-75-209, Lockheed Elec-
tronics Company, Inc., October 1975.
Figure 1. Bit Error Rate Test Configuration
65
An investigation was also conducted with NRZ data on the FM link at
a data rate of 1 Mbps. These tests employed the specified frequency devi-
ations of ± 2.36 MHz and ± 360 kHz, with various combinations of predetec-
tion filters. The frequency deviation of ± 360 kHz was first evaluated
with 1.439 MHz and 6.25 MHz IF filters and the results were verified with
the results from optimization tests previously performed. The frequency
deviation was then changed to ± 2.36 MHz and the tests repeated.
3.0 TEST RESULTS
The test results obtained on the 200 bps FM link are shown in Figure 2.
Test 1, which employed the 2.7 MHz IF filter-, split-phase data, and fre-
quency deviation of + 2.0 MHz, required a total received power of -86.4 dBm
to achieve a bit error rate of 1 xl0~^. By increasing the IF bandwidth to
6.25 MHz, a 4 dB improvement in system performance was noted. Test 3 used -
the 2.7 MHz IF filter with a frequency deviation of + 635 kHz and required
a total received power of -93.4 dBm for a bit error rate o f 1 x1 .
Figure 3 shows an improvement of approximately 23 dB for the 200 bps
data rate compared to a system operating at a rate of 1 Mbps with the same
bandwidth and nearly identical deviations-. Since the ratio of data rates.
is 5000 (37 dB), a much greater improvement might be expected. However,
the bandwidth and deviation which were selected for the 1 Mbps data rate
are not optimum for the lower rate. Additional improvement is likely to be
obtained if these parameters are optimized.
The results obtained from the test conducted with ± 360 kHz frequency
deviation and 1.439 MHz IF filter using NRZ data were compared with previ-
ously performed optimization tests, as seen in Figure 4. Performance
proved to be within 0.2 dB of the earlier tests. The frequency deviation
was then increased to the specified value of ± 2.36 MHz and, using the
Bit Error Rate
A Mod Level = 2,25 vpp,
Af = ±2.0 MHz, 2.7 MHz
IF Filter
O Mod Level =0.74 vpp,
Af = ±635 kHz, 2,7 MHz
IF Filter
a Mod Level =2.25 vpp,
Af = ±2.0 MHz, 6.25 MHz
IF Filter
ORIGINAL PAGE IS
QF POOR QUALHT
Total Received Power, -dBm
Figure 2. Bit Error Rate vs. Total Received Power Using 200 bps, Split-Phase
t Error Rate
67
Bit Error Rate
69
6.25 MHz IF filter, a system performance degradation of 11.5 dB was observed.
To, determine, whether the system was. bandwidth limited, the 6.25 MHz filter
was removed and the test was repeated with no IF filter. At a bit error
rate of 10"^, no significant difference was noted. A modulation level
investigation using no IF filter was conducted to support this conclusion.
Starting at a modulation voltage of 2.8 vpp, which produced a frequency
deviation of ± 2.36 MHz, the modulation voltage was attenuated by various,
amounts up to 10 dB and then increased by 0.3 dB. The bit error rate was
recorded as a function of modulation level, as shown in Table 1. The results
show that the specified value of ± 2.36 MHz is, in fact, not the optimum
frequency deviation.
4.0 SUMMARY AND CONCLUSIONS
Three primary tests were perfomed on the Low Data Rate FM Link.
The first test, which employed a, 2.7 MHz bandwidth IF filter and a frequency
deviation of + 635 kHz, resulted in a bit error rate of 1 x 10~^ for a .total
received power of -93.5 dBm (referenced to- 1. mill i watt in 50 ohms). The
frequency deviation was then increased to ± 2.0 MHz, while retaining the
2.7 MHz filter. This increase in frequency deviation caused a- 7.0 dB
degradation in system performance. Finally, while retaining the frequency
deviation of ± 2.0 MHz, a 6,25 MHz IF filter was inserted, resulting in a
bit error rate of 7.0x10'^ at a total received power of -90.4 dBm, still
3.1 dB worse than the lower deviation test..
An additional investigation was conducted with the FM link operating
at a data rate of 1 Mbps, with a NRZ data format, at a frequency deviation
of ± 2.36- MHz and using a 6.25 MHz IF filter. Test results revealed an
11.5 dB degradation in system performance, compared to the optimum condi-
tions, which employ a. 1.439 MHz IF filter and a frequency deviation of
Table 1. Modulation Level Investigation Summary
Modulation Input Voltage
Frequency Deviation
TBP-dBm
DBR
’^2.8 volts, peak- to-pea1< .
±2. '36 MHz
65.9
5.8 X 10"^
Voltage Attenuated 0.3 dO
, ±2.28 MHz'
65.9
2.8 X 10’^
Voltage Attenuated 0.6 dB
■ ±2.20' MHz
65.9 .
IBnsBKRHillllllll
Voltage Attenuated l.fldB
'±2.10 MHz
65.9
Voltage Attenuated 1.5 dB
• ±1.99 MHz ,
65.9 ■
1.1 X 10'^
Voltage Attenuated 2.0 dB
±1.87 MHz
65.9
2.7 X 10"^
^'oltage Attenuated 2.5 dB
±1.77 MHz
65.9
5.1 X 30'^
Voltage Attenuated 3.0 dD
±1,67 MHz
65.9
2.0 X 10"^
Voltage Attenuated' 4.0 dB
±1.49 MHz
65.9
. 1.5 X 10'^
Voltage Attenuated 5.0 dB
■±1.3 3 Mliz
65. 9
1.2 X 30"^
Voltage Attenuated 6.0 dB
±1.18 MHz ■
65.9
2.0 X 10'^
Voltage Attenuated 10.0 dB
±746 kHz
65.9
1.0 X 10’^
Voltage Increased 0.3 dB
±2.44
65.9
1.4 X 10'^
*De,viated ±2,36 M!lz
'vj
o
71
±36.0, kHz. Therefore., the. ±2.36 MHz frequency deviation is not an optimum
condition for thi!s' data: rate'.
APPENDIX B
SHUTTLE FSK DATA LINK OPTIMIZATION TEST REPORT
73
APPENDIX B
SHUTTLE FSK DATA LINK OPTIMIZATION TEST REPORT*
1.0 INTRODUCTION
The proposed use of a wideband FM digital data link for Shuttle com-
munications has prompted efforts directed at optimizing the performance of
such a link. The peak frequency deviation (Af) of the transmitted signal
and the intermediate frequency filter bandwidth (Bjp) of the receiver are
the parameters usually varied.
In particular, two reports dealing with the question of optimizing
FM system performance suggest that a definite relationship exists between
the bit rate and the optimum values of Af and Bjp for a given system.
Batson [1] concludes that, for an NRZ data format and matched-filter
(coherent)- detection of binary FSK data, a frequency deviation ratio (g) '
of 0.358 and a Bjp equal to or slightly greater than the bit rate will
result. in optimum performance. The basis for this selection of $ is that
the optimum system performance occurs when the correlation coefficient
between the two FSK tones is at its most negative value. For g equal to
0.358, the value of the correlation coefficient is -0.22, Trumpis [2] pre-
sents a compilation of several studies that conclude, for a limiter-
discriminator detection technique and NRZ-L data format, optimum FSK
performance occurs with g equal to 0.35 and Bjp approximately equal to
the' bit rate. These reports conclude that, while the coherent detection
scheme represents the optimum for FSK, the performance of the limiter-
dtscriminator detection scheme is only about 0.2 to 0,4 dB worse than the
theoretical optimum FSK performance.
★
This appendix is abstracted from NASA-dSC Internal Note JSC-09113,
prepared by Lockheed Electronics Company, Inc., under' Contract NAS9-12200,
December 1974.
74
An earlier effort was made to obtain experimental results under labor-
atory conditions that would substantiate these proposed system parameters.
The tests were performed using a split-phase data format and a threshold
extension FM demodulator having a modulation tracking loop. The test
report [3]‘ concluded that additional testing was required to experimentally
establish optimum parameters for the wideband digital FM channel. However,
the data from these earlier tests tended to indicate that a g equal to
approximately 0.75 proyided the best performance and that a Bjp equal to ■
the bit rate was inadequate for split-phase FH data reception.
Presented in this appendix are the results of the tests conducted to
determine g and Bjp that result in optimum performance of a binary FSK data
transmission system. Emphasis was placed on the use of split-phase data at
1.0 Mbps. However, split-phase data at 128 kbps and 256, kbps and NRZ-L data
at. 1.0 Mbps were also used. In all tests, the parameter used for the basis
of data comparison is the bit error rate as a function of the total received
power at the receiver input. A- Microdyne Corporation Model 7100-SS(3). FM
transmitter and a breadboard wideband FM receiver were used at an S-band
frequency of 2272.5 MHz. The threshold’ extension FM demodulator (Motorola
50 MHz Demodulator) and Monitor Model 335 bit synchronizer were used through-
out the test series. S-band spectrum photographs and calibration test data
\
were obtained in addition to the bi.t error rate test data. All test data
have been compiled in a data package [4].
2*.0 DISCUSSION OF TEST RESULTS
Test results presented include equipment, calibration data, equipment
performance verification data, and bit error rate test data required for
evaluation of the binary FSK data transmission, system.
.75
2.1 System Description
The binary FSK data transmission system was comprised of a data source,,
a FM transmitter, a calibrated radio frequency (rf) path, a wideband FM
receiver, and data detection -equipment. A block diagram of the system is
shown in Figure 1.
2.1.1 Equipment Calibration
Equipment calibration data includes all test data recorded for the
purpose of determining the transmitter modulator sensitivity, the rf path
calibration, the receiver. sensitivity, and IF filter bandwidth measurements.
The transmitter modulator sensitivity, expressed as MHz per volts peak-to-
peak, ranged from 0.787 at a sinewave frequency of 125 kHz to 0.998 at a
sinewave frequency of 3.0 MHz. This information was used when adjusting
the peak-to-peak voltage of the data signal into the modu.lator to provide
a particular g. The seven-bit pseudorandom sequence, 1100101, was selected
for the data signal. •
A major objective of this program was to determine the effects of
changes in system bandwidth on the bit error rate performance for various
frequency deviations and bit rates. Therefore, a system frequency respons,e
was performed for the FM receiver with each IF filter installed. The
filter characteristics are given in Table 1. ‘
The unfiltered FM receiver noise bandwidth is 13.8 MHz centered at
48.90 MHz. The response peaks from 50.89 MHz to 51.89 MHz, and is attenuated
0.2 dB at a frequency of 50.0 MHz. The measured carrier-to-noise ratio
values were within measurement accuracy of the calculated values for the
6.25" MHz IF filter configuration. The 0- dB carrier-to-noise ratio values
for each IF filter were as calculated.
2'. 7 MHz; 1.439 MHz; 0.982 MHz;
0.447 MHz
Figure 1. Binary FSK Data Transmission System
77
Table 1. Intermediate Frequency Bandpass -Filter Characteristics
Filter
Response i
at 50.00
MHz, dB
Peak.
Response,
MHz
6MHz MU -DEL
0
49.25 to SO. '50
5MHz I -TEL
0
49.5 to 50-25
3MHz TEXSCAN
0
49.5 to 50.25
2.5MHz TRW
■ -0,1
50.2 to 50.4
IMHz TEXSCAN
0
49.8 to 50.0
IMHz TRW
-0.1
49.95
256kHz
- TEXSCAN
-0.5
49.82 to 49.88
3dB System
Bandwidth,
MHz
6.0
5,45
3.2
1,37
0.90
0.420
5.082
3.352
2 .
1.439
0.982
- 0.-447
78 -
2.1.2 Data Processing Equipment Performance
Data processing equipment, as referred to in this discussion, includes
a Motorola 50 MHz FM demodulator and a Monitor Model 335 bit synchronizer.
Tests to verify proper operation of this equipment were conducted under
laboratory conditions. The performance of both pieces of equipment was
well within previous performance levels and was concluded to be adequate
for the FSK tests.
2.2 Bandwidth Requirements for 1.0 Mbps Data
S-band spectrum photographs were taken at the output of the Microdyne
FM transmitter for both split-phase and NRZ-L formats. Examples of these
photographs are 'shown in Figures 2 and 3, respectively. A complete set of
photographs are included in the Shuttle PCM/FM Test Data Package [4]. The
•bit rate was maintained at 1.0 Mbps and 3 was varied between 0.25 and 1.0
for both data formats. The following criteria were used in determining
approximate bandwidth requirements from the spectrum photographs:
■ \ * I
Spl it-phase . Include first sideband clock components and
all spectral' components within 10 dB of the peak response
■ of these sideband components.
• NRZ-L . Include all spectral components within 10 dB of the
peak response. ' .
These criteria were selected for ease of implementation and because of the ■
need to allow adequate power for sufficient recovery of data.
2.2.1 Split-Phase Data Format
\
When applying the aforementioned criteria to the spectrum photo-
graphs, it was possible to determine a miruimum bandwidth for which adequate
clock component power would be recovered. For 6 of 0.5 through 1.0, the
79
3 = 0.36
Vertical: 10 dB/div
Horizontal: 1 MHz/div
’3 = 0.62
Vertical: 10 dB/div
Horizontal: 1 MHz/div
Figure 2. FM Spectrum Photographs of 1.0 Mbps Split-Phase Data Format
ORIGINAL PAGE IS
OF POOR QUALITY
80
3 = 0.36
Vertical: 10 dB/d1v
Horizontal: 500 kHz/div
3 = 0.62
Vertical: 10 dB/div
Horizontal: 1 MHz/div
ORIGINAL PAGE IS
OP POOR QUALOT
Figure 3. FM Spectrum Photographs of 1.0 Mbps NRZ-L' Data Format
81
minimum required bandwidth was determined to be approximately 2.3 MHz. For
e of 0.25 and 0.36, additional bandwidth was required to include those com-
ponents within 10 dB of the first sideband clock components. These approxi-
mate bandwidths are 2.7 MHz and 2.5 MHz, respectively. These results are
presented in Table 2.
2.2.2 NRZ-L Data Format
The same technique in evaluating the photographs for split-phase
data format was used for the NRZ-L data format case. The evaluation revealed
that the approximate bandwidth requirement was slightly less than (B + R) for
e of 0.5 and less,- and was slightly more than (b+R) for B of 0.62 and
higher. The results of this evaluation are also presented' in Table 2.
2.3 FM Bit Error Rate Tests
Bit error rate tests were performed for the FSK data transmission
system using split-phase data format at 1.0 Mbps, 128 kbps and 256 kbps,
and NRZ-L data format at 1.0 Mbps. The values of B and B^p that provided
the best overall performance were determined for each set of conditions.
An overall summary of the test results for split-phase data is presented -
in Figure 4. ’ ■ • ‘
2.3.1 1.0 Mbps Split-Phase Data j
Using the criteria for bandwidth requirements discussed in Section
2.2 as an aid, bit error rate testing was performed whereby b was varied
from 0.25 to, 1.5 for each of several IF bandwidth conditions. Table 3 and-
Figure 5 show the total received power in dBrn^ that resulted in a- bit error
rate of 1 xlO"'^ for various values of b and B^p.
It is evident that a b of 0.62 provides the best bit error rate per-
formance of any B tested, regardless of IF filter used. As indicated by
82
Table 2. Approximate Two-Sided Bandwidth Required for 1.0 Mbps
Binary FSK . ■ •
Two Sided Bandwidth, MHz
Split-Phase
NRZ-L
0.2S
2.7
1.1
0.3,6
2.5 CFig-
1.3 (Fig. 3a)
0-.5 ■
. 2.3
1.4
0.62
2.3 (Fig. 2b)
■ 2.0 (Fig. 3b)
0.7S
2.3
2.4
. 0.86S
2.3
2.-4
1.0
2.3
2.6
FM Bit Error Rate
84
Table 3. Binary FSK System Performance for 1.0 Mbps Split-Phase
Data Format
Total received Power for T x 10“ ** Bit Error Rate
IF Filter Equivalent Noise Bandv;idth
Unfiltered
13.8 MHz
6.25
MHz
5.082
MHz
3.352
MHz ■
HI
1.439
MHz
a
-68.1
-68.6
1
-67.9
_
-67.0
-67.2
- •
1.0
-68.3
-68.3
-68.0
-68.7
-69.3
-59.8
0.865
-68.7
-68.7
-68.5
-69.2
-69.9
-70.5
“^-70. 9 V
-63.9
0.75
-69.1
-69.1
-69.4
-69.0
-69.5
-69.7
-70.2
-67.6 ‘
-69.4
0.62
I -69-. 4
0.5
-69.0
-69.1
-69.2
-69.9
• -70.3 .
IIQIIQ
QIIQI
-66.8
-67.0
-67.2
:67.7
, -68.0
-64.7
-65.5
0.25
-63.5
-63.7'
-64.0 ■
-64.4
-62.2
* ■ -
t : Designates best performance in each row as a function
{ of" and in each column as a function of 6.
•IF
Designates best combined performance (8, B-p) .
ORIGINAL
OF POOR QLAIi?rY
Figure 5. Total Received Power, Required to Provide, 1 xlO~^ Bit Error' Rate for 1.0 Mbps ••
Split-Phase Data. as- a Function of Peak Frequency Deviation
00
cr»
86
the .symmetry of the curves in Figure 5, a e equal to 0.62 appears to be a
near-optimum value.
The best combined performance for the 1.0 Mbps split-phase data, that
is, 3 of 0.62 and Bjp of 2.7 MHz, is shown as Curve 1 of Figure 4. This
same Information is shown on Figure 6 (Curve 1) as a function of signal -to-
noise ratio -in the bit rate bandwidth (Ej^/Nq) assuming an ideal bit syncho-
nizer, that is, adjusting E^/Nq by the measured bit synchronizer degradation'.
At a bit error rate of 1 xlO”"^, the required Ej^/NQ-for- split-phase FSK was
approximately 3.3 dB worse than theoretical optimum coherent PSK (11.7 dB
versus 8.4 dB).
As expected, bandwidth limitation was most apparent with the 1.439 MHz
Bjp. These results confirm the criteria of Section 2.2, and the data tend
to indicate that a Bjp slightly less than 2.7 times the bit rate at a 3 of
0.62 will provide optimum bit error rate performance for split-phase data. '
2.3.2 128 kbps Split-Phase Data
Bit error rate test results for a bit rate of 128 kbps and’ using a
Bjp approximately equal to 3.5 times the bit rate indicate that the best
performance occurred for the cases of 3 = 0.5 and 3 = 0.62. The total
-4 "
-received power required for a bit error rate of 1 xlO . is shown in Table 4
as a function of 3 for Bjp of 447 kHz (=3.5 R) and for Bjp equal to 2.7 MHz
(optimum Bjp for 1.0 Mbps data rate). Curve 3 of Figure 6 shows the bit
error rate as a function of E^/Ng for the best case test results (Bjp =
447 kHz, 3 = 0.62) and for an ideal bit synchronizer. At a bit error rate
-4
of 1 X 10 , the required Ej^/Ng was 5.5 dB worse than theoretical optimum
coherent PSK (13.9 dB versus 8.4 dB). Somewhat better bit error rate per-
formance would be expected if a narrower bandwidth (Bjp = 2.5 R) had been
Bit Error Rate
Theoretical \
Optimum
1 - FM, 1 .0 Mbps .Split- \-
Phase, Bjp = 2.7 MHz, \
6 = 0.62 \
2- FM, 1.0 Mbps NRZ, Btp =
1.439 MHz, 6 = 0.36
3 - FM, 128 kbps Split-Phase,
Bjp = 447 kHz, 6 = 0.62
4-FM, 256 kbps, Split-Phase,
B„ = 982 kHz, 6 = 0.62
Signal-to-Noise Ratio (dB) in Bit Rate Bandwidth (Ej^/Nq)
Figure 6. Bit Error Rate as a Function of Signal-to-Noise Ratio- in
Bit Rate Bandwidth (Ej^/Nq)
OBIGINAL page
OF POOR QUAXOT
rSTal
Table 4. Binary FSK System Performance for 128 kbps Split-Phase
Data Format
Total Received Power foi
r 1 X 10"** Bit Error Rate
IF Filter Equivalent Noise Bandwidth
447 kHz
2.7 MHz
H9||
-75.6
-74.4:
1.0
-77.0-
' -72.8
0.86-5
-77.4
■ -72.8 •
0.75
0.62
-72.8
2.8
.36
3.9.
4.84
-70.9
:T''-76.4/;-;
9'. 69
*74.6
............. Designates best performance in each column as a
J function, of B- I
Designates best combined performance (B , Brp).
89
used. Based on the 1.0 Mbps' results, this potential improvement should be
about 1- dB.
As shown in Figure 4, the 128 kbps performance using the optimized
1.0 Mbps parameters (Bjp = 2.7 MHz, Af =* 620 kHz, 3 = 4.84 at 123 kbps) was
only 2.0 dB worse than the best performance obtained at this lower rate.
This is also over 5 dB better than the 1.0 Mbps performance. Thus, a single
Bjp and Af might be used for both high and low bit rate data in order to
simplify the system design.
2.3.3 256 kbps Split-Phase Data
Bit error rate tests using a 256 kbps bit rate with a Bjp of 982 kHz
yielded best performance for the cases of 8 = 0.5 and B = 0-.62. These
results are tabulated in Table 5, along with results- obtained for a Bjp of
2.7 MHz. The best case results for both bandwidths are plotted in Figure 4,
Curves 2 and 3. Curve 4 of Figure 6 shows the bit error rate as a function
of Eij/Nq for the best case test results (Bjp = 982 kHz and .8 ='0;62) ‘and
■ ■ ■ • ■ ' _4
for an-ideal bit synchronizer. At a bit error rate of 1 x 10 , the required
Eb/Ng was 5.0 dB worse than the- theoretical optimum coherent PSK (13.4 dB
versus 8.-4 dB). • ‘ ' . .
Results for the 1.0 Mbps bit rate discussed in Section- 2.3.1 indicate ■
that the 982 kHz Bjp, or 3.8 R, was wider than optimum. An improvement of
about 1 dB could be expected if a Bjp of approximately 2.5 R, or 640 kHz,
had been available for the 256 kbps data.
As shown in Figure 4, the 256 kbps performance obtained using the opti-
mized 1.0 Mbps parameters (Bjp = 2.7 MHz, Af = 620 kHz, 8 = 2.42 at 256 kbps)
was only 1.4 dB worse than the best performance obtained at this lower rate.
This is also 3 dB better than the 1.0 Mbps performance. Thus, we conclude
90
Table 5. Binary FSK System Performance for 256 kbps Split-Phase
Data Format
Designates best performance in each column as
a function of B.
Designates best combined performance (B, Bjp) .
ORIGINAL. PAGE IS
OP POOR QUALinf
91 -
that the system might be optimized for the 1,0 Mbps rate and still perform
well at the lower rates.
2.3.4 1.0 Mbps NRZ Data ' . .
Bit error rate tests were performed with e varied from 0.25 to 1.0
for each of several IF bandwidth conditions. Table 6 and Figure 7 show the
total received power that results in a 1 xlO"^ bit error rate for various 6
and B.f. values.
IF
- It is apparent that a s of 0.36 provides the best bit error rate per-
formance of any g tested, regardless of IF filter used. The best overall
performance was the result of using the 1.439 MHz Bjp along with a g of 0.36.
Curve 2 of Figure 6 depicts these results in terms of bit error rate versus
Ejj/Nqj assuming an ideal bit synchronizer. At a bit error rate of 1x10"^,
the required Ejj/Nq for NRZ FSK is approximately 1.9 dB worse than theoretical
optimum coherent PSK (10.3 dB versus 8,4 dB). The best performance as a
function of and g shown in Table 6 and Figure 7 confirms the bandwidth
criteria of Section 2.2. These results generally agree with the analysis
of Batson [t] and Trumpis [2] for optimum g when NRZ-L data is transmitted,
but tend to indicate somewhat greater bandwidths are required for optimum'
performance. In particular, the abovementioned references indicate that an '
\
IF bandwidth of 1.0 R (or slightly greater) should minimize error probability
for binary FSK systems employing discriminator detection. The nearest filter
bandwidths available for testing were 0.98 R and 1.44 R. Results with the
1.44 R filter were 2.2 dB better than for the 0.98 R filter. A comparison
of results for all filters tested, shown in Figure 7, indicates that 1.44 R
(or slightly greater) values of B^p should yield the best performance.
As shown in Figure 6, Curve 2, an optimized NRZ FM PCM channel performs,
about 1.5 dB better than an optimized split-phase FM PCM channel.
d-p-
92
Table 6. Binary FSK System Performance for 1.0 Mbps NRZ-L Data Format
p
Total Received Power for 1 x 10“'* Bit Error Rate .
IF Filter Equivalent Noise Bandwidth j
6.25
MHz
5.082
MHz
3.352
MHz
2.7 1 1.439
MHz MHz
.982
MHz •
0.25
-67.1
-68.4
-69.6
-69.8 S -71.4
J
-69.3
0.31
-69.7
—
—
0.36
-70.3
-70.3
-71.5
-71.7 jr^;-75. i:^,^
-70.9 ;
0.5
-70.2
-70.1
-71.1
-71., 3 1 -72.0
t
-69.7
1
0.62
-69.7
-69.7
-70.6
-70.7 : -70.2
%
.-65.7
0.75
-69.0
-69..1
-69.8
-69.9 j -67.5
—
0.865
-68.4
-68.5
-69.1
, -69.1 j -65.1
—
I.O
-67.8
■ '67 -7
-68'. 2
-68.2 \ -56.7 ■
.• —
I j Designates best performance in, each row as a function
of BTr* ‘ind in each column as a function of 6.
Designates best combined performance (6, BVc) .
B
CO
TD
1
S-
0)
o
CL
"U
cu
>
(D
U
OJ
QC
fd
4->
O
Frequency Deviation Ratio (e)
Figure 7. Total Received Power Required to Provide 1 x 10“^ Bit Error Rate for 1
NRZ-L Data as a Function of Frequency Deviation Ratio
0 Mbps ‘
LO
CO
94
3.0 CONCLUSIONS
Extensive testing of a binary FSK system using 1.0 Mbps split-phase
data indicates that the best overall performance can be obtained with a
modulation index of 0.62 and IF bandwidth of 2.7 MHz. Additional tests at
. f
128 kbps and 256 kbps' indicate a similar conclusion,' that is, best perform-
ance should occur with modulation index of 0.62 and IF bandw.idth about 2.5
times the bit rate. Measured results for the optimized 1.0 Mbps bit rate
were within 3.6 dB of an ideal PSK system at a bit error rate of 1 xlO"^.'
The best case modulation index of 0.62' corresponds to a peak frequency
deviation of 620 kHz at a 1.0 Mbps split-phase bit rate. When the lower
bit rates were run with this same 620 kHz peak frequency deviation and
using the 2.7 MHz IF bandwidth (optimum for 1.0 Mbps), the bit error rate
performance degraded from the optimized xonditions by 1.0 to 2 dB', but still
remained superior to 1.0 Mbps performance by. 3 to 5 dB at the 1 xlO"^ bit
error rate. Consequently, a system optimized for the higher bit rate, and
providing adequate performance at that rate, could be expected to perform
satisfactorily at the lower rates while still using the same peak frequency
i * ■ * » . ^ ‘
deviation and receiver bandwidth.
Tests of the FSK system using 1.0 Mbps NRZ-L data indicated that the
best overall performance occurred with the use of a 6 of 0.36 and Bjp of
1.439 MHz. For these parameters', the FSK system performance was 1.9 dB
worse than an ideal PSK system when operating at a bit error rate of 1 xlO"^,
These results confirm the optimum modulation index of 0.36 predicted by
Batson [1] and Trumpis [2] but tend to indicate a somewhat greater optimum
bandwidth than the predicted value of 1.0 to 1.2 times the bit rate.
95
4.0 REFERENCES
1. Batson, B. H. Performance of Binary FSK Data Transmission Systems,
JSC-08097,. EJ-73-11 , EJ5-73-257, July 24, 1973.
2, Trumpls, B, D, Optimum Parameters for the Space Shuttle Wideband
Digital FM Direct Communication Link, Axiomatix Report No. R7406-1 , June 4,
1974.
3. Krafka, J. E. Shuttle Wideband FM Data Link Preliminary Test.
Report, EEu-74-204, LEC-3937, August 1974.. ,
4. Krafka, J. E. Shuttle PCM/FM Test Data Package, EE7-74-702,
LEC-4272, September 1974.
96
APPENDIX C
DEVELOPMENT FLIGHT INSTRUMENTATION {DFI} LINK
97
APPENDIX' C
DEVELOPMENT FLIGHT INSTRUMENTATION (,DFI) LINK
In addition to the operational C&T interface links, an SSO-to-STDN
S-band DFI link is provided to transmit telemetry consisting of one PCM'
channel and 15 FM subcarrier channels during Orbital Flight Tests (OFT).
1.0 FUNCTIONAL DESIGN
Figure 1 shows a functional interface configuration for this link.
The 128 kbps DFI PCM data in a bi-phase-L (Manchester II) format phase-
shift-keys (PSK) the 1.024 MHz subcarrier prior to frequency-division multi-
plexing with the 15 FM subcarrier channels. The multiplexed composite
signal is then used to frequency modulate the 2205.0 MHz carrier before
being power amplified and radiated from the' antenna. At the ground station,
an FM carrier demodulator in series with a 1.024 MHz subcarrier demodulator
is used to convert the DFI RF signal to the 128 kbps baseband signal, which
t.
is then detected by the bit synchronizer. For the 15 FM subcarrier channels,
the baseband signals are restored after the output of the FM carrier demodu-
I - j ^ -
lator is processed through 15 subcarrier FM demodulators-.
2.0 DATA CHARACTERISTICS
2.1 PCM Channel
The data content of the 128 kbps DFI PCM channel includes SSO status,
housekeeping information, and instrumentation-related data. The frame
structure is the same as the PCM frame format shown in Figure 4, page 10.
2.2 FM Subcarrier Channels
For the 15 FM subcarrier channels, there are 7 channels with 500 Hz
frequency response, 7 analog channels with 2000 Hz response, and 1 digital
bi-phase-L channel with 12 kbps external tank PCM data.
/(miGINAL PAGE IS
OF POOR QUALITY
Figure 1. SSO-to-STDN S-Band DFI Link Functional Configur4tion
99
3.0 RF CHARACTERISTICS
3.1 Modulation/Demodulation
The 128 kbps DFI PCM data in a bi-phase-L format phase-shift-keys the
1.024 MHz subcarrier and each of the 15 FM subcarrier signals frequency modu- .
lates its respective subcarrier. The FM subcarrier frequencies and peak-to-
peak frequency deviations are listed in Table 1. The frequency-division
multiplexed subcarriers frequency modulate the link RF carrier. The carrier
peak-to-peak frequency deviation by each subcarrier is listed in Table 1.
At the ground station, the 1.024 MHz subcarrier PSK demodulator coher-
ently demodulates the suppressed subcarrier to obtain the 128 kbps -DFI base-
band signal. Standard subcarrier FM demodulators are used to reconstruct
the FM subcarrier data signals prior to being processed by the ground signal
processor.
3 . 2 Effective Isotropic Radiated Power (EIRP)
The minimum EIRP from the SSO, which includes the SSO transmit power,
circuit loss, and antenna gain, is 0.4 dBW.
100
Table 1. SSO-to-STDN DFI.Link Interface Characteristics
Carrier
Frequency
SSO .
Minimum
EIRP
STDN
Minimum 6/T
Antenna
Polari- .
zation
STDN
Requirement
(Ppec/No)
Feet
dB/K
2205.0 MHz
0.4 dBW*
12
7.6
RCP
76.0 dB-Hz**
TBD
30
22.0
40
21.2
85
31 .2
Information
Channels
Subcarriers
Carrier
Peak
Deviationtt
No.
Signal
Format
Bandwidth
or Bit Rate
Frequencyf
Modu-
lation
Peak
Deviationtt
1 •
Analog
500 Hz
12
kHz
mm
1 kHz-
■■a
2
Analog
500 Hz
16
kHz
1 kHz
‘3
Analog
' 500 Hz
20
kHz
FM
1 kHz
20 kHz
4
Analog
500 Hz ■ ■
24
kHz
FM
1 kHz
20 kHz
5 .
Analog’
500 Hz
28
kHz
FM
-■1 kHz
20 kHz
6
Analog
500 Hz
3Z
kHz
. FM'
1 kHz—
20 kHz
7
Analog
500 Hz
36
kHz
FM ■
■1 kHz
20 kHz
8
Analog
2 kHz
48
kHz
FM
■ 4 kHz
33.6 kHz
9
Analog
2 kHz
64
kHz
FM
4 kHz
44.8 kHz
10
Analog ''
2 kHz
80
' kHz
FM
4 kHz
56.0 kHz
11
Analog
2 kHz
96
kHz
FM •
4 kHz
67.2 kHz
12
Analog
2 kHz
112
kHz
FM
4 kHz
78.4 kHz
13
Analog
2 kHz
128
kHz
FM
4 kHz
89.6 kHz
14
Analog
2 kHz
144
kHz
FM
4 kHz
100.0 kHz
15^
Bi-^-L
12 kbps
184
kHz
FM
-TBD-
—TBD—
PCM
Bi-(|.-L
128 kbps
1.
024 MHz
PSK
-N/A-
700.0 kHz
*Based on SSO antenna gain of 1 dB with’ about 54% coverage
**Based on 10 dB minimum SNR in 4 MHz predetection bandwidth
t±TBD%
tt±l 0%
AExternal tank PCM
101
APPENDIX D
APPROACH AND LANDING TEST (AL-T) TELEMETRY LINK
ORIGINAL PAGE IS
OF POOR QUAUrr
102
APPENDIX D.
APPROACH AND LANDING TEST (ALT) TELEMETRY LINK
During the Approach and Landing Test (ALT), the operational C&T links
and the DPI link are not implemented. The SSO ALT telemetry dat.a are trans-
mitted to the STDN ground station via an SSO-to-STDN S-band ALT telemetry
link. This link function continuously during both the mated and released
phases when 1 ine-of-sight exists. The SSO ALT telemetry data transmitted
consists of one 128-kbps pulse code modulated (PCM) digital data channel
and, simultaneously, 15 analog data channels. Figure 4,. page 10, shows the
PCM frame format.
Figure D-1 shows the functional interface configuration for this link.
In the SSO, the 128-kbps PCM data in a bi-phase-L (Manchester II) signal
format phase-shift-keys (PSK) a 1.024 MHz subcarrier, and each analog, data
signal frequency modulates (FM) a corresponding subcarrier. -The 16 modulated
subcarriers are frequency division multiplexed .(FDM), and the FDM composite'
signal "frequency modulates (FM) the 2205.0 MHz RF carrier, which is then
power amplified and radiated -from the antenna. At .the ground station, an FM
receiver,' a "PSK demodulator, and 15 FM subcarrier demodulators are used to-
convert the RF signal to the baseband. Bit detection of the 128-kbps PCM
data is performed in a bit synchronizer.
The carrier aircraft receives the modulated 2205.0 MHz RF carrier from
the SSO, translates the RF frequency to 2250.0 MHz, and retransmits the modu-
lated 2250.0 MHz RF carrier to the STDN station. This relay functions con-
tinuously during both the mated and released phases.
The* pertinent signal characteristics and interface parameters for the
SSO-to-carrier aircraft S-band link are summarized in Table D-1. Table D-2
summarizes the signal characteristics and interface parameters for the SSO-
to-STDN S-band ALT telemetry link.
UOOd >10
rjvtQ>)X30
Figure D-1 .
SSO-to-STDN S-Band ALT Telemetry Link Fu
Frequency
Translation
FM Receiver
*Links to and from carrier
aircraft are not covered
by ICp 2-0D004.
Configuration
103
Table D-1 . SSO-to-Carrier Aircraft S-Band Link Characteristics
SSO
Carrier Aircraft
Frequency
EIRP*
Antenna
Polari-
zation
Frequency
Antenna
Polari-
zation
g
S/N
Degradationt
EIRP
2205.0 MHz
±TBD MHz
7.0 dBW^
RCP
2205.0 MHz
•± TBD MHz
.(Received)
2250.0 MHz
■± TBD MHz
(Transmitted)
RCP
TBD
Total
1 dB
TBD
A Based on nominal +3.0 dB SSO antenna gain.
* Effective isotropic radiated power.;
** Receive antenna gain/system temperature, where system temperature is. referred to the antenna
terminal. :
t Signal-to-noise ratio degradation in. the process .of receiving, translation, and retransmitting.
105
Table D-2. SSO-to-STDN S-Band ALT Telemetry Link
Interface Characteristics
Carrier
Frequency
SSO
Minimum
EIRP
STDN
Minimum
G/T
Antenna
Polari-
zation
STDN.
Requirement
(Prec/^o)
2205.0 MHz
±TBD
0.0 dBW*
7.6 dB/K**
RCP
76.0 dB-Hz^
Information
Channels
Subcarriers
Carrier
Peak
Deviation
(kHz).tt
No.
Signal
Format
Bandwidth
or Bit Rate
Frequency
(kHz)t
■
Modu-
lation
Peak
Deviation
(kHz) ft
1
Analog-
500 Hz
12
•' FM
■ = 1
20
2
Analog
500 Hz
16
FM
1
20
3
Analog.
500 Hz
• 20
FM
1
20
■ 4
■ Analog
■ 500 Hz- ...
24
FM
■ 1 •
• 20
- 5 .
Analog
500- Hz
'28 • '
-■ FM
. . 1
- '20
6
-Analog
500 Hz
' 32
• FM.
. 1
‘20
7
Analog
500 Hz
- 36
FM- -
1
20 "
8
Analog
2 kHz ,
48
FM
• 4
33.6
9
Analog
2 kHz
64“
FM '
4
44.8 ■
10
Analog
2 kHz.
80
FM
. 4
• 56.0
11
Analog
2 kHz
96 ■ .
FM
4
.67.2
12
Analog
2 kHz
112
FM
4
78.4
13
Analog
2 kHz
128
FM
4
89.6
14
Analog
2 kHz
144
FM •
. 4
100.0
15
Analog
8 kHz
184
FM
16
257.0
PCM
Bi-({)-L
128 kbps
1.024 MHz
PSK
NA
700.0 .
* Based on SSO antenna gain of -4 dB with about 36% coverage.
** STDN 12-foot antenna.
A Based on 10 dB minimum SNR in 4 MHz predetection bandwidth,
t ± TBD’%
ft ± 10%
OBIGINAL page i-
T>rkm?. OUAIATY