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Revision 10 6-25 450-SNUG
Table 6-8. SSA Return Service Configurations (cont’d)
Configuration supported
Notes: - Configuration not supported
1. For DG1 mode 1 and 2 configurations, where the minimum source data rates are 0.1 kbps for DG1 mode 1 and 1 kbps for DG1 mode 2:
a. Data on a single I or Q channel, but not both channels: BPSK modulation is used where the data is modulo-2 added to the PN code.
b. Data on both the I and Q channels: SQPN modulation is used and the SN supports I:Q power ratios of 1:1 to 1:4 for all the configurations, except the
alternating I and Q data bit configuration, which requires a balanced I:Q power ratio.
c. The alternating I/Q data bit configuration: the SN requires the I channel lead the Q channel by a half symbol. Similarly, the SN requires the I and Q
channels be independently differentially formatted (-M,-S).
2. For DG1 mode 3 configurations:
a. The modulation is QPSK, where the I channel data is modulo-2 added to the PN code, and the Q channel data directly modulates the carrier at +/2
radians.
b. The SN supports I:Q power ratios of 1:1 to 1:4.
c. Rate 1/3 coding is supported for the Q channel only. (Rate 1/2 coding is supported on both the I and Q channels.)
3. For DG2 configurations:
a. Single data source configurations with data on one channel: BPSK modulation is used.
b. Single data source configurations with data on both channels: SQPSK modulation and an I:Q power ratio of 1:1 is used. For the alternate I/Q bit
configuration, the SN requires the I and Q channels be independently differentially formatted (-M,-S).
Dual data source configurations: SQPSK must be used when there are identical baud rates on the I and Q channels (see paragraph 6.3.2.1.b); QPSK is
used for all other configurations; for both SQPSK and QPSK, either an I:Q power ratio of 1:1 or 4:1 is supported. For unbalanced QPSK, the I channel
must contain the higher data rate and when the data rate on the I channel exceeds 70 percent of the maximum allowable data rate, the Q channel data
rate must not exceed 40 percent of the maximum allowable data rate on that Q channel.
4. Noncoherent configurations (DG1 mode 2 and DG2 noncoherent) require a customer transmit frequency uncertainty of + 700 Hz. If a customer cannot
accurately define their transmit frequency to within + 700 Hz, a customer can request a reconfiguration which would expand the oscillator frequency search to
+ 3 kHz for DG1 and SQPSK DG2 configurations and + 35 kHz for BPSK and QPSK DG2 configurations after the start of service.
5. Periodic convolutional interleaving (PCI) recommended on S-band return service for channel baud rates > 300 kbps. When interleaving is not employed for
channel baud rates > 300 kbps, S-band performance may not be guaranteed.
6. Biphase symbol formats are not allowed with PCI. Use of biphase symbol formats on S-band services at baud rates > 300 kbps should be coordinated with
GSFC Code 450.
7. For all configurations and modes, the SN is capable of providing SSA support of uncoded links; however, performance is not guaranteed in RFI and must be
coordinated with GSFC Code 450.
8. TDRSS may be capable of supporting other return signal configurations, such as residual carrier Phase Modulation signals; however, performance will have to
be handled on a case-by-case basis with GSFC Code 450.
9. Unless otherwise noted, all data rates are to be interpreted as data bit rates, and not as data symbol rates. Refer to Section 3, paragraph 3.6 for a description
of SN data interfaces, associated constraints, and WDISC capabilities.
10. Appendix B describes the functional configurations and associated I-Q channel and data polarity ambiguities. Additionally, Figure B-10 depicts the SN
supported convolutional coding schemes.
11. For S-band DG2, dual data channel, balanced power configurations, the minimum total (I+Q) data rate must be 60 kbps or greater.
12. Data rates and modulation schemes are based upon support through the SSAR SN ground terminal receivers. Other data rates and modulation schemes are
possible through the SSA return automated IF services, which is available on a case-by-case basis. Please refer to paragraph 6.3.6 and contact GSFC Code
450 for further information.
13. The NTIA will not grant TDRSS customers an S-band return service frequency allocation greater than 6 MHz. If a frequency allocation greater than 6 MHz is
required, the SN should be notified and the NASA GSFC Spectrum Manager may petition the NTIA for a temporary waiver.