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Table 6-1. TDRSS SSA Forward PSK Service Signal Parameters (cont’d)
Notes (cont’d):
3. The SN is capable of supporting BPSK signals at data rates less than 300 kbps; however, its use
will be controlled and must be coordinated with GSFC Code 450.
4. After the start of the SSA forward PSK service, if a customer MOC is unable to accurately define
fo (the nominal center frequency of the customer platform receiver), the forward service carrier
frequency can be swept. The SSA forward service frequency sweep will be initiated by the SN
ground terminal at fo -3 kHz and linearly swept to fo +3 kHz in 120 seconds and held at fo +3 kHz
thereafter. The SSA forward service frequency sweep does not impact simultaneous SN ground
terminal Doppler compensation of the SSA forward service carrier and PN code rate (if
applicable).
5. Customers who operate in a SS-BPSK mode for one service cannot reconfigure any of their
Forward Services (i.e., MAF, SMAF, SSAF, KuSAF, or KaSAF) to an SS-UQPSK mode. Contact
Code 450 if additional flexibility is required.
6. The NTIA will not grant TDRSS customers an S-band forward 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.
c. Asynchronous Data Modulation. For data rates < 300 kbps, the forward service
data received at the SN ground terminal from the NISN data transport system is
directly modulo-2 added by the SN ground terminal to the command channel
PN code sequence. The forward service data will be asynchronous with the
carrier and the PN code.
NOTE:
When the command channel does not contain any actual
forward service data, the forward service command channel
signal is the command channel PN code sequence with or
without an idle pattern.
d. Functional Configurations. A further description of the functional configurations,
the I-Q channel ambiguity, and data polarity ambiguity is found in Appendix B,
paragraph B.2.2.
e. Doppler Compensation. The TDRSS SSA forward service carrier frequency (F)
and the PN chip rate transmitted by a TDRS can optionally be compensated by
the SN ground terminal for Doppler. When compensated, the carrier, FR ,
arrives at the customer platform receiving system within a predictable tolerance
(E) of fo as defined in Table 6-1. This feature minimizes the Doppler resolution
requirements of the customer platform receiver and is available continuously to
facilitate reacquisition by the customer platform in the event of loss of lock of
the TDRSS SSA forward service signal. Doppler compensation may be
inhibited and the TDRSS will transmit a fixed frequency SSA forward service
carrier and PN code chip rate.
Revision 10 6-6 450-SNUG