SN User's Guide - ESC Home - NASA

customer platform transmitted signal characteristics within the constraints
specified in Table 8-9. Customer platform parameters exceeding these
constraints can also degrade TDRSS KaSA return service performance. Refer
to Section 3, paragraph 3.5 for guidelines if the constraints in this paragraph
cannot be met. Definitions of user customer platform constraints are given in
Appendix E.
d. Multipath. The SN ground terminal will provide lockup and interference
protection from multipath signals reflected from the Earth.
8.3.3.3 Signal Tracking
TDRSS provides KaSA 225 MHz return signal tracking (carrier, symbol synchronization,
Viterbi decoder synchronization) for non-powered flight dynamics. During a customer
KaSA return service support period, loss-of-lock (carrier, symbol synchronization, and
Viterbi decoder) indications appear in the periodically updated UPD (every 5 seconds).
The KaSA return service shall maintain signal tracking for the following conditions:
a. Cycle Slips. The mean time-between-cycle slip in the SN ground terminal
carrier tracking loop for each TDRSS KaSA return service will be 90 minutes
minimum. This value applies at carrier tracking threshold, which is 3 dB less
than the minimum Prec for BER listed in Table 8-7, and increases exponentially
as a function of linear dB increases in Prec. Cycle slips may result in channel
and/or data polarity reversal. The SN ground terminal can correct for these
reversals under the same conditions as the SN ground terminal can resolve
channel and/or data polarity ambiguity as discussed in Appendix B. The time
for the SN ground terminal to recover from a cycle slip will be consistent with
the time required for the SN ground terminal receiver to detect and
automatically reacquire the signal.
b. Bit Slippage. For each TDRSS KaSA return service operating with a minimum
Prec required consistent with the Prec for BER of Table 8-7 and data transition
densities greater than 40% for NRZ symbols, the minimum mean time between
slips caused by a cycle slip in the SN ground terminal symbol clock recovery
loop is either 90 minutes or 10 10 symbol periods, whichever is greater. For a
KaSA return service operating with 1 dB more than the minimum Prec required
for the BER, and NRZ symbol transition densities between 25% and 40%, the
minimum mean time between slips is either 90 minutes or 10 10 symbol periods,
whichever is greater.
c. Loss of Symbol Synchronization. For each TDRSS KaSA return service with
data transition densities greater than 40% for NRZ symbols, the SN ground
terminal symbol synchronization loop will not unlock for a Prec that is 3 dB less
than the minimum Prec required for BER in Table 8-7 (refer also to note 3 of
Table 8-7). For NRZ symbol transition densities between 25% and 40%, the
SN ground terminal symbol synchronizer loop will not unlock for a Prec that is 2
dB less than the minimum Prec required for the BER. In both cases, the BER
performance will be degraded when the Prec is less than the minimum required
for BER.
Revision 10 8-26 450-SNUG