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convolutional interleaving of either rate 1/2 or rate 1/3 convolutional encoder
symbols is defined in Appendix F.
6.3.3.3 Signal Tracking
TDRSS provides SSA return signal tracking (carrier, PN, symbol synchronization,
convolutional deinterleaver synchronization, Viterbi decoder synchronization) for both
powered and non-powered flight dynamics. During a customer SSA return service
support period, loss-of-lock (carrier, symbol synchronization, and Viterbi decoder)
indications appear in the periodically updated User Performance Data (UPD) (every 5
seconds).
a. Non-powered Flight Dynamics. For all valid return service signals operating
under non-powered flight dynamics, the SSA return service shall maintain
signal tracking for the following conditions:
1. Cycle Slips. The mean time-between-cycle slip in the SN ground terminal
carrier tracking loop for each TDRSS SSA return service will be 90
minutes minimum. This value applies at the carrier tracking threshold,
which is 3 dB less than the minimum Prec for BER, 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.
2. Bit Slippage. For each TDRSS SSA return service operating with a
minimum Prec required consistent with the Prec for BER and data transition
densities greater than 40% for NRZ symbols or any transition density for
biphase 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 an SSA
return service operating with 1 dB more than the minimum Prec required for
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.
3. Loss of Symbol Synchronization. For each TDRSS SSA return service
with either rate 1/2 or rate 1/3 convolutional encoding and data transition
densities greater than 40% for NRZ symbols and any transition density for
biphase 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. 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 BER. In both cases, the BER
performance will be degraded when the Prec is less than the minimum
required for BER.
b. Powered Flight Dynamics. TDRSS will provide signal tracking with a probability
of more than 0.99 over 90 minutes for a customer with powered flight dynamics
Revision 10 6-34 450-SNUG