Datum Systems PSM-500L Manual do Utilizador descarregar pdf (Página 27)

Datum Systems PSM-500, 500H & 500L VSAT/SCPC Modem Specification

Rev. 0.86

A-27

Acquisition Performance

The following table shows typical acquisition performance for the Fast Acquisition mode using the

standard Viterbi FEC and the DSP acquisition processor. The times shown are for the average and

95% of acquisition probability at a 6.0 dB Eb/No. These times are measured over 1000

acquisitions.

Fast Acquisition Timing

Bit Rate

in kbps

Modulation FEC Rate Typical Average

Fast Acquisition

Time for ±30 KHz

(seconds)

Typical 95%

Probability Fast

Acquisition Time for

±30 KHz (seconds)

2.4

QPSK Vit 1/2 1.230 1.453

2.4

BPSK Vit 1/2 0.750 0.819

9.6

QPSK Vit 1/2 0.315 0.371

9.6

BPSK Vit 1/2 0.174 0.183

QPSK Vit 1/2 0.196 0.231

BPSK Vit 1/2 0.144 0.163

QPSK Vit 1/2 0.116 0.135

BPSK Vit 1/2 0.097 0.110

QPSK Vit 1/2 0.071 0.082

BPSK Vit 1/2 0.050 0.057

8PSK TCM 2/3

16QAM Vit 1/2

Fast acquistion performance is optimized in Viterbi FEC rate ½. When changing to rate ¾ or 7/8

the penalty is approximately 3.5 to 4 times the acquisition time. This is due to the decreased

symbol rate and the FEC and acquisition processors having to deal with twice the number of

ambiguities in determining signal type and lock. Acquisition times with the Turbo Product Codes

FEC are 2 to 4 times that of the Viterbi FEC. Fast acquisition is optimized under normal noise

conditions, where the absence of noise adds time for AGC operation.

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