A comparison study of low bit rate DE-QPSK and TCM 8-PSK fully digital demodulators over a land mobile satellite link

The synchronization and detection techniques used to overcome the Rician channel impairments are described. The acquisition and bit error rate (BER) performances of this modem have been evaluated by computer simulation over an AWGN (additive white Gaussian noise) and a Rician faded channel, and compared with a DE-QPSK demodulator with similar architecture. In an AWGN channel the TCM (trellis coded modulation) 8-PSK system is found superior to the DE-QPSK. In terms of the overall BER over realistic satellite channel conditions the two systems show comparable results because of the greater susceptibility of TCM schemes to carrier synchronization errors. However, the outage of the coded 8-PSK system is superior to the DE-QPSK one. The errors of the coded 8-PSK are characterized by short periods of high error rates with longer gaps of very low error rates. In contrast, the errors of the DP-QPSK system are distributed uniformly and occur more frequently