Hybrid trellis-coded 8/4-PSK systems

It is shown how trellis-coded 8-PSK (phase-shift-keying) signals can be modified to become more robust against carrier phase variations, thus allowing more stable carrier recovery. A more robust performance can be achieved by using rate 2/3 trellis-coded 8-PSK and 4-PSK signals in a time-varying manner. In its simplest form, trellis-coded 8-PSK and 4-PSK signals alternate in time. The distance spectra and bit error probability are evaluated with and without phase offset. Simulation results of bit error rate (BER) and performance of the recovery loop (S-curve) are also presented. At 7.5 degrees RMS phase jitter, the cycle slip rate of the conventional trellis-coded 8-PSK system is about 25%. For the new schemes it is reduced to less than 0.1%. This is achieved with almost no penalty in BER in blocks received without cycle slips.<
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