Performance of coded 8PSK signaling for satellite communications

Quaternary phase-shift keying (QPSK) is currently the prevalent modulation proposed for digital satellite communications. The use of 8PSK in conjunction with a coding of rate 2/3 for forward error correction can provide the same spectral efficiency as that offered by uncoded QPSK, while increasing the power efficiency. Computer simulations have been made to evaluate the potential coding gain of coded 8-phase signaling both for an additive white Gaussian noise channel and for a band-limited nonlinear satellite channel. Viterbi decoding of soft-detected 8-phase symbols is employed for maximum likelihood path decoding of coded 8PSK signals. Coding gain relative to uncoded QPSK has been evaluated for codes of three complexities. At practical values of probability of bit error, coding gains greater than 3 dB have been obtained for a code of memory gamma = 4 bits or 16 states. The gain is about 0.5 dB higher for a code with gamma = 6 or 64 code states.