Phase-Noise Effects on Turbo Trellis-Coded Modulation Over -ary Coherent Channels

Phase-Noise Effects on Turbo Trellis-Coded Modulation Over -ary Coherent ChannelsThe average mutual information (AMI) for specific constellations, such as 8-phase-shift keying and 16-quadrature amplitude modulation, is calculated in the presence of carrier phase error caused by imperfect carrier tracking over an additive white Gaussian noise channel. The AMI is obtained to determine a permissible amount of phase noise for a given signal-to-noise ratio and to discuss the effect of phase noise from an information-theoretic point of view. The bit-error rate (BER) performance of a turbo trellis turbo-coded modulation (TTCM) scheme is then investigated to verify whether a TTCM scheme with the ability to approach a channel capacity limit performs well over the channel. For this purpose, an optimal branch metric which best fits the channel characteristics is derived. Furthermore, simple branch metrics (suboptimal, simplified, and Gaussian metrics) are derived, and applied to the decoding of the TTCM scheme, with those metrics evaluated regarding the tradeoff between BER performance and computational complexity. By numerical analysis, the system is seen to be much more robust against phase noise than is the case with a conventional trellis-coded modulation scheme.