We present the channel capacity, specifically the mutual information, of an additive white Gaussian noise (AWGN) channel in the presence of phase noise, and investigate the effect of phase noise impairment on powerful error-correcting codes (ECCs) that normally operate in low signal-to-noise ratio (SNR) regions. This channel-induced impairment is common in digital coherent transmission systems and is caused by imperfect carrier tracking of the phase error detector for coherent demodulation. It is shown through semi-analytical derivation that decreasing the information rate from its ideal capacity to an information rate lower than its inherent capacity significantly mitigates the impairment caused by phase noise, and that operating systems in the low SNR region also lessen the phase noise impairment by transforming typical phase noise behavior into Gaussian-like behavior. We also demonstrate by computer simulation using turbo-trellis coded modulation (TTCM) with high-order quadrature amplitude modulation (QAM) signals that the use of capacity-approaching codes (CACs) makes transmission systems invulnerable to phase noise. To verify the effect of CACs on phase noise, simulation results of TTCM are also compared to that of trellis-coded modulation (TCM), which is used as an example of a conventional ECC operating at a relatively high SNR.

This paper considers a wireless coherent system that enables high-speed-data transmission in the presence of carrier phase error over an additive white Gaussian noise (AWGN) channel. Carrier phase noise is caused by imperfect carrier tracking of the coherent demodulation. The channel characteristics of the system were modeled using phase noise whose stochastic process followed the Tikhonov distribution. For this model, we first propose an optimum detector that produces the most suitable decoding metric for a soft-input/soft-output (SISO) decoder, and then develop some simpler forms of the optimum detector to obtain efficient implementation at close to optimal performance. Those simple detectors that have a wide range of performance/complexity tradeoffs are promising in various applications. To evaluate the effectiveness of the proposed detectors, we have applied them to a bandwidth-efficient turbo-coded modulation scheme in which a component decoder based on SISO principles necessitates more exact channel measurement than is possible with a conventional decoder based on Viterbi decoding. Simulation results have demonstrated that the optimum detector enables excellent bit error rate (BER) performance that exceeds that with a normal detector designed for AWGN channels by more than 1 dB at a BER of 10-6 under a severe phase noise environment.

In this paper, the separate coding scheme is applied to space-time turbo-coded modulations (ST-TuCM). The separate coding for ST-TuCM uses the plural number of component encoders, each of which is a binary turbo encoder in the transmitter. The receiver has component decoders corresponding to the component encoders. The likelihood values derived by the component decoders are employed as a-priori information of transmitted signal from other transmit antennas in iterative demodulation-decoding. Simulation results under the fast Rayleigh fading channel show that separate coding and iterative demodulation-decoding improve the bit error rate performance.

The effects of noisy estimates of fading on turbo-coded modulation are studied in the presence of flat Rayleigh fading, and the channel capacity of the system is calculated to determine the limit above which no reliable transmission is guaranteed. This limit is then compared to the signal-to-noise ratio required for a turbo-coded modulation scheme to achieve a bit-error-rate of 10-5. Numerical results are obtained, especially for QAM signals. Our results show that even slightly noisy estimates significantly degrade the theoretical limits related to channel capacities, and that an effective use of capacity-approaching codes can lower the sensitivity to noisy estimates, though noise that exceeds a certain threshold cannot be offset by the performance improvement associated with error-correcting capability.