Performance of skewed phase shift keying

Source-matched digital transmission techniques are proposed to maximize robustness, recovered signal quality, as well as bandwidth efficiency. Miki et al. (1993) proposed a pseudo-analog transmission technique where adaptive differential pulse code modulation (ADPCM) samples were transmitted using nonsymmetric skewed differential phase shift keying (SDPSK). The SDPSK transmission format linearly maps the ADPCM samples to the signal constellation points so that transmission errors due to adverse channel conditions result in proportional distortion on the recovered source signal. The performance of such a system was evaluated using computer simulations without a comprehensive supporting theory. In this paper we analyze the performance of transmitting PCM samples using skewed phase shift keying. Both theoretical and simulation results are presented which are found to corroborate well. Optimal skewing angles are obtained for various quantizer resolutions for both the Gaussian channel and for Rician fading channels. The source-matched digital transmission schemes considered in this paper have possible applications in a subclass of wireless personal communication systems (PCS) where low delay is an important requirement. This implies operating at relatively high channel signal-to-noise ratios without or with limited channel coding and interleaving