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Communications systems rarely have perfect channel state information (PCSI) when demodulating received symbols. This paper shows that the symbol error rate (SER) of a flat fading communications system can be expressed in closed form by expressing the demodulator outputs as random variable (RVs) that have a complex ratio distribution, which is the ratio of two correlated complex Gaussian RVs. To complete the analysis, the complex ratio probability density function (PDF) and cumulative distribution function (CDF) are both derived. Finally, using several scenarios based on M-QAM signaling, the SER performance of imperfect channel state information (ICSI) systems is analyzed.

Statistical channel models based on BER performance are presented for a frequency-and time-selective vehicle-to-vehicle wireless communications link in an expressway environment in Atlanta, Georgia, where both vehicles traveled in the same direction. The models are developed from measurements taken using the direct sequence spread spectrum (DSSS) technique at 2.45 GHz. A collection of tapped delay line models, referred to as a "partitioned" model in the paper, is developed to attempt to capture the extremes of BER performance of the recorded channel. Overall and partition models are compared to the recorded channel in terms of the BER statistics obtained when the channels are inserted in a dedicated short range radio (DSRC) standard simulation system. The quality of the match between synthesized and recorded channel BER statistics is analyzed with respect to type of modulation (fixed or adaptive), the frame length, and the length of the interval over which the BER was calculated.