Equalization of differentially coherent QPSK operating over slowly fading Rician channels

The effects of a simple equalizing system on the performance of a differentially coherent QPSK (quaternary phase-shift-keying) system operating over selectively and slowly fading Rician channels are analyzed. The proposed receiver consists of linear matched filters cascaded with linear equalizers and postdetection diversity combining systems. The bit-error probability, which is the performance measure, is computed using the characteristic function approach and assuming a canonical receiver. The final expression is found as a function of the elements of the covariance matrix of the fading environment. The simulation results show that the superiority of this receiver over a receiver not using an equalizer is uncontestable. Moreover, even though the simplest equalizer configuration was used by introducing a moderate modification of the circuitry at the receiver, it resulted in significant improvement of the system performance. The proposed system represents a new approach to transmission of data using cellular communications