Imrpoving QPSK Transmission in Band-Limited Channels with Interchannel Interference Through Equalization

This paper describes the use of equalization in conjunction with channel filtering to improve QPSK transmission subject to both intersymbol interference (ISI) and interchannel interference (ICI). Performance bounds are computed using the nonclassical Gaussquadrature rule (GQR) method. The signal-to-noise ratio (SNR) gain due to linear equalization over nonequalization is thereby obtained and presented. The performance of a linear equalizer thus obtained is compared with the Viterbi algorithm sequence estimator (VASE). In the absence of bounds for the VASE receiver under the channel conditions considered, simulation results are used to make the comparison. With a possible difference in the accuracies of the performance thus obtained it is shown that the VASE provides improved performance over the linear equalizer under the channel conditions considered.