DESIGN AND PERFORMANCE STUDY OF DIGITAL COMMUNICATIONS RECEIVERS FOR FAST RAYLEIGH CHANNEL

Abstract

Conventionally, it has been assumed that coherent detection over the AWGN channel has to be achieved with the use of some carrier tracking phase-locked loop. However, in practice, the tracking capability of the phase-locked loop is limited, especially when operating over fast fading channels. In this thesis, four channel estimation receiver structures for the purpose of coherently detecting MPSK signals over the AWGN channel with fast, frequency-nonselective, Rayleigh fading are presented. The four receiver structures concerned are, namely, the symbol-by-symbol sampled matched filter receiver, symbol-by-symbol optimum sampled receiver, sequence estimation sampled matched filter receiver and sequence estimation optimum sampled receiver. All the receiver structures considered include an estimator to perform channel estimation. Either the Kalman filter or the adaptive filter can be employed to track the rapidly fluctuating fading process. Unlike the Kalman filter, the adaptive filter does not require any a priori knowledge of the channel. Besides that, both the first-order and third-order Butterworth fading spectra are investigated. The simulation results agree closely with the theoretical results for the SBSSMF receiver and the SE-SMF receiver. The simulation results indicate that the SE receivers that utilise a Viterbi-algorithm to perform efficient metric computations and path search are superior to the SES receivers in terms of BEP performance. The simulation results also indicate that the OS receivers are superior to the SMF receivers in term of BEP performance due to its ability to produce an estimate for each sample of the fading process. Unlike the OS receivers, the SMF receivers only produce an estimate for the average fading gain within each symbol interval. To summarise, the four receivers proposed in this thesis perform well under the fast, frequency-nonselective, Rayleigh fading channel.