Performance of digital open loop carrier synchronization in rician fading channels

Abstract

In this dissertation work, we investigate the performance of the digital carrier synchronization which has the open loop structure. Open loop structure has the advantages over the closed loop structure much like PLL(Phase-locked Loop) such as hangup free, noncausal structure, and the good low SNR performance, et cetera. The fading channels which can be modeled with Rician statistics are prevail on many radio communication systems such as the micro cellular mobile system and the satellite links. First, we find out the maximum likelihood(ML) phase estimator for carrier synchronization in Rician fading channels. We prove this estimator becomes the ML estimator in Rician fading channels by computer simulation. Although this ML estimator requires too much computation to be realized, we can have the insight of the optimal phase estimator structure in Rician fading channels from this ML estimator. We have found that, in deep fading channel conditions, the ML estimator in Rician fading channels gives much better performance than the Viterbi``s phase estimator which is an ML estimator in Gaussian noise channels. In moderately faded channels, the performance of the Viterbi``s estimator is comparable to that of the ML estimator. Secondly, we mathematically analyze the performance of the nonlinear phase estimator(NLPE) in terms of the phase error variance. NLPE is a low SNR approximation of the ML estimator for fully phase modulated signals in Gaussian noise channels. We show that the analysis results well coincide with the results from the computer simulation in the tracking region. Increasing the estimator memory length of NLPE gives the better performance in the various fading channel conditions. But there is a tradeoff between the tracking performance and the fast acquisition because increasing the estimator memory length means the more delayed acquisition time. A.M. Viterbi declared that the performance of the NLPE degrades quickly in the presence of frequency offset....