ON THE PERFORMNACE ANALYSIS OF COMBINED (TIME SHARED) COMPOSITE MULTIPATH/SHADOWING AND UNSHADOWING FADING CHANNELS

Abstract

Combined (time-shared) shadowed/unshadowing fading environments are frequently encountered in different mobile realistic scenarios. These wireless channels are generally modeled as a time-shared sum of Rician multipath fading (unshadowing) and different Composite multipath/shadowing fading. In this thesis, we present the closed-form expression of composite (Weibull/Log-normal shadowed) fading using the efficient tool proposed by Holtzman. Using this result, the closed-form expression of combined (time-shared) shadowed/ Unshadowed fading is presented. We have derived closed form expressions for performance measuring parameters such as Probability Density Function (PDF) of Signal to Noise ratio (SNR), Amount of Fading (AOF), Outage Probability (Pout) and Channel Capacity(C/B). Simulated exact expressions are carried out to validate the accuracy of our derived closed form expressions. The performance of diversity systems of MRC combiner in the presence of log normal shadowing also analyzed in this thesis. We have used Fenton-Wilkinson method to estimate the parameters for a single log-normal distribution that approximates the sum of log-normal random variables (RVs). PDF, CDF, AOF, Pout and channel capacity are analyzed and expressed in closed form. The average bit error probabilities of MQAM and MPSK in the presence of log normal shadowing using Maximal Ratio Combining technique for L diversity branches are computed using Holtzman approximation. We proposed an analytical approach for the evaluation of important second order statistical parameters, as level crossing rate (LCR) and average outage duration (AOD) of MRC combiner in Log-Normal shadowed channels. New expressions have been derived for LCR and AOD in closed form. The results are valid for an arbitrary number of independent identically distributed diversity branches in the presence of Log -Normal shadowed. LCR and AOD have been plotted and also tabulated for different number of diversity branches. We have also proposed new statistical modeling of channel capacity for MRC combiner in the presence of log normal shadowing. This new approach to estimate higher order moments of channel capacity is simple and easy with compare to well-known results. We also provide the performance analysis of Maximal Ratio Combiner (MRC) output for MQAM in Multiple Rician fading channels. The approximate formula of symbol error rates (SER) for MQAM over Gaussian channel have been used. Approximation is within 1 dB error for M ≥ 4 and 0 ≤ SNR ≤ 30 dB. vi The proposed results in this thesis are supposed to be of great importance in assessing the performance of communication systems in composite fading channels.