Performance analysis of dual selectionbased macrodiversity system over channels subjected to Nakagami fading and gamma shadowing Nikola M. Sekulovic, Edis S. Mekic, Dragana S. Krstic, Aleksandra D. Cvetkovic, Martina Zdravkovic * , Mihajlo C. Stefanovic Faculty of Electronic Engineering, Department of Telecommunications University of Nis Aleksandra Medvedeva 14 Serbia * Faculty of Occupational Safety University of Nis Carnojevica 10A Serbia sekulani@gmail.com Abstract:  This paper studies wireless communication system following microdiversity to mitigate the effects of short-term fading and macrodiversity processing to reduce shadowing effects. N-branch maximal-ratio combining (MRC) is implemented at the micro level (single base station) and selection combining (SC) with two base stations (dual diversity) is implemented at the macro level. Model in the paper assumes a Nakagami- m density function for the envelope of the received signal and a gamma distribution to model the average power to account for shadowing. Analytical expressions for the probability density function (PDF), cumulative distribution function (CDF) and moments of signal after micro- and macrodiversity processing are derived. These expressions are used to study important system performance criteria such as the outage probability, average bit error probability (ABEP), average output signal value and amount of fading (AoF). Various numerical results are graphically presented to illustrate the proposed mathematical analysis and to show the effects of various system parameters to the system performance, as well as enhancement due to use of the combination of micro- and macrodiversity. KeyWords:  Gamma shadowing, Macrodiversity, Microdiversity, Nakagami-m fading. 1 Introduction In wireless communication systems, the received signal can be exposed to both short-term fading, which is the result of multipath propagation, and long-term fading (shadowing), which is the result of large obstacles and large deviations in terrain profile between transmitter and receiver [1]. The reliability of communication over the wireless channels can be improved using diversity techniques, such as space diversity techniques [2], [3]. The most popular space diversity techniques are selection combining (SC), equal-gain combining (EGC) and maximal- ratio combining (MRC). MRC is optimal combining technique in the sense that it achieves the best performance regardless of the fading statistics on the diversity branches. However, MRC requires the knowledge of the channel fading amplitudes and phases of each diversity branch which must be continuously estimated by the receiver. These estimations require separate receiver chain for each branch of the diversity system increasing its complexity. EGC provides performance comparable to MRC, but with simpler implementation complexity. EGC does not require the estimation of the channel fading amplitudes since it combines signals from all branches with the same weighting factor. SC is the least complicated technique. It is reposed on processing only one of the diversity branches. SC combiner chooses the branch with the highest signal value. Diversity techniques at single base station (microdiversity) reduce the effects of short-term fading. Impairments due to shadowing can be mitigated using macrodiversity techniques which employ the processing of signals from multiple base stations. The use of composite micro- and macrodiversity has received considerable interest due to the fact that it simultaneously combats both short-term fading and shadowing. Rayleigh, Rician and Nakagami-m statistical models are the most frequently used to describe fading envelope of the received signal. The Rayleigh distribution is frequently used to model WSEAS TRANSACTIONS on COMMUNICATIONS Nikola M. Sekulovic, Edis S. Mekic, Dragana S. Krstic, Aleksandra D. Cvetkovic, Martina Zdravkovic, Mihajlo C. Stefanovic ISSN: 1109-2742 77 Issue 3, Volume 10, March 2011