Bit Error Rate Performance Analysis of a Threshold-Based Generalized Selection Combining Scheme in Nakagami Fading Chann
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Bit Error Rate Performance Analysis of a Threshold-Based Generalized Selection Combining Scheme in Nakagami Fading Channels Ahmed Iyanda Sulyman Electrical and Computer Engineering Department, Faculty of Applied Science, Queen’s University, Kingston, ON, Canada K7L 3N6 Email: [email protected]
Maan Kousa Electrical Engineering Department, College of Engineering Sciences, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia Email: [email protected] Received 2 September 2004; Revised 25 January 2005; Recommended for Publication by C. C. Ko The severity of fading on mobile communication channels calls for the combining of multiple diversity sources to achieve acceptable error rate performance. Traditional approaches perform the combining of the different diversity sources using either the conventional selective diversity combining (CSC), equal-gain combining (EGC), or maximal-ratio combining (MRC) schemes. CSC and MRC are the two extremes of compromise between performance quality and complexity. Some researches have proposed a generalized selection combining scheme (GSC) that combines the best M branches out of the L available diversity resources (M ≤ L). In this paper, we analyze a generalized selection combining scheme based on a threshold criterion rather than a fixedsize subset of the best channels. In this scheme, only those diversity branches whose energy levels are above a specified threshold are combined. Closed-form analytical solutions for the BER performances of this scheme over Nakagami fading channels are derived. We also discuss the merits of this scheme over GSC. Keywords and phrases: diversity systems, generalized selection combining, threshold-based GSC, mobile communications, Nakagami-m fading.
1.
INTRODUCTION
Diversity techniques are based on the notion that errors occur in reception when the channel is in deep fade—a phenomenon more pronounced in mobile communication channels. Therefore, if the receiver is supplied with several replicas, say L, of the same information signal transmitted over independently fading channels, the probability that all the L independently fading replicas fade below a critical value is pL (where p is the probability that any one signal will fade below the critical value). The bit error rate (BER) of the system is thus improved without increasing the transmitted power [1]. This is traditionally referred to as the diversity gain of the system. Most diversity considerations have always assumed that the spatial separations among the (mulThis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
tiple) diversity antennas are large enough so that the diversity branches experience uncorrelated fading, and therefore the signals received from the different diversity antennas are independent. In some practical mobile systems; however, large antenna spacings are not feasible, and therefore the
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