Chapter

Fading and Shadowing in Wireless Systems

pp 313-416

Date:

Diversity Techniques

  • P. Mohana ShankarAffiliated withElectrical and Computer Engineering, Drexel University Email author 

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Abstract

In this chapter, we investigat the impact of diversity in wireless channels. Our study is limited to those fading and shadowing models based on the Nakagami or gamma densities. The benefits of diversity can be understood by carrying out the computations of the error rates and outage probabilities. The error rates and outage probabilities show reductions with diversity. Maximal ratio combining (MRC) diversity provides maximum improvement in performance. We also explore the need to have diversity at the microlevel and macrolevel. This mitigates the channel impairments in shadowed fading channels. The hybrid diversity implemented at the microlevel through generalized selection combining offers a compromise between pure selection combining on one end and MRC on the other end. It must be understood that the trends in improvement with diversity will be similar regardless of the specific models used for fading or shadowing. There is a large body of published work available in the literature of wireless which examines diversity in fading and shadowed fading channels modeled using other density functions. The improvements seen in Weibull channels through the implementation of the GSC algorithm have been reported by several researchers (Bithas et al. 2003; Alouini and Simon (2006) Wireless Comm. & Mobile Comp. 6:1077–1084). Results on other diversity algorithms in Weibull channels are additionally available (Sagias et al. (2003) Electronics Letters 39(20):1472–1474; Sagias et al. (2004) Communications, IEEE Transactions on 52(7):1063–1067; Karagiannidis et al. (2005) Wireless Communications, IEEE Transactions on 4(3):841–846). While the diversity in generalized gamma channels was briefly discussed earlier on, several published results which undertook detailed studies of generalized gamma fading channels are available (Bithas et al. (2007a) Communications Letters, IEEE 11(12):964; Aalo et al. (2007) Communications, IET Proceedings 1(3):341–347; Samimi and Azmi (2008) Int. J. Electronics & Comm. (AEU) 62:496–605). The case of shadowed fading channels modeled using Rician-lognormal density has been studied by researchers (Wang and Stuber (1999) Vehicular Technology, IEEE Trans. on 48(2):429–436; Zhang and Aalo (2001) Communications, IEEE Transactions on 49(1):14–18). Diversity in Nakagami-Hoyt channels has also been studied (Iskander and Mathiopoulos (2005) Proceedings. IEEE 233–239; Zogas et al. (2005) Wireless Communications, IEEE Transactions on 4(2):374–379; Fraidenraich et al. (2008) Communications, IEEE Transactions on 56(2):183–188).