Performance Study of Diversity Combining Techniques for Error-floor Reduction in Fast Fading Channels

Abstract: We investigates the effect of mobile speed, channel estimation rate, diversity order on performance degradation due to error floor in a mobile Single-Input-Multiple-Output (SIMO) wireless communication system. Each diversity channel is assumed to be fast Rayleigh fading process, which is modeled as a first order autoregressive process. Diversity channels are assumed to be independent and identically distributed (i.i.d) with identical channel correlation parameters and channel estimation rates at each receiving antenna. Two receiving diversity combining techniques are used: maximum ratio combining (MRC) and selection combining (SC), and two binary modulation schemes are considered: coherent PSK (BPSK) and differentially coherent PSK (BDPSK). The performance is investigated in terms of the overall average output received signal-to-noise-ratio (SNR) and bit error rate (BER). Closed-form expressions for the average received SNR and BER are derived. We show that these expressions are also applicable for slow fading scenarios. Numerical results demonstrate the negative affects of error floor on system performance under fast fading channels. For coherent detection, we show that increasing the channel estimation rate improves performance and reduces the error floor especially when higher diversity order is used. For differentially coherent detection, with low channel estimation rates, the results reveal that increasing diversity order reduces error floor compared to coherent detection. Our results also show that MRC provides better performance compared to SC irrespective of the value of the correlation parameter, the channel estimation rate, and the used modulation scheme.