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Spectral efficiency of adaptive OFDM systems over high mobility Nakagami-m fading channels

ABSTRACT In this paper, we investigate the impact of rate and power adaptation (RPA) and rate adaptation (RA) using square M-ary quadrature amplitude modulation (MQAM) on the average spectral efficiency (ASE) of orthogonal frequency division multiplexing (OFDM) systems under instantaneous bit-error-rate (BER) constraint over high mobility Nakagami multipath fading (NMF) channels. Especially, the closed-form expressions for the average spectral efficiency (ASE) of RPA and RA are obtained when these adaptive schemes are used over NMF channels with existence inter-carrier interference (ICI) caused by the high mobility. By comparing the ASE of RPA and RA under different number of subcarriers, a simplified rate and subcarriers bandwidth adaptation (RSBA) algorithm is obtained. Simulation results indicate that RSBA is more suitable for high-speed communication environment than RA.