This paper proposes a new adaptive modulation scheme, which is robust to a fast time-variation of Rayleigh fading. Adaptive modulation, which chooses an appropriate modulation format according to the instantaneous carrier-to-noise power ratio (CNR) of the fading channel, is an efficient technique capable of improving the transmission performance in a multipath fading channel. However, in a fast fading channel environment, the performance improvement will drastically be reduced. When CNR varies during the transmission burst, the transmission often fails since the modulation format chosen at the beginning of the burst to obtain the required bit error rate (BER) does not satisfy the required BER at the end of the burst. In order to overcome this problem, we propose a new adaptive modulation scheme, which employs the array antenna based Doppler spread compensator. Computer simulation results show the proposed adaptive modulation scheme drastically improves the packet error rate and throughput performance in fast fading environment.
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