Performance of Adaptive Modulation in Multipath Fading Channel

Adaptive modulation and coding schemes are promising technique to support the demands for high data rates and wideband proposed for 4G mobile communication system standards. The spectrally efficient modulation schemes are the dominant trend in mobile communication system after 3G mobile system and the adaptive modulation system is suggested to be the best solution for bandwidth efficient system. In this paper, adaptive modulation based on M-QAM modulation scheme is analyzed through simulation and compared with GMSK, DQPSK, 8-PSK. The performance analysis in terms of Bit Error Rate (BER) and Spectral Efficiency (SE) for downlink channel system environments with different values of constellation size under Rayleigh multipath fading channel is done. The result is analyzed, compared and investigated for many proposed standards which enhances data rate, symbol rate and frequencies for variable rate MQAM with different values of constellation size M=2^k, k=3......10. Four models have been examined for each of the mentioned schemes. The adaptive modulation model is based on predicted channel. It has been observed that MQAM system gives better performance in terms of bit error rate.