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Adaptive modulation techniques are becoming very important for mobile communication systems due to dynamic characteristics of the medium. Diversity is another technique which further improves the performance of mobile communication system. In this paper the performance of adaptive M-QAM modulation technique has been evaluated in term of BER with diversity. A comparison of different values of the constellation size M has been done by simulation for variable number of paths variable number of paths, L = 1, 2, 3, 4, 5, 6. The performance is compared with the performance of GMSK, DQPSK, and MPSK modulation in the same diversity environment using MRC technique. A detailed performance comparison of modulation techniques shows that the diversity improves the performance of all modulation schemes, especially at lower values of diversity orders. The improvement in the performance is less at higher values of diversity orders. It is noticed that the improvement in BER performance is significant if the number of paths is less than 4, and there is no substantial improvement in BER performance if the number of paths is greater than 6, due to the increase of estimation errors.