ABSTRACT

OFDM (Orthogonal Frequency Division Multiplexing) is a multicarrier technique where linearly modulated data streams are divided into number of substreams each occupying a bandwidth less than the total bandwidth of the signal. However, full justice was done in proper utilization of bandwidth in OFDM where subcarriers overlap orthogonally. M-ary modulation schemes are preferred because in these schemes more than one bit can be grouped & transmit at a time which is very effective for band limited channels. MQAM (M-ary Quadrature Amplitude Modulation) is the most effective digital modulation technique as it is more power efficient for larger values of M. The basic idea of M-ary QAM & OFDM has been discussed in the paper. The Simulink based model of the MQAM-OFDM system with normal AWGN channel and Rayleigh fading channel has been made for study error performance under different channel conditions. Lastly a comparative study of BER performance of 64QAM-OFDM & 128QAM-OFDM under AWGN channel & Rayleigh fading channel has been given.