JELE_V3_N1_RP3 Eiman Mutwali Abdelmageed Hussain Journal on Electronics Engineering 2249 – 0760 3 1 17 35 Channel Impairments, Multipath, QAM, OFDM, Spectral Efficiency, Channel Capacity ISI In wireless communication systems, the transmitted signal is subject to different channel impairments, such as noise and multipath propagation. The demand for more reliable and higher speed wireless services has led to the development of digital communication techniques. This new development direction resulted in an increasing interest in new modulation formats that overcome the limitations associated with the wireless communication channel which degrades the performance of the communication system. The new sought modulation formats are expected to have high spectral efficiency and better immunity to transmission impairments. Of these modulation formats are the Quadrature Amplitude Modulation (QAM) and the Orthogonal Frequency Division Multiplexing (OFDM). This paper analyses through computer simulation the performance of: QAM, OFDM and QAM combined with OFDM under different channel impairments and compares which technique gives better performance under these conditions. The analysis was carried out using MATLAB and the results showed that QAM is used to effectively increase the channel capacity while OFDM is attractive because of its effective way in reducing the effect of inter-symbol interference (ISI). Furthermore a combination of these techniques has been proven to enhance the performance of a communication system. September – November 2012 Copyright © 2012 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=2035