Requirement of portable, mobile and high speed connectivity for internet access is increasing day by day. WiMAX will be playing an important role in the Broadband Wireless Technology (BWT) sector, since it is more cost-effective and easy to install technology. It is a fixed Broadband Wireless Access (BWA) system based on the IEEE 802.16 standards and will be used to provide “last mile” access to the broadband and Internet access services. The WiMAX technology is based on the IEEE 802.16-2004 Air Interface Standard and is rapidly proving itself as a technology that will play a significant role in fixed broadband wireless metropolitan area networks. It is based on the concept of orthogonal frequency division multiple access technique in wireless communication. This paper investigates the performance of WiMAX network under AWGN and SUI Channel Model by varying physical layer parameter such as higher M-ary modulation, coding scheme and cyclic prefix.