International Journal of Power Control Signal and Computation(IJPCSC) Vol. 4. No.2 . pp.148 - 156 April - June 2012 ISSN: 0976-268X www.ijcns.com Analysis and Performance Evaluation of BWR Mechanism in MAC 802.16 for WiMAX Nandini Prasad K S 1 Sridevi G R 2 Thimmaraju S N 3 1,3 Dept. of ISE, Dr.AIT Bangalore 560056 nandiniks1@gmail.com , thimmaraju_sn@yahoo.com 2 Pooja Bhaghavat Memorial Mahajana PG Centre Mysore Abstract— Wireless network is a network of computers, computer peripherals and various other devices that are connected to each other without wires. This enables ease of communication, especially for mobile computing platforms. WiMAX [Worldwide Interoperability for Microwave Access] is the latest contender as a last mile solution for providing broadband wireless Internet access and is an IEEE 802.16 standard. In IEEE 802.16 MAC protocol, Bandwidth Request (BWR) is the mechanism by which the Subscriber Station (SS) communicates its need for uplink bandwidth allocation to the Base Station (BS). The performance of the system is affected by the collisions of BWR packets in uplink transmission, that have the direct impact on the size of the contention period in uplink sub frame, uplink access delay and uplink throughput. Network simulator-2 (NS-2) is extensively used by the networking research community. It provides substantial support for simulation of TCP, routing, multicast protocols over wired and wireless (local and satellite) networks, etc. The simulator is event- driven and runs in a non-real time fashion. It consists of C++ core methods and uses Tcl and Object Tcl shell as interface allowing the input file (simulation script) to describe the model to simulate. Key terms: WiMAX, Wireless, Bandwidth, allocation, simulation. 1. INTRODUCTION Bandwidth Request (BWR) is the mechanism by which the SS communicates its need for uplink bandwidth allocation to the BS. A single cell in WiMAX consists of a Base Station (BS) and multiple Subscriber Stations (SSs). The BS schedules the traffic flow in the WiMAX i.e., SSs do not communicate directly. The communication between BS and SS are bidirectional i.e., a downlink channel (from BS to SS) and an uplink channel (from SS to BS). The uplink channel is shared by various SS’s through Time Division Multiple Access (TDMA). The duration of sub frames, slots and the number are determined by the BS scheduler. The downlink sub frame contains Uplink map (UL map) and Downlink map (DL map).The DL map contains information about the duration of sub frames and which time slot belongs to a particular SS as the downlink channel. The UL map consists of Information Element (IE) which includes transmission opportunities. Pervasive computing refers to the emerging trend towards numerous, easily accessible computing devices connected to an increasingly ubiquitous network infrastructure. This trend will likely create new opportunities and challenges for the Information Technology (IT) companies to place high-performance computers and sensors in virtually every device, appliance, and piece of equipment in buildings, homes,