Implementation and Performance Analysis of DCWA MAC Protocol for Multihop Wireless Networks.

Abstract

Performance of multi-hop ad hoc networks is severely affected by the hidden and exposed node problems. The e RTS/CTS based handshaking protocol used in the IEEE 802.11 standard was designed to solve the hidden node problem, however it was not successful in completely solving the problem. This paper presents a performance evaluation of adaptive backoff algorithm based on Deterministic Contention Window Allocation (DCWA) on top of IEEE 802.11 Distributed Coordination Function (DCF) standard. The DCWA protocol relies on real-time measurements of the number slots being used in specified cycle time. This algorithm judiciously sets the upper and lower bounds for the contention window in order to adapt to the congestion level in the shared medium at that point in time. This work provides an extension to DCWA in evaluating its performance over noisy channels with varied network density. In this work, the % age of effective utilized time in current and past cycles are used to predict the next cycle’s upper and lower bounds of contention window to suit the number of active users at any point in time. Thus overall contentious attempts can be reduced and also system idle time is also kept at best possible minimum values. The performance of DCWA protocol is evaluated via simulations using NS2 simulator. The test results reveal that DCWA based CW allocations perform relatively better with connection less (CL) Constant Bit Rate application protocol (CBR over UDP) traffic than Connection Oriented (CO) protocols application protocols like, File Transfer Protocol traffic (FTP over TCP). In some cases CO traffic performs better than 802.11 DCF, but it is not consistent with all network sizes.