Performance Evaluation of Cross layer Design in Multi-hop Relay WiMAX Networks

Abstract

Many cross-layer design schemes have been proposed to overcome the limitations of protocol architectures in following strict layering principles. The core idea is to maintain the functionalities associated to the original layers but to allow coordination, interaction and joint optimization of protocols crossing different layers. In this study, we focus on the overhead deriving from the overlap of Transmission Control Protocol (TCP) and Automatic Repeat reQuest(ARQ) functionalities at different layers, where several acknowledgements are generated for a single data block transmitted in wireless channels reducing theavailable bandwidth resources, and taking a long time to be delivered causing a delay. To the aim of reducing unnecessary burden on the wireless link, we propose a cross-layer ARQ approach, called ARQ Proxy. It is a software module located in the protocol stack of the wireless Base Station (BS) to locally generate the TCP ACK for every data packet destined to the Mobile Host (MH) confirming successful data reception, and releases it to the Fixed Host (FH) when requested by the ARQ client which is located in the protocol stack of the MH. Then there is no need for TCP ACK transmission over the wireless link, the saved time can be used by other nodes for data packet delivery which increases overall network capacity. A MATLAB code simulates 802.16j environment with two hops is written and the proposed solution is applied on it. Results show a clear improvement in the chosen network performance parameters. Where there is an increment in the average of throughput and the efficiency and there is a decrement in the Round Trip Time (RTT) and the number of time outs after applying ARQ proxy which improves the efficiency of the proposed solution.