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Journal of Information Science and Engineering, Vol. 24 No. 4, pp. 1065-1079 (July 2008)

A Modified EDCA with Dynamic Contention Control for Real-Time Traffic in Multi-hop Ad Hoc Networks

Yang-Jing Wu, Jen-Hung Chiu and Tsang-Ling Sheu
Department of Electrical Engineering
National Sun Yat-Sen University
Kaohsiung, 804 Taiwan

EDCA (Enhanced Distributed Channel Access), developed for providing service differentiation in wireless LANs, has become a MAC standard in IEEE 80.2.11e. However, unexpected packet delay due to collisions and retransmissions may occur when the wireless LAN becomes congested. To support the increasing demand of delay-sensitive multimedia applications, this paper presents a modified EDCA with dynamic contention control (DCC) for real-time traffic in multi-hop ad hoc networks. The proposed scheme not only reduces the average packet delay but also increases the percentage of packets meeting real-time constraints by two approaches: (1) dynamically adjusting the priority level of a traffic flow based on the estimated per-hop delay, and (2) generating a nonuniformly distributed backoff timer for retransmitted frames according to their individual end-to-end delay requirements. For the purpose of evaluation, we perform simulations on ns-2. We compare the performance of the proposed DCC scheme to EDCA and a previous work, AEDCF (adaptive EDCF). The simulation results demonstrate the effectiveness and superiority of our proposed DCC scheme.

Keywords: EDCA, multi-hop ad hoc networks, real-time traffic, per-hop delay, end-toend delay

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Received July 27, 2006; revised February 13, 2007; accepted April 3, 2007.
Communicated by Ten-Hwang Lai.