Extended EDCA for delay guarantees in wireless local area networks

Despite of their very broad diffusion, IEEE 802.11 Wireless Local Area Networks are not able to provide service differentiation and to support real-time multimedia applications, due to their channel access methods. To overcome these limitations, the 802.11e working group has proposed the Enhanced Distributed Coordination Access (EDCA) scheme which achieves service differentiation on statistical basis by properly mapping user QoS requirements to channel contention parameters. Such a scheme will be included in the emerging 802.11n standard and in the revision of the 802.11 standard. However, it has been widely demonstrated that, especially at high network loads, EDCA does not provide an effective usage of the channel capacity. In particular, it is unable to provide a bounded delay service to all kind of multimedia flows because flows with lower channel access priorities are starved to advantage only the ones with the highest priority. To fix this undesired behavior and improve wireless LAN performance, this paper proposes the new Extended EDCA (EDCA) scheme, that is compliant with 802.11e specifications. By exploiting a closed loop control algorithm, EDCA performs a distributed dynamic bandwidth allocation, providing guarantees on average/absolute delays to real-time media flows, regardless of their priorities. Moreover, an innovative Call Admission Control procedure has been developed. Using the ns-2 simulator, the effectiveness of the algorithm has been investigated in realistic network scenarios, involving a mix of audio, video, and FTP flows, at several network loads and with random losses. Results have shown that the proposed scheme is able to provide a bounded delay service to multimedia flows in a wide range of network loads and frame loss ratios. Index Terms QoS, Wireless LAN, Real-time Applications, Distributed Bandwidth Allocation. A short preliminary version of this paper was presented at ACM/IEEE MSWiM’06 Conference. Authors are with the “Dipartimento di Elettrotecnica ed Elettronica Politecnico di Bari”. Via Orabona, 4 – 70125 BARI, Italy. E-mail: {g.boggia, camarda, a.grieco, g.piro}@poliba.it.