Proposal and Evaluation of a Mesh Wireless Local Area Network Architecture with Dual DCF-HCCA Channel Access Scheme in the Vicinity of Gateway Access Points

Luis LOYOLA  Masakatsu OGAWA  Kengo NAGATA  Satoru AIKAWA  

IEICE TRANSACTIONS on Communications   Vol.E89-B   No.10   pp.2752-2762
Publication Date: 2006/10/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.10.2752
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Mobile Multimedia Communications)
mesh networks,  IEEE 802.11,  wireless LAN,  HCCA,  multi-radio,  

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The gateway access point (AP) in a wireless mesh network becomes the natural bottleneck node around which all the traffic relayed by APs that is exchanged among the terminals and the Internet tend to concentrate. So far most of the practical deployments of mesh wireless local area networks (WLANs) focused on public safety and public access have taken place in rural or suburban areas where the low density of users and the low data-rate applications in use do not impose stringent traffic conditions, making the conventional single-radio DCF-based system defined by IEEE 802.11 a feasible implementation option. However, under relatively high traffic-load conditions, the large number of packet collisions produced by the accumulation of traffic in the vicinity of gateway APs may greatly reduce the overall network throughput and largely increase the delay, especially in case of packets that traverse several hops, thus affecting real-time applications like voice over IP (VoIP). To cope with this problem a polling mechanism compliant with the IEEE 802.11e hybrid-coordination-function controlled channel access (HCCA) which operates in a single network interface card (NIC) in the vicinity of gateway APs has been proposed in this paper. The polling scheme is complemented with a Distributed Coordination Function (DCF) channel access that also operates in the vicinity of gateway APs in a different NIC and on a different channel. The HCCA NIC allows any gateway AP to exchange data frames with its surrounding APs in a scheduled and bidirectional way while the DCF NIC provides gateway APs a contention-based way to receive data frames from their respective surrounding APs. Computer simulations carried out in OPNET version 10.0 to evaluate the combination of both contention-based and contention-free access schemes in the area surrounding gateway APs show that the proposed mechanism can largely increase the total throughput while providing low transmission delay. As no changes to the IEEE 802.11 related protocols are required, the proposed scheme represents an attractive option to implement a mesh WLAN.