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.

The mesh topology based on the standard IEEE 802.11 for wireless LANs (WLANs) appears to be a very promising architecture on the way to realizing an ubiquitous high-speed wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single Access Point (AP) environments and many problems related to the wireless meshed interconnection of APs and Mobile Terminals (MTs) remain unsolved. Some proposed solutions to build such mesh architectures are based on ad-hoc-oriented single-channel schemes that modify IEEE 802.11 protocol. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself when the network becomes larger or the offered traffic load increases. The task group IEEE 802.11s is currently discussing and working out a standard for IEEE 802.11-compliant mesh architectures for various usage scenarios including residential, office and campus/community/public access network but much work is ahead since the group was recently established. In this paper we propose a new multi-radio multi-channel mesh architecture for WLAN hot spots, which works using a Distributed Coordination Function (DCF)-based technique for interconnecting APs, and also a radio-aware packet forwarding scheme among APs. A major advantage of the system is that, putting routing issues aside, it introduces no changes into the MAC protocol of IEEE 802.11. The simulation results obtained in OPNET v.10.0 show the great potential of our mesh architecture to support real-time traffic with any packet size, and the effectiveness of the radio-aware forwarding scheme in improving the delay performance of the mesh network.