Research On Key Technologies Of Medium Access Control In Wireless Mesh Networks Based On 802.11

With the development of wireless communication techniques, wireless networks change people's daily life dramatically by providing the mobile Internet access. Wireless Local Area Network (WLAN), working as the last hop connection to Internet, has come in to market nowadays. In WLANs, terminals access Internet through Access Point (AP) which connects to wired networks directly. Since WLAN strongly depends on wired network, so the coverage of WLAN is very small due to the limited transmission range and the cost of deployment is still too expensive. To extend the coverage of wireless access networks and reduce the deployment cost, Wireless Mesh Network (WMN) is introduced.WMNs are multi-hop wireless networks. Deployed in Mesh topology, Internet access is provided by wireless multi-hop relay in WMNs. A WMN is composed of Mesh Routers, Mesh Clients, and Mesh Gateways. Mesh Gateways are the WMN-and-Internet joints; Mesh Routers with fixed locations and stable power supplies constitute the backbone of WMN; Mesh Clients access WMNs by connecting to Mesh Routers, they can be routers also in some special scenarios. It has been noticed by former researches that the performance achieved does not satisfied the requirement of users with existent MAC, routing and transport protocols. So it is very necessary to modify these protocols to enhance the transmission performance in WMNs.1) Routing protocols designed for Ad Hoc can't work perfectly with WMNs for the difference in topology, node type and traffic patterns. This paper proposes an efficient and adaptive cross-layer routing scheme coined Path Cost-Based Routing (PCBR) scheme for multi-channel, multi-hop Wireless Mesh Networks (WMNs). In our scheme, paths are selected based on the path cost determined by the three important metrics: end-to-end delay, available bandwidth and path packet loss rate. The end-to-end delay and available bandwidth are redefined based on the 802.11s MAC protocol to fit the multi-channel, multi-hop WMNs. Mesh Routers (MRs) process most route discovery work in themselves to reduce the number of retransmissions in flooding the route discovery packets. The route prefers less end-to-end delay, more bandwidth and less power consumption by adapting the coefficient of the three metrics.2) A novel Scheme of Cooperative MAC for multi-hop multi-radio Wireless Mesh Networks (WMNs) has been exploited to improve the performance of the IEEE 802.11s MAC draft protocol. The proposed scheme allows transmitter (cooperative source node.) request multiple intermediate nodes for cooperatively transmitting data to receiver (cooperative target node.) when the direct transmission lead to throughput degradation. These intermediate nodes work as a Virtual Node (VN). If the transmission base on two hops cooperation can not satisfied the transmission request, the cooperative source node can request to establish three hops or more hops cooperative transmission. Thus, a slow one-hop transmission can be transformed into a faster two-hop or more hops transmission and the proposed scheme utilizes multiple channels for parallel transmission, thereby decreasing the transmission time and increasing the throughput significantly.3) Wireless Mesh Networks (WMNs) are the most potential technology for last-mile broadband Internet access. The achievable capacity of WMNs is constrained by network topology, traffic patterns, multi-radio interactions and optimal of the protocol. We analyze the theoretical capacity bound in scenarios with different topologies and traffic patterns for WMNs because existing model are not very suit for WMNs.