Research On Wireless Mesh Networks Cross-layer Techniques

With the further development of mobile wireless communication, there will be more and more demand of wireless voice and data services, especially high-data-rate Internet services. Data rate of long-distance wireless communication is very limited because of attenuation. Wireless multi-hop communication can provide much bigger bandwidth and subscriber can access Internet through multi-hop wireless router. Under such circumstance, wireless multi-hop Mesh networks appear as a new technique. Cross-Layer techniques mainly involves key techniques and their effect on each other in every layer of wireless Mesh network, especially how MAC protocol affects routing protocol performance in network layer.We firstly introduce the basic idea, structure, application, key technique and problem to be researched of wireless multi-hop Mesh networks. Secondly, we mainly analyze key technique and solve key problems of WLAN Mesh networks. Most MAC protocols used in wireless multi-hop networks are IEEE 802.11 based; witch is designed especially for single hop networks. We present problems such as instability,unfairness,incompatibility encountered when IEEE 802.11MACprotocol works with TCP in a wireless multi-hop network. Results of experiment indicate that those problems are rooted in the"hidden node"and"exposed node"problems encountered in IEEE 802.11MAC protocol. In wireless multi-hop network,"hidden node"and"exposed node"problem will bring much more influences, because in the big range of multiple hops,all network nodes will receive and transmit in one channel,they disturb each other very severely. Simultaneous communication will be blocked,which makes it difficult for wireless multi-hop network to expand. Network performance will decline when number of hops increase. We secondly introduce multi-channel, which make network nodes receive and transmit synchronously and. Simulation results indicate that, network performance will be not much influenced when number of hops increase. Finally,with cross-layer-design idea, we take the effect of 802.11 MAC information from MAC layer into account , choose routing on noninterference channel,which adapts to wireless multi-hop network. Then we consider the characteristics of WLAN Mesh network, such as immovability, present cross-layer table-driven routing combined with on-demand routing. We validate our idea with simulation at the end of this paper.