Mac And Routing Protocols For Multi Hop Wireless Networks

Abstract: "Wireless systems for industry have mostly used cellular-phone-style radio links, using point-to-point or point-to-multipoint transmission. Past research has indicated that these network architectures are not suitable for several industrial applications because of their rigid structure, meticulous planning requirements, and dropped signals. In contrast, wireless mesh networks are multi-hop systems in which devices assist each other in transmitting packets through the network, and they provide a reliable, flexible system that can be extended to thousands of devices. Some inherent advantages with mesh networks are scalability, non line-of-sight communications, high data rates, and low-cost deployment. Mesh networks have been deployed by MIT researchers and a few companies on a small scale. Mesh networks have not been deployed widely, in part because of some fundamental problems with the current protocols with regards to QoS support and scalability. To meet these requirements, the MAC protocol should be able to guarantee near constant capacity for networks of different sizes, and the routing protocol should perform admission control. Current CSMA-based MAC protocols have been shown to perform inadequately in terms of throughput and scalability in multi-hop deployments. The key problem with using protocols like IEEE 802.11 is that the link throughput is affected severely due to the exposed terminal problem, uncoordinated contentions, and wasteful backoffs. With the 802.11 MAC protocol, our results show that the capacity falls to about 1/10th for a chain and below 1/20th for a grid with horizontal constant bit rate flows. We have developed the WisperNet MAC and routing protocols, which provide end-to-end QoS guarantees over a multi-hop mesh network. By exploiting the topology information and the fact that fixed wireless nodes separated by 3 hops or more can transmit simultaneously, we eliminate collisions and maximize network utilization. The WisperNet routing protocol performs admission control. We show that the WisperNet MAC protocol can guarantee up to 9 times more capacity than IEEE 802.11, and this capacity remains nearly constant as the network grows. Also included is a performance analysis of different routing policies, and their effect on network utilization."