Self-adaptive Multi-channel MAC for Wireless Mesh Networks

In order to enhance the transmission rate, multiple channels and multiple transceivers are employed in wireless mesh networks (WMNs). However, the bandwidth utilization rate is still low, and it is hard to design efficiency MAC. There are mainly three reasons. The first reason is that there are different kinds of nodes in WMN: some nodes are single transceiver and some nodes are multiple transceivers or multiple radios (Ian & Wang, 2005). The MAC needs to be suitable for single transceiver nodes and multiple transceiver nodes at the same time. The second reason is that the MAC not only needs to control multiple nodes but also multiple transceiver or multiple radios to access multiple channels. How to coordinate all the nodes and the transceivers, radios of each node to access the channels and enhance the bandwidth utilization rate is a multi-parameter optimization problem. The third reason is that the traffic load on each link is varying. The channel allocation scheme need be adaptive to the load of links. Common control channel (CCC) based multi-channel MAC is a representative proposal (Benveniste & Tao, 2006) for WMN. All the MAC control signals are exchanged on a common control channel, and the data are sent on data channel. This MAC scheme is very flexible to combine with existing channel allocation schemes. However, the handshaking is made on the control channel, which can’t avoid the interference of the non CCC based MAC on data channel. The second problem is that the switching time on the data channel is longer than the transmission time of sending a data packet, which will reduce the efficiency of CCC. Moreover, when there is only one radio, CCC will have the hidden terminal problem (N. Choi, et al. 2003). Based on CCC, a self-adaptive multi-channel MAC is proposed in this chapter. To keep the flexibility of CCC, common control channel still remains in our scheme. To reduce the channel switching delay and avoid interference from non-CCC based MAC, spreading code based channel division scheme is employed on the data channel. Our scheme can inherit the merits of CCC and remove its faults. Moreover, based on the common control channel framework, we proposed a self-adaptive channel allocation scheme which can adjust the medium access process according to the number of idle channels, and the load of the links on a node to maximize the bandwidth utilization rate of the WMN system. The rest of this chapter is organized as follows: section 2 makes a survey of the existing multi-channel medium access schemes, section 3 proposes our scheme and makes theory analysis and simulation, and conclusion is drawn in the last section.