Multichannel MAC Protocols for Multihop Wireless Networks

Wireless Networks The design of MAC protocols in ad hoc networks that coordinate access to the shared radio channel and minimise collisions is a considerably more difficult task than in a wired or cellular network. Two phenomena have major impact on the capacity of an ad hoc network: the hidden and the exposed terminal problems. The activity focuses on multiple channel MAC schemes. The use of multiple channels may provide some performance advantages and design flexibility. It can give further benefits such as a more simple way to support Quality of Service. It is usually assumed that a wireless node is a half-duplex device: it can only transmit or listen on one channel at a time, but cannot do both simultaneously. Therefore, the need for a separate control channel arises. A sender and a receiver should agree on the channel that the communication will take place on. Different strategies for handling this control channel are considered, as well as algorithms for the choice of the communication channel. To achieve efficient bandwidth utilisation and to cope with the exposed terminal problem, it is proposed to send all control frames, including acknowledgement frames, on the control channel. It is pointed out that in the case of multichannel CSMA schemes, RTS/CTS message exchange gets additional functionality, namely a sender and a receiver have to exchange information to choose one of the available data channels. If ACK is sent on the control channel, it is the receiver who decides on the data channel. (Tatiana K. Madsen)