A robust token passing protocol for peer-to-peer radio LANs

Digital signals propagating through the indoor channel are subject to severe distortion due to multipath propagation and shadowing. The received signal is often severely faded, and because it is dispersed, intersymbol interference may occur. We consider a peer-to-peer radio local area network (LAN). Each station in the network is free to exchange packets with every other station and there is no base station to coordinate the operation of the network. Access to the radio channel is controlled using token passing. In practice, because of severe fading, it is likely that direct communication between some stations in the network will not be possible all the time. For example movement of a station may place an obstacle between it and another station, resulting in severe shadow fading. However, if there are several stations in the network it is very unlikely that any one station will be in a fade with respect to every other station. It is therefore proposed that packets that should have used failed links be relayed via intermediate stations using an appropriate routing algorithm. We explain exactly how such routing can be implemented in a token passing peer-to-peer radio LAN. Failed radio links are not the only consequence of signal distortion by the indoor channel. The error rate on links that are usable is relatively high when compared to that of optical fibre or cable networks. To guarantee reliable token passing an error recovery mechanism is required. We consider stop-and-wait ARQ as an example because it is easy to implement and leads to simpler mathematical analysis.