Colouring Link-Directional Interference Graphs in Wireless Ad Hoc Networks

In this paper, we clarify inter-link interference in wireless ad-hoc networks by using link-directional interference graphs (I-graph). Most of the interference graphs in the literature simply model the DATA and ACK traffic of a link by a single vertex. They fail to capture the link-directionalities. In fact, some instances of directional traffic can actually transmit simultaneously but are prohibited by the interference graphs. Thus, in our link-directional interference graph, a link is represented by two vertices, one for DATA traffic and the other for ACK traffic. We then apply a colouring algorithm in the I-graphs. The colouring results provide insights in order to boost network capacities in TDMA or FDMA ad-hoc networks. We show that the network capacities can be improved by 100% in a triangular topology and 33% in a lattice topology. Simulations also show that a distributed dual channel protocol assigning channels according to link-directionalities can boost the capacities by 70% in large-scale random networks. We believe this is a first paper in the literature to take into account link-directionalities in interference graphs.