Spectrum-aware network coded multicast in mobile cognitive radio ad hoc networks

Secondary users (SUs) can flexibly access licensed channels to improve the spectrum utilization in cognitive radio networks (CRNs). In mobile cognitive radio ad hoc networks (MCRAHNs) where nodes can move, SUs are intermittently connected because of node mobility, as well as the uncertain channel availability. Providing multicast services in MCRAHNs is urgently needed with the compelling demand on service qualities and varieties, and the proliferation of cognitive technology. The benefits of network coding over multicast in traditional wireless networks or CRNs have been well demonstrated in existing works. However, the existing studies merely address the two crucial issues (i.e., uncertain channel availability and node mobility) together and, thereby, cannot be applied to network coding-based multicast in MCRAHNs. In this paper, we study the problem of network coding-based multicast in MCRAHNs considering both channel uncertainty and node mobility. We utilize discrete-time Markov chains to model the channel availability and node mobility in MCRAHNs, and we then formulate a spectrum-aware network coded multicast problem as an optimization problem, which minimizes the total transmission cost, subject to the timely successful delivery constraint and link transmission constraint. Since the formulated problem is hard to tackle according to mixed integer programing, we further design a distributed spectrum-aware cost-based (SACB) scheme based on the metric of forwarding benefit. With extensive simulations based on both synthetic and realistic traces, we show that, compared with existing schemes, SACB can achieve almost the minimum transmission cost while maintaining high multicast success probability.