Relay-assisted Routing in Cognitive Radio Networks

Cognitive radio has been proposed in recent years to promote spectrum efficiency by exploiting the existence of spectrum holes. The heterogeneity of both spectrum availability and traffic demand among secondary users has brought significant challenge for efficient spectrum allocation in cognitive radio networks. Observing that spectrum resource can be better matched to traffic demand of secondary users with the help of relay nodes, in this paper we propose to utilize cooperative relays to assist the transmission and improve spectrum efficiency. Different from traditional cooperative communication within a single channel, in our scheme a relay node may be selected for a link to bridge the link's source and destination using its different common channels with those two nodes. With these new logical links composed of both direct link and relay link, new routing protocols are needed so that end-to-end performance can be better improved. Therefore, we define a new link cost, relay-aware link cost, which considers several aspects including channel availability, channel condition, channel utilization and potential relays. Based on this link cost, a relay-assisted routing (RAR) protocol is proposed which includes routing discovery and local adjustment. Simulation results demonstrate the effectiveness of the proposed routing scheme.