On Sensing-Access Tradeoff in Cognitive Radio Networks

In cognitive radio networks (CRNs), the design of an optimal spectrum sensing scheme is an important problem that has recently been drawing consideration attention. Various sensing-related performance tradeoffs have been studied as an efficient means to maximize the secondary network performance. Despite its importance, however, the sensing-access tradeoff--between sensing overhead and the MAC-layer contention among secondary users in accessing the thus-discovered spectrum opportunities--has not yet been accounted for. In this paper, we show that the secondary network throughput can be improved significantly by incorporating the sensing-access tradeoff in the design of spectrum sensing. We first introduce a new concept of (alpha,beta)-contention spectrum sharing and analyze the sensing requirement to meet a certain channel contention constraint by using the improper list-coloring in graph theory. Specifically, we derive the relationship among the sensing requirements, the secondary network density, and the transmission power of secondary users. To maximize the network throughput, we propose a distributed spectrum-sharing algorithm, called SmartShare, which exploits channel contention and heterogeneous channel conditions to maximize the secondary network throughput. We also describe how to realize SmartShare in an 802.11 MAC protocol for its practical use and evaluation. Our simulation-based evaluation shows that, sensing an optimal number of channels for given network density can improve the achievable throughput of SmartShare by up to 60% over a single-channel sensing strategy.