Optimal Bandwidth Selection in Multi-Channel Cognitive Radio Networks: How Much is Too Much?

Cognitive radio improves spectrum efficiency by allowing secondary users (SU) to dynamically exploit the idle spectrum owned by primary users (PU). This paper studies optimal bandwidth allocation for SUs. Consider the following tradeoff: a SU increases its instantaneous throughput by accessing larger bands, but channel switching overhead (due to the dynamics of PU activities) and contention among multiple SUs create higher liability for larger bandwidths. So how much is too much? In this paper, we find the optimal bandwidth allocation in both the single SU and multiple SU cases, accounting for the effects of channel switching overhead. Our result is validated through both numerical simulation and real channel activity traces. We also study the impact of various factors on SU performance, namely, PU channel idle time and probability, PU channel correlation, and SU sensing and access schemes. The work sheds light on the design of spectrum sharing protocols in cognitive radio networks.