Mobility Reduces the Number of Secondary Users in Cognitive Radio Networks

In this paper, we study the capacity and delay scaling laws for cognitive radio networks (CRN). The primary network consists of $n$ static, randomly and evenly distributed primary users (PUs), which require high throughput with low delay. The secondary network consists of $m=O(n^{1+\delta})$ randomly and evenly distributed cognitive secondary users (SUs) with $\delta>0$, which move in different area according to the hierarchical i.i.d. mobility model. The secondary network is carefully designed to support the primary network, so that PUs may achieve near-optimal performance in both capacity and delay aspects. Then by utilizing hierarchical cooperation among SUs with different mobility, a new hierarchical relay algorithm is proposed to improve the delay performance extensively. Under optimal condition, this algorithm may provide $\Omega(n^{- \delta'})$ per-node throughput and $O(n^{\delta''})$ average delay for PU with $\delta',\delta''>0$, and significantly improve the performance of SU at the same time.