Short Paper: On Optimal Sensing and Transmission Strategies for Dynamic Spectrum Access

The listen-Before-Talk (LBT) strategy has been prevalent in cognitive radio networks where secondary users opportunistically access under-utilized primary band. To minimize the amount of disruption from secondary users to primary signals, secondary users generally are required to detect the presence of the primary user reliably, and access the spectrum intelligently. The sensing time has to be long enough to achieve desirable detection performance. Weaker primary signals require longer sensing time, thereby reduce the secondary transmission opportunities. In this paper, we generalize the packet-level LBT strategy by allowing the secondary user to potentially transmit multiple packets after one sensing, and study the optimal control policy to determine the conditions under which the secondary user should sense the channel. We show that the optimal spectrum access control policy has a simple threshold-based structure, where the secondary user transmits consecutive packets until the estimated probability of the primary user being idle falls below a threshold, and senses the channel otherwise. The result applies to systems with both perfect and imperfect packet collision detection with the primary users.