Active Sensing for Cognitive Radio

Spectrum sensing is inevitable for cognitive systems to locate the spectrum holes. In the IEEE 802.22 proposal, very short quiet periods are arranged inside frames to perform a coarse intra-frame sensing whose results are then utilized to decide whether a fine inter-frame sensing is needed. The purpose of intra-frame sensing is to make an early alarm about the presence of primary users. However, the placement of short quiet periods in intra-sensing requires quiet period synchronization and degrades the transmission rate. In this paper, we propose active sensing as an alternative for intra-frame sensing to save the short quiet periods so that the system throughput is increased. In active sensing scheme, the sensing is performed by some inactive CPEs when the cognitive system is active. The motivation comes from the facts that we have much more received samples for active sensing and we only need a coarse result.