Hierarchical sequential detection in the context of dynamic spectrum access for cognitive radios

Dynamic Spectrum Sharing is a recent concept where unlicensed devices are allowed to opportunistically access unused spectrum bands. The goal of this paper is to develop and analyze a novel secondary user sensing strategy that on the average minimizes the need to take sensing measurements and therefore maximizes throughput. In particular, we focus on the IEEE 802.22 standard where the goal is to detect TV signals. A secondary or unlicensed user must continuously monitor the band it is using and relinquish it as soon as it detects a primary or licensed user. The secondary user has to minimize its probability of missed opportunity to transmit while adhering to the probability of detecting the primary user. In this paper, we have applied the methods of sequential detection to reduce the sensing time. A collaborative detection scheme with the energy detector at the secondary user running a sequential detection test is used. The central node runs a parallel sequential test. Performance gains have been quantified for hard and soft decision combining at the central node and compared with the IEEE 802.22 Wireless Regional Area Network standard. The proposed scheme delivers a 3 - 204 times increase in throughput for SNRs in the range -10 dB to 0 dB.