Cooperative spectrum sensing: State of the art review

Spectrum sensing is the key mechanism in enabling spectrum awareness in Cognitive Radio. The performance of the spectrum sensing depends on the local channel conditions, such as the multipath, shadowing and the receiver uncertainty issues. The conjunction of these conditions can result in regimes where the signal SNR is below the detection threshold of the sensor, resulting in missed detections. To overcome this limitation there have been several proposals made in the research community towards the use of cooperation in spectrum sensing. Since the signal strength varies with the sensor location, the worst fading conditions can be avoided if multiple sensors in different spatial locations share their local sensing measurements, i.e. take advantage of the spatial diversity. In this paper we review the so far proposed methods and do a review of the still open challenges and give an outlook of future research directions.