Detection of joint space and spectrum opportunities in cognitive radio systems

In cognitive radio, spectrum sensing is necessary to timely find the temporarily unoccupied spectrum of the primary users (PUs) in time, frequency, code, and spatial domains. In this paper, we consider a primary network sharing a given frequency band with a cognitive network and perform spectrum sensing in space and frequency domain. With the exploitation of the antenna array equipped at the secondary user base station (SU BS), the whole space area in the view of the SU BS can be sliced into multiple partially overlapped beam areas for each frequency subband channel. We derive the energy detection probability of the PUs at a given beam for each subband channel, which is intrinsically the probability of the given beam and the given subband channel occupied by the PUs, and the conditional probabilities of that the PUs are located respectively at each neighboring beam under the condition of the PUs located at the given beam and the given subband channel. Comparing these probabilities with a given threshold, the joint space and spectrum opportunities can be thus determined. Simulation results show the efficacy of the proposed method.