Abstract
                                                                        In this paper, we propose beamformed energy  detection (BFED) spectrum sensing schemes for a single  secondary user (SU) or a cognitive radio to detect a primary  user (PU) transmission in the presence of an interferer. In the  millimeter wave (mmWave) band, due to high attenuation,  there are fewer multipaths, and the channel is sparse, giving  rise to fewer directions of arrivals (DoAs). Sensing in only  these paths instead of blind energy detection can reap  significant benefits. An analog beamforming weight vector is  designed such that the beamforming gain in the true DoAs  of the PU signal is maximized while minimizing interference  from the interferer. To demonstrate the bound on the system  performance, the proposed sensing scheme is designed under  the knowledge of full channel state information (CSI) at the  SU for the PU-SU and Interferer-SU channels. However, as  the CSI may not be available at the SU, another BFED  sensing scheme is proposed, which only utilizes the estimate  the DoAs. To model the estimates of DoAs, perturbations  are added to the true DoAs. The distribution of the test  statistic for BFED with full CSI schemes is derived under  the null hypothesis so that the threshold of the NeymanPearson detector can be found analytically. The performance  of both schemes is also compared with the traditional energy  detector for multi-antenna systems.  Index Terms—Beamforming, direction of arrival (DoA),  energy detection, mmWave, spectrum sensing.