New Methods for Sensing Bandlimited Signals in Cognitive Radio

In a cognitive radio, it is required to design an interface for use by secondary broadband users on a noninterfering basis in spectrum allocated to TV broadcast service or some other primary user. Spectrum is being utilized in that new devices (secondary users) can use the spectrum that is not being used by the primary user at the current time and location, as measurements indicate low spectrum utilization by primary users at all places at all times. Since the secondary user (cognitive radio) has to guarantee that it will not interfere with the signal of the primary user, the cognitive radio faces a difficult challenge, i.e., detecting the presence of the primary user in low SNR region. In this paper, a method for blindly detecting the presence of band-limited primary signals is proposed. The proposed method combines oblique projection along with QR decomposition of the (oversampled) received signal matrix. Computer simulations show that the proposed sensing algorithm performs much better than the commonly used energy detector.