Spectrum Sensing for OFDM-Based Cognitive Radio

Abstract-Given the ever growing demand for radio spectrum,cognitive radio has recently emerged as an attractive wireless technology. Since orthogonal frequency division multiplexing (OFDM) is one of the major wideband transmission techniques, detection of OFDM signals in low signal-to-noise-ratio (SNR)scenario is an important research problem. In this paper, it is shown that the cyclic prefix correlation coefficient (CPCC) algorithm, which has been introduced as a simple and computationally efficient spectrum sensing test for OFDM signals, is a special case of the constrained generalized likelihood ratio test(GLRT) in the absence of multipath. As such, the performance of this algorithm degrades in a multipath scenario where OFDM is usually implemented. Moreover, by considering the multipath correlation in the GLRT algorithm and employing the inherent structure of OFDM signals, a simple and low complexity algorithm, called multipath-based constrained-GLRT (MP-based CGLRT)algorithm is obtained. The MP-based C-GLRT algorithm is shown to outperform the CPCC-based algorithm in a rich multipath environment. Further performance improvement can be achieved by simply combining both the CPCC-based and MPbased C-GLRT algorithms.