Three-stage centralized spectrum sensing of OFDM signals

We propose a three-stage centralized spectrum sensing for cognitive radios in OFDM systems, where local decisions of cooperative sensors are combined at the fusion center. The fusion center, if necessary, can invoke a third stage for finer sensing. The first two stages employ distributed energy detectors and a centralized voting rule, while the third stage exploits the OFDM signal correlation. The overall probability of detection is optimized by jointly designing the optimal thresholds at the three stages, for a given probability of false alarm. The detection performance and the average sensing time are analyzed theoretically and compared by simulations with spectrum sensing that employs only the two-stage centralized detector or the correlation-based detector.