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Likelihood-based spectrum sensing of OFDM signals in the presence of Tx/Rx I/Q imbalance

We consider the spectrum sensing problem in orthogonal frequency-division multiplexing-based cognitive radio networks under I/Q imbalance. We derive the likelihood ratio test in the presence of colored noise and I/Q imbalance at the analog front-ends of both of the primary and secondary users. Furthermore, we derive the probabilities of detection and false alarm and develop the receiver operating characteristics. We also examine the impacts of both transmit and receive I/Q imbalance on the performance of the likelihood ratio test. We compare the performance of our likelihood ratio test with that of the energy detector through extensive simulations and show the superiority of the former over a wide range of signal-to-noise ratios.