On the Effect of I/Q Imbalance on Energy Detection and a Novel Four-Level Hypothesis Spectrum Sensing

Direct-conversion transceivers are in demand due to low implementation cost of analog front ends. However, these transmitters or receivers introduce imperfections such as in-phase and quadrature-phase (I/Q) imbalances. In this paper, we first investigate the effect of I/Q imbalance on the performance of primary system and show that these impairments can severely degrade the performance of cognitive radio system that are based on orthogonal frequency-division multiplexing (OFDM) multiple-access scheme. Next, we design a new four-level hypothesis blind detector for spectrum sensing in such cognitive radio system and show that the proposed detector is less vulnerable to I/Q imbalance than conventional two-level detectors.