Cognitive Radio Spectrum Sensing under Joint TX/RX I/Q Imbalance and Uncalibrated Receiver

In high-speed wireless communication systems, direct-conversion transceivers (DCTRs) are in demand due to low implementation cost of analog front ends. However, the DCTRs are more susceptible to radio frequency impairments like in-phase and quadrature (I/Q) imbalance. This has been shown to significantly limit the spectrum sensing (SS) capability of a secondary user to find spectrum holes. Another source of performance limitation in multiantenna cognitive radio (CR) systems is the uncalibrated receivers across the antennas. Unlike previous works, which considered these two impairments separately, we model the received signal as a single-input multiple-output CR system in the presence of transmit (TX) and receive (RX) I/Q imbalances and when the receiver is uncalibrated across the antennas. In such a scenario, we model the SS problem as a composite binary hypothesis testing problem, apply the likelihood ratio test principle, and develop a new robust SS approach. The performance of the proposed SS algorithm is evaluated using extensive Monte Carlo simulations to illustrate the superiority of the proposed detector in comparison with the existing SS algorithms in the literature. The obtained results indicate that the proposed SS algorithm has constant false alarm rate property with respect to any nonuniform noise variance uncertainties as well as RX I/Q imbalance parameters, thereby being a robust and blind detector.