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Spectrum Sensing in Full-Duplex Cognitive Radio Networks Under Hardware Imperfections

Direct-conversion radio transceivers can offer reprogrammable and low-cost hardware solutions for full-duplex (FD) cognitive radio networks (CRNs). However, they are susceptible to radio-frequency (RF) impairments, such as in-phase (I) and quadrature (Q) imbalance (IQI), which can significantly limit spectrum sensing capabilities. This paper is devoted to quantifying and evaluating the effects of IQI in single- and multichannel energy detectors operating in FD mode under both cooperative and noncooperative spectrum sensing scenarios. In this context, closed-form expressions are derived for the false alarm and detection probabilities in the general case, where partial self-interference suppression (SIS) and joint transmitter (TX) and receiver (RX) IQI are considered. Furthermore, simplified closed-form expressions for the special cases, where either the RF front end is ideal or the SIS technique is perfect, are also presented. The presented analytical results have been verified through extensive simulations and indicate that the IQI and partial SIS can significantly affect spectrum sensing accuracy in FD-based CRNs. Specifically, if ideal RF front end is assumed, spectrum sensing error can significantly increase, leading to a reduction in the CRN performance and a negative effect on the performance of primary (PR) networks. Hence, when designing spectrum sharing algorithms for FD-based CRNs, the hardware impairments should be considered to improve the CRN performance while minimizing the negative effects on PR users.