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The Combined Effect of Various Receiver Nonlinearities on Spectrum Sensing in Cognitive Radio Systems

Khaled M. Gharaibeh
College of Engineering, Applied Science University-Bahrain, Manama, Kingdom of Bahrain
Abstract--Cognitive Radio (CR) systems which employ Direct Conversion Receivers (DCR) are susceptible to nonlinearities in the receiver path, especially when strong interferes exist. This paper aims to model the combined effect of RF nonlinearities, baseband nonlinearities and I/Q imbalances in wideband CR receivers when strong interferers exist. The analysis presented in this paper is based on considering a cascade of memoryless nonlinearities that model RF nonlinearity, BB nonlinearity and IQ imbalance and an input that consists of a desired and interfering signals. The combined output of the cascade is calculated and nonlinear distortion is identified and related to spectrum sensitivity. The analysis is verified by simulation results which show that nonlinear distortion from the interaction of multiple signals by the RF nonlinearity is significantly enhanced when other BB nonlinearities exist in the receiver path. The simulations also enable the linearity requirements for maintaining the reliability of the CR receiver for spectrum sensing to be estimated.
Index Terms—Low noise amplifier, IQ imbalance, cognitive radio, nonlinear distortion, software defined radio, direct conversion receiver, wideband transceiver architecture

Cite: Khaled M. Gharaibeh, "The Combined Effect of Various Receiver Nonlinearities on Spectrum Sensing in Cognitive Radio Systems," Journal of Communications vol. 15, no. 4, pp. 350-358, April 2020. Doi: 10.12720/jcm.15.4.350-358
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