Analysis and Optimization of Transceiver IQ Imbalances in Artificial Noise Shielded FH Communication

The artificial noise (AN) shielded frequency-hopping (FH) architecture can effectively resist wiretapping and electromagnetic interference, but its wide hopping bandwidth will raise a non-negligible in-phase and quadrature (IQ) imbalance at transceiver oscillators, yielding significant signal distortions during IQ mixing. Considering this, first, signal distortions raised by transceiver IQ imbalances are modelled in this study, and their characteristics are mathematically investigated as well. Next, the signal to distortion-plus-noise ratio (SDNR) is extracted to measure the quality of the obtained signal after AN cancellation, and the secrecy capacity is subsequently derived to evaluate system secrecy under multiple wiretappers. Then, based on the performance evaluations, the transmitting power ratio of AN to information signals is optimized to counteract the secrecy degradation raised by transceiver IQ imbalances. Simulations show that both the AN cancellation and system secrecy performance will decline sharply as the amplitude or phase imbalance deteriorates. Besides, compared with the case where the power ratio of AN to information signals is 2, the average secrecy enhancements of an equal power scheme, a power scheme ignoring IQ imbalances, and our proposed power scheme approximate 8.4%, 9.66%, and 11.05% for a fixed phase imbalance, and approximate 10.88%, 12.61%, and 14.26% for a fixed amplitude imbalance, respectively.