Impact of Frequency Offset on Nonlinear Distortion Suppression in Cooperative Jamming Communications

In the existence of multiple eavesdroppers, cooperative jamming has recently drawn significant interest to ensure confidential communications with the help of a cooperative jammer. Meanwhile, the legitimate users will inevitably suffer from the undesired jamming, which are commonly presumed to have the capability of complete self-jamming (SJ) cancellation. However, due to the oscillator instability between a jammer and legitimate users, the frequency offset always exists in SJ. Besides, as transmit power increases to effectively jam the eavesdroppers, the inherent nonlinearity of power amplifier will be introduced to SJ unavoidably. Herein, the joint non-ideal effects of frequency offset and nonlinear distortion are characterized to explicitly analyze the SJ cancellation (SJC) degradation. The expressions for the normalized mean square error (NMSE) and SJC capability are derived to evaluate the nonlinearity modeling accuracy and the nonlinearity suppression performance, respectively. Furthermore, simulations are performed to validate the NMSE and the SJC capability, which provide more clear insights into the impact of frequency offset on nonlinear distortion suppression in a practical cooperative jamming scenario.