Effects and suppression of signal correlation on radio frequency cancellation of full-duplex system

In a full-duplex system where correlation exists between self-interference signal and useful signal, direct radio frequency (RF) coupling cancellation structure, which is based on the minimum mean square error (MMSE) criterion, is adopted to conduct self-interference cancellation; however, such cancellation damages the useful signal. In regards to this problem, this paper designs a new RF cancellation scheme: (1) On the basis of cancellation structure, phase shifter controlled by error signal power is thereby introduced to shift the phases of transmitted signal, decreasing the correlation of self-interference signal and useful signal; (2) New Time-varying Step-size Normalized Least Mean Square (NTVSSNLMS) algorithm, which utilizes the auto-correlation and time parameters t of real-time error signal to cooperatively control the step factor μ ( t ) , is proposed to adjust the attenuator weight vectors, in order to assure a high interference cancellation ratio (ICR) and satisfy the requirements of phase shifter on algorithm convergence performance at the same time. Simulation results indicate that the new RF cancellation scheme can increase the ICR, while effectively reducing the damages on the useful signal simultaneously.