Improved Fractional Delay Method for Canceling the Self-Interference of Full Duplex

For achieving the high spectral efficiency of the co-frequency co-time full duplex (CCFD), the self-interference (SI) should be cancelled drastically using the signal processing techniques. The radios frequency (RF) canceler uses the reconstructed SI symbol to cancel that arriving from the air interface, where the accurate time-alignment of the two symbols is required so that the cancellation is made at per entire symbol basis. Though using the variable fractional delay (VFD) method allows the exact time-alignment, it deforms inevitably the waveform of the reconstructed SI symbols in the practical application. Actually, the waveform deformation of the reconstructed SI symbol can impair the quality of the cancellation performance. To address this problem, we propose a new cost function that converts the mathematical error of the conventional VFD to the residual SI power directly. The sufficiency of the new cost function is proved and the superior performance is conformed by the simulation results.