Impact of Pilot Sequence on Self-Interference Cancellation for Full-Duplex Radios

This paper investigates the impact of pilot sequences on the digital self-interference cancellation (SIC) in full-duplex systems. Nonlinearity may be introduced to the self-interference (SI) signal by the circuits, especially the high power amplifier, which needs to be modeled and estimated for SIC. Applying the parallel Hammerstein model, the nonlinearity and the multipath channels are jointly estimated based on pilot sequence. By implementing the Pseudo-Noise (PN) and Zadoff-Chu (ZC) sequences, we evaluate the estimation accuracy and SIC performance. In addition, the impact of the power misalignment between the pilot and the data is studied. The results suggest that the SI can be almost completely removed with both PN and ZC sequences when the transmit power is low. However, with high transmit power where the nonlinearity effect is more severe, the PN sequence outperforms the ZC sequence due to their different nonlinearity behaviors. Then, by comparing different power level settings, we show that the best strategy for digital cancellation is to set the transmit powers of the pilot and the data be approximately the same.