A novel self-interference cancellation scheme for full duplex with differential spatial modulation

In this paper, a novel self-interference (SI) cancellation scheme operated in the digital domain is proposed for the full duplex (FD) system configured with two antennas. The basic idea of our scheme is to transfer the strong SI to the inter-symbol interference (ISI), which is easier to cope with, through a combination of the signals received in successive time slots based on the assumptions that the SI channel is reciprocal and the previous transmitted data can be stored. However, this transfer may result in an un-removable error floor when the transmit antenna remains the same during the time slots in the SI cancellation. To solve this problem, we propose to apply differential spatial modulation, which forces two antennas to take turns to transmit signals in every two consecutive time slots. To further compensate for the loss of spatial degrees of freedom owing to the transfer, we propose to involve more time slots in the SI cancellation and allow the transmit antenna to be selected randomly by spatial modulation starting from the third time slot. Simulations on the bit error rate (BER) are conducted, whose results show that the performance of the proposed scheme is improved as more time slots are involved in the SI cancellation, and the proposed scheme with four time slots outperforms the conventional FD system with 3 dB interference-to-noise ratio (INR) for QPSK modulation.