Precoding Design for Full-Duplex Transmission in Millimeter Wave Relay Backhaul

As the amount of user equipment and massive volumes of data continue to increase, high data rate requirements remain a major challenge, particularly in cellular networks. In networks composed of small cells, applying full-duplex (FD) millimeter wave (mmWave) wireless backhauls is a more effective and convenient approach than utilizing conventional optical fiber links. The mmWave communication technology is promising for future wireless communications due to its considerable available bandwidth, which is the basis of a high transmission rate. However, the short wavelength of mmWave leads to high propagation loss and shortens the transmission distance of the system. FD relaying can expand the coverage of the base station and achieve higher spectral efficiency than half-duplex (HD) transmission. However, the residual self-interference (SI) may degrade the performance of FD. The combination of mmWave and FD technologies compensates for the high path loss and realizes efficient transmission. In this paper, we consider an FD mmWave relay backhaul system and the SI of FD communication. We first propose an FD SI channel model in the mmWave band, which is composed of two parts: line-of-sight (LOS) SI and non-line-of-sight (NLOS) SI. According to the special mmWave MIMO structure limitation, two SI cancellation precoding algorithms are proposed to eliminate the SI in the system and achieve high spectral efficiency. The decoupled analog-digital algorithm eliminates the SI by utilizing the zero space of the channel, and the enhanced algorithm achieves higher performance. The spectral efficiency of the subconnected structure is analyzed. With appropriate performance loss, the simplified structure achieves significantly low configuration complexity.