Superimposed Pilot Aided Wireless Communications in Full-Duplex Cellular Networks: Channel Estimation and Performance Analysis

Full-Duplex (FD) has been widely recognized as one of the core technologies to enhance the spectral efficiency (SE) in the fifth generation (5G) cellular networks. FD technology (compared to traditional Half-Duplex (HD) technology in theory) can achieve twice the SE of cellular networks, but it introduces severe self-interference (SI) and co-channel-interference (CCI). Multi-domain (antenna-, radio frequency- and digital-domain) SI cancellation (SIC) techniques are proposed to reduce SI to a level close to the noise floor. However, due to the severe impact of Doppler shift and the absence of prior information, eliminating CCI is more challenging than eliminating SI, which has become a prominent obstacle to improving the performance of FD cellular networks. To achieve high-performance CCI cancellation (CCIC), perfect channel state information (CSI) is required. In this paper, we propose a superimposed pilot (SP) scheme for CCIC in FD cellular networks. Moreover, to address the Doppler shifts in FD cellular networks, two new SP-based channel estimation algorithms are developed for CCI channel and uplink/downlink channel, respectively. Furthermore, the Cramér-Rao Lower Bounds (CRLBs) are also theoretically derived. In addition, we derive maximum achievable sum rate with imperfect CCIC in FD cellular networks. Finally, numerical results show that our proposed SP scheme outperforms the conventional time-multiplexed pilot (TP) scheme in terms of CCIC performance, BER performance and maximum achievable sum rate.