Multi-Antenna Beamforming Techniques in Full-Duplex and Self-Energy Recycling Systems: Opportunities and Challenges

Full-duplex technique is considered as an essential component of the coming 5G wireless systems. Since the SI from its transmit antennas dominates over the signal received from remote sites, the suppression of SI is the first priority challenge in the design of FD systems, and thus combinations of analog SI cancellation with radio frequency domain approaches are considered. Applying BF techniques with multiple antennas on top of these combined approaches can further strengthen the SI suppression capability so that wireless systems can enjoy the benefit from FD operation without much concern on SI. However, various factors affect the design of BF in FD networks, and hence they provide a set of research challenges. Also, S-ER is an alternative way of utilizing SI in FD networks, where the RF radiation from a node is reused as an energy source. In this article, we go through these opportunities and challenges along with a survey of technical results developed so far in regard to the BF for handling the SI of FD systems. We look at various network models, the strategies for handling the SI, relay protocols, and antenna structure to see how these provide technical challenges for the BF design.