Energy-Efficiency of Millimeter-Wave Full-Duplex Relaying Systems: Challenges and Solutions

Full-duplex (FD) relaying is a promising solution for fifth generation (5G) wireless communications due to its potential to provide high spectral efficiency (SE) transmission. However, FD relay nodes consume much higher power than half-duplex relay nodes, especially in millimeter (mm)-wave band. Therefore, energy-efficiency (EE) is an important issue to address for mm-wave FD relaying systems, which highlights the green evolution of 5G wireless communications. Existing FD relaying related research is SE-oriented, which is not efficient in cutting carbon footprint. This particle is different in that it addresses the critical EE challenges in implementing FD relaying in mm-wave systems, including low drain efficiency of power amplifier, high circuit power consumption, and additional power required by FD relays to mitigate self-interference. Based on the features of mm-wave communications, we outline a number of promising EE-oriented solutions for designing FD relaying enabled systems, including adaptive self-interference cancellation, transmission power adaptation, hybrid relaying mode selection, multi-input-multi-output (MIMO), and massive MIMO FD relaying. Some EE-oriented future research is also envisaged for mm-wave FD relaying systems.