Is Two-way Relay More Energy Efficient?

Two-way relay transmission (TWRT) is more spectral efficient than direct transmission (DT) and one-way relay transmission (OWRT). In this paper, we try to find out if TWRT is also more energy efficient in practice. To this end, we first derive and compare the energy efficiency of DT, OWRT and TWRT systems, when either the receiver processing power consumption is taken into account or not. We then compare the maximal energy efficiency achieved by TWRT and OWRT, as well as the corresponding spectral efficiency. Both analytical and simulation results show that TWRT is not always more energy efficient than DT and OWRT, depending on the channel condition, processing power consumption and the bidirectional date rate requirements. Generally speaking, in high spectral efficiency and large path loss attenuation region, the TWRT provides high energy efficiency.