Energy Efficient Space–Time Line Coded Regenerative Two-Way Relay Under Per-Antenna Power Constraints

In multiple-input multiple-output (MIMO) systems, per-antenna power constraint (PAPC) has been considered to enhance the power efficiency of the multiple power amplifiers. Under PAPC, however, a conventional space-division multiple access (SDMA)-based two-way relay (TWR) method suffers a significant bit-error-rate (BER) performance degradation due to the seriously down-scaled transmit power to fulfill the PAPC, which results in energy-efficiency (EE) degradation. In this paper, a new space-time line code (STLC)-based TWR method is proposed to improve the EE. The proposed method can utilize maximum power budget with a low peak-to-average power ratio so that can achieve a better BER performance at the cost of higher power consumption, as verified in numerical simulation results. The benefit of the proposed STLC-based TWR method is justified in terms of EE. The STLC-based TWR system achieves higher EE than the conventional SDMA-based TWR when the maximum transmit power is low, such as a small base station with 23-dBm maximum transmit power. Furthermore, compared with the SDMA-based TWR, the proposed STLC-based TWR can reduce computational complexity by order of magnitude two; therefore, it can be readily extended to a TWR system with a large number of antennas, e.g., a massive MIMO system, which is one of the promising candidates for 5G communications.