Performance Analysis Of Two-Way Relay Systems Based On Energy Harvesting

The relay communication technology can expand the coverage of wireless networks and improve the system performance,which is one of the key technologies for mobile communications in the future.The relay communication system is divided into one-way relay systems and two-way relay systems and two-way relay systems have two links for transmitting signals at the same time comparing with one-way relay systems,which its spectral efficiency is twice that of one-way relay systems.On the other hand,with the 5G research,energy harvesting(EH)technology has become increasingly popular.In wireless communication networks,energy-constrained devices can collect energy through EH technology based on the fact that radio-frequency(RF)signals can carry information and energy at the same time,which can extend the lifetime of the wireless network.The relay node in relay systems is usually energy-limited,and combining EH technology with the relay system,the relay node can prolong the lifetime of itself by harvesting energy.Compared with single-pair two-way relay systems where only one-pair users exchange information at the same time,multi-pair users exchange information simultaneously in multi-pair two-way relay systems,which greatly improves the spectrum efficiency of two-way relay systems.However,there has serious interference problem between user pairs in the communication process of multi-pair two-way relay systems.Configuring large-scale antenna arrays in the relay,massive multiple-input multiple-output(MIMO)technology is applied in multi-pair two-way relay systems,which can reduce or even eliminate interference between user pairs through beamforming technology of massive MIMO.Similarly,EH can extend the lifetime of multi-pair twoway relay systems.Two-way relay systems based on EH and EH-based massive MIMO multi-pair twoway relay systems are studied in this article.The main research contents are as follows:(1)Utilizing the amplify and forward(AF)protocol and the EH protocol of power splitting-based relay(PSR)in the relay,the two-way AF relay system model based on PSR protocol is researched in the EH-based two-way relay system.And based on the goal of maximizing sum rate,an optimal power allocation scheme for joint optimization of the sources power,the relay power and the power split ratio is proposed,which significantly enhances the sum rate of the system.Considering a special case that the power of the relay itself is zero,an optimal power allocation scheme for joint optimization of the sources power and the power split ratio is researched.When the power of the relay itself is zero,the closed-form solutions of the sources power and the power split ratio is presented.According to the simulation results,when the channel quality is better,it can obtain the system performance which is similar to the optimal power allocation scheme for joint optimization of the sources power,the relay power and the power split ratio.(2)The massive MIMO multi-pair two-way relay system model based on PSR protocol is researched in the EH-based massive MIMO multi-pair two-way relay system and the lower bound expressions of achievable rate are obtained for the linear receiving and precoding technology of maximum ratio combining/maximum ratio transmission(MRC/MRT)and zero-forcing reception/zero-forcing transmission(ZFR/ZFT)in the relay.According to the lower bound expressions,an optimal power allocation scheme based on maximizing sum rate is proposed.Simulation results show the effectiveness of the optimal power allocation algorithm.(3)Considering the asymptotic conditions of high signal-noise-ratio(SNR)and infinite large antennas in the EH-based massive MIMO multi-pair two-way relay system,the simplified lower bound expressions of achievable rate for MRC/MRT and ZFR/ZFT in the relay are presented and an asymptotically power allocation scheme is researched.Simulation results present that the system performance of asymptotically power allocation scheme is closed to optimal power allocation scheme in the asymptotic conditions of high signal-noise-ratio(SNR)and infinite large antennas.