On The Transmission Schemes Design And Performance Analysis Of Buffer-aided Wireless Relay Networks

With the rapidly development and widely use of wireless communication network,the demand for wireless communication service is increasing day by day.For instance,the fifth generation(5G)wireless communication network is required to provide more widely seamless coverage,higher throughput,lower delay and mass connection.In recent years,buffer-aided relaying technology has attracted lots of attention and research,due to it can improve the performance of cooperative network in many aspects,such as throughput,diversity,signal-to-ratio(SNR)and so on.In order to meet the demands on high throughput and wide coverage in future communication network,this thesis combines buffer-aided relaying technology with multiple antenna technology and non-orthogonal multiple access(NOMA),designs buffer-aided relaying protocols,which could achieve higher throughput.On the other hand,as an effective technique approach to reduce energy consumption in wireless communication network,energy harvesting technology is considered as a key technique of green communication with low energy consumption.This thesis brings data buffer and energy buffer into energy harvesting relay networks,analyzes the throughput performance and throughput-delay tradeoff of buffer-aided energy harvesting relay networks,designs adaptive buffer-aided energy harvesting relaying protocols.Firstly,a three-node energy harvesting relay network with data buffer and energy buffer is considered,in which the power splitting based simultaneous wireless information and power transfer(SWIPT)scheme is adopted.For the buffer-aided energy harvesting relay network,two buffer-aided relaying protocols are proposed,namely the harvest-then-transmit(HtT)protocol and the adaptive joint link selection and power allocation(JLSPA)protocol.For the HtT protocol,the expressions of the average throughput and the optimal power splitting factor are obtained in close form.For the JLSPA protocol,based on the channel state information(CSI)and buffer state information(BSI),a joint link selection and power allocation protocol which maximizes the average throughput is presented.Furthermore,for the adaptive JLSPA protocol,the bounds on average throughput,average length of data buffer queue and average delay are analyzed.The simulation results show that the proposed buffer-aided relaying scheme could improve the throughput performance of energy harvesting relay network significantly.Secondly,considering a power beacon(PB)assisted wireless powered cooperative network with data buffer and energy buffer,a buffer-aided harvest-store-transmit(HST)protocol and an adaptive buffer-aided joint mode selection and power allocation(JMSPA)protocol are investigated.For the HST protocol,the expressions of the system average throughput is derived in close form.For the JMSPA protocol,maximizing the average throughput is formulated as an optimization problem.Then,an optimal adaptive mode selection scheme and a power allocation strategy are obtained by solving the optimization problem through the Lyapunov optimizationtheory.In addition,the throughput-delay tradeoff is analyzed for the adaptive JMSPA protocol by using the Lyapunov method.Simulation results validate the throughput performance gain of the proposed buffer-aided relaying protocols and verify the theoretical analysis.Thirdly,the multiple antennas scenario is considered in buffer-aided relay network.In the first,a data buffer-aided multiple antennas relay network is studied.For the purpose of maximizing the system average throughput,a CSI based buffer-aided joint link selection and data stream power allocation protocol is developed.It is shown that,compared to the relaying protocol without buffer,the proposed buffer-aided adaptive link selection relaying protocol can improve the throughput performance of relay network.In addition,with the multiplexing gain introduced by multiple antennas,the throughput performance can be improved further.In the next,a multiple antennas energy harvesting relay network with data buffer and energy buffer is studied,and the SWIPT in space domain is implemented by adopting the Alamouti coding scheme.Based on this fact,the close form expression of system average throughput is firstly derived for a buffer-aided store-then-forward relaying protocol.Then,a buffer-aided joint link selection and power allocation relaying protocol is studied.Based on CSI and BSI,an adaptive link selection and a power allocation strategy are obtained.Simulation results demonstrate that the proposed buffer-aided multiple antennas relaying protocol can effectively improve the throughput performance of multiple antennas energy harvesting relay network.Finally,a data buffer-aided multi-user relay network is investigated,where the orthogonal multiple access(OMA)and NOMA are considered in turn.For the OMA transmission mode,the expression of system average sum rate of the without buffer relaying scheme is obtained in close form firstly.Then,a CSI/BSI based buffer-aided link selection relaying protocol is explored,through Lyapunov optimization theory,an optimal adaptive link selection scheme,which maximizes the average system sum rate,is obtained.For the NOMA transmission mode,similarly,the close form expression of system average sum rate of the without buffer relaying scheme is derived firstly.Then,maximizing the system average sum rate is formulated as an optimization problem,by dealing with the problem with Lyapunov optimization theory,a CSI/BSI based buffer-aided joint mode selection and user power allocation relaying protocol is obtained.Moreover,for both the OMA and NOMA transmission mode,the throughputdelay tradeoff in adaptive buffer-aided relaying protocols are analyzed theoretically by using the Lyapunov method.Simulation results show that,NOMA transmission mode can achieve a better average sum rate performance than that of OMA transmission mode.In addition,the proposed buffer-aided relaying protocol can improve the sum rate performance of multi-user relay network further.