Research On Multi-user Buffer-aided Relay Strategy

As the amount of data in the mobile service grows exponentially,people have put forward higher requirements on the throughput,network coverage and stability of the communication system."buffer-aided relay technology",that is by providing a buffer at the relay node,according to the channel state of the each link,the transmission mode which is most favorable to the long-term average throughput state of the system is selected at each moment.As a new direction in wireless network transmission,buffer-aided relay technology can further enhance throughput,network coverage and other performance of system.However,its related research is fewer in multi-user networks with complex topology.In this paper,MIMO technology is employed into multi-user buffer-aided relay system,each transmission link is adopted Alamouti space-time block coding transmission scheme,aim to optimize link selection and power allocation variables,use Lagrangian multiplier method and KKT condition to solve the variable optimization problem,then Multi-user MIMO buffer-aided strategy is proposed and effectively improves the average throughput of the multi-user buffer-aided relay system.The main contents of this dissertation can be summarized as follows:(1)Study a single-user buffer-aided relay strategy.The adaptive link selection,system average throughput and optimal transmission scheme are analyzed in detail,Comparing single-user buffer-aided relay strategy and traditional relay strategy,simulation results show that the introduction of the buffer node at the relay enables the system to obtain additional the gain of decision freedom,increase the system throughput performance,reduce the impact of channel quality imbalance on both sides of the relay and acquire higher stability.(2)Study a multi-user buffer-aided relay strategy.In each time slot,the user with the best channel is selected to transmit information by using random fluctuations of different user fading channels,similar to the single-user buffer-aided relay network analysis method,comparing multi-user buffer-aided relay strategy and no-buffer-aided optimal user selection strategy,simulation results prove that the multi-user buffer-aided relay strategy can obtain both decision-making degree and multi-user diversity gain,the throughput gain is better than the optimal user selection strategy.(3)Study a multi-user buffer-aided relay strategy with MIMO technology.we establish a system model and analyze the Alamouti transmission and adaptive link selection scheme,aim to optimize the link selection and power allocation variables,we use Lagrange multiplier method and KKT condition to solve the variable optimization problem,then the optimal link decision conditions and power allocation method are presented,a multi-user MIMO buffer-aided relay strategy is proposed.The analysis results show that the optimal link selection and optimal power allocation scheme depend on the instantaneous channel state and related link channel statistics.Comparing the multi-user MIMO buffer-aided relay strategy,the single-user MIMO buffer-aided relay strategy and the multi-user buffer-aided relay strategy,the simulation results indicate that the multi-user MIMO buffer-aided relay strategy can make the system achieve the multiplexing gain by multiple antennas and multi-user diversity gain in the case of equal power distribution,and the throughput performance is the best of the three strategies.Under optimal power distribution conditions,the average throughput of the multi-user MIMO buffer-aided relay system is improved further,feasibility and effectiveness of the raised strategy is proved by simulation.The multi-user MIMO buffer-aided relay strategy proposed in this dissertation based on ideal conditions which there is unrestricted buffer space and no delay in system has certain significance for expanding system capacity,improving transmission efficiency and increasing system stability.