Research On Buffer-aided Relaying Protocols In Wireless Multi-user Networks

Network capacity is one of the most significant performance,which is always pursuing by the underlying communication protocols in wireless networks.For relay networks,efficient methods to enhance the network capacity include cooperation communication and network coding.However,most of works on relaying protocols follow the thinking pattern that the relay forwards the information immediately after receiving.These conventional protocols are carried out by executing the transmission modes sequentially under a prefixed scheduling,which ignores the fact whether the reception or transmission of the network device is in favour of the channel variations in a given time under fading.Buffer-aided relaying protocol breaks the mindset,introduces the buffer for the intermediate nodes and designs the optimal transmission strategy to maximize the network capacity.In particular,depending on the channel state information,buffer-aided relaying protocol could make the reasonable selection the transmission mode or link,which is beneficial to the long-term average system throughput under fading.The benefits of buffer are not only for temporarily storing data,but also for providing the possibilities of intelligent decisions in relay protocols.Compared to conventional relaying protocols,these buffer-aided relaying protocols provide significant gains in terms of throughput and diversity.Though numerous research has made certain progress in single-user relay networks,the results in more complex multi-user topology are very limited.Thus the dissertation mainly focus on the buffer-aided relaying protocols in wireless multi-user networks.Firstly,the dissertation focuses on multi-user one-way relay network without direct links,in which multiple user equipments(UEs)can only reach the base station(BS)through the relay station(RS).By employing the buffer at the RS,the protocol obtain the decision freedom.Based on the study of adaptive link selection buffer-aided relaying protocol,an optimal joint power allocation and adaptive link selection strategy for buffer-aided relaying protocol is proposed.The joint optimization protocol achieves the maximum average system throughput with the constraint of the total average power budget for all the nodes in the network.In each time,based on the optimal transmission strategy,the system determines the selected link and optimize the power of transmitter for the corresponding link.The simulation results show power allocation could further enhance the average throughput of buffer-aided relaying protocols.Secondly,the dissertation focuses on multi-user one-way relay network with direct links,in which multiple UEs can either connect to the BS by direct links or by relayed links.We employ a buffer at the relay and propose a family of buffer-aided relaying protocols based on the multi-user decoding capability.To fully exploit the network characteristic,we devise three type of the transmission mode(Z1-Z3):(Z1)multiple UEs transmit directly to BS at the rates that enable BS to decode them;(Z2)multiple UEs transmit,the RS can decode the information completely,while the BS partially and the buffer only has to store part of information for future forwarding;(Z3)RS extracts the information in the buffer and forwards them,which are going to be combined and decoded entirely at the BS,while simultaneously a number of UEs send new information to the BS.We analyze the achievable rates and dynamics of the buffer in each mode.Then we formulate the optimization problem and obtain the optimal strategy.The results show that the proposed protocol outperforms several state-of-the-art buffer-aided relaying.Further,if RS and BS could allow a certain degree of multiple access,the performance of the proposed protocol is even beyond the outer bound of the capacity of multiple-access relay channel.Finally,the dissertation focuses on multi-user two-way relay network,in which multiple UEs can keep two-way communication by direct path or relayed path.In order to introduce the decoupling,under the framework of buffer-aided relaying,we develop orthogonal/non-orthogonal decoupled uplink(UL)and downlink(DL)buffer-aided relaying protocols,noted by ODBA and NODBA.In ODBA,the decisions for UL and DL are decoupled,such that we optimize the link selection for UL and DL transmission respectively.By formulating the optimization problems individually,ODBA achieves the maximal throughput in UL and DL independently.In NODBA,we devise two novel transmission modes which UL and DL can be active simultaneously,while with the help of successive interference cancellation at the RS or BS,the achievable rates of both links can be decoded.With building blocks of the all devised transmission modes and aiming to maximize average two-way sum-rate,we formulate the corresponding optimization problem and get the optimal decision policy theoretically.The simulation results no only verify the efficiency of decoupling transmission,but also show that when RS-to-BS link is good,both ODBA and NODBA can improve the system performance significantly.