An Opportunistic Scheduling Scheme For Bidirectional Buffer-aided Multi-relay Network

For relay techniques,it is assumed that the source and the destination exchange information with the assistance of a relay,a direct link between the source and the destination is not present.Relay techniques can effectively overcome the impact of multi-path fading and enhance the reliability of transmission.Owing to the buffer utilized.buffer-aided relay techniques are capable of storing a packet from the source instead of receiving a packet from the source in one time slot and immediately forwarding it to the destination in another one.According to the simultaneous link quality and the state of data in buffer,the system could choose link to send or receive data adaptively,and buffer also provides more opportunities for multiple relay networks to choose the optimal relay.The combination of buffer and relay techniques has a significant contribution to improving the throughput,diversity gain and signal-to-noise ratio of the relay system.This thesis studies buffering in a bidirectional multi-relay network and focuses on opportunistic scheduling scheme which can achieve the largest average end-to-end sum rate for the bidirectional buffer-aided multi-relay network.Firstly,several basic transmission modes and different relay forwarding strategies have been introduced,and some relay selection schemes based on different communication indexes are mentioned also.Secondly,current buffer-aided relay techniques have been researched.For the single-relay network,several link selection policies are proposed.For the multi-relay network,relay selection schemes are mentioned.And buffering in a bidirectional network is studied.Thirdly,for bidirectional buffer-aided multi-relay network,opportunistic scheduling scheme ? to maximize the average end-to-end sum rate is proposed.In addition to the opportunistic scheduling of the communication links,we incorporate adaptive relay selection,transmission mode selection and transmission rate selection into the scheduling scheme ?based on the channel state information(CSI)of the involved links.It is assumed that the buffer size is large enough that no overflow happens,and by using the Karush-Kuhn-Tucker(KKT)conditions,the optimization problem can be solved.Simulation results show that the proposed opportunistic scheduling scheme ? can achieve larger average end-to-end sum rate compared to TDBC,MABC and traditional two-way protocols.And finally,given a power budget for each node,a scheme ? based on the proposed opportunistic scheduling scheme ? with fixed transmit powers is proposed.In each time slot,based on the instantaneous CSI,the system allocates the optimal powers to each node for sum rate maximization.Simulation results are presented to corroborate that the power allocation scheme outperforms the scheme with fixed transmit powers in terms of average end-to-end sum rate.