Research On Buffer-aided Relay Networks With Multicast Transmission

Relay is becoming a vital technology of wireless communication today because it can provide an attractive way to improve the system throughput and extend the coverage of wireless networks.In traditional relay networks,the relay alternates between reception and transmission in successive time slots,and its performance is largely influenced by the channels condition and cannot adapt its reception and transmission time slots based on the channel quality.Therefore,traditional relay networks cannot have a good throughput performance,especially when channel condition from source to relay or from relay to destination is terrible.Buffer-aided relay could overcome the defects of traditional relay transmission scheme.A relay with buffers can adapt its reception and transmission time slots based on the quality of the involved channels,because the buffers provide higher flexibility in exploring the network's infrastructure.Hence buffer-aided relay has more freedom degree to decide the transmission links.As the demand for broadband multimedia service over wireless networks,such as Mobile TV and Internet Protocol Television(IPTV),grows around the world,multicast communication,where the same content is transmitted to multiple receivers simultaneously,has increasingly emerged as a vital technique in next generation cellular networks.Besides,it has already been included into the current communication standard.Therefore,we consider a more general relay network where buffers and multicast communication are both taken into account in this paper.Compared to traditional link selection schemes,our relay is able to choose whether to multicast or unicast adaptively.Firstly,we give a brief introduction to multicast transmission and relay technology.After that we focus on the three-node buffer-aided system,and we mainly study the link selection schemes under adaptive rate transmission mode and fixed rate transmission mode in this system,respectively.For adaptive rate transmission,we propose a protocol which chooses either the source-relay or the relay-destination link for transmission according to the CSI.Besides,we also get the expression of system throughput and which could achieves higher throughput gain compared to conventional relaying schemes.For fixed rate transmission,we also derive the expression of outage probability and give an upper bound of it.Our simulation results reveal that the buffer-aided relaying scheme could yield a diversity gain of two.Secondly,In contrast to most of the existing literature where the buffer-aided relay can only unicast,we introduce the multicast communication into the buffer-aided relay network.We develop an optimal link selection scheme which maximizes the throughput of the network,under the necessary condition that the input/output throughput at relay is balance.We solve this optimization problem by relaxing the discrete constraints and applying the KKT conditions.Compared to traditional link selection schemes,our relay is able to choose whether to multicast or unicast adaptively depending on the CSI of each links.Our analytical and simulation results show that the proposed link selection scheme in the relay network combining buffers and multicast communication achieves significantly higher throughput gain compared with existing approaches,and buffers and multicast communication of relay can promote the performance of each other.Similarly,we also present a suboptimal link selection scheme that could largely reduce the computational complexity.Finally,since the optimal link selection scheme we present before cannot guarantee the QoS of users in the relay system,we study the throughput QoS guarantee technology and delay QoS guarantee technology,respectively.For throughput QoS guarantee,based on the optimal link selection scheme,we obtain the link selection scheme that could maximize the system throughput on the premise that the users throughput can be guaranteed.Then we derive the throughput expression of the system.For delay QoS guarantee,we propose two schemes to control delay to guarantee the delay QoS of users.One scheme is to limit the arrival rate at relay to control the delay and we derive a corresponding upper bound on the average delay.The other one is to limit the buffer size of relay.Our results show that the buffer-aided and multicast relaying with QoS guarantee technology achieves significant throughput gain compared to conventional relaying schemes.