Designs Of Cooperative Relay Selection And Transmission Strategies

The core idea of “cooperation” is that related entities participate in cooperativetransmission through contribution and sharing of resources to realize a common goalwhile at same time achieving an extra gain. In cooperative communication, the networknodes share their channel resources to form a virtual MIMO (multi-input multi-output)system so as to obtain space diversity gain provided by discrete network nodes orexpand the coverage by relay transmission, which eventually improve the reliability ofcommunication. The theoretical basis of cooperative communication originates from theconclusion that relay channel capacity can exceed direct transmission. Since then, thestudy of cooperative communication has continuously developed to improve systemperformance in homogeneous wireless communication networks with different terminalcooperation or different technical cooperation, and to obtain the "emergence" gain in thecollaboration between heterogeneous wireless communication networks.Although the idea of cooperation provides a new way for the realization of thedevelopment and application of wireless communication, the cooperativecommunication strategies have an impact on system performance. For example, theperformance gain can be different by selecting nodes in different locations to participatein cooperation due to different channel conditions. An important content of concern incooperative relay transmission is how to select the best node quickly and effectively inwireless communication networks with multiple potential cooperative network nodes. is.In particular, when multiple user concurrent to transmit, how to choose nodes enhancethe system performance maximum while at the same time consider the business QoS(quality of service) demand, transmission delay, and fairness performance gain is verycomplicate. Moreover, cooperative resource allocation can improve the networkperformance further, which indicates that joint relay selection and resource allocation isan important part of cooperative strategy research.The study of system performance and diversity gain of existing cooperative relayselection and transmission strategies are mostly focused on single user scenario.However, the research on relay strategy and resource allocation in multi-usermulti-relay scenario, relay selection with OFDM technology and bidirectional relaytransmission are insufficient and need to be further studied.In this paper, we focus on cooperative relay selection and transmission strategy design. The studies highlights include: relaying strategies in OFDM systems; relayselection in multi-user density networks; geometric-based cooperative relay selectionand transmission design; bidirectional relaying with asymmetric traffic.The main contents and results of this paper include：1) In single-source multi-relay with one destination scenario, cooperative relayselection and resource allocation in OFDM system is examined. In order to eliminatethe bottleneck of selective OFDM relaying that cooperative diversity is limited by theworst paired sub-carrier channel quality, a bit reloading selective cooperative relayingscheme is presented. In this scheme, a single relay node is selected to retransmits theentire OFDM symbol at each hop through adaptive bit loading and Min-Max method.In this way, the outage probability lower bound of selective cooperative relaying isachieved. Theoretical analyzed the outage performance of the relay scheme anddesigned relay selection and power allocation strategy for fixed transmission rate andfixed transmission power scenarios. The outage performance and end-to-end achievablerate of the proposed scheme are verified by simulation.2) In mobile ad hoc networks (MANET), neither random method nor SNR basedmethod can ensure an full diversity gain in multi-user cooperation. As a result ofneglecting the channel state, fixed priority transmission is supposed to bring a reducedcooperative gain. In order to achieve full diversity, a two-stage automatic cooperativetransmission strategy based on user zone cooperation and relay zone cooperation isproposed. It divides the relay selection into two phases: relay selection among users andrelay selection among idle nodes. In relay selection, each node decides independentlyon whether to relay and relay for whom. Because user zone cooperation can notguarantee each user have a relay, relay zone cooperation utilize idle nodes to find relayfor the user failed to have a relay in the first phase. In order to avoid multiple user selectthe same relay node, relay zone is introduced in this protocol. It is formulatedautomatically though idle nodes’ self decision. Compared with FPT protocol, the papersimulated the package delivery rate and SEP, which verified the effectiveness of thealgorithm.3) For multi-hop mobile ad hoc networks, with the assumption of nodes locationinformation, geometric based energy effectively relay selection strategy is studied. Thefocus is how to select the next hop and corresponding relay in a cooperative mobile adhoc network with location information. For single user multi-hop scenario, a methodbased on the position information to determine the next-hop and the corresponding relay node is introduced. In order to improve the spectrum efficiency, two users locate atdifferent direction is supposed concurrent transmission; a relay selection scheme withminimum energy consumption is develed. In next hop node selection, using abeaconless greedy forwarding (BCGF) and beaconless recovery forwarding (BCRF)respectively in the positive progress area (PPA) and negative progress area (NPA) forthe next hop node selection; in the relay selection stage, a position based prioritydecision and relay selection strategy.aiming at the minimal energy consumption isdesigned according to the nodes location information.4) For the case of AF-OFDM bidirectional relaying system, this chapter study onthe energy efficiency strategy with asymmetric data rate requirements. Because the twousers have different transmission rate requirement, high data rate requirement user issupposed to assign more subcarriers. Because the two users are assigned differentnumber of subcarriers, some subcarriers have to work in the two-way transmissionmode, and the rest will work in the one-way transmission mode. With the purpose ofsystem efficiency, a combinatorial optimization problem which joint optimizes relaytransmission mode selection, power allocation and bit loading is constructed. For theproblem formulated is a mixed integer programming problem, an approximateoptimization algorithm is proposed. It is divided into two stages: in the first stage,optimize the power allocation of one-way transmission and two-way transmission withfixed subcarrier set; in the second stage, search the best subcarrier number according tosome linear structures to avoid exhaustive search and decrease the computationalcomplexity.