Research On Relay Node Selection In Wireless Cooperative Networks

Wireless network has attracted a lot of attention, but the wireless channel fading is one of the most serious weaknesses of wireless communication because it can re-duce the performance of wireless channel greatly. Moreover, Spatial diversity has been shown to be very effective in copping fading in wireless channel by employing multiple transceiver antennas on a wireless node (i.e., MIMO).However, with the rapid development of micro-electronic technology, the size of wireless node becomes smaller and smaller, and so it may be infeasible for equipping multiple antennas on a wireless node in practice. In order to cope the weakness of multiple antennas on the same node, the researchers have proposed the cooperative communication (CC) technology to achieve spatial diversity by using distributed single antenna nodes. Under this communication scheme, each node is equipped with only a single antenna and can use the antennas on other (relay) nodes to achieve the spatial diversity. However, the choice of different relay nodes will affect the performance of CC greatly. Thus, this thesis study how to select the relay nodes in wireless cooperative network, so as to increase the transmission capacity or reduce the energy consumption of wireless network. Specially, we consider both the single-hop and multi-hop network environments for wireless network; we also consider the cooperative communication schemes with only one relay node and with multiple relay nodes respectively. The main research points and contributions of this thesis are as following:●Maximal lifetime scheduling for multiple transmission pairs in wireless co-operative networksWe first consider the CC scheme with at most one relay node. In the relay as-signment problems of single-hop wireless network, most previous works assume that there are multiple transmission(source-destination) pairs and multiple relay nodes in a network where each node only serves as one role:either transmission node or relay node. However, this assumption will not always hold in practice where each node has its own information to transmit. Thus, we study the maxi-mal lifetime scheduling problem for cooperative communication with guaranteed capacity in a network environment where there are multiple source-destination pairs and each node can serve as both two roles:transmission node and "relay" node. We propose that each two pairs can cooperate with each other to use CC to improve the lifetime. After that, we design an optimal polynomial-time algorithm to maximize the network lifetime and also prove the optimality of this algorithm. The simulation results show that the algorithm can prolong about199%lifetime than that of direct transmission.●Truthful relay assignment in wireless cooperative networksSince the choice of deference relay nodes will affect the performance of CC great-ly and there are multiple transmission pairs compete for the same relay node set, each pair may cheat others to get a better relay node so as to achieve more in-dividual revenue in practice. However, the cheating behavior may decrease the overall performance of network greatly. Thus, we propose a relay assignment protocol (RA-VCG) for cooperative communication to maximize the total social value (i.e. the total true value of all source-destination pairs) while guaranteeing truthfulness in an auction-theoretic sense by charging each pair an extra payment. Then, we prove the validity of this protocol and use the simulation results to show the efficiency of this protocol.●Multiple relay nodes assignment in wireless cooperative networksMost of the existing results on relay assignment problem with multiple transmis-sion pairs are limited to assign each single pair at most one relay node. Moreover, for a given pair, the capacity gain obtained by employing multiple relay nodes for cooperative communication may be greater than that can be obtained by selecting only a single relay node. Therefore, this thesis studies the cooperative relay as-signment problem in a network environment, where multiple transmission pairs compete for the same pool of relay nodes, but each pair can employ multiple re-lay nodes for cooperative communication to maximize the minimum transmission capacity among all pairs. We first formulate this problem into a0-1non-linear in-teger program. Because this problem is NP-hard, we develop a polynomial-time approximation algorithm to solve this problem and we also analyze the approx-imation ratio of this algorithm. The simulation results show that this algorithm can increase the object value by about56%and65%comparing with ORA and NCR schemes respectively.●Energy efficient tree-based cooperative data aggregationAt last, we extend the CC technology to a multi-hop wireless network, and we consider how to use CC to reduce the energy consumption of data aggregation operation in wireless sensor networks. Data aggregation is an essential operation in wireless sensor networks where the tree-based underlying network structure is often used to support this operation because of its simplicity and energy effi-cient. Moreover, there is always a special situation that some nodes may have the same aggregate data in a dynamic tree-based data aggregation process, and so we can use the CC technology to reduce the energy consumption. Specially, we first formally define the tree-based cooperative data aggregation problem, and then design an optimal centralized algorithm to solve this problem. After that, a distributed algorithm is proposed for this problem in which each sensor node only use local information. The simulation results show that the proposed algorithms can reduce the energy consumption by about23%and31%comparing with MCT and PEDAP algorithms respectively.