Cooperative Scheme And Resource Allocation For Wireless Cooperative Communication

Wireless cooperative communication, which can achieve spatial diversity gain and drastically improve transmission performance by allowing users to share their resource, has attracted considerable research interests and become one of the hotspots in wireless communication area. The performance improvement of the cooperative communication depends on the applicational scene, the adopted cooperative scheme and the resource allocation for the application scenario. Therefore, designing cooperative scheme and resource allocation algorithm for a specific application scenario becomes one of the research emphases in cooperative communication. This dissertation addresses the cooperative scheme and the resource allocation for several typical application scenarios based on the commom flat fading single carrier system and the OFDM system. The main contributions are summarized as follows.Cooperative schemes and resource allocation algorithms for the single carrier system with flat fading channel are investigated. Firstly, the outage performances of Amplify-and-Forward (AF) and Decode-and-Forward (DF) are analyzed over Rayleigh fading channel respectively. Based on the analysis, the joint power allocation with optimal relay selection algrorithm, which depends on the statistical channel information, is proposed to minimize the average outage probability. Secondly, with individual power constraint on each node, two algorithms are proposed for the two-way AF relaying, one algorithm can maximize the capacity and the other can minimize the average outage probability. These two algorithms can be directly handled by exsiting convex optimization tools. Moreover, compared with each node transmitting in its maximum power, these two algorithms can not only improve the system performances, but also save the power consumption significantly.In order to improve the feasibility of the cooperative system with STC, an adaptive relay selection and transmission scheme, based on DF with Alamouti's Coding, is proposed for the single carrier systems under flat fading channel. In this scheme, the opportunistic relaying is applied to cooperative Alamouti's STC transmission. Therefore, it can achieve the same order of diversity as opportunistic relaying, while achieving higher coding gain than opportunistic relaying. Meanwhile, because only two relays are needed during the STC transmission, this scheme is easy to implement.For the OFDM system with individual power constraint on each node, a cooperative transmission scheme, based on AF with Alamouti's STC, is proposed. Since only one relay takes part in the STC transmission and hence the complexity of the destination's decoding is low, this scheme is very feasibile. Moreover, under this scheme, a power allocation algorithm is proposed to maximize system capacity. In this algorithm, the optimal problem is decomposed into three sub-problems to be solved step by step, and the objective functions and the results are linearly handled. Therefore, the algorithm reduces the computational complexity and meanwhile improves system capacity significantly.For cooperative DF OFDM system with individual power constraint on each node, the outage performance of single relay selection based on maximum capacity is analyzed. And a margin compensation power allocation algorithm (MMPAA), which is based on modified linear water-filling algorithm, is proposed to maximize system capacity. The MMPAA is realized as follows. First, channel capacity of each hop is firstly maximized by water-filling power allocation respectively. Then fix the power allocation of one node and modify the power allocation of the other node to improve system capacity interatively. Finally, reclaim the additional power which is not consumed by the node to save power.In conventional cooperative DF OFDM system, the data bits that are received by a relay in one subcarrier are forwarded in an appointed subcarrier, which will restrict the spectrum efficiency of the cooperative system. To solve this problem, a novel transmission scheme named bit reloading DF (BRLDF) and an algorithm which combines relay selection with power allocation are proposed. In this scheme, the relay collects the received data bits of all subcarriers, and then reloads these data bits according to the each subcarrier's channel gain on relay-destination link. The analysis indicates that the system capacity of BRLDF always excesses that of the conventional DF scheme. Furthermore, through rate adaptive power allocation in each node, BRLDF selects the relay whose channel capacity is maximal. And through margin adaptive power allocation, system capacity is maximized and total power consumption is minimized at the same time.For the multi-relay cooperative DF OFDMA system, the outage performance of allocating subcarriers according to the equivalent channel gain is analyzed. In order to maximize system capacity, a resource allocation algorithm, which joints subcarrier matching, subcarrier allocation and power allocation together, is proposed under the total power constraint. This algorithm is realized by the following steps. Firstly, for each relay, sort subcarriers of the two links. Secondly, match the subcarriers and allocate each pair of subcarriers to the relay which has maximum equivalent channel gain. Finally, allocate total power to each subcarrier pair according to the linear water-filling power allocation algorithm. The analysis indicates that the proposed algorithm improves spectrum efficiency, decreases the system complexity comparing to the exhaustive attack method and the iterative water-filling power allocation algorithm.Considering a cell network in which several relays are placed in fixed positions, a cooperative scheme based on the incremental relay and the corresponding resource allocation algorithm are proposed. In order to maximize the transmission rate of each user, the greedy algorithm is used by the base station to load bits to each subcarrier with the consideration of the user power, the QoS requirement and the channel gain of each subcarrier. During the transmission of the relays, a low-complexity resource allocation algorithm, which joints the data symbol allocation, subcarrier allocation, and relay selection together, is proposed to decrease power consumption. The proposed scheme considers spectrum efficiency, transmission rate and QoS holistically. Thereby, it provides an optimized scheme to the application of cooperative communication in the cell network.