Performance Analysis For Cooperative Communication Systems In Wireless Network

As a hotspot in academic community during the recent years, cooperative communication technology serves to mitigate wireless channel impairment, enhance communication reliability and increase transmission rate. Single-antenna and potable mobile nodes share resources of each other with apt coordination under wireless scenario. Accordingly, multiple communication links between the source node and the destination node are established with a virtual multiple-input and multiple-output (MIMO) system formed at the same time, providing a new technique for MIMO implementation of small and mobile terminals.It is likely that cooperative communication technology will become one of the most promising transmission technologies for future wireless communications. Profound evaluation of its performance, however, is a requisite before its employment in practical applications. The thesis begins with a summary of efforts poured into the topic by both domestic and international researchers. Although fruitful achievements have been achieved, there are still some insufficiencies. On one hand, mentioned previous analyses, however, have assumed Rayleigh fading models while Nakagami fading models may represent miscellaneous real channels. Furthermore, although cooperative communication technology can deduce advantages in terms of diversity, it is not the best choice from the throughput point of view. Fortunately, it is more than compensated with cross-layer design scheme. Little literature attention has been focused on the cross-layer design for cooperative communication.Therefore, we will solely focus on the study of performances of both parallel and serial cooperative systems under Nakagami fading channels. With different network topologies and relaying strategies, cross-layer design schemes will be proposed accordingly and the performances of average throughput will be analyzed. Detailed contents are listed as:Researches at the physical layer include:Investigation is made upon performances of parallel cooperative communication systems with opportunistic relaying over Nakagami fading channels, under which scenario each relaying node solely receives the messages from the source node. Moreover, the decode-and-forward (DF) strategy is adopted at the relaying nodes, whilst maximal-ratio-combining (MRC) and selection-combining (SC) schemes are employed separately at the destination nodes. Particularly, exact and closed-form symbol error rate (SER) and outage probability (OP) expressions are derived, based upon which the diversity properties are discussed. Furthermore, simulations for both reception schemes are conducted and the performances of repetition-based cooperative communication systems are compared accordingly. It is obviously observed that the performances of cooperative systems using opportunistic relaying outperform that of repetition-based cooperative technique. In addition, relying on statistical channel information, the optimum power allocations for the source and the relays are determined.Investigation is made upon the performances of serial cooperative communication systems over Nakagami fading channels. Each receiver receives the messages from the source as well as the messages from partial or all relays. According to the DF state that the receivers are not informed of whether previous relays successfully decoded the received messages and forward it, the performances for serial cooperative systems with adaptive-MRC (A-MRC), blind-MRC (B-MRC) and blind-equal-gain-combining (B-EGC) schemes are examined respectively. Exact SER expressions and asymptotic results are derived for the A-MRC scheme together with examination on the asymptotic SER performances for B-MRC and B-EGC schemes, based on which the diversity properties are intensively addressed. The results demonstrate that the performance for B-MRC scheme is the worst among the three schemes, while the diversity order for B-EGC scheme is found to be identical to that of A-MRC scheme but with less than satisfactory practical realization.Researches on cross-layer design concerning physical layer and data link layer include:A novel cross-layer design scheme is proposed for parallel cooperative systems adopting amplify-and-forward (AF) relaying over Rayleigh fading channels. Four schemes are proposed with average throughput expressions based on assorted relaying strategies. The effects of selecting system parameters on average throughput are discussed, with both merits and limitations of the four schemes investigated.A specific novel cross-layer design scheme, named selective-node-based retransmission (SN-RT) scheme, is proposed for parallel cooperative systems with DF relaying over Rayleigh fading channels, with which an optimal relay is selected relying upon the instantaneous signal-to-noise ratio of the relay-to-destination link at each stage of retransmission. After that, the source together with the optimal relay transmits signals to the destination nodes following Alamouti-based space-time coding. Simulation results show that SN-RT scheme better exploits the relaying nodes in wireless network as opposed to the existing fixed-node-based retransmission (FN-RT) scheme, and thus phenomenally improve system's average throughput.Another novel cross-layer design scheme is proposed for multihop communication systems over Nakagami fading. One-relay-based cross-layer scheme is considered at first, where only a single node is allowed to retransmit packet in each hop, it is not until the packet is successfully received by the destination node that the next new packet transmission can be started. The idea is generalized to multiple-relay-based scenarios with the random selection of single relay transmission and two relays transmission. Finally, expressions for average throughput of different cross-layer schemes are derived.In summary, detailed investigations are made on the performances of cooperative communication systems at the physical layer. Some novel cross-layer design schemes are proposed, optimizing the system average throughput. Those achievements serve as productive theoretical tools for further researches and applications. In addition, broad prospects for various applications are uncovered for the cooperative models and cross-layer design schemes under consideration, e.g., cellular networks, wireless local area networks, Ad-Hoc networks, sensor networks and WiMAX networks.