【作者】 徐峰；

【导师】 岳殿武；

【作者基本信息】 大连海事大学 ， 通信与信息系统， 2009， 博士

【摘要】 作为抵抗无线衰落损伤、提高通信系统可靠性和增加系统传输速率的一种有效手段,协作(Cooperative)通信技术无疑是近几年学术界研究的热点之一。在无线环境中,单天线便携式移动节点可以协调地共享其它节点的资源,在源节点与目的节点之间构建多条通信链路,形成一个虚拟的MIMO系统,从而为小型移动设备的MIMO实用化提供了一条崭新的出路。鉴于协作通信技术将会发展成为未来无线通信领域广泛采用的传输技术之一。因此,在投入实际应用之前则非常有必要详尽地探讨和评估其各方面性能。本论文首先追踪报道了国内外与协作通信有关的研究进展。关于协作通信理论,迄今虽已取得较为丰富的研究成果,但还存在明显不足。一方面,已有工作大多是局限在Rayleigh信道环境下研究的。事实上,Nakagami衰落信道模型尽管相对复杂,但是它能够代表更为广泛的实际信道情形。另一方面,协作通信技术尽管能够引入更多的分集增益,但是从吞吐量角度看其并非是最佳选择。而跨层设计思想可以很好地弥补这一缺陷。然而目前针对协作通信的跨层设计的研究却很少。为此,在物理层下,我们主要研究Nakagami衰落信道环境下的并行、串行协作系统性能;在跨层设计方面,针对不同的网络结构和中继转发方式,我们提出了相应的跨层方案,并分析其吞吐量性能。具体研究工作如下:物理层下的研究工作主要包括:在Nakagami衰落环境下,研究了带有机会中继转发的并行协作通信系统的性能。每个中继节点只接收来自源节点的信息,中继节点采用前向译码中继转发方式(DF),目的节点分别采用最大比合并(MRC)与选择合并(SC)接收处理技术。推导出了精确的符号错误概率(SER)与中断概率(OP)的数学表达式。依据提供的理论公式,讨论了并行协作通信系统所能获得的分集增益。仿真分析了这两种接收合并技术下的并行协作系统性能,并与基于重复发送的并行协作通信系统进行对比。结果显示带有机会中继的并行协作通信系统性能远远好于基于重复发送的并行协作通信系统的性能。此外,基于统计信道信息,对选择合并接收方式的并行协作通信系统给出了最优功率分配方案。在Nakagami衰落环境下,研究了串行协作通信系统下的性能。每个接收节点既可以接收源节点信息,又可以接收部分或全部中继节点广播的信息。根据每个接收节点是否准确获悉前面中继节点的DF状态,分别分析了A-MRC、B-MRC、B-EGC三种不同接收方式下的串行协作系统性能。针对A-MRC接收方式下的串行协作系统,我们给出了精确的SER表达式和高信噪比下的渐近结果,同时又分析了B-MRC和B-EGC和接收方式下串行协作通信系统的渐近SER性能。根据给出的SER渐近表达式,深入地分析了这三种接收方式下的分集增益。结果表示:B-MRC接收方式下的性能最差,而B-EGC与A-MRC接收方式能获得一致的分集增益,且B-EGC接收方式更易于实现。物理层与数据链路层的跨层设计方式下的研究工作主要包括:在Rayleigh衰落环境和基于前向放大中继方式(AF)的并行协作框架下,提出了新的跨层设计方案。根据中继节点AF处理方式与对最优中继节点选择方式的不同,提出了四种备选方案,并且分别给出了平均吞吐量的数学表达式。讨论了系统各参数对平均吞吐量的影响,全面地对比了这四种方案的优缺点。在Rayleigh衰落环境和基于DF中继转发方式的并行协作框架下,提出了一种基于选择中继重传(SN-RT)的跨层设计方案。在重传过程,根据中继节点与目的节点间的瞬时信道状态选择一个最佳的中继节点,并联合源节点以Alamouti编码方式进行重传操作。通过与已有的固定中继重传(FN-RT)的跨层设计方案进行对比,发现SN-RT跨层方案更加充分地利用了网络的中继节点,进而显著地提高了系统的平均吞吐量。在Nakagami衰落环境下,设计出了一种新颖的多跳通信下的跨层设计方案。首先考虑单中继跨层设计方案,即允许每一跳的节点间可以重传操作,直到接收节点获取无差错的数据包后,信息传输方可进行下一跳。接下来将这一思想推广到基于多中继跨层设计情形,提出了随机选择单中继传输和随机选择两中继传输方案。对不同的跨层设计情形分别给出了平均吞吐量的数学表达式。综上所述,本文针对物理层下的协作通信系统进行了详细的性能分析,在跨层设计方面提出了新的设计方案,提高了协作通信系统的吞吐量性能。这些研究成果可以为将来进一步研究工作和实际应用提供丰富的理论依据。并且,本文所考虑的协作模型和设计方案具有广阔的应用前景,可以应用在蜂窝网络、无线局域网、Ad-Hoc网络、传感器网络和WiMAX网络中。更多还原

【Abstract】 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.更多还原