【作者】 李屹；

【导师】 纪红；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2008， 博士

【摘要】 无线通信在世界范围内的高速发展促使人们对无线系统提出了更高的业务需求。为了满足多速率多媒体通信的要求,下一代无线系统必须采用更先进的算法和技术,不仅要提高数据速率,还要使系统能确保不同媒体所要求的服务质量。协作通信是近几年发展起来的能够有效对抗衰落,提高频谱效率和通信可靠性的容量增强技术,如今正受到学术界的广泛关注。本论文针对协作通信领域的四个热点问题:协作时机、伙伴选择、协作ARQ和协作频谱感知做了相关研究,进行了详尽的理论分析和仿真验证,并提出了对应的解决方案。论文的主要工作包括三个方面,概括总结如下:1.提出无线局域网中一种支持QoS的协作分集算法。a)根据用户的QoS指标判断是否协作,即按需协作。如果直接发送无法达到业务所需的最低数据速率,源节点将利用伙伴协作发送;反之,由源节点直接发送,若传输失败了,再寻求伙伴协作重传。b)选择能够满足用户QoS需求的伙伴执行协作。无线局域网小区中每个移动站都维护一张数据速率统计表,需要伙伴协作时,搜索该表,选择能够满足相应业务QoS需求的移动站作为自己的伙伴。支持QoS的协作分集算法能够显著改善系统吞吐量和能量效率。2.提出无线Ad hoc网络中协作ARQ机制的改进方案。a)区分协作与非协作数据帧,解决了协作重传过程中出现的ACK/NAK指向不明问题,防止了应答对象的混淆和协作扩散,简化了协作进程的复杂度。b)在节点内部设定业务流优先级,使协作重传的帧总有机会先被发送出去,避免了协作过程中,在同一个协作组内,旧的协作重传尚未结束,新的协作重传就已开始的协作混乱问题。c)采用基于优先级的退避机制,对节点之间相同优先级的业务流进一步区分优先级,选择瞬时信道条件最优的节点重传,使协作重传的过程处于一种“有序”的状态,降低了碰撞概率。改进的协作ARQ机制提高了重传成功率,改善了吞吐量性能。3.提出异构无线网络中基于多用户分集的协作频谱感知策略。a)在整合了TD-SCDMA和WiMAX的异构无线网络中,将WiMAX用户分成若干个簇,选择每个簇内瞬时信道条件最好的WiMAX终端协作检测频谱,有效降低了虚警概率。b)利用软硬结合的判决手段,提高了判决结果传输的可靠性,同时使控制信道的开销和判决算法的复杂度较低。基于多用户分集的协作频谱感知策略保证了频谱感知的准确性,达到了提升频谱利用率和系统吞吐量的目的。更多还原

【Abstract】 The rapid development of wireless communications in the world incurs the increasing service demanding from the human being. The next generation wireless communication systems are required to adopt more advanced algorithms and technologies, in order to provide higher transmission rate, more application functions and better quality of service for people. Cooperative communication is a capacity enhancement method, which can effectively increase the spectrum efficiency and robustness of wireless systems. For the past few years, this new technique draws widely attention of research worker. In this paper, several hotspots of cooperative communication field are investigated, their mathematics models are built, and corresponding solutions are proposed. This paper focuses on the moment of cooperation, partner selection algorithm, cooperative ARQ protocol and cooperative spectrum sensing. The contribution of the paper is listed as follows:1. Propose a QoS supported cooperative diversity algorithm in wireless LANs.a) According to different services, cooperative diversity is invoked only if the minimum data rate required to have a successful transmission cannot be achieved. This is a demand cooperation scheme. Direct transmission will be used if only it can meet QoS requirements of some type of application. When direct transmission fails, partners will assist the source nodes in retransmiting data, i.e. cooperative retransmission.b) Partners are determined based on user-specific QoS requirements. In a WLAN, each station will listen to all ongoing transmissions and maintain a table of rate statistics that can be used to select suitable partners when source nodes are in need of help.It is proved that the QoS-aware cooperative diversity algorithm can mitigate the negative effects of unconditional cooperation, and improve the system performance in terms of throughput and energy efficiency.2. Present an improved cooperative ARQ scheme for wireless Ad hoc networks.a) Cooperative and non-cooperative frames are distinguished so as to avoid ambiguous ACK or NAK. In addition, this method can prevent cooperation process diffuse from one cooperation group to another, and simplify cooperation compexsity.b) Introducing traffic categories within node so that each node first help other nodes to retransmit a frame and then send its own data, which prevent that a new cooperation process begins but the previous does not finish yet in the same cooperation group. As a result, the cooperation processes will not become disordered.c) Through implementing a priority-based back-off algorithm, the most appropriate node is selected to help the source node retransmit data frame according to instantaneous channel conditions. Theoretical analysis and simulation results indicate that the collision problem caused by cooperation can be alleviated.The improved cooperative ARQ scheme can increase the probability of successful retransmission, and then improve throughput greatly.3. Propose a robust cooperative spectrum sensing strategy based on multi-user diversity.a) In heterogeneous wireless environment consisting of TD-SCDMA and WiMAX, the WiMAX users are separated into a few clusters and the most favorable user is selected in each cluster to detect spectrum. This approach can enhance the sensing performance by reducing the false alarm probability.b) A softened hard decision scheme with two-bit overhead is adopted for the reliable transmission of decision results. This means achieve a good tradeoff between detection performance and complexity.Cooperative spectrum sensing strategy based on multi-user diversity guarantee the accuracy of spectrum detection, and achieves the end that improving spectrum efficiency and throughput.更多还原