【作者】 梁慜；

【导师】 杨大成；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2010， 博士

【摘要】 协作中继作为一种虚拟多天线技术,可以在慢衰无线信道中获取显著增益。最初,大多数解决方案需要通过设计分布式空时编码方案以实现同频段上中继传输的同时进行。然而,如果存在多个中继节点相互协作,复杂的分布式空时编码需要知道网络全局信息。由于这些困难的存在,本文采用可以获得与基于空时编码的协作中继相同分集-复用增益折中的机会中继来实现协作中继,即用户只与一个“最佳”中继节点协作。协作中继充分利用无线传输的广播特性,以低成本的构建方案显著提升了系统的容量、覆盖和可靠性,在无线传感器网络、无线Ad Hoc网络、无线Mesh网络以及移动蜂窝网络中有着广泛的应用前景。因此,本文以无线中继网络为研究背景,对其无线资源管理中的频率复用和中继选择进行了全面而深入的研究。在无线中继网络中,中继节点的增加使得数据从源节点到达目标节点的传输占用更多的无线资源。因此,为提高频谱利用率,需要使用较小的频率复用因子,例如同一小区内的不同中继节点使用相同的频率资源与其服务的移动终端进行通信。然而,这种资源复用使得无线中继网络存在较大的共道干扰。针对这个问题,本文在固定两跳蜂窝中继网络中提出一种基于静态资源规划的频率复用方法,在两种不同的中继复用准则下分别加以阐述,并进行理论与仿真分析。该方法通过频段在划分区域的特定分配及复用和方向性天线的使用,消除了小区内干扰,并最小化小区间干扰,最终提高小区的频谱效率。通过分析干扰分布,从直传用户和中继用户的信干噪比表达式中提取出影响共道干扰的关键参数：中继站与基站的发射功率之比。在优化的中继站和基站发射功率下,提出的频率复用方法较已有方法可以获得明显的频谱效率性能提升。由于无线中继网络的协作分集是通过节点之间的相互合作完成的,所以中继协作策略对系统性能至关重要。中继协作策略包括协作方式和中继选择,前者决定了协作条件和协作形式,而后者决定了协作对象。中继协作策略在设计时需要根据具体应用场景综合考虑节点自身性能、网络整体性能以及节点间公平性等因素,其设计将直接影响节点乃至整个网络的性能。本文在中继选择方面的工作分别针对基于中继站协作和用户协作的两种无线中继网络为背景展开。首先,研究了固定两跳蜂窝中继网络下的中继选择问题。提出一种分布式中继选择方法,该方法利用基于非合作博弈论的功率分配结果,即功率-效用对,在消耗能量最小化和数据速率最大化两个优化目标下分别对发射功率和数据速率进行联合优化。同时,该方法考虑了中继站的负载情况,不会导致小区负载失衡现象的出现。相对于基于信干噪比的中继选择算法,我们设计的两种中继选择算法在其优化目标上均获得了相应的增益,并保证了小区的负载平衡。其次,研究了用户协作无线中继网络的中继选择问题。推导出了中继节点在既定目标速率约束下是否可用的充分条件和必要条件。充分条件的应用可以缩减最佳中继节点的搜索时间,并降低计算复杂度,但有些许性能损失。提出两种基于不同开销的半分布式中继选择算法。这两种低复杂度、低开销算法均以中断概率为优化目标,同时确保源节点之间的公平性。开销较大算法较开销较小算法可以获得更好的容量性能。之后,将这两种算法应用到固定两跳蜂窝中继网络中。在这两种网络环境下,两种算法较现有算法均可以大幅降低中断概率,保证源节点之间的公平性,且至少没有容量损失。更多还原

【Abstract】 Cooperative relay has been proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowkedge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We adopt opportunistic relaying that elimates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. This scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and destination. Information theoretic analysis of outage probability shows that this scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex schemes, where coordination and distributed space-time coding for M relay nodes is required. Cooperative relay is based on the broadcast nature of the wireless medium, which can promote the capacity, coverage and reliability without requiring significant infrastructure deployment costs. Hence, cooperative relay has been widely used in wireless sensor networks, wireless Ad Hoc networks, wireless Mesh networks and mobile cellular networks. Focus on wireless relay networks, we study the frequency reuse and relay selection these two wireless resource management techniques in this thesis.The cooperation between source and destination in wireless relay networks requires more wireless resources because of the relay links. Reducing frequency reuse factor is an effective way to improve spectral efficiency. For example, different relay nodes in the same cell serve their mobile stations by using the same frequency bands. However, these frequency reuse methods induce serious co-channel interference in wireless relay networks. We address this problem and propose a novel static frequcny reuse method for two-hop cellular relay networks with fixed relay stations. In this method, inter-cell interference is eliminated and intra-cell interference is minimized by special frequency bands allocation in divided regions and usage of directional antennas. This method is expounded and analyzed under two different relay reuse factors. Additionally, a key parameter, relay stations and base stations transmission power ratio r, is found in the signal to interference plus noise ratio (SINR) expressions of one-hop and two-hop mobile stations. When optimal r is used, the proposed frequency reuse method can achieve significant improvement on spectral efficiency compared to existing methods.Since cooperative diversity in wireless relay networks is accomplished by the cooperation among nodes, cooperative strategy is crucial to the system performance. Cooperative strategy is composed of cooperative mode and relay selection. The former one determines cooperative condition and cooperative manner, and the latter one determines cooperative objects. Cooperative strategy design should consider performance and fairness of nodes as well as system performance according to the application instances. We address the relay selection in wireless relay networks based on relay cooperation and user cooperation, separately.Firstly, we propose a decentralized relay selection method for two-hop cellular relay networks with fixed relay stations. By utilizing the results of non-cooperative power allocation game via pricing, i.e., power-utility pairs, joint optimation of transmission power and data rate is done under terminal energy consumption minimization and data rate maximization these two optimization objectives, in which load balancing solution is integrated. Simulations verify that the two proposed relay selection algorithms perform more advantages depending on the desired optimization objectives rather than the SINR-based relay selection algorithm, respectively.Secondly, beginning with the derivation of a tight threshold-based sufficient condition on the feasibility of a relay node, i.e., ensure that user relaying via the node can achieve its target rate, two semi-distributed relay selection algorithms with different system overhead are proposed for user cooperation based wireless relay networks. Both algorithms minimize outage probability and ensure the fairness among sources with low computational complexity and system overhead. The algorithm with high system overhead has better capacity than the one with low system overhead. Then, we apply these two algorithms in two-hop cellular relay networks with fixed relay stations. In these two application instances, both algorithms can decrease outage probability significantly; ensure the sources’fairness and keep capacity at least compared to existing algorithms.更多还原