【作者】 冯维；

【导师】 冯穗力；

【作者基本信息】 华南理工大学 ， 信息与通信工程， 2014， 博士

【摘要】 无线网状网(WMN)作为一种特殊的宽带无线网络，因为其部署方便快捷、初期建设成本低、覆盖范围广、可扩展性好等优点，在许多领域都有广泛的应用。但是WMN自身的一些特性，如时变的无线信道，可变的网络拓扑，节点资源和网络带宽受限等，都给网络带来很多不确定性，因此WMN不能完全照搬有线宽带网络的协议栈。跨层设计已经被证明是解决这些问题最行之有效的方法之一。跨层设计允许在协议栈的各层之间传递特定的网络状态信息，甚至允许联合多个协议层次进行建模。这种方式使得网络各层能够快速感知网络状态的变化，自适应的调整无线资源的分配策略和各层的机制，以满足不同业务的QOS需求，最终实现资源的最优化配置。目前，大多数针对WMN网络的跨层资源分配算法都是基于这样一些假设：网络是静态的，所得到的网络状态信息是完美的，非时变的。实际上，由于无线信道的时变性，节点的可移动性，网络传播时延等因素，任何一个无线网络都不可能是纯静态的。基于此，本文针对WMN跨层资源动态优化分配算法展开研究，在考虑无线网络上述变化特性的基础上，运用误差补偿等方法，提出了一系列能够更准确，更快速感知适应无线网络变化的跨层资源分配方法。具体的研究内容及创新成果包括：(1)利用松耦合跨层设计方法，在分析WMN特点和现有路由算法不足的基础上，提出了一种能够感知网络拥塞和干扰情况,并且快速适应网络拓扑变化的跨层多径链路状态路由协议——WHMRA。该算法相较于传统路由算法有如下几方面的创新:a)通过跨层信息反馈的方法,在网络层、MAC层和物理层间设计了全新的跨层接口，得到了一种新的路由权值。和现有的路由权值相比，该路由权值不仅能够动态地反映流路径间干扰，流路径内干扰和流量负载特性，而且具有保序性，保证了路由协议能够运用复杂度较低的算法得到端到端的最短路径，提高路由协议的选路性能。b)将传统基于覆盖的多点中继(MPR)选择算法扩展到基于链路状态的MPR选择算法，在链路质量和路由开销之间取了折衷。仿真结果表明，基于链路状态的MPR技术能够帮助网络层找到质量更好的路由，较之传统的MPR选择机制，能够进一步提高网络的吞吐量。c)将基于链路状态的MPR选择算法和模糊视觉理论相结合，使路由算法能更快速地感知物理层网络状态如流量，拓扑等的变化，以最低的开销快速获知网络状态信息，以调整自身的路由配置。仿真结果表明，该算法能够自适应网络动态拓扑的变化，降低路由开销，提高路由协议的可扩展性。(2)利用紧耦合跨层设计方法，在考虑过时的信道状态信息对链路容量的影响上，得到了无线多跳网络中基于SINR模型的条件容量闭式表达式，并提出了一种基于过时信道状态信息的联合拥塞控制，信道分配和功率控制的跨层优化算法。具体工作如下：a)由于无线网络频谱资源有限，无线网络通常采用空间上的频率复用来提高系统容量，所以工作在同一信道上的不同链路之间会产生干扰。在无线多跳环境下，相互干扰的链路数更多。此场景下基于SINR模型在无线多跳网络中求得条件容量是一个相当复杂的过程。本文通过先求得已知过时信道状态信息下当前信道的条件概率密度函数，然后基于SINR模型得到了已知过时信道状态信息下的条件容量闭式表达式。b)在无线多跳网络中考虑了过时的信道状态信息对跨层资源分配算法的影响，并且提出了一个联合考虑MAC层的信道分配、物理层的功率控制和传输层拥塞控制的跨层资源分配算法。该算法在流量公平性的QOS要求下，考虑过时信道状态信息的影响，利用该条件下的平均容量来建模链路数据率约束，将跨层资源分配问题建模为一个通用的网络效用最大化问题(NUM)，并提出了求解该优化问题的集中式和分布式算法。该算法能够保证收敛，并且能较好地补偿资源分配的误差，有效提高网络的资源利用率。(3)利用紧耦合跨层设计方法，在考虑网络公平性和过时信道状态信息影响的基础上，提出了一种基于信道预测的联合拥塞控制，信道分配，功率控制，速率分配，调度和路由的跨层优化算法。a)将拥塞控制，信道分配，功率控制，速率分配，调度和路由所涉及到的跨层资源分配问题建模为一个考虑比例公平性的非线性混合整数规划问题。由于集中式算法具有较高的计算复杂度等缺点，不适应于动态变化的无线多跳网络。基于此，本文通过求解原始优化问题的对偶问题，将原始问题分解为不同的子问题，并且通过不同的网络状态参数如拥塞价格等动态地协调这些子问题如：传输层的业务流速率调整、路由层的路由功能，链路层的速率分配和链路调度、物理层的功率控制以及MAC层的信道分配的求解。该算法能够保证收敛，而且网络的总效用，能量效用指标明显优于现有的算法。b)考虑到信道的时变特性和CSI的反馈延时，通过信道预测技术扩展了前面跨层资源分配的研究成果，较好地补偿了过时CSI带来的影响，进一步提高了算法在动态网络下分配资源的正确性。仿真结果表明，该算法能够补偿过时信道状态信息带来的性能损耗，明显优于现有的算法。更多还原

【Abstract】 Wireless mesh network (WMN), which is known as a special broadband wirelessnetwork structure, has been widely applied due to its particular advantages, such as fastconstruction, low upfront costs, large coverage area, good scalability, etc. However, thecharacteristics of WMN itself, such as time-varying channel, unstable topology, limitedresources of nodes and link bandwidth and so on, bring in uncertainty to the netowrk, andmight even make the wire wideband network protocol stack unavailable. To address theseproblems, cross-layer design is proposed. With cross-layer design, the network stateinformation can be exchanged between different layers and different layers can even bejointly modeled and designed. And in this way, each layer can detect the change of networkstatus quickly, adaptively adjust the resource allocation in order to satisfy different QOSrequirements and eventually realize the optimal resource allocation.Until now, most of researches on cross-layer resource allocation algorithm are based onsuch assumptions that the network is static, and network state information is perfect andtime-invariant. Actually, the network is dynamic due to the time-varying channel, mobility ofnodes, feedback delay and so on. Based on it, the dynamic cross-layer resource allocationalgorithm for WMNs is further studied in the paper. With consideration of dynamiccharacteristic, using error compensation, a series of cross-layer resource allocation algorithm,which can quickly detect and automatically adapt to network changes, is proposed for WMNs.The main contributions are as follows:(1) Using loosely coupled cross-layer design, a cross-layer multipath link state routingprotocol WHMRA, which can not only capture the network congestion and interference, butalso adapt to the network changes quickly, is proposed based on careful analysis on thecharacteristics of WMN and the limitation of the existing method. It differs from thetraditional routing protocol as follows:a) Using loosely coupled cross-layer design, multiple interfaces are designed betweennetwork layer, MAC layer and physical layer and a new routing metric is obtained. Comparedwith existing ones, on one side, the new metric can capture the inter-flow/intra-flowinterference and traffic load; on the other side, it is isotonic so that low computationcomplexity algorithm can be used to compute the efficient routing for data packets.b) By extending the coverage-based Multipoint Relay (MPR) selection algorithm to alink-quality-based MPR selection algorithm, the routing protocol makes a tradeoff betweenrouting quality and routing overhead. The simulation results show that the link-quality-based MPR selection algorithm can make network layer find a good-quality path and improvesystem throughput.c) By combining the link-quality-based MPR selection mechanism and fuzzy slightedphilosophy, WHMRA can use lower overhead to detect the changes of physical layer statussuch as traffic, topology quickly, and then coordinate the routing configuration. Simulationresults show that WHMRA can adapt to the topology change, reduce the routing overhead,and improve the routing scalability.(2) Using tightly coupled cross-layer design, a SINR-based conditional average capacityis obtained with the consideration of outdated CSI and a joint optimal congestion control,channel allocation and power control algorithm for WMN with outdated CSI is proposed. Thedetails are described below:a) Due to the limitation of spectrum resource, frequency reuse in space is usuallyadopted to improve system capacity of wireless networks, so that interference occurs betweendifferent links in the effective jamming range. Interference links increase especially in amulti-hop environment. According to this, it is a relatively complex process to compute theSINR-based conditional average capacity for WMN. By firstly obtaining the probabilitydensity function of current channel gain on outdated channel gain, the closed-form expressionfor the expectation of conditional capacity under SINR model can be further derived througha multiple integration process.b) The impact of outdated CSI on cross-layer resource allocation is firstly considered indynamic multi-hop wireless networks and a framework with outdated CSI is proposed tojointly optimize congestion control in the transport layer, channel allocation in the data linklayer and power control in the physical layer. In the proposed framework, the network ismodeled as a generalized network utility maximization (NUM) problem with elastic link datarate and power constraints and consequently, the NUM problem is solved in both a centralizedand a distributed manner. Both two are convergent, and can compensate the error of resourceallocation and improve the resource utilization efficiently.(3) Using tightly coupled cross-layer design, an analytical framework is proposed for theoptimization of network performance through joint congestion control, channel allocation,rate allocation, power control, scheduling and routing with the consideration of fairness andoutdated CSI in the multi-channel WMN.a) The joint congestion control, channel allocation, rate allocation, power control,scheduling and routing problem is modeled as a complex non-linear mixed integerprogramming problem. Due to the computation complexity, the centralized algorithm is impractical especially for a mobile network. According to this, using the dual decompositiontechnique, the primal problem is decomposed into several subproblems:1) flow control intransport layer,2) next-hop routing,3) rate allocation and link scheduling in data link layer,4)power control in physical layer and5) channel allocation in MAC layer, and finally thesesubproblems are solved by the coordination of different dynamic network state parameterssuch as congestion price and so on. The algorithm keeps the convergence, and significantlyoutperforms the existing algorithms on network utility and energy efficiency.b) Considering the time-varying channel and feedback delay of CSI, the research resultsin a) are extended by channel prediction technology, the error brought by outdated CSI iscompensated and the correctness of resource allocation algorithm in a dynamic environmentis improved. Simulation results demonstrate that the prediction-based algorithm compensatesthe performance cost brought by outdated CSI and shows better performance than the existingones.更多还原