【作者】 李虎；

【导师】 刘元安；

【作者基本信息】 北京邮电大学 ， 电子科学与技术， 2014， 博士

【摘要】 卫星通信系统在国防和民用的多个领域有着广泛的应用,具有广阔的发展前景。近年来,由于卫星网络用户数量骤增及网络服务需求的多样化,使得如何合理的分配网络资源,发现并利用容量、能量和时延之间的关系,最优化网络性能成为一个重要的问题。然而,由于卫星通信系统自身的特性,不能直接使用地基通信系统的通信技术,也不能直接套用地基通信系统的研究结论。所以有必要对卫星通信系统进行针对性的研究。本文以李雅普诺夫方法为理论工具,以卫星通信系统的用户接入部分和卫星网络部分为研究场景,以容量、能量和时延这三个网络性能指标为出发点,主要在网络层针对这三个性能指标的解析关系和优化算法进行了较为深入的研究。主要内容归纳如下：(1)对于带有卫星网络支持的混合移动无线自组织网络利用李雅普诺夫方法进行了分析。对于这类混合网络建立了基于单元格的模型,对任意卫星覆盖范围、任意(平稳遍历)移动过程得到了该网络的平均网络容量的上界和最小能量函数上界的精确表达式。本部分的研究工作通过必要性和可能性两个角度,得到了平均最大网络容量和最小能量函数的一个上界,这两个界限可以为其他混合移动自组织网络的优化研究工作提供理论指导。在分析平均网络容量和能量函数的过程中,还构造了用于最大化容量和最小化能量的李雅普诺夫算法,这些算法对于其他混合网络算法的设计有一定的借鉴意义。还对于极限情况的容量进行了分析,发现了极限网络容量、节点密度和卫星覆盖范围的关系,对于这类网络的设计提供了指导。此外,对于本部分的研究内容在基于单元格的网络模型上进行了仿真验证。(2)设计适应于度受限情况下的卫星网络的跨层调度算法。首先对于这类网络模型进行建模,将星间链路数量的限制转化为对于节点的入度和出度的限制并将卫星网络建模为随机网络。而后本文建立了关于网络流量的效用函数,并使用李雅普诺夫方法对于这类网络进行分析,提出了一种能够保证网络稳定性、并能够合理的分配链路资源和能量资源的算法(DLSA),使得该算法满足节点的入度和出度的限制。采用李雅普诺夫方法对于本文提出的算法进行分析,给出了一个效用函数与网络时延的关于算法中的参数的一阶倒数量级的折衷关系。此外,对于本部分的研究内容在有度限制的网络模型上对算法进行了仿真验证。(3)针对卫星网络节点间距离较大导致传播时延较大的问题,利用一种队列更新方程将传播时延进行了建模,从而将该类网络化归到李雅普诺夫方法的处理范围之内。而后利用李雅普诺夫方法对这类网络模型进行分析,建立了与流量有关的效用函数,并提出了一种基于跨层设计的资源调度算法。通过李雅普诺夫方法分析得到,该算法由于考虑了传播时延的影响,其性能以传统的李雅普诺夫算法的不同。此外,对于本部分的研究内容,在包含6个节点的网络模型上进行了仿真验证。(4)分析了两类变种李雅普诺夫算法,分别是采用李雅普诺夫函数偏移的全部的算法以及使用系统稳定时的李雅普诺夫函数的算法。分析并解释了传统的李雅普诺夫算法在设计时直接采用了李雅普诺夫偏移的一阶部分并且该李雅普诺夫算法并非系统稳定时的算法的原因和优势。通过理论分析,得出了这两个变种算法的队列性能以及效用函数性能,并且与传统的李雅普诺夫算法进行对比,证实了传统的李雅普诺夫算法的设计原因。此外,在分析的过程中,得到了一种获取李雅普诺夫算法稳定点的算法(QLA-VPDQ),该算法在获取稳定点时需要的队列长度较小。该算法还可用于FQLA-G算法来改善其队列性能。更多还原

【Abstract】 Satellite communication system has been widely used in various scenes of both civil and national defense domain, and has broad prospects for development. In recent years, as number of users increases and demands for service varies, how to allocate network resource and how to use relationship among capacity, energy and delay have become important issues. However, due to the characteristics of satellite communication system itself, technology and conclusions of ground-based communication system cannot be directly applied to satellite communications system. Hence, it is of necessity to research satellite communication systems specificly. By using Lyapunov method in access networks and satellite networks, research on the analytical relationships are researched, and optimization algorithms are developed. Main contributions are listed as follows:(1) Research on hybrid Adhoc networks with satellites has been carried out by using cell-partitioned model. First, theorems about analytical expressions of network capacity and upper bound of minimum energy function are proposed and proved. Algorithm aiming at maximizing capacity and minimizing energy cost are presented and analyzed by Lyapunov drift method. Second, these two theorems are applied to several types of Ad Hoc networks. Expressions of network capacity and minimum energy function are obtained. Third, capacity property of a type of hybrid Ad Hoc networks is analyzed in detail. Relationship among limitation of capacity, node density and coverage of base stations are investigated. Numerical analysis and simulation are carried out.(2) Research on degree-limited satellite networks has been carried out. The problem of flow control together with power allocation to antennas on satellite with arbitrary link states has been considered, so as to maximize the utility function while stabilizing the network. Inspired by Lyapunov optimization method, a Degree-Limited Scheduling Algorithm (DLSA) is proposed with a control parameter V, which requires no stochastic knowledge of link state. Discussion about implementation is carried out about the complexity of DLSA and several approximation methods to reduce complexity. Analyze shows DLSA stabilizes the network and the gap between utility function under DLSA and the optimal value is arbitrarily close to zero on the order of O(1/V). Simulation results verify DLSA on a simple network.(3) Research on satellite networks with large propogation has been carried out. A model of satellite networks with propagation delay is given first. Then a Quadratic Lyapunov function based Algorithm specific for satellite networks with propagation delay is proposed to greedily minimizing an expression containing Lyapunov drift. We prove satellite networks with propagation delay under QLA is stable and power constraints are met no matter how large propagation delay is. Theoretical analysis establishes upper bounds of queue backlogs and a lower bound of utility function, and also demonstrates how propagation delay jeopardizes utility performance. Simulation of QLA is carried out in a scenario consists of six nodes, and simulation results are in accordance with theoretical conclusions.(4) The performance of using Lyapunov drift and perturbation in QLAs has been investigated. By analyzing attraction points and utility performance of four variants of OQLA (Original QLA), we examine the rationality of OQLA for using the first-order part of an upper bound of Lyapunov drift of a function L1. It is proved that either using the real Lyapunov function (L2) of networks under QLA or using the entire expression of Lyapunov drift doesn’t improve backlogutility performance. The linear relationship between the attraction point of backlog and perturbation in the queue is found and thus average backlog can be controlled using perturbation. As an example of manipulation of the backlog by perturbation, an algorithm named QLA-VPDQ (QLA with Variable Perturbation of Data Queue) is proposed to serve as a substitution of OQLA when estimating the attraction point in the Phase One of FQLA-G (Fast-QLA-General) consuming less buffer, which is useful for networks with less buffer. Simulations verify the results above.更多还原