【作者】 石璟；

【导师】 仇佩亮； 张朝阳；

【作者基本信息】 浙江大学 ， 通信与信息系统， 2007， 博士

【摘要】 人们对随时随地进行自由通信的渴望促进了无线网络的迅速发展。Adhoc(自组织网)、mesh(网格网)这类基于中继的无线网络的出现令传统无线网络一直存在的可伸缩性低和健壮性差等诸多问题迎刃而解，关于无线中继系统的研究也因此蓬勃发展起来。近几年出现的合作分集(cooperative diversity)技术便是这一发展趋势下的产物，是提高无线信道容量和可靠性的一种有效手段。为了在有限的资源限制下进一步提高传输速率，从链路层对无线资源进行优化分配有着极其重大的现实意义。不同于传统的单跳网络，无线中继系统的资源优化分配必须结合链路多跳特性对资源在各跳之间进行合理配置。考虑到宽带通信中无线信道的频率选择性衰落特性，正交频分复用(OFDM)技术将被未来的通信系统广泛采用。结合了OFDM技术的无线中继系统中的资源优化分配问题变得更加复杂，需要把子载波和功率资源联合地分配给系统中的各跳节点，以求最大限度地提高系统吞吐量。由于这方面的研究并不成熟，本文将OFDM无线中继系统中的资源优化分配作为挑战和努力的方向之一。无线中继系统的多跳传输通过节点之间的相互合作完成，合作策略对系统性能的影响至关重要。合作策略包括合作方式选择与合作伙伴选择，合作方式选择决定了合作条件与合作形式，而合作伙伴选择决定了合作对象。合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的性能、系统整体性能以及所有节点间的公平性。合作策略的恰当与否将直接影响节点的传输速率乃至整个系统的吞吐量，因此意义重大。结合无线中继系统特性提出有效的合作策略是本文的另一个努力方向。本文在无线资源优化分配方面的工作以OFDM无线中继系统为具体研究对象。首先，研究了OFDM再生多跳链路的子载波和功率优化分配问题。针对各态历经信道，为了获得更高的传输效率和可靠性，提出了三种基于贪婪算法的资源优化分配策略，从而通过对无线资源的合理配置提高了链路的遍历信道容量。针对非各态历经信道，为了最大化链路的即时传输速率，提出了两种分别适用于正交频分复用-时分多址接入(OFDM-TDMA)和正交频分复用-频分多址接入(OFDM-FDMA)方式的自适应资源优化分配算法。与固定的资源分配策略相比，这两种自适应算法都能够有效地提高链路的吞吐量。其次，研究了有合作分集的OFDM中继链路的最优功率分配和子载波配对问题。根据功率受限方式以及各节点处的信道状态信息获得情况，将上述问题分成四种类型加以讨论。在子载波配对模式确定的前提下，分别针对这四种类型的问题提出了功率最优分配算法。进一步地，将所提出的功率分配算法与匈牙利算法相结合，提出了一种联合的功率分配与子载波配对方案，该方案能够有效地提高链路的即时信道容量。本文在合作策略方面的工作以一般的无线中继系统为背景展开。首先，研究了基于部分信道状态信息(CSI)的合作中继策略。提出了一种以最小化链路中断概率为目标的选择中继(selection relaying)策略，该策略只需利用节点的地理位置信息，避免了繁琐的信道估计。进一步地，将该策略推广到大规模网络中，提出了一种基于最小-最大(min-max)准则的合作伙伴选择方案，成功实现了最小化网络中所有用户的最大中断概率的优化目标。其次，研究了合作中继策略的博弈论方法。提出了一个由两个用户和一个接入点组成的三节点模型。该模型中每个用户都既是源又是对方的潜在中继，用户地位完全对等。在此基础上，根据合作博弈理论提出了一个基于纳什讨价还价解的合作带宽分配策略。该策略给出了用户之间的合作条件以及合作方式，能够有效地提高用户各自的效用以及系统的总效用。此外，文中针对功率控制和网络实现等问题也进行了一些讨论。更多还原

【Abstract】 The aspiration of communicating anywhere at any time boosts the evolution of wireless network. The relay based wireless networks, such as ad-hoc, mesh, have solved many problems that exist in the traditional wireless networks, e.g. lack of expansibility and robustness, and thus the researches on these systems become flourishing. Cooperative diversity, as an efficient approach of enhancing channel capacity and reliability, is a newborn technique under this prosperity. To further improve the transmission rate, resource optimization at the data link layer is vital. Different from single-hop networks, resource optimization in relay system must take the speciality of multi-hop into account and assign resources suitably among the hops. In view of the frequency selective fading of wireless channel in broadband systems, Orthogonal Frequency Division Multiplexing (OFDM) will be widely adopted in the future communication systems. The problem of resource optimization becomes more complicated in OFDM based wireless relay system where the subcarrier and power resources are required to be jointly allocated to each hop for the maximization of system throughput. Since researches in this area are not mature, we take the problem of resource optimization in OFDM based wireless relay system as a challenge of this dissertation.The transmission of relay system is accomplished by the cooperation among nodes; hence cooperation strategy is crucial to the system performance. Cooperation strategy comprises selection of cooperation mode and cooperative partner; the former one determines the cooperation condition and pattern, and the latter one determines the cooperation object. While designing cooperation strategy, system throughput as well as fairness and performances of nodes are required to be comprehensively considered due to the current application instance. Cooperative strategy is of great significance for its tremendous influence on the link transmission rate and the entire system throughput. Therefore, the other challenge of this dissertation is to propose effective cooperation strategies in wireless relay system.OFDM based wireless relay system is the object of our research on wirelessresource optimization. Firstly, the problem of subcarrier and power allocation in regenerative multi-hop system is studied. In order to heighten transmission rate and reliability, three resource allocation strategies based on greedy algorithm are proposed for ergodic channel, which enhance the link capacity by effectively assigning resources. On non-ergodic channel condition, in order to maximize instantaneous transmission rate, two adaptive resource optimization algorithms are presented for OFDM-TDMA and OFDM-FDMA manners respectively. Both two algorithms improve the link throughput comparing with fixed resource allocation strategy. Secondly, the problems of power allocation and subcarrier pairing are addressed in the relay system with cooperative diversity. The problem is divided into four types according to the power limitation and the channel information knowledge at nodes. Given the subcarrier pairing result, optimal power allocation algorithms are proposed for those four types. Combining Hungary algorithm, a joint power allocation and subcarrier pairing scheme is presented, which boosts the channel capacity effectively.The researches on cooperation strategy in this dissertation is based on general wireless cooperative relay system. Firstly, partial channel state information based cooperation-strategy is studied. A selection relaying strategy which aims at minimizing link outage probability is proposed. Since only the geographical information of nodes are required in the proposed strategy, heavy and complicated channel estimation is avoided. Further, this strategy is extended into large-scale networks, we propose a min-max criteria based partner selection scheme that can successfully achieve the goal of minimizing the maximum outage probability among all the nodes. Secondly, the game theory method of cooperation strategy is studied. A system model constructed by two peer to peer users and one access point is presented, in which each node is source as well as potential relay to the other. Then, a cooperative bandwidth allocation strategy based on Nash bargaining solution is proposed, which effectively increases the utility of user and the entire system.更多还原