【作者】 贾会玲；

【导师】 李式巨； 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】 当第三代移动通信(3G)技术在全球范围内曲折前进的时候，终端制造商和网络运营商已经开始着手研究第四代移动通信系统(4G)的关键技术。在目前已经提出的几种主流4G解决方案中，最受推崇的是多系统融合演进的发展路线。业界和学术界人士普遍认为，下一代无线通信系统应该是一个能够将现有的和未来将要出现的各种无线接入系统有机地融合在一起的开放式的异构无线网络。本论文以异构无线网络为背景，在协同无线资源管理思想的指导下，研究了异构无线网络中的接入选择和准入控制问题。本论文在以下的四个方面展开了深入的研究，概括如下：为了综合利用异构无线网络中的集群增益和多接入分集增益，本文研究了异构无线网络中的集中式接入选择问题，并将该问题建模成一个以最小化网络总带宽占用为目标的整数线性规划问题，提出了两种低复杂度的次优求解算法。与利用枚举法寻找最优解的方式相比，这两种次优算法大大降低了求解过程的计算复杂度。而与没有利用多接入分集增益的载荷平衡算法相比，这两种次优算法以略微增加计算复杂度为代价，有效地提高了异构无线网络的资源利用率和网络容量，明显降低了接入选择过程中的中断概率。为了保证多模终端在整个通信过程中保持永远最佳连接(Always Best Connected)，本文研究了异构无线网络中的分布式接入选择问题。针对能够同时支持多个活跃应用的多应用终端提出了一种基于终端电池状态的自适应接入选择算法。利用该算法，用户可以根据终端电池中剩余电量的变化来动态调整代价函数中各种策略参数的权重因子，并根据自身需求的动态变化来对终端中不同应用的接入选择行为进行协调，从而在用户的带宽需求满意度与终端电池的生存周期之间取得了灵活的折衷。而且，为了减小分布式接入选择中的切换同步效应对网络性能和用户的服务质量(QoS)所造成的影响，本文提出了一种自适应的切换时刻决策算法。与现有的切换时刻决策算法相比，该算法明显提高了切换稳定期对于系统状态变化的敏感度，有效地减少了不必要的垂直切换。为了对异构无线网络的各组成系统中原有的准入控制策略进行协调，从而向进行系统间漫游的多模终端提供无缝QoS保证，本文研究了分布式接入选择条件下的准入控制问题。针对一个由蜂窝无线系统和无线局域网所组成的异构无线网络提出了一种面向无缝QoS的准入控制策略，将准入控制问题建模成为一个以最小化整个网络的服务等级(GoS)为目标的带有QoS公平因子约束的优化问题，从而能够针对不同的业务载荷条件来为异构无线网络配置最佳数量的保护信道和平衡信道，在充分利用各系统中的无线资源的同时为多模终端提供了无缝QoS保证。本文研究了将异构无线网络中的分布式接入选择与准入控制相结合的问题。针对由基于码分多址接入(CDMA)和正交频分多址接入(OFDMA)技术的两种软容量系统所构成的异构无线网络，研究了在多模终端中利用系统广播信息中的资源分配信息来进行系统载荷估计的问题，提出了一种CDMA系统中的接收功率估计算法和一种OFDMA系统中的发送功率估计算法。基于系统载荷估计的结果，提出了一种基于功率门限的分布式准入预测机制和一种基于终端发送功率的分布式接入选择算法，从而能够利用分布式的准入预测来协助终端作出明智的接入选择决策，在满足用户业务需求的同时高效地利用了异构无线网络中的无线资源。更多还原

【Abstract】 As the technology of the third generation mobile communication (3G) slowly marches forward, device manufacturers and network operators have already started to do research on the key technologies of the fourth generation mobile communication system (4G). Among all the proposed mainstream resolving scenarios, the idea of multi-system integration and evolution is the most promising one. It is well accepted by both the industrial circles and the academic circles that 4G should be an open network environment-heterogeneous wireless networks (HWN), which can intelligently integrate the existing and the future radio access systems. In this dissertation, under the guidance of the coordinated radio resource management theory, the problems of access selection and call admission control in HWN are intensively studied. The contents of this work are listed as follows:In order to make full use of the trunking gain and the multi-radio access diversity gain in the HWN, the problem of centralized access selection is studied, which is modelled as an integer linear programming problem optimized to minimize the overall bandwidth occupation in the HWN. Two suboptimal solution algorithms are proposed, which greatly reduce the computational complexity of the optimal algorithm, i.e., the enumeration method. In comparison with the traditional load balancing algorithm, those two algorithms effectively enhance the network capacity and reduce the outage probability during access selection, at the cost of a slight increase in computational complexity.In order to keep the multi-mode mobile terminal (MT) always best connected (ABC) in the HWN, the problem of distributed access selection is studied in the second part. First, an adaptive battery-situation-aware access selection scheme is proposed for MTs with multiple active applications. In the proposed scheme, the weight factors in the cost function are dynamically adjusted according to the available battery energy, and the access selection behaviors of the different applications are adaptively coordinated according to the changing service requirement. As a result, a flexible tradeoff is realized between the satisfaction degree of bandwidth requirement and the battery lifetime. Then, an adaptive handoff time decision scheme is proposed to avoid the handoff synchronization effect, which greatly enhances the sensitivity of the handoff stability periodand reduces the unnecessary vertical handoffs.Call admission control (CAC) in the HWN is studied in the third part, aiming to coordinate the existing CAC schemes in the access systems, and provide seamless quality of service (QoS) to the inter-system roaming MTs. A seamless-QoS-oriented CAC scheme is proposed for an integrated cellular/WLAN network, in which the CAC problem is modelled as an optimization problem aiming to minimize the overall grade of service (GoS). Accordingly, the optimum numbers of guard channels and balance channels are determined under different traffic loads, which guarantees full use of the radio resource and seamless QoS at the same time.Integration of access selection and call admission control in a HWN made up of two soft capacity systems (based on the technologies of CDMA (Code Division Multiple Access) and OFDMA (Orthogonal Frequency Division Multiple Access) respectively) is studied in the fourth part. First, a receive power estimation algorithm and a transmit power estimation algorithm are proposed for the CDMA system and the OFDMA system respectively, in order to estimate the traffic load in these access systems dis-tributedly. Accordingly, a power threshold based call admission prediction algorithm and a transmit power based access selection algorithm are proposed. With the aid of distributed system load estimation, wise access selection decision is made in the MT, achieving a great improvement in resource utilization.更多还原