【作者】 朱斌；

【导师】 洪佩琳；

【作者基本信息】 中国科学技术大学 ， 通信与信息系统， 2009， 博士

【摘要】 在过去的20年间,宽带无线接入技术得到了迅猛发展,各种无线通信领域的先进手段和方法不断引入,以实现更高的频谱利用率、更丰富的业务接入能力、更好的QoS水平。其中最有代表性的是以IEEE 802.16系列标准为技术基础的宽带无线城域网标准。802.16系列标准的提出是为了满足“最后一公里”宽带无线城域网接入的问题,它不仅集成了Wi-Fi无线接入技术的移动性与灵活性,还拥有DSL与Cable Modem等基于线缆的传统宽带接入技术的高带宽特性和相对理想的服务质量。IEEE 802.16标准为运营商带来可运营、可管理网络的一个重要特点是QoS保证,为此,IEEE 802.16标准在MAC层定义了一套QoS机制,支持不同的服务等级,然而这个QoS机制中并没有规定接纳控制算法和数据调度算法的具体实现方案,所以无法直接应用。IEEE 802.16e标准增加了对移动性的支持,而移动设备通常使用电池供电,为了降低功耗,延长移动设备的电池使用时间,IEEE 802.16e又定义了休眠模式,然而802.16e协议也只是给出了休眠模式相关概念的定义和具体的信令交互机制,没有说明参数如何选择,也没有对休眠模式的性能作出评估。因此,本文将从QoS机制和节能机制这两个方面对IEEE 802.16展开深入研究和探讨。论文主要贡献如下:(1)提出了一种适用于802.16e/WiMAX网络的公平接纳控制算法FCAC分析了已有的802.16e/WiMAX网络接纳控制算法存在的问题——它们单纯依赖于业务的优先级,保证高优先级的业务更容易被接纳,而对于相同优先级的业务则采用先到先分配资源的策略。在实际应用中,这就会产生不公平的现象。针对这个问题,论文提出了一种公平接纳控制算法FCAC。FCAC根据用户已有的业务情况,动态确定该用户新业务接入的门限,并从理论上得到了该门限的最优值。仿真实验显示,FCAC能够提高网络资源在用户之间分配的公平性而不降低网络的吞吐量。(2)对多业务场景下,802.16e的休眠模式的性能进行分析,并提出了一种改进的休眠算法——协作休眠算法COPS在802.16e系统中,如果一个MS上同时运行了实时业务和非实时业务,它就同时需要激活功率节省类I和功率节省类II。论文首先对这种场景下移动站休眠模式的的能量消耗情况进行了理论分析,发现由于这两种功率节省类侦听窗口不同步,移动站的节能效率很低;然后提出了一种多功率节省类的协作休眠方法COPS,通过调整功率节省类I的休眠参数,同步功率节省类I和II的侦听窗口,从而提高节能效率;随后又对COPS的性能进行了理论分析,给出了相关性能参数的闭合表达式。仿真实验验证了本文的理论分析,并显示COPS不仅提高了节能效率还降低了MAC帧的反应时间。(3)从网络竞争的角度出发,针对多用户实时业务场景提出一种增强的休眠算法分析了802.16e系统中多用户实时业务的情况下侦听窗口的分布对网络中MS平均节能效果的影响,然后提出了一个简单实用的改进休眠算法EPSM。该算法通过调整新加入的MS休眠模式的启动时间,在使得不同连接的侦听窗口尽量分散的同时,又兼顾系统负载在OFDM帧上的均匀分布,从而提高网络中MS的平均节能效果。EPSM没有改变802.16e标准休眠算法的操作流程,算法的实施也不需要MS的参与,因此具有很好的兼容性和扩展性。实验仿真验证了EPSM的节能效果,同时我们还发现EPSM还能够降低系统的整体信令开销,提高系统的QoS。(4)分析休眠模式和数据调度的关系,提出一种节能的数据调度算法从平滑BS调度器的输入和改进实时业务的调度策略这两个方面入手,提出一种节能的数据调度算法EESM。EESM一方面通过调整新加入的MS休眠模式的启动时间,降低了休眠的MS之间数据调度的竞争;另一方面对目前广泛使用的实时业务调度算法EDF进行了改进,在决定数据分组的调度期限时考虑了休眠窗口的影响,提高了处在休眠状态的MS的数据调度优先级,以降低休眠的MS因数据调度而退出休眠模式的概率。仿真实验表明,EESM在保证系统QoS的同时,不仅能够较大的提高了网络的平均节能效率,还降低了系统的整体信令开销。更多还原

【Abstract】 In the past 20 years, broadband wireless access technologies have being developed rapidly. Various advanced tools and methods in the wireless communication field were introduced to it in order to get higher spectrum efficiency and to support more kinds of services as well as to achieve better QoS. The typical broadband wireless access technology is the IEEE 802.16 standards which are proposed for the need of the last mile broadband wireless access. It not only integrates the mobility and flexibility of Wi-Fi, but also possesses high bandwidth features and relatively better QoS as the traditional wire broadband access technologies such as DSL and Cable Modem.One of the important features of IEEE 802.16 standards is the QoS grantee, which can make the network operate-able and manageable. So the IEEE 802.16 standards define a QoS mechanism that can supports different service level in its MAC. But it can’t be put into practice directly because it does not indicate a complete solution for access control and packet scheduling. The 802.16e standard becomes to support mobile stations which are usually powered by battery. So the 802.16e standard defines sleep mode to save the mobile station’s energy. But it neither indicates how to choose the parameters of the sleep mode nor evaluates the performance of the sleep mode. Therefore, this dissertation presents deeply studies from two aspects: the QoS mechanism and energy-saving mechanism. The main contributions of this dissertation are as follows:(1) Proposed a fair connection access control scheme for 802.16/WiMAX networkThe IEEE 802.16e standard provides Quality of Service (QoS) guarantees for users based on the conception of connection-oriented service. However, fairness has not been considered in existing connection admission control solutions, which is very important for user experience. This dissertation proposes a fair connection admission control scheme (FCAC) to improve the system’s fairness on bandwidth allocation to users by setting a dynamic admitting threshold. Simulation results show that FCAC can improve service fairness for users without degrading the performance of the system.(2) Theoretically analyzed the performance of the sleep mode under the scenario the mobile station has both real-time service and non-real-time service, then proposed a Cooperative Power Saving MechanismWhen a mobile station with real-time and non-real-time services enters sleep mode, both Power Saving Class of type I and Power Saving Class of type II are activated. In this dissertation, we theoretically analyze the performance of the sleep mode, and find that due to the asynchrony of the listening windows the efficiency of power saving is very poor. Then we propose a COoperative Power Saving Mechanism (COPS) to resolve this problem. The basic idea behind COPS is to synchronize the listening windows of different power saving classes cooperatively. Furthermore, we analyze the performance of COPS in the multi-service environment and give closed-form expressions of performance metrics. Simulation results validate our analysis and show that COPS not only improves the energy efficiency but also reduces the average frame response time.(3) Proposed an enhanced power saving mechanism for multiple users with real-time services in 802.16eIn the 802.16e system, when multiple Mobile Stations (MSs) with real-time services enter sleep mode, the efficiency of power saving is impacted by the competition of the data scheduling in the overlapping listening windows. This dissertation analyzes the impaction and proposes an enhanced power saving mechanism. The proposed mechanism tries to make the listening windows of different MSs lie dispersedly and balance the system load among OFDM frames by adjusting the start time of sleep mode of the new connection. The simulation result shows the proposed mechanism not only improves the energy efficiency but also decreases the signaling overhead as well as improves the OoS of the network.(4) Analyzed the relation between sleep mode and data scheduling, then proposed an energy efficient scheduling schemeWhen multiple mobile stations (MSs) with real-time services are in sleep mode, the scheduling result of the Base Station (BS) not only determines the QoS of the services, but also impacts the average energy efficiency of the network. This dissertation focuses on this problem and proposes an energy efficient scheduling mechanism. The proposed mechanism first tries to smooth the input of the scheduler by making the listening windows of different MSs lie dispersedly and balancing the system load among OFDM frames. Then it improves the widly used EDF mechanism and promotes the packets’priority of the sleeping MSs. The simulation result shows the proposed mechanism not only improves the energy efficiency but also decreases the signaling overhead as well as grantees the OoS of the network.更多还原