【作者】 李秀媛；

【导师】 吴晓娟；

【作者基本信息】 山东大学 ， 通信与信息系统， 2010， 博士

【摘要】 IEEE 802.16协议定义的宽带无线接入系统(BWA, Broadband Wireless Access System)具有组网安装维护方便,运营价格低廉,面向连接且保证服务质量的特点,正在成为未来网络接入技术的主导方向。本文对IEEE 802.16 BWA系统基于竞争的带宽资源分配机制及冲突解决机制、带宽申请的许可机制进行了分析研究,提出一些新的算法,具体工作如下：1、IEEE 802.16的子站SS向基站BS发送数据前需申请带宽,申请的方式有预留方式和竞争方式。当SS采用竞争方式共用竞争时隙发送带宽申请时,冲突将不可避免。IEEE 802.16协议并未指出具体的分配机制。相关的带宽分配算法大多假设BS能监测到要发送带宽请求SS的数量,然而实际中很难实现。本文提出一种在竞争的轮询机制中,自适应分组的组播带宽分配算法。首次提出在带宽分配机制中,引入网络流量分析方法和自适应分组算法。首先对网络流量的自相似、长相关、突发性进行分析,并结合不同类型业务流的特性参数,构成线性半参数回归模型,计算下一个传输周期中所有不活跃SS发送带宽申请的概率。然后以此概率为依据,把不同概率的SS自适应分组,分组之间采用虚拟令牌环技术。仿真结果表明,该算法能有效减少竞争冲突发生,同时避免浪费大量空闲时隙。2、完整的冲突解决机制,不仅包括冲突前的资源分配机制,还包括冲突后的解决方法。标准定义的冲突的解决方法是截短的二进制指数后退算法,通过扩大重传后退时间窗(或称：退避时间窗)的大小,降低冲突发生。由于二进制指数后退算法的后退窗口会随着冲突次数的增加而迅速增大,在申请带宽SS数量较小时,会造成部分竞争时隙浪费。已有的改进算法大多是动态更新后退时间窗口方式,如乘法增加线性减少算法(MILD),快速冲突解决算法(FCR)等。因为不同业务流的容许延迟不同,而且多次冲突的SS应授予较高竞争优先级,以满足公平性要求。因此本文提出一种融合优先级和公平性的更新后退时间窗的冲突解决算法。该算法提出SS根据冲突次数和申请带宽相应连接的优先级,采用模糊控制方式定义下一周期带宽申请的后退时间窗的大小和起始窗口值,以提高优先级较高业务的服务质量,并保证子站申请带宽的公平性。仿真结果表明算法对系统性能有一定提高。3、IEEE 802.16并未定义基站BS侧和子站SS侧的带宽许可机制(或称调度机制),以保证不同类型业务的服务质量,然而这些调度方式对网络性能有着重要影响。BS的调度要根据请求信息给SS分配带宽,应考虑不同SS的服务质量(QoS)需求和公平性问题；SS的调度要为不同业务流分配由BS授权的带宽。关于调度算法的研究较为充分,考虑到传输信道的信噪比直接影响SS物理层的调制方式和MAC层传输分组大小,本文提出一种跨层调度算法。该算法采用Nakagami缓慢变化的时变信道模型, BS根据信道信噪比(SNR)决定某一时刻允许接入带宽资源的总量,并为每个活跃的SS分配带宽；SS根据SNR决定自适应编码调制方式,并根据自身不同业务流的服务质量要求,二次分配BS为其分配的带宽。仿真结果表明,算法在时变信道,对不同业务流能满足服务质量的要求。本文的创新点包括：1、提出一种组播轮询机制中,针对网络中不活跃站点突发数据的概率估算方法。通过对网络流量特性分析,根据自相似性计算线性相关参数,根据不同业务流的流量特征确定非线性相关参数,采用线性半参数回归模型估算不活跃SS下一个传输周期的突发带宽申请概率。2、提出一种在竞争的组播轮询机制中自适应的带宽分配算法。以不活跃站点的突发带宽请求概率为依据,把SS自适应分配到不同的分组,分组间采用虚拟令牌环技术轮询。该算法能有效减少竞争冲突发生,同时避免浪费大量空闲时隙。3、提出一种融合优先级和公平性的更新后退时间窗的冲突解决算法。该算法提出SS根据冲突次数和申请带宽相应连接的优先级,采用模糊控制方式定义下一周期带宽申请的后退时间窗的大小和起始窗口值,提高优先级较高业务的服务质量,保证子站申请带宽的公平性。4、提出一种BS和SS侧的跨层调度算法。采用Nakagami缓慢变化的时变信道模型,BS根据信道信噪比(SNR)允许接入带宽资源的总量；SS根据SNR决定自适应编码调制方式,并根据自身不同业务流的服务质量要求,二次分配BS为其分配的带宽。该算法能在时变信道满足不同业务流的服务质量要求。更多还原

【Abstract】 The IEEE 802.16 BWA (Broadband Wireless Access) system has many advantages, such as easy installation and maintenance, inexpensive operation, connection-oriented service and quality of service guarantee. It is becoming the dominant network access technology in the future.In this thesis, analytic and researching contributions to bandwidth allocation, collision resolution, and bandwidth admission control are shown for the IEEE 802.16 BWA system.The details are as follows.1. According to the IEEE 802.16 standard, substations (SSs) should reserve the required bandwidth before transmitting data packets to the base station (BS). When the SSs share the transmission opportunities to transmit requests, the collision will be inevitable. IEEE 802.16 protocol does not point out the operational mechanism. Most bandwidth allocation algorithms suppose that BS can estimate the number of active SSs,which is not easy in real wireless network. This paper presents a multicast polling mechanism based on the adaptive grouping algorithm. This mechanism brings network traffic analysis and adaptive grouping algorithm in the multicast polling. Firstly, the traffic characteristics such as self-similar, long relative,burst character are analyzed in this mechanism. Secondly, a linear semi-parametric regression model is constituted to evaluate the requesting probability of the non-active SSs.Then the adaptive grouping algorithm based on the virtual Token Ring technology is proposed that operates with the evaluated requesting probability. Simulation results indicate that this polling algorithm can effectively decrease the number of the idle slots and collision slots. 2. A completed contention resolution mechanism includes a pre-contention resource allocation and post-contention collision resolution. The mandatory method of contention resolution that shall be supported by the 802.16 standard is based on a truncated binary exponential backoff algorithm, with the initial backoff window and the maximum backoff window controlled by the BS. With the number of conflicts increasing, the backoff window size is growing rapidly in the algorithm. At the same time, the number of SSs which transmit the bandwidth request relatively keeps the normal level, and there will cause a lot of waste competitive slots. Most algorithm promotion is focus on tuning bandwidth size, for example,MILD algorithm and FCR algorithm. Because of fairness, different types of service flows have an optimal allocation on allowed delay, and retransmitted times of SSs. This article presents a hybrid backoff algorithm which considers both the priorities and fairness. The type of service flow determines the priority and the more times of retransmission hav the higher priority because of fairness. The maximum backoff window and the initial backoff window is controlled based on the fuzzy control method in the next competitive cycle for bandwidth in order to improve high-priority services’ quality and ensure fairness between different SS.3. IEEE 802.16 protocol does not define the scheduling methods to guarantee the quality of different services in the BS and SSs.Because that channel quality has a great influence on the modulation and coding scheme in the PHY layer and the transmitting packet size in the MAC layer, a cross-layer scheduling algorithm is proposed in this thesis for the slow time-varying channel in the BWA system. The algorithm adopts the Nakagami channel model. The BS estimates the total allowed bandwidth resources and allocates bandwidth for each active SS according to the signal to noise (SNR) of the channel; SSs again allocate the authored bandwidth according to the QoS of different connections and the adaptive coded modulation and coding methods (AMC) according to SNR.The innovations of this paper include as follows.1. This thesis presents an evaluated algorithm of the bandwidth request of non-active SSs. Firstly, the characteristics such as self-similar, long relative, burst character are analyzed in this mechanism.Secondly, a linear Semi-parametric regression model is constituted to evaluate the requesting probability of non-active SSs based on the evaluated probability and characteristics of service flows.2. This thesis presents a multicast polling mechanism based on the adaptive grouping algorithm.The adaptive grouping algorithm based on the virtual Token Ring technology is proposed that operates with the evaluated requesting probability. Simulation results indicate that this polling algorithm can effectively decrease the number of the idle slots and collision slots.3. This thesis presents a hybrid backoff algorithm which considers about the priorities and fairness.The type of service flow determines the priority and the more times of retransmission are granted the higher priority of an SS because of fairness.In the next competitive cycle, the maximum backoff window and the initial backoff window are controlled based on the fuzzy control method in order to improve high-priority services’quality and ensure fairness between different SS.4.This thesis presents a cross-layer scheduling algorithm for the slow time-varying channel in the BWA system. The algorithm adopts the Nakagami channel model. The BS estimates the total allowed bandwidth resources and allocates bandwidth for each active SS according to the channel signal to noise ratio (SNR); SSs again allocate the authored bandwidth according to the QoS of different connections and the adaptive coded modulation and coding methods (AMC) according to SNR.更多还原