【作者】 刘宴兵；

【导师】 孙世新；

【作者基本信息】 电子科技大学 ， 计算机应用技术， 2007， 博士

【摘要】 作为个人计算机网络通信的一个重要的组成部分,无线网络已经掀起了移动计算的新浪潮,在现实及未来的社会生活中将得到广泛的应用。无线网络接入算法及其QoS性能定量分析是计算机网络和通信系统研究与应用的重要理论基础和支撑技术,也是近年国内外研究的热点之一。无线网络技术发展的历史,就是一个创新的过程。随着宽带无线接入网以及第3代移动通信网络(3G)技术的推进,无线网络接入协议、相关算法的理论基础以及理论依据需要进一步地研究、改进和完善。无线接入网的服务质量的研究还处于开始阶段,最新标准中尚未提出可行、可靠的解决方案。另外对无线接入网服务质量性能的定量分析也是一个新的研究课题。本论文主要对无线网络接入相关的退避算法、信道分配算法、AP负载均衡算法、控制策略接入算法及GPRS分组呼叫接入控制算法及QoS性能进行系统分析和系统研究。论文的主要研究工作包括以下5个方面:1.基于IEEE 802.11 DCF提出一种p′概率退避算法P PBA,并对算法进行性能定量分析。P PBA算法根据网络负载信息来动态地修改竞争窗口值,有效降低碰撞概率,改进完善了IEEE 802.11标准CSMA/CA协议。仿真结果表明P PBA算法在保持高吞吐量的同时维持较小接入时延,提高了网络性能。2.针对信道的不可靠性和用户的移动性,评估当前使用信道的性能,采用信道“借用”分配技术,提出基于IEEE 802.11 MAC协议的支持实时业务的信道分配算法和队列缓存计算方法,并建模对新算法进行QoS性能分析。与IEEE 802.11标准协议进行实验对比,该算法性能更稳定、高效。3.提出在新终端接入过程中综合考虑信号强度和APs的负载信息的负载均衡新算法。算法中借助邻居图,APs通过分布式系统交互信息,降低终端接入延迟。仿真实验结果表明,本论文提出的算法由于同时考虑信号强度和AP的负载,无线网络接入的整体性能比标准传统方法高。4.以G/M/c/∞排队系统为理论基础建立新的系统模型,结合虚拟AP技术综合考虑网络服务提供者的收益和用户的业务优先级,提出一种基于马尔可夫决策的接入控制OPMAC算法,可作为IEEE 802.11e标准协议的补充。通过示例定量计算、分析,验证了模型正确性。仿真实验对比表明,算法可以有效地为不同要求的业务提供不同的服务质量。5.在GPRS信道呼叫接入机制和信道建模的基础上,提出基于ON/OFF状态的吞吐量计算、带宽分配系统分析模型和新的呼叫接入控制算法。给出马尔可夫接入过程的解析分析和Qos定量计算,得到与实际吻合的、具有实践指导意义的理论解析式。计算和实验表明:解析数值结果与仿真结果基本一致。更多还原

【Abstract】 Wireless network as an important part of personal computer communication has been expanding a new wave in the field of mobile computing. It would be applied widely into our social life in the future. As a research hotspot at present, access algorithm in wireless network and its quantitative performance analysis are regarded as significant theoretical fundamentals and supporting technology of studies and application in computer network and communication system.The development of wireless network is supposed to be an innovation process. With the advancement of broadband wireless access network and the third generation mobile communication, theoretical basis of access protocol and correlative algorithm in wireless network should be studied and improved further. However, the investigation to quality of service (QoS) in wireless access network just lies in start stage. Meanwhile a feasible and reliable solution has not been proposed in standard protocol. Additionally, the quantitative analysis of QoS is a new challenge in wireless access network.The paper mainly conducts quantitative analysis of and systemic research on Backoff algorithm, channel allocation algorithm, AP load balancing algorithm, access control algorithm and GPRS access algorithm in wireless access network.The main works of the paper include the following five parts:In the first part, a novel p’ -Persistent Backoff Algorithm (P_PBA) based on IEEE 802.11 DCF is proposed and quantitative analysis has been carried out. The P_PBA algorithm can adjusts contention window size dynamically according to network load in order to decrease collision probability effectively and perfects CSMA/CA protocol in IEEE 802.11. The simulation results indicate P_PBA, while decreasing the frame delay, can offer a higher throughput, thus enhancing network performance significantly.In the second part, we evaluate the performance of occupied channel and employ "borrow" allocation technology based on channel unreliability and user mobility. Further channel allocation algorithm supporting real-time traffic and computation measure for queue buffer is proposed respectively, and a corresponding model is put forward for QoS quantitative analysis. The simulation results demonstrate that the improved channel allocation strategy performs more effectively performance and stabilization than the standard access algorithm in IEEE 802.11.In the third part, we propose an efficient load balancing method concerning both signal strength and each AP’s current load on the basis neighbor graph. And each AP interacts with distributed system to decrease access delay. The simulation results indicate that the whole access performance in wireless network proves to be more efficient than it in traditional method when taking account for signal strength and AP current load synthetically.In the fourth part, a systemic model is created based on of G/M/c/∞queue system, which is regarded as a theoretical basis of optimal strategy. In the discussion of the benefit of service provider and the traffic priority of access user in wireless network, a novel strategy control model and access control algorithm OPMAC based on Markov process are proposed as a supplement to IEEE 802.11e standard protocol combining with virtual AP technology. Then correctness of the model is validated by quantitative computing and theoretical analysis. Finally, the comparison of some simulation experiments proved that the new algorithm can effectively provide different QoS to traffics with diverse requirements.The fifth part studies call admission in GPRS and channel modeling, and further puts forward an analytical model for throughput Computation and bandwidth allocation and a novel GPRS access algorithm based on ON/OFF state in mobile wireless network. Moreover, we accomplish QoS quantitative analysis and computation of Markov process. Eventually, some analysis formulas are obtained, which are of significant value both theoretically and practically. Computations and experiments indicate that the numerical results from analysis formula are consistent with our simulations.更多还原