【作者】 岳东涛；

【导师】 李恒超；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2011， 硕士

【摘要】 如何最大限度地在宽带无线接入系统中为不同要求的服务提供QoS保证是一个非常重要的问题。MAC层的带宽调度是实现QoS保障的关键,使用一种高效的带宽调度算法对保障MAC层的QoS十分重要。虽然IEEE802.16 MAC层协议提出要对各种不同的业务提供QoS保证,但并没有对如何调度来达到QoS要求进行标准化,这样不同设备商的产品的QoS性能就会因机制不同而有较大的差别。本文首先分析了802.16技术标准及其协议栈,接着对MAC层协议进行了深入学习,然后在学习MAC协议的基础上详细介绍了QoS调度服务类型。之后本文介绍了几种常用调度类型并仔细分析了一种不同服务类型间的带宽调度算法,该算法牺牲nrtPS时延及吞吐量性能来满足rtPS业务的时延要求。受该算法启发,本文提出了一种牺牲其他低优先级业务的QoS性能来满足高优先级业务的时延性能要求的算法,这种算法可以在一些对特定业务性能要求较高的场合下得到应用。本文算法通过牺牲nrtPS及BE类型业务的时延及吞吐量来提高ertPS类服务流的时延性能,并设置门限值以保证nrtPS及BE类型业务的最低QoS需求。在IEEE 802.16e的机制中,当带宽不足以让各个SS使用单播轮询的方式发送带宽请求时,BS会让SS使用多播轮询和广播轮询的方式竞争传输带宽请求的时隙。为了降低冲突产生的时延迟,提出一种让ertPS的服务流利用免竞争期取得带宽请求传输的时隙的方法。该方法将原竞争期分为两部分：一部分为免竞争期用于传输ertPS带宽请求,另一部分与原竞争期相同但竞争周期时间被减少,该竞争期用竞争的方式传输其他的带宽请求消息。该方法最终达到为ertPS类型服务流减少延迟、增加吞吐量的目标。本文使用OPNET进行仿真,仿真结果表明,在BE客户端逐渐增加的情况下,可以看到增强的实时轮询服务的相比原机制有更好的延迟性能和吞吐量性能。更多还原

【Abstract】 How to provide QoS guarantees for various traffic with different QoS requirements in fixed BWA system is a very important problem. With bandwidth scheduling in MAC layer being the key parts to guarantee QoS, it is very important to use an high efficiency MAC bandwidth scheduling algorithm. Although IEEE 802.16 MAC protocols have been proposed to support QoS guarantees for various kinds of applications, they do not suggest how to schedule traffic to fulfill QoS requirements. So the QoS performance of different vendors’ equipment will be disparate owing to different QoS mechanism.Technology standard and protocol stack of 802.16 is analyzed first in this paper, and then the MAC protocol is deeply studied, following that five service classes of QoS are also introduced in detail. After analyzing several traditional scheduling types, a bandwidth scheduling algorithm between different type of services is analyzed in detail. In order to meet the delay requirements of rtPS services, delay and throughput of nrtPS are sacrificed in this algorithm. Inspired by this algorithm, a scheme is proposed in this paper:the high-priority business requirements of delay performance can be improved at the expense of the QoS performance of other service whose priority is low, which can be used in some occasions that have high requirements of a certain type of service. To improve the delay performance of the ertPS service, delay and throughput of nrtPS and BE service will be sacrificed. Threshold is set to ensure the minimum QoS requirements of nrtPS and BE being guaranteed.In the scheme of 802.16e, when bandwidth is not sufficient to allow each SS using unicast polling to get bandwidth, BS will form a group of stations that utilize multicast polling and broadcast polling to contend the slots of transmitting bandwidth request. In order to decrease the delay caused by collisions, a scheme was proposed that could utilize contention free period (CFP) to get slots for bandwidth request of ertPS. The original contention period was devided into two sections:one is CFP, transmiting bandwidth requests for ertPS, the other is the same as the original contention period but shortened which was utilized to transmit other bandwidth requests. The aim of decreasing average delay and increasing average throughput is eventually attained. The simulation results in OPNET show that our method achieves lower delay time and better performance of ertPS flows due to the increasing number of BE stations.更多还原