【作者】 何晴；

【导师】 陈光；

【作者基本信息】 东华大学 ， 通信与信息系统， 2011， 硕士

【摘要】 随着无线移动通信技术的迅猛发展,移动通信给人们的生产、生活方式带来了深刻的变革。现有的无线网络技术,如Wi-Fi、WiMAX、TD-SCDMA、Ad Hoc等,都有各自的特点和适用的环境,任何一种网络都不能独立支持所有业务发展的需要。在未来,网络的发展必然是互补共存,而不是简单的取代,只有融合各种技术优势才能提供更好更全面的服务。WiMAX是一种宽带无线接入技术,其数据传输速率要高于TD-SCDMA所能提供的速率,基站信号覆盖范围也更广,但WiMAX的缺陷在于移动性受到限制。TD-SCDMA继承了蜂窝网络连续覆盖的能力,能实现无缝漫游要求,支持高速移动,这正是WiMAX所欠缺的。可以说,WiMAX主要提供中低速移动性下的高速率数据业务,而TD-SCDMA主要提供高速移动性下的中低速率语音和数据业务。考虑到WiMAX和TD-SCDMA的互补性,这两种网络的融合将会为用户提供高质量的、多样化的、无处不在的服务。目前,对同构网络的研究比较成熟。对异构网络的研究虽然在近年来慢慢受到越来越多的关注,但是由于WiMAX和TD-SCDMA这两种技术都是新兴起的技术,国内外对两者融合问题的研究还很少、而且现有的研究也尚处于初级阶段,因此对其进行深入的研究是十分重要和极有意义的。本文主要对WiMAX/TD-SCDMA异构网络融合及其切换机制进行了研究。对于WiMAX/TD-SCDMA异构网络的融合,文中首先研究了WiMAX技术和TD-SCDMA技术,并比较了两种技术的特点；接着分析了WiMAX与TD-SCDMA融合的可行性,并提出WiMAX与TD-SCDMA网络融合方案,其中包括了紧耦合和松耦合两种方案。对于WiMAX/TD-SCDMA异构网络的切换机制,文中着重进行了垂直切换判决算法和垂直切换执行算法的研究。本文将切换分成两类：移动节点驱动的切换和基站驱动的切换。针对移动节点驱动的切换,提出了基于模糊控制预判决辅助的WiMAX/TD-SCDMA垂直切换判决算法。与一般的垂直切换判决算法不同,本算法采用了预判决辅助机制,能有效地节省系统开销、提高切换判决效率。而且本算法基于多指标判决模糊控制,一方面能够较为全面地考虑到切换判决的因素；另一方面简化了对切换判决指标的处理,避免建立精确的数学模型,有利于增强算法的适应能力。仿真结果表明,该算法能做出及时准确的切换判决,有效抑制乒乓效应,减少不必要的切换。针对基站驱动的切换,提出了基于代价函数的WiMAX/TD-SCDMA垂直切换判决算法。在该算法中,给出用于计算移动节点切换代价的代价函数,选择切换代价值低的移动节点进行切换,以缓解当前接入网络的重负载,达到平衡整个网络系统负载、最大化网络资源利用率和最小化呼叫阻塞率及呼叫掉线率的目的。鉴于垂直切换执行过程对于垂直切换的性能至关重要,本文提出了基于MIHF的快速层次移动IPv6垂直切换执行算法,同时给出了在WiMAX/TD-SCDMA异构网络下的垂直切换执行过程。该算法的特点在于引入了媒介独立切换功能(MIHF),并且结合了层次型移动IPv6 (HMIPv6)和快速移动IPv6 (FMIPv6)各自的优点,使得该算法相比于MIPv6、HMIPv6和FMIPv6更具优势。仿真结果表明,该算法能明显改善垂直切换的性能,切换延时小、信令开销少、数据丢包率低。更多还原

【Abstract】 With the rapid development of wireless communication technologies, mobile communications have changed people’s life deeply. The existing wireless technologies, such as Wi-Fi, WiMAX, TD-SCDMA and Ad Hoc, have their respective advantages, but any of them cannot support all kinds of services independently. Next generation wireless communication systems are expected to relay on integrated networks consisting of multiple wireless technologies to offer high quality of services to mobile users.WiMAX is a kind of broad band wireless access technology, whose data rate is much faster than that of TD-SCDMA and whose coverage of a base station (BS) is also larger. However, the weakness of WiMAX is its mobility limitation. TD-SCDMA supports seamless access and higher mobility. Given the complementary characteristics of WiMAX (faster data rate, lower-cost, hotspot access, only support lower mobility) and TD-SCDMA (slower data rate, higher-cost, seamless access, support higher mobility), it is significant to combine them to provide multiple services and ubiquitous access for the users.At present, researches on homogeneous networks are relatively mature. In recent years, researches on heterogeneous networks have been gradually developing, but researches on heterogeneous wireless networks based on WiMAX and TD-SCDMA are still rare and immature at home and abroad because both WiMAX and TD-SCDMA are new emerging technologies. Therefore, studies on WiMAX and TD-SCDMA heterogeneous wireless networks are necessary and meaningful.In this paper, we have deeply studied network integration and handoff mechanism based on WiMAX and TD-SCDMA. By comparing the respective characteristics of the two technologies, the feasibility of integration between WiMAX and TD-SCDMA was analyzed and their network integration schemes were proposed in this paper. The schemes were including tightly-coupled scheme and loosely-coupled scheme.For the studies on handoff mechanism of WiMAX and TD-SCDMA, we have laid emphasis on vertical handoff decision algorithm and vertical handoff execution algorithm. In this paper, handoffs were divided into two classes:handoffs initiated by MNs and handoffs initiated by BSs. For the handoffs initiated by MNs, a novel vertical handoff decision algorithm based on fuzzy control in aid of pre-decision method was proposed. Different with the ordinary vertical handoff decision algorithms, this algorithm used pre-decision method which could save system overhead and raise the efficiency of handoff decisions. In addition, fuzzy control was introduced into this algorithm which helped simplify the process on handoff decision criteria and enhanced the adaptability of the algorithm. The simulation results showed that the proposed algorithm could make accurate handoff decisions, reduce unnecessary handoffs and eliminate the ping-pong effect. For the handoffs initiated by BSs, a cost function based vertical handoff decision algorithm was proposed to select the MNs with lower cost values. Then the selected MNs were handed over to relieve heavy load of the current network and decrease the probability of call blocking and dropping. The proposed algorithm took the entire network performance into consideration and balanced the overall load which was more thoughtful than the existing vertical handoff decision algorithms. Vertical handoff execution is critical to the performance of vertical handoffs. In this paper, MIHF based FHMIPv6 vertical handoff execution algorithm was proposed and the WiMAX/TD-SCDMA vertical handoff execution processes were presented. The proposed algorithm introduced MIHF and combined the advantages of HMIPv6 and FMIPv6, which made this algorithm more effective than MIPv6, HMIPv6 and FMIPv6. The simulation results showed that the proposed algorithm could obviously improve the performance of vertical handoffs with lower handoff latency, smaller signal overhead and lower packet loss.更多还原