【作者】 单文浩；

【导师】 范平志；

【作者基本信息】 西南交通大学 ， 交通信息工程及控制， 2002， 博士

【摘要】 移动通信业务的飞速发展，使得频谱资源和用户需求间的矛盾越来越突出；对于CDMA系统，系统容量和链路干扰间的矛盾也日益尖锐。对于前者，采用多层蜂窝系统(HCS)，使得宏蜂窝覆盖低话务量地区并为快速呼叫提供服务，而微蜂窝覆盖高话务量地区并为慢速呼叫提供服务，这样既保证较高的频谱利用效率，又能有效地降低呼叫的切换次数。对于后者，在系统容量受下行链路限制的CDMA系统中，采用快速蜂窝选择(FCS)可以有效地减小下行链路干扰，从而提高系统链路容量和数据吞吐量。 本论文围绕HCS中初始蜂窝的选择(ICS)、呼叫溢出方案的分析与设计、基于动态保护信道配置(DGCA)的双向呼叫溢出方案设计、FCS算法分析与设计等四个方面进行了深入的理论和仿真研究。 通过对现有HCS存在问题的分析，本文提出了ICS的概念。根据移动台的速度、在不同蜂窝中的停留时间、网络响应时间(NRT)和呼叫持续时间等参数，对HCS中ICS进行了分析。论文讨论了NRT对HCS服务质量(GoS)的影响，并基于一定的GoS要求，给出了根据移动台最高速度进行呼叫接入的方法。分析结果表明，切换次数与系统GoS间存在着密切关系，而ICS能有效地降低呼叫切换次数和呼叫失败概率。 基于马尔可夫过程提出了分析HCS中呼叫流的通用模型，并利用它比较了不同呼叫溢出方案(无呼叫溢出、单向呼叫溢出、双向呼叫溢出方案)对HCS系统性能的影响。分析结果表明双向呼叫溢出方案能给用户带来最低的呼叫阻塞概率和切换失败概率。其原因在于它能平衡微蜂窝层和宏蜂窝层间的呼叫流量，且慢速、快速呼叫能共享所有信道资源。为了验证算法，论文还将其中部分理论分析结果与仿真结果进行了比较分析。 在双向呼叫溢出方案的基础上，作者分析了速度门限和移动台最高速度对系统GoS的影响，即当呼叫流量在一定范围内时，提高速度门限和降低移动台的最高速度均能减小呼叫的失败概率。 在现有大多数方案中，所有呼叫通常首先向微蜂窝发出接入请求。本文提出了改进的双向呼叫溢出方案，使得慢速呼叫首先向微蜂窝发出接入请求，而快速呼叫首先向宏蜂窝发出切换请求。这样能大大降低呼叫发起的切换次数。 与新呼叫阻塞相比，用户更不能容忍对已有呼叫的中断，因此可通过在第VI页 西南交通大学博士研究生学瞅文HCS中设置保护信道来保证切换用户更高的接入优先权，但保护信道的引入会对呼叫阻塞概率和切换失败概率产生截然不同的影响。因此，改进的双向呼叫溢出方案基于DGCA的思想，在将呼叫合理分配到各层蜂窝的同时，充分考虑呼叫阻塞概率和切换失败概率间的折衷关系，从而使用户的不满意度最低。 与软切换相比，高速下行包接入（HSDPA）采用FCS能有效地减小下行链路干扰，提高链路容量，但它也存在一些缺点，如增加不必要的切换次数，造成各蜂窝的业务负载不平衡等。本论文综合考虑了公用导频信道（CPICH）的信号强度、蜂窝的呼叫到达率和基站的可用功率三个主要因素，借鉴模糊数学思想，提出了一种模糊 FCS（FFCS）算法，并通过仿真对软切换、FCS和 FFCS进行了性能比较。仿真结果表明，FFCS通过平衡各蜂窝的业务量，能有效提高业务量繁重小区的容量和数据吞吐量，还能在一定程度上避免呼叫产生不必要的切换。更多还原

【Abstract】 With the fast development of mobile communication services,the conflict between spectrum resources and customer’s demand grows more and more rapidly. For CDMA system,the contradiction between the system capacity and link interference is greatly incisive,too. To solve the former problem,hiarachical cellular system (HCS) could be applied,where macrocells cover low-teletraffic areas and serve slow calls,while microcells overlay high-teletraffic areas and serve fast calls. By this means,better spectrum efficiency can be achieved and the number of handoffs can be decreased. To solve the latter problem,fast cell selection (PCS) can be used to reduce its interference effectively and then improve the link capacity and data throughput in CDMA system whose capacity is mainly restricted by the downlink.In this thesis,theoretical analysis and computer simulation are carried out in the following aspects:initial cell selection (ICS),analysis and design of call-overflow scheme,design of bidirectional call-overflow scheme based on dynamic guard channels assignment (DGCA),analysis and design of PCS algorithm.Based on the analysis of various existing problems in HCS,this thesis puts forward ICS. Then,ICS in the HCS is analyzed with respect to various parameters such as the mobile velocity,the residence time in different cells,network response time and the call lifetime. In the thesis,the effect of network response time (NRT) on HCS grade of service (GoS) is discussed. On the basis of a certain GoS requests,the method of calls’ access is proposed according to the maximum speed of the mobile. The analysis shows that there is a close relationship between the number of handoffs and GoS,and ICS can reduce the number of handoffs and unsuccessful probability of the calls.According to Markov process,a general model for call flow in HCS is introduced,which is utilized to compare different call-overflow schemes. The analysis shows that bidirectional call-overflow scheme can lead to the lowest call blocking probability and the lowest handoff failure probability. The reason for this is that the scheme can balance the teletraffic between the microlayer and macrolayer,and both the slow and fast calls can share all the channel resources. To verify our algorithm,parts of theoretical and simulated results are compared.Based on bidirectional call-overflow scheme,the author then analyzes the velocity threshold and the maximum mobile velocity’s influence on the system GoS. That is,when the teletraffic is in a certain range,both increasing the velocity threshold and decreasing the maximum velocity can reduce the unsuccessful probability of calls.In most existing schemes,the calls usually request the access to microcells firstly. This thesis proposes an improved bidirectional call-overflow scheme,i.e. slow calls request the access to microcell firstly while fast calls request the access to macrocells firstly. In this way,the total number of handoffs can be reduced.Compared with the blocking of new calls,the users are more dissatisfied with the existing call interrupt. So the handoff calls should have higher priority,which is ensured by assigning the guard channels in the HCS. However,the introduction of guard channels will have quite different effects on blocking probability and handoff failure probability. Therefore,based on DGCA,the improved bidirectional call-overflow scheme can allocate the teletraffic to different layers. While considering the tradeoff between two different probabilities,it can make the dissatisfaction grade of users the lowest.In comparison with the soft handoff,PCS in high-speed downlink packet access (HSDPA) can reduce the downlink interference effectively,and therefore improve the link capacity. However the current PCS also has shortcomings,i.e. increase of unnecessary handoff and unbalance of the teletraffic among different cells. Using fuzzy mathematical idea,the thesis proposes a fuzzy PCS (FFCS) algorithm,which takes into account of three main factors,i.e. the signal strength of common pilot channe更多还原