CDMA网络优化中的掉话分析

lily6189

<h1 style="MARGIN: 17pt 0cm 16.5pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">CDMA</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">移动通信系统中，网络优化较为重要，因为</span><span lang="EN-US" style="FONT-FAMILY: Arial;">CDMA</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">移动通信系统是干扰受限的通信系统。系统的容量是软容量，网络优化不仅能改善网络的性能和服务质量，还能增加系统的容量。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></h1><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">加强网络优化，提高网络的运行效率，实现服务水平、服务质量、经营效率以及竞争能力的提高，已成为发展的必然。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">移动通信网络优化的目标是尽可能利用系统资源，如系统基础结构和频谱，使系统性能达到最佳。为了测量通信系统的性能，需要一些可以量化的指标对网络进行评估。指标的选择依赖评估者对不同网络性能的侧重。无线网络的性能通常由话音质量、无线覆盖、掉话率、起呼失败率、止呼失败率、系统容量和建筑物穿透率等确定。而</span><span lang="EN-US" style="FONT-FAMILY: Arial;">CDMA</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">网络还包括误帧率、软切换比率等。优化过程的结果是寻找一系列系统变量的最佳值，优化有关性能指标参数，提高网络质量。本文着重分析掉话方面的基本概念和实例等。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">一、</span><span style="FONT-FAMILY: Arial;">
                </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话的基本概念及掉话机制</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话定义为在没有经过用户同意的情况下由基站或移动台释放业务信道。掉话率定义为掉话次数与总的通话次数的比率。与接入测试一样，掉话测试应在正常负载条件下测试，收集尽可能多的数据，一般需要大于</span><span lang="EN-US" style="FONT-FAMILY: Arial;">500</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">次呼叫。通常定义掉话率在</span><span lang="EN-US" style="FONT-FAMILY: Arial;">5%</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">以下为可接受，具体的目标值可由运营商确定，如联通规定优化目标值为</span><span lang="EN-US" style="FONT-FAMILY: Arial;">2</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">％。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话率是网络运营商最为关注的指标，因其在用户方面的负面影响最为直接。对一个确实的网络，影响其掉话率的因素是很多的：如硬件问题、干扰问题、覆盖问题、切换问题、软件问题、数据库参数、邻区参数等。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话率是评估</span><span lang="EN-US" style="FONT-FAMILY: Arial;">CDMA</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">系统性能的重要指标，移动台侧的掉话机制在标准中已经制定，但在标准中并没有具体规定基站侧的掉话机制的实现，具体实现由各设备厂家来决定。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">标准中规定在通话过程中需要移动台与基站之间有闭合的信令交换，即移动台和基站双方对收到的信令必须响应。如果由于某种原因交换失败，移动台就不能正确调整它的发射机，因此重新初始化或返回空闲状态。在功控和软切换过程中也都需要这种信令交换。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">移动台的掉话机制主要有三种：</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基于坏帧数：移动台在连续收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">12</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">个坏帧后停止发射机工作，在</span><span lang="EN-US" style="FONT-FAMILY: Arial;">5s</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">内连续收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">2</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">个好帧后重新激活发射机。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基于移动台定时器：前向高误帧率意味着前向链路正在变差，移动台维持一个衰落定时器，连续收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">2</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">个好帧后重置该定时器。如果在定时器期满前不能重置，移动台将重新初始化。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基于基站证实失败：移动台在重发需要证实的消息</span><span lang="EN-US" style="FONT-FAMILY: Arial;">N1m</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">次</span><span lang="EN-US" style="FONT-FAMILY: Arial;">(95A</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">中为</span><span lang="EN-US" style="FONT-FAMILY: Arial;">3</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">95B</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">中为</span><span lang="EN-US" style="FONT-FAMILY: Arial;">9)</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">后，如果还未收到基站的证实，移动台将重新初始化。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基站掉话机制主要有两种：</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基于坏帧数：由设备商设定，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">95</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">规范中未明确规定。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">基于移动台证实失败：</span><span lang="EN-US" style="FONT-FAMILY: Arial;">95</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">规范中未明确规定。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">二、</span><span style="FONT-FAMILY: Arial;">
                </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话原因分析及其优化</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">1.</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">接入和切换冲突引起的掉话</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">当移动台在小区覆盖边界发起呼叫时，由于移动台在小区覆盖的边界，即将进行切换。因为</span><span lang="EN-US" style="FONT-FAMILY: Arial;">IS-95A</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">不支持接入状态下的切换，如果在接入期间移动台移出了服务小区的覆盖区域，在接入过程完成前不能切换到新的小区或扇区，接入过程和切换过程存在竞争，切换过程必须等待。如果接入过程过长，在切换过程完成前呼叫可能已经掉话。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">2.</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">切换失败引起的掉话</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">此类掉话的特征是移动台的发射功率达到最大，移动台的接收功率不断增加，而导频的</span><span lang="EN-US" style="FONT-FAMILY: Arial;">Ec/Io</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">不断下降，在重新同步到新导频上后又很快增加，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">TX-GAIN-ADJ</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">的幅度保持平坦。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">导频的</span><span lang="EN-US" style="FONT-FAMILY: Arial;">Ec/Io</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">随着移动台的接收功率不断增加而不断下降说明有新的强导频成为干扰源，应当进行切换。当导频强度降低到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">-15dB</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">以下时，前向链路的质量严重下降，当前向链路不能成功解调时移动台将关闭它的发射机。因为移动台不再发射信号，反向闭环功控比特将被忽略，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">TX-GAIN-ADJ</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">的幅度保持平坦，一般是正的几</span><span lang="EN-US" style="FONT-FAMILY: Arial;">dB</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">。很高的移动台接收功率将使开环功控过程低估所需的移动台发射功率。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">掉话原因有：</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">1) </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">切换准许算法引起的软切换失败：如果</span><span lang="EN-US" style="FONT-FAMILY: Arial;">BS</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">日志显示</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SMM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">消息中有合适的导频且有可用资源，但没有发送包含强导频的切换指示消息（</span><span lang="EN-US" style="FONT-FAMILY: Arial;">HDM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">），则是切换准许算法问题。可能的原因有：不允许多于</span><span lang="EN-US" style="FONT-FAMILY: Arial;">3</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">路的软切换；切换算法不完善；不允许切换到不属于邻集列表中的导频上。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">2) </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">资源分配引起的软切换失败：当进行软切换时，需要向目标基站申请资源。系统必须保证有足够的资源来支持软切换，如果系统的激活用户数很多或由于切换率过高，最终所有的资源都用尽了，从而由于没有可用资源导致切换失败。若为切换呼叫预留过多的资源将导致新呼叫阻塞概率的增高，因此接入控制过程可能不会为切换预留足够的资源，从而导致切换失败。可能的原因有：网络负载过大；切换率过高。可以通过调整切换参数</span><span lang="EN-US" style="FONT-FAMILY: Arial;">T-DROP</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">T-TDROP</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">和切换准许算法来解决。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">3) </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">切换信令引起的软切换失败：有了可用的资源，切换准许算法也允许，软切换是否成功还依赖于适当信令消息的及时传输和接收。如果用于切换的信令不完整和及时，也可能导致切换失败。如果基站日志上记录没有接收到包括强导频的导频强度测量消息（</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SMM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">）或延迟很长时间收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SMM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">，则是切换信令出现问题。主要原因有：</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">强的可用导频没有被检测到：移动台向基站报告检测到的强导频，如果移动台检测导频很慢或没有检测到所有的导频，切换就不会及时地进行。若移动台没有发送包括强导频的</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SMM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">或发送的很慢，则是移动台没有检测到强导频。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">可能的原因是：搜索窗口太小、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">T-ADD</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">太高、移动台的导频搜索太慢。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">可以调整的参数有：</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SERACH-WIN-A</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SERACH-WIN-N</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">SERACH-WIN-R</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">T-ADD</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">、</span><span lang="EN-US" style="FONT-FAMILY: Arial;">ILOT-INC</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">反向链路性能下降（反向</span><span lang="EN-US" style="FONT-FAMILY: Arial;">FER</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">高）：随着服务导频强度的不断降低，切换信令必须及时地发送。如果反向链路下降得太快，基站将永远不会接收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">PSMM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">，因此导致切换失败。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">前向高</span><span lang="EN-US" style="FONT-FAMILY: Arial;">FER</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">使接收的切换指示消息（</span><span lang="EN-US" style="FONT-FAMILY: Arial;">HDM</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">）出错或被丢失：如果前向链路降低，移动台可能接收不到切换指示消息，从而导致切换失败。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;">3</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">．长时前向干扰掉话</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">长时是指持续时间超过移动台的衰落计时器的设定值。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">此类掉话的特征是移动台的接收功率不断增加，而导频强度</span><span lang="EN-US" style="FONT-FAMILY: Arial;">Ec/Io</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">在不断降低，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">TX-GAIN-ADJ</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">的幅度保持水平。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">随着移动台的接收功率不断增加而导频强度</span><span lang="EN-US" style="FONT-FAMILY: Arial;">Ec/Io</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">在不断降低，表示在前向链路存在干扰源造成强干扰。当导频强度低于</span><span lang="EN-US" style="FONT-FAMILY: Arial;">-15dB</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">时，前向链路的质量严重下降，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">FER</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">增高，不能成功解调。连续收到</span><span lang="EN-US" style="FONT-FAMILY: Arial;">12</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">个坏帧后，移动台关闭发射机，衰落计时器启动。反向闭环功控比特被忽略，</span><span lang="EN-US" style="FONT-FAMILY: Arial;">TX-GAIN-ADJ</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">的幅度保持平坦，一般是正的几</span><span lang="EN-US" style="FONT-FAMILY: Arial;">dB</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: Arial; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">。如果这种情况持续直到衰落计时器期满，发生的掉话称为长时掉话。</span><span lang="EN-US" style="FONT-FAMILY: Arial;"><p></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt;"><span lang="EN-US" style="FONT-FAMILY: Arial;"><p>&nbsp;</p></span></p>