标题: LTE 移动管理及其对通话控制影响之研究
A Study on LTE Mobility Management and Its Impact on Call Control
作者: 刘仁煌
Liou, Ren-Huang
林一平
Lin, Yi-Bing
资讯科学与工程研究所
关键字: 通话控制;增强单一无线语音呼叫连续性;位置更新;长期演进技术;移动管理;呼叫;全球行动通讯系统;Call Control;enhanced Single Radio Voice Call Continuity (eSRVCC);Location Update;Long Term Evolution (LTE);Mobility Management;Paging;Universal Mobile Telecommunications System (UMTS)
公开日期: 2013
摘要: 为了提供行动宽频服务,第三代行动通讯规格组织(3GPP)制订了长期演进技术(LTE),其网路架构演进自全球行动通讯系统(UMTS)。LTE的移动管理(Mobility Management)机制追踪使用者设备(User Equipment)的位置,以便于通知使用者来电。在通话建立之后,如果使用者在通话过程中移动,LTE通话控制(Call Control)机制负责维持通话的稳定性,避免通话在使用者移动过程中无故断线。本研究探讨LTE系统的移动管理效能以及其对通话控制之影响。

在LTE的网路架构中,细胞(Cells,基地台的无线电讯号覆盖范围)被分类成不同的追踪区域(Tracking Areas),这些追踪区域再被进一步被分类成追踪区域清单(Tracking Area Lists)。移动管理的机制包含位置更新(Location Update)与呼叫(Paging)。当使用者设备离开目前的追踪区域清单时,它会透过位置更新机制向网路端回报自己的新位置。当网路端尝试对使用者设备建立连线时,网路端会透过呼叫机制要求追踪区域清单中相对细胞的基地台去寻找使用者设备。本论文先分析 LTE 的移动管理效能。接着比较LTE移动管理效能与以移动次数为基础(Movement-based)和以移动距离为基础(Distance-based)的移动管理效能。研究结果显示,在某些移动模式下,LTE的移动管理会有较好的表现。我们也提出一个LTE的动态呼叫方法,此方法根据使用者设备移动和呼叫的行为即时决定呼叫细胞的顺序。研究结果显示,动态呼叫方法可以有效降低呼叫讯息流量。

在通话控制方面,3GPP提出增强单一无线语音呼叫连续性(eSRVCC)机制,允许使用者设备在通话过程中,在LTE与UMTS领域中转换。如果使用者设备在通话过程中频繁地转换,可能会产生大量的转换讯息流量。针对此议题,本研究限制一通电话能转换的最大次数,来降低转换的讯息流量。我们研究eSRVCC在转换次数限制下的效能。研究结果显示,适当的转换次数限制可以有效降低转换讯息流量,并且维持较高的LTE使用率。

针对以上的研究题目,我们分别发展数学模型与模拟实验,以精确分析各种交通流量或移动模式对效能的影响。本论文的研究成果可提供电信业者各项移动管理与通话控制之参数建议,以期提升LTE系统的效能。
3rd Generation Partnership Project (3GPP) proposed Long Term Evolution (LTE) which evolved from Universal Mobile Telecommunications System (UMTS) to support mobile broadband services. The LTE mobility management tracks the locations of the User Equipments (UEs) so that incoming calls can be delivered to the UEs. After a call is established, if the UE moves around the service area of the LTE network during the call, the call control technique such as enhanced Single Radio Voice Call Continuity (eSRVCC) is responsible to maintain the connectivity of the ongoing call. In this dissertation, we investigate the LTE mobility management and its impact on call control.

In the LTE mobility management architecture, the cells (the radio coverages of base stations) are grouped into the Tracking Areas (TAs), and the TAs are further grouped into the TA List (TAL). Mobility management procedures include location update and paging. The location update is executed when the UE leaves the current TAL. When the network attempts to connect to the UE (e.g., when an incoming call arrives), the network executes the paging procedure by sending the paging messages to the cells in the UE's TAL. In the dissertation, we first study the performance of the LTE mobility management. Then we compare the LTE mobility management scheme with two well-known mobility management schemes: the movement-based scheme and the distance-based schemes. Our study shows that under some traffic/mobility patterns, the LTE mobility management scheme outperforms the previously proposed schemes. We also propose a dynamic paging scheme that determines the paging sequence of cells in real time according to the UE movement and call behavior. Our study indicates that the dynamic paging scheme can effectively reduce the paging traffic.

For the call control, 3GPP proposed eSRVCC to support the access transfer between LTE and UMTS during a call. If the UE frequently moves back and forth between LTE and UMTS during a call, it may incur large access transfer traffic. To resolve this issue, the number of access transfers should be limited in an eSRVCC call (referred to as the transfer limit) to reduce the transfer traffic. We investigate the performance of eSRVCC with the transfer limit. Our study indicates that an appropriate transfer limit effectively reduces the access transfer traffic with good LTE utilization.

We also develop analytic and simulation models to study the impacts of different traffic/mobility patterns. Our study provides guidelines for the telecommunications operators to achieve higher system performance by selecting appropriate parameter values in LTE.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079855803
http://hdl.handle.net/11536/74229
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