移动LTE系统事件介绍

LTE系统事件介绍

一、LTE事件概述

LTE切换时需要UE上报测量的结果（包括RSRP，RSRQ等），而上报又分为周期性上报和事件触发的上报。

周期性上报由基站配置，UE直接上报测量的结果。

事件触发的上报又分为系统内的事件和系统间的事件。

LTE系统内切换主要事件包括：

A1事件，服务小区质量高于门限；这个事件可以用来关闭频间测量。

A2事件，服务小区质量低于门限；这个事件可以用来打开频间测量和系统间测量，因为这个事件发生后可能发生切换等操作。

A3事件，邻小区质量好于服务小区质量；这个事件一般用于频内/间基于覆盖的切换。

A4事件，邻小区质量好于门限；这个事件一般用于基于负荷的切换。

A5事件，服务小区质量低于一个门限并且邻小区质量高于一个门限；这个事件也可以用于频内/间基于覆盖的切换。

目前LTE同频切换都是基于A3/A5事件进行的切换（现网主要是基于A3事件的）

二、切换流程举例

- RRC Connection Reconfiguration（Measurement Control）测量控制，一般在初始接入或上一次切换命令中的重配消息里携带

- Measurement Report

测量报告，终端根据当前小区的测量控制信息，将符合切换门限的小区进行上报

- HO Request

源小区在收到测量报告后向目标小区申请资源及配置信息（站内切换的话为站内交互，站

间切换会使用X2口或者S1口，优先使用X2口）

- HO Request Ack

目标小区将终端的接纳信息以及其它配置信息反馈给源小区

- RRC Connection Reconfiguration（HO Command）

将目标小区的接纳信息及配置信息发给终端，告知终端目标小区已准备好终端接入，重配

消息里包含目标小区的测量控制

- SN Status Transfer

源小区将终端业务的缓存数据移至目标小区

- Random Access Preamble

终端收到第5步重配消息（切换命令）后使用重配消息里的接入信息进行接入

- Random Access Response

目标小区接入响应，收到此命令后可认为接入完成了，然后终端在RRC层上发重配完成消

息（第9步）

- RRC Connect Reconfiguration complete（HO Confirm）

上报重配完成消息，切换完成

- Release Resource

当终端成功接入后，目标小区通知源小区删除终端的上下文信息

四、协议对LTE事件的定义和说明

4.1 A1事件定义

Event A1 (Serving becomes better than threshold)

The UE shall:

1> consider the entering condition for this event to be satisfied when condition A1-1, as specified

below, is fulfilled;

1> consider the leaving condition for this event to be satisfied when condition A1-2, as specified

below, is fulfilled;

1> for this measurement, consider the primary or secondary cell that is configured on the frequency

indicated in the associated measObjectEUTRA to be the serving cell;

Inequality A1-1 (Entering condition)

-

Ms>

Hys

Thresh

Inequality A1-2 (Leaving condition)

Ms<

+

Thresh

Hys

The variables in the formula are defined as follows:

Ms is the measurement result of the serving cell, not taking into account any offsets.

Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within

reportConfigEUTRA for this event).

Thresh is the threshold parameter for this event (i.e. a1-Threshold as defined within reportConfigEUTRA for this event).

Ms is expressed in dBm in case of RSRP, or in dB in case of RSRQ.

Hys is expressed in dB.

Thresh is expressed in the same unit as Ms.

4.2 A2事件定义

Event A2 (Serving becomes worse than threshold)

The UE shall:

1> consider the entering condition for this event to be satisfied when condition A2-1, as specified

below, is fulfilled;

1> consider the leaving condition for this event to be satisfied when condition A2-2, as specified

below, is fulfilled;

1> for this measurement, consider the primary or secondary cell that is configured on the frequency

indicated in the associated measObjectEUTRA to be the serving cell;

Inequality A2-1 (Entering condition)

+

Ms<

Hys

Thresh

Inequality A2-2 (Leaving condition)

Ms>

-

Hys

Thresh

The variables in the formula are defined as follows:

Ms is the measurement result of the serving cell, not taking into account any offsets.

Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within

reportConfigEUTRA for this event).

Thresh is the threshold parameter for this event (i.e. a2-Threshold as defined within reportConfigEUTRA for this event).

Ms is expressed in dBm in case of RSRP, or in dB in case of RSRQ.

Hys is expressed in dB.