-
实用文档
内容
:参数
功能及设置、切换原理、信令流程、优化案例等。
1
LTE
切换原理
1.1
Intra-
eNodeB
切换
触发事件:
A3
事件(同频切换)
,
A5
事件(异频切换)
当
UE
从当前所处的服务小区切换到同一
eNo
deB
下的另一小区时,会发生
Intra-
eNodeB
切换。
基于
X2
接口的切换
触发事
件:
A3
事件(同频切换)
,
A5
事件(异频切换)
当两个
eNodeB
之间存在
X2<
/p>
接口时,
UE
从当前所驻留的服务小区切
换到另一
eNodeB
时,可采用基于
X2
接口的切换。
基于
S1
接口的切换
触发事件
:
A3
事件(同频切换)
,
A5
事件(异频切换)
当两个
eNodeB
之间不存在
X2<
/p>
接口,
或
X2
接
口不可用时,
UE
从当前所驻留的
服务
小区切换到另一
eNodeB
时,可采用基于
< br>S1
接口的切换。
1.1.1
LTE
< br>到
3G
的切换
实现
LTE
到
3G
的切换首先需要满足几个前提:
1.
网络侧,
LTE
系统和
3G
系统均支持
LTE
到
3G
的<
/p>
PS
切换
2.
UE
侧
,
UE
需要支持
LTE
到
3G
的
PS
切换,
UE
的
Feature
Group
Indicator
bit
位
8
和
bit
位
22
数值必须为
1
。
LTE
到
3
G
切换的流程概述:
1.
LTE
基站如果收到
UE
上报的
A2
测量报告,发现
LTE
的覆盖较差。
2.
LTE
基站通过
RRC
重配置消息对
< br>UE
配置
B2
事件的测量的相关
参数。
3.
LTE
基站收到
B2
事件的测量报告
后,
通过
MobilityFromEutranComman
d
通
知
UE
发
起到
3G
的切换。
4.
LTE
基站收到
UE
上发的
Mobility
ToUtranComplete
,切换成功。
主要的
LTE
RRC
空口信令:
?
UE
上报
B2
测量报告:
Measuremen
t Report
?
UE
在
LTE
小区收到往
3
G
切换命令:
MobilityFromEutranComm
and
?
UE
向
LTE
小区反馈到
3G
切换成功:
MobilityToUtranComplete
实用文档
具体的切换信令流程如下:
1
.切换准备信令流程(
3GPP
23.401
)
UE
Source
eNodeB
Target
RNC
Source MME
Target
Target
SGSN
Serving GW
Serving GW
PDN
GW
HSS
Uplink and Downlink
User
Plane PDUs
1. Handover
Initiation
2.
H
andover
Required
3. Forward
Relocation Request
4. Create
Session Request
4a. Create
Session Response
5.
Relocation
Request
5a.
Relocation
Request
Acknowledge
6. Create
Indirect Data Forwarding Tunnel Request
6a. Create Indirect Data Forwarding
Tunnel Response
7. Forward Relocation
Response
reate
Indirect Data Forwarding Tunnel Request
8
.
C
reate Indirect
Data Forwarding Tunnel Response
8
a
.
C
2
.切换执行信令流程(
3GPP
23.401
)
实用文档
UE
Source
eNodeB
Target
RNC
Source MME
Target
Target
SGSN
Serving GW
Serving GW
PDN
GW
HSS
Uplink and Downlink User Plane
PDUs
1. Handover
Command
2. HO from E-UTRAN
Command
-
4.
UTRAN Iu Access Procedures
4a. Handover
to UTRAN Complete
Sending of
uplink data
possible
Downlink
User Plane PDUs
If Direct
Forwarding applies
Via
Target SGSN in case Direct Tunnel is not
used
5. Relocation
Complete
6. Forward
Relocation Complete
6a.
Forward Relocation Complete Acknowledge
7. Modify Bearer Request
If Indirect Forwarding
applies.
For Serving GW
relocation Steps 7, 8 and 9,
and the
following User Plane path, will be
handled by Target Serving GW
(A)
8. Modify
Bearer Request
8a. Modify
Bearer Response
9. Modify
Bearer Response
Uplink and
Downlink User Plane PDUs (Via Target SGSN if
Direct Tunnel is not used)
10. Routeing Area Update procedure
11. Delete Session Request
11b. Release Resources
11a. Delete Session Response
(B)
12. Delete
Indirect Data Forwarding Tunnel
1.1.2
LTE
到
2G
的切换
LTE
到
2G
的具体切换信令流程:
1.
切换准备信令流程(
3GPP
23.401
)
实用文档
UE
Source
eNodeB
Target
BSS
Source MME
Target
SGSN
Target
Serving GW
Serving GW
PDN
GW
HSS
Uplink and Downlink
User Plane
PDUs
1. Handover
Initiation
2. Handover
Required
3. Forward
Relocation Request
4. Create
Session Request
4a. Create
Session Response
5. PS
Handover Request
5a. PS
Handover Request Acknowledge
6. Create Indirect Data Forwarding
Tunnel Request
6a. Create
Indirect Data Forwarding Tunnel
Response
7. Forward
Relocation Response
8.
Create Indirect Data Forwarding Tunnel
Request
8a. Create Indirect
Data Forwarding Tunnel Response
2.
切换执行信令流程(
3GPP
23.401
)
实用文档
UE
Source
eNodeB
Target BSS
Source
MME
Target
Target SGSN
Serving GW
Serving GW
Uplink
and Downlink User Plane PDUs
PDN
GW
HSS
1. Handover Command
2. HO from E-UTRAN Command
4. GERAN A/Gb Access
Procedures
5. XID
Response
Downlink User Plane
PDUs
Sending of
uplink data
possible
Only if
”Direct Forwarding”
applies
Only if ”Indirect Forwarding”
applies
6. PS Handover
Complete
7. XID
Response
8. Forward
Relocation Complete Notification
8a. Forward Relocation Complete
Acknowledge
9. Modify Bearer
Request
For Serving GW
relocation Steps 9, 10 and 11,
and the
following User Plane path, will be
handled by Target Serving GW
12. XID Negotiation for LLC
ADM
12a. SABM UA
exchange
re-establishment
and XID negotiation for LLC ABM)
Uplink and Downlink User Plane
PDUs
13. Routeing Area
Update procedure
14. Delete Session
Request
14b. Release
Resource
(B)
14a. Delete Session Response
(A)
10. Modify
Bearer Request
10a. Modify
Bearer Response
11. Modify
Bearer Response
1.1.3
3G
到
LTE
的切换
3G
到
LTE
的具体切换信令
流程:
1.
切换准备信令流程(
3GPP
23.401
)
实用文档
UE
Source
RNC
Target
eNodeB
Target
Serving
GW
PDN
GW
Source
SGSN
Target MME
Serving GW
HSS
Uplink and
Downlink
User Plane PDUs
(via Source SGSN
in case
Direct Tunnel
is
n
ot
used)
1. Handover Initiation
2. Relocation Required
3. Forward Relocation
Request
4. Create Session
Request
4a. Create Session
Response
5.
Handover
Request
5a. Handover
Request Acknowledge
6
.
C
reate
Indirect Data Forwarding
Tunnel Request
6
a
.
C
reate
Indirect Data Forwarding Tunnel
Response
7
.
Forward Relocation Response
.
C
reate
Indirect Data Forwarding Tunnel
Request
8
8a.
Create
Indirect
Data Forwarding Tunnel Response
2.
切换执行信令流程(
3GPP
23.401
)
实用文档
UE
Source
RNC
Target
eNodeB
Source
SGSN
Target MME
Target
Serving
GW
Serving GW
PDN
GW
HSS
Uplink and
Downlink User Plane PDUs (via Source SGSN if
Direct Tunnel is not used)
1. Relocation Command
2. HO from UTRAN Command
4. E-UTRAN Access Procedures
5. HO to E-UTRAN Complete
Sending of
uplink data
possible
Downlink Payload User Plane PDUs (via
Source SGSN if Direct Tunnel is not
used)
If Direct Forwarding
applies
Via Source SGSN in
case Direct Tunnel is not used
If Indirect Forwarding
applies
6. Handover
Notify
7. Forward Relocation
Complete Notification
7a.
Forward Relocation Complete Acknowledge
8. Modify Bearer Request
For Serving GW relocation Steps 8, 9
and 10,
and the following User Plane
path, will be
handled by Target Serving
GW
(A)
10. Modify
Bearer Response
9. Modify
Bearer Request
9a. Modify
Bearer Response
Uplink and
Downlink User Plane PDUs
11. Tracking Area Update procedure
12. Delete Session Request
12b. Iu Release Procedure
(B)
12a. Delete
Session Response
13. Delete
Bearer
1.1.4
2G
到
LTE
的切换
2G
到
LTE
的具体切换信令
流程:
1.
切换准备信令流程(
3GPP
23.401
)
实用文档
UE
Source
BSS
Target
eNodeB
Source
SGSN
Target
MME
Target
Serving
GW
Serving GW
PDN GW
HSS
Uplink and
Downlink
User Plane
PDUs
1. Handover Initiation
2. PS Handover Required
3. Forward Relocation
Request
4. Create Session
Request
4a. Create Session Response
5. Handover Request
5a. handover
Request Acknowledge
6. Create Indirect Data Forwarding
Tunnel Request
6a. Create Indirect Data Forwarding
Tunnel Response
7. Forward Relocation
Response
8. Create Indirect
Data Forwarding Tunnel Request
8a. Create
Indirect Data Forwarding Tunnel
Response
2.
切换执行信令流程(
3GPP
23.401
)
实用文档
UE
Source
BSS
Target
eNodeB
Source
SGSN
Target MME
Target
Serving
GW
Serving GW
PDN
GW
HSS
Uplink and
Downlink User Plane PDUs
Only if 'Direct Forwarding'
applies
Only if 'Indirect
Forwarding' applies
1. PS HO
Required Acknowledge
2. PS
Handover Command
4. E-UTRAN
Access Procedures
5. HO to
E-UTRAN Complete
6. Handover
Notify
Sending of
uplink data
7. Forward
Relocation Complete Notification
possible
7a.
Forward Relocation Complete Acknowledge
8
.
Modify Bearer Request
9.
Modify Bearer Request
For
Serving GW relocation Steps 8, 9 and 10, and
the following User Plane path, will be
handled by
Target Serving GW
(A)
9a. Modify
Bearer Response
10. Modify
Bearer Response
Uplink and
Downlink User Plane PDUs
11. BSS Packet Flow Delete
Procedure
12. Tracking Area
Update procedure
13. Delete Session
Request
13a. Delete Session
Response
14. Delete Indirect
Data Forwarding Tunnel Request
14a. Delete Indirect Data Forwarding
Tunnel Response
2
LTE
切换问题优化方法及流程
2.1
LTE
主要切换问题
2.1.1
邻区配置
邻区配置不合理案例:
问题描述:<
/p>
通过统计观察到到小区
70736-4
的
切换成功率为
0%
,
而到
70272-2
的切换尝试次数为
0
。
实用文档
问题分析:经检查配置发现
70736-4
和
70272-2
这两个小区配置
了相同的
PCI
,而且正确的目标切换小区应该是
70272-2
。
p>
问题解决:
通过删除
70736-4
的邻区关系后,
到
70272-2
的切换成功率恢复到
100%
。
< br>
2.1.2
参数设置
参数设置不合理案例:
问题描述:<
/p>
通过观察基站侧统计发现有很多切换准备成功率为
0%
的邻区关系,
共同点是目标小区都属于同一个基站
(
基站
ID
4506-70483)
。
问题分析
:通过分析发现该基站
(
基站
ID 4
506-70483)
计数器
pmHoPrepRejInLi
cMob
的数值很高,
计数器
pmHoPrepRejInLicMob
解释:统计由于目标基站缺
少切换相关的
license
而导致切换失败的次数。
问题解决:在激活目标基站的
license
之后,切换成功率恢复
100%
。
p>
实用文档
2.1.3
无线环境引起的切换异常
案例介绍:
问题描述:路测中武昌路
段切换序列混乱,而且切换成功率较低。
< br>问题分析:
通过测试
log
分析
发现武昌路(红圈
1,2,3
)主要占用
SN
黄海饭店
2
小
< br>区(
PCI_238
)
,
SN
黄海饭店
2
小区
(
PCI_238
)天线挂高
70m,
越区覆盖严重,
问题解决:通过调整
SN
黄海饭店
2
小区(
PCI_238
)机械下倾角下压到
< br>10
度,控制
越区减小对其他小区干扰。
优化后武昌路主要占用世纪之星
3
小区信号(
PCI74
)
(下图红
框所示)
,信噪比改善,越区覆盖消除,切换恢复正常。
实用文档
2.2
LTE
切换问题优化流程
LTE
切换异常主要有以下几个现象:
1.
UE
向
源小区发送测量报告后没有收到切换命令
2.
UE
在
源区收到切换命令,在目标邻小区发送随机接入(
MSG1
)但
是未收到
随机接入响应
(MSG2)
。
3.
小区之间乒乓切换。
4.
小区之间切换序列混乱。
5.
切换过程中数据中断
针对这些切换异
常,应该从参数配置,邻区配置,基站传输,硬件告警,上下
行干扰等几个方面入手分析
问题。
切换问题分析流程:
其中参数合理性检查主要包括以下等几个方面:
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