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1、内容内容：参数功能及设置、切换原理、信令流程、优化案例等。 1 LTE 切换原理切换原理 1.1 Intra-eNodeB 切换切换 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 eNodeB 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 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
2、（异频切换） 当两个 eNodeB 之间不存在 X2 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 S1 接口的切换。 1.1.1 LTE 到 3G 的切换1.1.1 LTE 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 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 3G 切换的流程概述：
3、 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 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 MobilityFromEutranCommand 通 知 UE 发起到 3G 的切换。 4. LTE 基站收到 UE 上发的 MobilityToUtranComplete，切换成功。 主要的 LTE RRC 空口信令： UE 上报 B2 测量报告：Measurement Report UE 在 LTE 小区收到往 3G 切换命令：MobilityFromEutra
4、nCommand UE 向 LTE 小区反馈到 3G 切换成功：MobilityToUtranComplete 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 RNCSource MMETarget SGSN Serving GWHSS 1. Handover Initiation 2. Handover Required 3. Forward Relocation Request 5. Relocation Request 5a. Relocation Request Acknowledge 8. Create Indi
5、rect Data Forwarding Tunnel Request 7. Forward Relocation Response PDN GW 8a. Create Indirect Data Forwarding Tunnel Response Uplink and Downlink User Plane PDUs Target Serving GW 4. Create Session Request 4a. Create Session Response 6. Create Indirect Data Forwarding Tunnel Request 6a. Create Indir
6、ect Data Forwarding Tunnel Response 2切换执行信令流程（3GPP 23.401） UE Source eNodeB Target RNCSource MMETarget SGSNServing GWHSS PDN GW Uplink and Downlink User Plane PDUs 1. Handover Command 2. HO from E-UTRAN Command - Sending of uplink data possible 4. UTRAN Iu Access Procedures 5. Relocation Complete 6.
7、 Forward Relocation Complete 6a. Forward Relocation Complete Acknowledge 7. 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) 4a. Handover to UTRAN Complete Downlink User Plane PDUs If Direct
8、Forwarding applies If Indirect Forwarding applies. Target Serving GW (A) 8. Modify Bearer Request Via Target SGSN in case Direct Tunnel is not used 10. Routeing Area Update procedure 11. Delete Session Request (B) 11a. Delete Session Response 11b. Release Resources For Serving GW relocation Steps 7,
9、 8 and 9, and the following User Plane path, will be handled by Target Serving GW 12. Delete Indirect Data Forwarding Tunnel 1.1.2 LTE 到 2G 的切换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） UE Source eNodeB Target BSSSource MMETarget SGSNServing GWHSS 1. Handover Initiation 2. Hando
10、ver Required 3. Forward Relocation Request 5. PS Handover Request 5a. PS Handover Request Acknowledge 8. Create Indirect Data Forwarding Tunnel Request 7. Forward Relocation Response PDN GW 8a. Create Indirect Data Forwarding Tunnel Response Uplink and Downlink User Plane PDUs Target Serving GW 4. C
11、reate Session Request 4a. Create Session Response 6. Create Indirect Data Forwarding Tunnel Request 6a. Create Indirect Data Forwarding Tunnel Response 2. 切换执行信令流程（3GPP 23.401） UE Source eNodeB Target BSSSource MMETarget SGSN Serving GWHSS PDN GW Uplink and Downlink User Plane PDUs 1. Handover Comma
12、nd 2. HO from E-UTRAN Command Sending of uplink data possible 4. GERAN A/Gb Access Procedures 5. XID Response 6. PS Handover Complete 8. Forward Relocation Complete Notification 8a. Forward Relocation Complete Acknowledge 9. Modify Bearer Request 11. Modify Bearer Response Uplink and Downlink User P
13、lane PDUs 7. XID Response 12. XID Negotiation for LLC ADM 12a. SABM UA exchange re-establishment and XID negotiation for LLC ABM) Downlink User Plane PDUs Only if ”Direct Forwarding” applies Target Serving GW For Serving GW relocation Steps 9, 10 and 11, and the following User Plane path, will be ha
14、ndled by Target Serving GW (A) 10. Modify Bearer Request 10a. Modify Bearer Response 13. Routeing Area Update procedure 14b. Release Resource 14. Delete Session Request (B) 14a. Delete Session Response Only if ”Indirect Forwarding” applies 1.1.3 3G 到 LTE 的切换1.1.3 3G 到 LTE 的切换 3G 到 LTE 的具体切换信令流程： 1.
15、切换准备信令流程（3GPP 23.401） UE Source RNC Target eNodeB Source SGSNTarget MMEServing GWHSS 1. Handover Initiation 2. Relocation Required 3. Forward Relocation Request 5. Handover Request 5a. Handover Request Acknowledge 8. Create Indirect Data Forwarding Tunnel Request 7. Forward Relocation Response PDN G
16、W 8a. Create Indirect Data Forwarding Tunnel Response Uplink and Downlink User Plane PDUs (via Source SGSN in case Direct Tunnel is not used) 6. Create Indirect Data Forwarding Tunnel Request 6a. Create Indirect Data Forwarding Tunnel Response Target Serving GW 4. Create Session Request 4a. Create Session Response 2. 切换执行信令流程（3GPP 23.401） UE Source RNC Target eNodeB Source SGSNTarget MMEServing GWHSS PDN GW Uplink and Downlink User Plane PDUs (via Source SGSN if Direct Tunnel is not used
