1. 教育部補助「行動寬頻尖端技術跨校教學 聯盟計畫 - 行動寬頻網路與應用 - 小細胞基 站聯盟中心計畫」 Small Cell 創新應用與服務專題 課程單元：基本 LTE 換手之研究 計畫主持人：許蒼嶺 授課教師：李宗南、簡銘伸、李名峰 教材編撰：謝秉融 國立中山大學 資訊工程系

2. Preliminary HO is a mechanism of mobility management to maintain a UE’s connection for the UE moving from a cell coverage to other The LTE HO is a network-controlled mechanism In the specification TS 36.300 [1], Section 10 describes the LTE HO in detail In the description below, We focus on the intra E-UTRAN mobility, not inter-RAT mobility 2

3. LTE HO signaling flow Measurement Three phases (like WiMAX HO) Preparation Execution Completion e.g., E-RAB attributes and RRC context Contention based or free Dedicated RACH preamble PDCP SN information regarding roaming restrictions release any U-plane/TNL resources release radio and C-plane related resources 3

4. LTE HO: measurement Measure the signal condition of the connection between the UE and the serving eNB (by L1 measurement) Send L3 measurement reports to the serving eNB 4

5. LTE HO: measurement L1 measurement UE measures the difference of Reference Signal Receiving Power (RSRP) The difference is similar to Signal to Interference Noise Ratio (SINR) L1 measurement every 10 ms (T L1 ) The nth L1 measurement 5 s: the serving eNB t: the target eNB

6. LTE HO: measurement (cont.) L3 measurement A UE’s RRC layer (L3) samples the L1 measurements for filtering The UE sends a measurement report to the serving eNB every end of a L3 measurement period T L3 N L3 is the number of L1 measurements during T L3 The nth L3 measurement 6, where a is a filter coefficient

7. LTE HO: preparation HO decision (HO trigger) Prepare UE context in the target eNB HO command 7

8. LTE HO: HO trigger HO trigger method of eNB based on the A3 event condition If all of the L3 measurements achieve the A3 event condition for T TTT, the HO procedure starts Then the Time-to-trigger (TTT) timer which is set for T TTT will starts where H is the HO threshold, Hysteresis Margin 8

9. LTE HO: execution Detach Contention-free random access procedure Response RRC connection reconfiguration complete (control plane between the UE and the target eNB is complete) 9

10. LTE HO: completion Path switch at the serving gateway (SGW) Release UE context in the serving eNB 10

11. D2D or group Handover D2D scenario Group scenario The demo in NSYSU 11

12. Signaling overhead In the future D2D communication can be applied in LTE system The group HO (or joint HO) for D2D pair or multiple UEs moving together can reduce the HO signaling overhead One of the D2D pair or the UEs triggers a HO, and then all of them operate HO procedure together Save the resource or computation in the serving eNB 12 Reference: [3]

13. Connection-broken probability of the Proximity Service (ProSe) Assume the channel condition of the ProSe between/or among UEs The continuity of the ProSe can be a performance index, e.g., connection-broken probability Mix it with the HO condition to trigger a group HO 13 Reference: [3]

14. Ping Pong (PP) can be one of the condition 14

15. Conclusion In the group HO scenario There is a chance of improvement We introduce the important performance indices of LTE HO Choose the appropriate one to improve We still need to consider the constrains in our ITRI platform to develop the further design Revisable RRM protocol stack in eNB Two eNBs for HO (simple deployment) Commercial device of UE 15

16. Reference [1] 2015 (v12.5.0) 3GPP TS 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 [2] 2012 (v11.1.0) 3GPP TR 36.839, Evolved Universal Terrestrial Radio Access (E-UTRA); Mobility enhancements in heterogeneous networks [3] H. Chen, M. Shih, H. Wei, “Handover Mechanism for Device-to- Device Communication” in IEEE CSCN 2015 16