LTE Handover LTE Handover Mobility Management 2 LTE

課程單元目標 • 了解 LTE系統交遞 (Handover) • 了解 LTE Handover 的條件 • 了解 Mobility Management 2

LTE系統交遞 (Handover) 3

Description of PCI (2/2) Resource element (k, l) Not used for transmission Reference symbols 7

The role of PCI in LTE OVSF Code 2 OVSF Code 1 RB 1 Primary Scrambling code 2 Cell 2 RB 2 Physical Cell Identity 2 Primary Scrambling code 1 Cell 2 Physical Cell Identity 1 Cell 1 Channel Code (OVSF) Scrambling code Signal combine User 1 Data User 2 Data User 3 Data User n Data x x x UMTS DL Data transmission UMTS LTE 8

Mobility Strategy of LTE Idle Mode Connected Mode LTE UE moving out of LTE coverage Handover UE moving out of LTE coverage Cell reselection to Utran / GERAN Cell reselection to LTE Camping priority: LTE > Utran > GERAN Broadcasted in GERAN/Utran/ LTE UE moving into LTE coverage Utran/GERAN 9 Reference: TTC CS Fallback to Utran/GERAN by direction Redirection to Utran / GERAN

交遞程序 10 交遞程序方向/網路元素描述 Measurement Configuration e. NB → UE 指引UE對鄰細胞（NB Cell）進行量測 Measurement Report UE → e. NB 回報量測結果 Handover Decision Source e. NB 決定目標細胞及交遞型式（X 2或S 1） Handover Preparation 視何種交遞決定準備進行細胞交遞 Handover Execution 視何種交遞決定進行細胞間交遞 Handover Completion 視何種交遞決定切換資料路徑（S-GW, PDN-SG）

The Type of Handover Signa l Inter/Intra-MME al Sign Intra Frequency Band Intra Frequency Intra- RAT Intra Site Signal LTE Handover S 1 Handover X 2 Handover GSM/GPRS Inter- RAT 11 WCDMA

LTE Handover 的條件 12

Handover的機制 1. 如果UE 服務細胞（Serving Cell）的RSRP超過門檻值TH 1，則UE不需要量測Neighboring Cell 的訊號。 2. 如果UE Serving Cell的RSRP介於門檻值TH 1與 TH 2之前，則僅量測同頻段的Neighboring Cell。 3. 如果UE Serving Cell的RSRP低於門檻值TH 2，則需量測行其他系統（如2 G, 3 G）的 Neighboring Cell。 14

交遞程序 15 交遞程序方向/網路元素描述 Measurement Configuration e. NB → UE 指引UE對鄰細胞（NB Cell）進行量測 Measurement Report UE → e. NB 回報量測結果 Handover Decision Source e. NB 決定目標細胞及交遞型式（X 2或S 1） Handover Preparation 視何種交遞決定準備進行細胞交遞 Handover Execution 視何種交遞決定進行細胞間交遞 Handover Completion 視何種交遞決定切換資料路徑（S-GW, PDN-SG）

Handover與門檻值 • Event A 1: UE Serving Cell 訊號好於絕對門檻值。 • Event A 2: UE Serving Cell 訊號差於絕對門檻值。 • Event A 3: LTE Neighbor Cell 的訊號好於Serving Cell某一特定偏移值（Offset）。 • Event A 4: LTE Neighbor Cell 的訊號好於絕對門檻值。 • Event A 5: Serving Cell訊號差於絕對門檻值且 LTE Neighbor Cell好於絕對門檻值。 • Event B 1: Non-LTE Neighbor Cell 訊號好於絕對門檻值。 • Event B 2: Serving Cell訊號差於絕對門檻值且 Non-LTE Neighbor Cell好於另一個絕對門檻值。 16

Events of HO Defined by 3 GPP A 1 Serving becomes better than threshold A 2 Serving becomes worse than threshold A 3 Neighbor becomes offset better than PCell A 4 Neighbor becomes better than threshold A 5 PCell/ PSCell becomes worse than threshold 1 and neighbour becomes better than threshold 2 B 1 Inter RAT neighbor becomes better than threshold B 2 Serving becomes worse than threshold 1 and inter RAT neighbor becomes better than threshold 2 17

Summary of Handover Event 事件名稱觸發條件事件定義進入條件離開條件 A 1事件 Serving becomes better than threshold ：Serving Cell 訊號品質高於一設定門檻，滿足此條件的事件被回報時，停止鄰細胞量測。 A 2事件 Serving becomes worse than threshold：Serving Cell 訊號品質低於設定門 Ms+Hys<Thresh 檻，滿足此條件的事件被回報時，啟動鄰細胞量測。 Ms-Hys>Thresh A 3事件 Neighbor becomes offset better than serving：NB Cell 品質優於 Serving Cell品質，滿足此條件的事件被回報時，啟動 Better Cell Handover。 Mn+Ofn+Ocn-Hys> ms+Ofs+Ocs+off Mn+Ofn+Ocn+Hys< ms+Ofs+Ocs+off A 4事件 Neighbor becomes better than threshold：NB Cell 品質高於設定門檻，滿 Mn+Ofn+Ocn-Hys> 足此條件的事件被回報時，啟動負載平衡交遞請求 (HO required) Thresh Mn+Ofn+Ocn+Hys< Thresh A 5事件 Serving becomes worse than threshold 1 and neighbor becomes better than Ms + Hys < Thresh 1 & threshold 2：Serving Cell 品質低於設定門檻 1且 NB Cell 品質高於設定門 Mn + Ofn + Ocn - Hys 檻 2，啟動涵蓋交遞(Coverage Handover) >Thresh 2 Ms - Hys > Thresh 1 or Mn + Ofn + Ocn + Hys < Thresh 2 B 1事件 Inter RAT neighbor becomes better than threshold：異系統NB Cell品質高於一定門檻，滿足此條件事件被回報時，source e. Node. B啟動異系統交 Mn+Ofn-Hys> Thresh 遞請求 Mn+Ofn-Hys< Thresh B 2事件 Serving becomes worse than threshold 1 and inter RAT neighbor becomes Ms+Hys<Thresh 1 better than threshold 2：Serving Cell品質低於一定門檻且異系統NB Cell Mn+Ofn-Hys> Thresh 2 品質高於一定門檻。 Ms+Hys>Thresh 1 Mn+Ofn-Hys< Thresh 2 18 Ms-Hys Ms+Hys <Thresh >Thresh

Event A 1 The LTE Event A 1 is triggered when the serving cell becomes better than a threshold. (Value of Hysteresis: 0 ~ 30 d. B) Trigger: Mserv - Hyst > Threshold Stop : Mserv + Hyst < Threshold RSRP UE does not measure and report intra-frequency neighbor list. Event A 1: Mserv - Hyst > Threshold 1 Thresh 1 + Hyst Threshold 1 (LNCEL: 0~97 d. B, 1 d. B) Thresh 1 - Hyst Serving Cell Time Serving Cell 19 UE measures intra-frequency neighbor list and reports A 3 or A 5 if conditions are met.

Event A 2 The LTE Event A 2 is triggered when the serving cell becomes worse than a threshold. (Value of Hysteresis: 0 ~ 30 d. B) Trigger: Mserv + Hyst < Threshold Stop : Mserv - Hyst > Threshold RSRP Event A 2: Mserv + Hyst < Threshold Thresh + Hyst Threshold 2: Threshold 2 Inter. Freq Threshold 2 Wcdma Threshold 2 GERAN Thresh - Hyst Serving Cell Time Serving Cell 20 UE measures inter-frequency neighbors (reports A 3 or A 5) and inter-RAT NB (reports B 2)

• • Threshold 2 a：啟動事件A 1, 解除事件A 2（異頻測量，異系統測量）異頻交遞測量停止條件： – Serving RSRP>threshold 2 a-140 – 持續在a 1 Time. To. Trigger. Deacttime. Meas（例: 480 ms）時間內，服務細胞RSRP一直大於 threshold 2 a +hys. Threshold 2 a，則觸發事件A 1，停止異頻和異系統的測量。 21 Resource: Nokia, TTC redraw

Event A 3 The LTE Event A 3 is triggered when a neighboring cell becomes better than the serving cell by an offset. Trigger: Mn + On, f + On, c - Hyst > Ms + Os, f + Os, c + Offset Stop : Mn + On, f + On, c + Hyst < Ms + Os, f + Os, c + Offset RSRP Event A 3: NB > P-Cell + offset Relative Parameter: A 3 offset (LNCEL: -15~15, 0. 5 d. B) A 3 Report. Interval (120 ms(0)~60 min(12) a 3 Time. To. Tigger (LNCEL: 0 ms(0)~5120 ms(15) Total Offset Serving Cell Neighbor Cell 22 Time

Description of Event A 3 The LTE Event A 3 is triggered when a neighboring cell becomes better than the serving cell by an offset. 23 Resource: Nokia, TTC redraw

Event A 4 The LTE Event A 4 is triggered when a neighboring cell becomes better than a threshold. Trigger: Mn + On, f + On, c - Hyst > Threshold Stop : Mn + On, f + On, c + Hyst < Threshold RSRP Event A 4: Mn + Offset- Hyst > Threshold When Neighbor Cell + offset – Hyst>Threshold Event A 4 will be trigged (Load Balance Handover) Time Neighbor Cell 24

Event A 5 The LTE Event A 5 is triggered when the serving cell becomes worse than threshold -1 while a neighboring cell becomes better than threshold-2. Trigger: Ms + Hyst < Threshold-1& Mn + On, f + On, c - Hyst >Threshold-2 Stop : Ms - Hyst > Threshold-1 or Mn + On, f + On, c + Hyst <Threshold-2 RSRP Event A 5: Serving < TH 1 & NB > TH 2 Threshold 1 Serving Cell Neighbor Cell 25 Time

Description of Event A 5 在a 5 Time. To. Trigger時間內，服務細胞RSRP持續小於Threshold 3，而鄰近細胞RSRP一直大於Threshold 3 a，則觸發事件A 5 UE回報A 5 Event，A 5報告時間之間隔由a 5 Report. Interval決定。 26 Resource: Nokia, TTC redraw

Event B 1 The LTE Event B 1 is triggered when a neighboring inter-system cell becomes better than a threshold. Trigger: Mn + On, f - Hyst > Threshold Stop : Mn + On, f + Hyst < Threshold RSRP Event B 1: Mn + On, f - Hyst > Threshold Serving Cell Inter-system Cell 27 Time

Event B 2 The LTE Event B 2 is triggered when the serving cell becomes worse than threshold-1 while a neighboring inter-system cell becomes better than threshold-2. Trigger: Ms + Hyst < Threshold-1& Mn + On, f + On, c - Hyst >Threshold-2 Stop : Ms - Hyst > Threshold-1& Mn + On, f + On, c + Hyst <Threshold-2 RSRP Event B 2: Serving < TH 1 & NB > TH 2 Threshold 1 Serving Cell Inter-system Cell 28 Time

Mobility Management 29

Mobility Principles • EPS • complete realization of multi-access convergence: • a packet core network that supports full mobility management • access network discovery • and selection for any type of access network. • The functionality of mobility management • the network can “reach” the user • a user can initiate communication towards other users or services • ongoing sessions can be maintained as the user moves EPC 30

Mobility within 3 GPP Family of Accesses • Cellular Idle-Mode Mobility Management • Not be practical to keep track of a UE in idle mode every time it moves between different cells. • Not practical to search for the UE in the whole network for every terminating event (incoming call) • Cells are grouped together into “registration areas” EPC 31

Cellular Idle-Mode Mobility Management (1/7) EPC 32

Cellular Idle-Mode Mobility Management (2/7) • Base stations broadcast registration area information. • UE compares the broadcasted registration area information with its own information EPC 33

Cellular Idle-Mode Mobility Management (3/7) • In EPS the registration areas are called Tracking Areas (TAs). • As long as the UE moves within its list of allocated TAs, it does not have to perform a tracking area update. • Periodic updates are used to clear resources in the network for UEs that are out of coverage or have been turned off. EPC 34

Cellular Idle-Mode Mobility Management (4/7) • In GSM/WCDMA there are two registration area concepts: • the PS domain (Routing Areas, RAs) • the CS domain (Location Areas, LAs). • The Routing Areas are a subset of the Location Areas and can only contain cells from the same LA. EPC 35

Cellular Idle-Mode Mobility Management (5/7) • A summary of the idle mobility procedure in EPS: • A TA consists of a set of cells • The registration area in EPS is a list of one or more TAs • The UE performs TA Update when moving outside its TA list • The UE also performs TA Update when the periodic TA Update timer expires. • An outline of the Tracking Area Update procedure is shown in the figure of next slide. EPC 36

Cellular Idle-Mode Mobility Management (6/7) EPC 37

Cellular Idle-Mode Mobility Management (7/7) • Paging is used to search for Idle UEs and establish a signaling connection. EPC 38

References 1. 電信技術中心 TTC Notes. 2. M. Olsson, Shabnam Sultana, Stefan Rommer, Lars Frid, and C. Mulligan, “EPC and 4 G Packet Networks, ” Second Edition: Driving the Mobile Broadband Revolution, Elsevier, 2013 EPC 39