Mobility Management. Sara Modarres Razavi

Transcription

1 Mobility Management Sara Modarres Razavi

2 Background BSc in Electrical Engineering ( ), Ferdowsi University, Iran MSc in Hardware for Wireless Communications ( ), Chalmers, Sweden PhD in Infra-informatics ( ), Linköping University, Sweden Radio Network Planner at Taliya Network Operator ( ) Researcher at SICS Swedish ICT (6 months in 2014) Experienced Researcher at Ericsson (Linköping) since August 2014 Ericsson Internal Page 2

3 LTE Architecture and protocols Ericsson Internal Page 3

4 Mobility management It aims to track the users and to allow calls, SMS and other mobile phone services to be delivered to users. The Mobility Management Entity (MME) is the control node that processes the signaling between the UE and the core network (CN). [Over Non Access Stratum (NAS) protocols] Functions supported by MME: Functions related to bearer management (Session management layer) Functions related to connection management (Connection establishment, and security between the network and UE) o Location Management o Paging and Search o Radio Resource Management (RMM) Ericsson Internal Page 4

5 Users in different technologies In GSM: The mobile terminal (MT) is in idle or busy state. In GPRS: The mobile station (MS) is in idle, ready, or standby state. In UMTS: The user equipment (UE) is in PMM-detached, PMM-idle, cell-connected, or URA-connected state. (PMM: packet mobility management) In LTE: The UE is in LTE-detached, LTE-idle or LTE-active state. Ericsson Internal Page 5

6 UE states in LTE LTE-Idle The network knows the location of the UE to the granularity of a group of cells (forming a TA). In the idle mode, the UE is in power-conservation mode and does not inform the network of each cell change. LTE-Active The network knows the cell which the UE belongs to, and UE can transmit and receive data from the network. No TAU/paging is necessary for active UEs. LTE-Detached In this mode either the UE is powered off or it is in the transitory state in which the UE is in the process of searching and registering to the network. Ericsson Internal Page 6

7 Location management Tracking Area Update Paging Tracking Areas Location Area (LA) in GSM Routing Area (RA) in GPRS and UMTS Tracking Area (LTE) Ericsson Internal Page 7

8 Tracking Area update Update message from user over the uplink control channel Signaling for updating the database TAU is costly for the network (Why?) Ericsson Internal Page 8

9 Tracking area update signaling UE MME HSS TAU Request TAU Request TAU Accept TAU Accept Ericsson Internal Page 9

10 Tracking area update The user registers its new TA with the current enodeb to allow the forwarding of incoming calls. Each update is a costly exercise: Use of network bandwidth Core network communication Modification of location database The aim is to reduce the number of update signaling messages. Ericsson Internal Page 10

11 Paging Determining the location at cell level of a specific UE Polling signals are sent over the downlink control channel to all cells where a user is likely to be present. All the users listen to the paging message and only the called user sends a response message back over the uplink control channel. Paging is costly for the network (why?) Ericsson Internal Page 11

12 Paging signaling UE enodeb MME Paging Paging Paging Response Paging Response Ericsson Internal Page 12

13 paging The network needs to precisely determine the current enodeb location of a UE to be able to route an incoming call. The network sends a paging query to all enodebs of the TA where the user is registered. The aim is to reduce the number of paging signaling messages. Ericsson Internal Page 13

14 Basic trade-off Ericsson Internal Page 14

15 Signaling overhead calculation Overhead s ij ( t) 1 0 i N if t j N: j i i t otherwise u ( c h (1 S ( t)) c j ij ij p u i S ij ( t)) c u = Cost of a single update c p = Cost of a single paging α = Call intensity factor (percentage of the users being called) u i = Cell load of i h ij = Cell handover between i and j Ericsson Internal Page 15

16 S-matrix properties Binary indicating whether or not two cells are in the same TA. Symmetric indicating the obvious fact that if cell a and b are in a same TA, the cells b and a are also in the same TA. Transitive meaning that whenever cells a and b are in the same TA, and b and c are in the same TA, then a and c are also in the same TA. Ericsson Internal Page 16

17 Some Tau strategies Static Update Schemes: - Always Update - Never Update - Reporting Cells - Forming TA Dynamic Update Schemes: - Selective TA Update - Time-based - Profile-based - Movement-based - Distance-based Ericsson Internal Page 17

18 Static update schemes Static Update Schemes: - Always Update - Never Update - Reporting Cells - Forming TA R R R Ericsson Internal Page 18

19 Dynamic update schemes - Selective TA Update - Time-based - Profile-based - Movement-based - Distance-based Ericsson Internal Page 19

20 Paging strategies Blanket polling (simultaneous paging) Shortest-distance-first Sequential paging Velocity paging Ericsson Internal Page 20

21 summary There is a tradeoff between TAU and paging procedure. A signaling overhead calculation method is presented to compute the total overhead of TAU and paging. There exists many TAU and paging schemes to reduce one of these parameters. For any network setup, there exists a TA configuration which minimizes the total signaling overhead of TAU and paging. Ericsson Internal Page 21

22