Mobility Management. Sara Modarres Razavi

(1)

Mobility

(2)

›

BSc in Electrical Engineering (2000-2004), Ferdowsi University, Iran

›

MSc in Hardware for Wireless Communications (2004-2006), Chalmers, Sweden

›

PhD in Infra-informatics (2008-2014), Linköping University, Sweden

›

Radio Network Planner at Taliya Network Operator (2006-2008)

›

Researcher at SICS Swedish ICT (6 months in 2014)

›

Experienced Researcher at Ericsson (Linköping) since August 2014

(3)

LTE Architecture and

protocols

(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

(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:

(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.

(7)

Location management

Tracking Area Update

Paging

Location Area (LA) in GSM

Routing Area (RA) in GPRS and UMTS

Tracking Area (LTE)

(8)



Update message from user over the uplink control channel



Signaling for updating the database



TAU is costly for the network (Why?)

(9)

Tracking area update

signaling

UE

MME

HSS

TAU Accept

TAU Request

(10)

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.

(11)



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?)

(12)

Paging signaling

UE

eNodeB

MME

Paging

Paging Response

Paging

(13)

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

.

paging

(14)

(15)

Signaling overhead

calculation

 











N

i

j

N

j

i

ij

i

p

ij

u

t

S

u

c

t

S

h

c

Overhead

:

))

(

))

(

1 (

(



otherwise

t

if

t

s

_ij

i



j









0

1 )

(

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

(16)

›

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.

(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

(18)

Static update schemes



Static Update Schemes:

- Always Update

- Never Update

- Reporting Cells

- Forming TA

(19)

Dynamic update

schemes

- Selective TA Update

- Time-based

- Profile-based

- Movement-based

- Distance-based

(20)

Paging strategies



Blanket polling (simultaneous paging)



Shortest-distance-first



Sequential paging



Velocity paging

(21)

›

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.

(22)