Mobilility_LTE

7/28/2019 Mobilility_LTE

1/48

1 Copyright 2010 AIRCOM International

LTE Mobility


2/48


Air InterfaceRel99 / Rel 4

IDLE

CELL DCH

QoS

CELL FACH

NO QoS

CELL URA CELLPCH


3/48


4/48


UE Power upUE Power up

DL Syn and Physical Channel ID

Find MIB System BW

MCC +MNC

SIBs supported

PCFICH Processing-

Knows the set up of PDCCH

Retrieval of SIBs

Cell Selection Parameters

Cell Selection

SuccessfulPre-amble / Attach

Yes

Acquire another

LTE Cell

PLMN ID

matches

Cell Barred

After AttachDefaulf

Bearer/IP adress


5/48


LTE-UE

Evolved UTRAN (E-UTRAN)

MME

S6a

Serving

Gateway

S1-U

S11

Evolved Packet Core (EPC)

S1-MME

PDN

Gateway

Internet

PCRF

S7

S5

Evolved

Node B

(eNB)

X2

LTE-Uu

HSS

MME: Mobility Management Entity

EPS Mobility Management

EPS Mobility Management 2 states:

EMM-DEREGISTERED

EMM-REGISTERED


6/48


EPS Mobility Management 2 states

EMM-DEREGISTERED: In this state the MME holds no valid location

information about the UE

Successful Attach and Tracking Area Update(TAU) procedures lead to transition to EMM-

REGISTERED

MME

MME

EMM-REGISTERED:

In this state the MME holds location

information for the UE at least to the

accuracy of a tracking area

In this state the UE performs TAUprocedures, responds to paging messages

and performs the service request procedure

if there is uplink data to be sent


7/48


Tracking Area update - IDLE

MME HSS

s6a

NAS: Tracking Area

update

LTE Non Access Stratum (NAS) The LTENAS protocol software enables

communication with the MME in the LTE

core network and handles functions of

mobility

Tracking AreaTracking AreaHome

Tracking Area Identity = MCC (MobileCountry Code), MNC (Mobile NetworkCode) and TAC (Tracking Area Code


8/48


Tracking Area update - IDLE

TAI1-2

TAI2

TAI2

TAI2

TAI3

TAI3

TAI3

TAI3

TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI2

TAI1

TAI1

TAI1

TAI1-2

Tracking areas are

allowed to overlap: onecell can belong to

multiple tracking areas

NAS: Tracking Area

updateMME


9/48


MME

Serving

Gateway

S1-MME(Control Plane)

S1-U

(User Plane)

NAS Protocols

S1-AP

SCTP

IP

L1/L2

User PDUs

GTP-U

UDP

IP

L1/L2

eNB

LTE Functional Nodes- Management Entity(MME

Tracking area (TA) is similar to Location/routing area in2G/3G

Tracking Area Identity = MCC (Mobile Country Code),

MNC (Mobile Network Code) and TAC (Tracking AreaCode

Tracking Area Update RequestS-TMSI/IMSI,

PDN address allocation Tracking Area Update Accept

Tracking Area Update Complete


10/48


MME

S1-MME

(Control Plane)

NAS Protocols

S1-APSCTP

IP

L1/L2

eNB

LTE Functional Nodes- (MME)

Tracking Area Update Request

S-TMSI/IMSI,

Home -HSS V-HSS

S6a

IMSI:Used to uniquely identify a subscriber world-wide.

Its structure is kept in form of

MCC+MNC+MSIN:MCC

MSIN: mobile subscriber identification number

MME uses the IMSI to locate the HSS holding thesubscribers permanent registration data for trackingarea updates and attaches.


11/48


MME

S1-MME

(Control Plane)

NAS Protocols

S1-APSCTP

IP

L1/L2

eNB


Tracking Area Update Request

S-TMSI/IMSI,

S-TMSI:Itis dynamically allocated by the serving MME.

Its main purpose is to avoid usage of IMSI on

air.

Internally the allocating MME can translate S-

TMSI into IMSI and vice versa.


12/48


Summary

EMM

deregisteredEMM

registered

Attach

Detach

EMM-DEREGISTERED:

In this state the MME holds no valid

location information about the UE

Successful Attach and Tracking

Area Update (TAU) procedures

lead to transition to EMM-

REGISTERED

EPS Mobility Management


13/48


RRC States Idle OR Connected

In the early deployment phase, LTE coverage will certainly be restricted to

city and hot spot areas.

LTE

Connected

LTE _IDLE

Cell DCH

Connected

Cell FACH

Cell URA

Cell PCH

IDLE GSM/GPRS

IDLE

GSM

Connected

GPRS

PacketTransfer

Handover Handover

Cell Selection

/Reselection

Connection

Establishment/ReleaseConnection

Establishment/Release

Connection

Establishment/

Release


14/48


MME

RRC Connected Always ON HSS

MME triggered SAE bearer setup: This happens typically

during the attach procedure of an UE.

HO Handovers supported Signaling Bearer to MME

S1-U

LTE-Uu

S5Internet

eNB Serving

GatewayPDN

Gateway

DEFAULT SAE Bearer ServiceExternal Bearer

Service

S11

System Architecture Evolution- SAE

S1-MME

(Control Plane)


15/48


MME

S1-MME

(Control Plane)

RRC Connected HSS

MME triggered SAE bearer setup:

Depending on the information coming

from HSS, the MME will set up aninitial SAE bearer, also known as the

default SAE bearer. This SAE bearer

provides the initial connectivity of the

UE with its external data network

S1-U

LTE-Uu

S5Internet

eNB Serving

GatewayPDN

Gateway

DEFAULT SAE Bearer ServiceExternal Bearer

Service

S11

System Architecture Evolution- SAE

IP Address Allocation with Default bearer

S1-MME

(Control Plane)


16/48


Setting up a default bearer

IDLE RRC

Connected

Cell Selection done by UE

Based on UE measurements

Controlled by parameters

Network controlled handovers


ALWAYS ON

CCCH:RRC Connection Request

CCCH:RRC Connection Set up

DCCH:RRC Connection Set up Complete

Connected

Admission control

MUST PERFORM ATTACH

DEFAULT BEARER SET UP

IP Address Allocation with Default bearer


17/48


LTE Functional Nodes- default SAE bearer.

S1-U

LTE-Uu

S5

Internet

eNB Serving

GatewayPDN

Gateway

default SAE bearer NGBRSIP

SIP server

The default SAE bearer is created after the UE performs the attach.

Subsequent SAE bearers are known as dedicated SAE bearers.

They are expected to be allocated on a per application base

dedicated SAE bearers - GBRVoIP

Dedicated SAE bearers are to be triggered by Service Request


18/48


Set up dedicated SAE bearers.

S1-U

LTE-Uu

S5

Internet

eNB Serving

GatewayPDN

Gateway

default SAE bearer NGBRExternal Bearer

Service

SERVICE REQUEST SERVICE REQUEST MME

Initial ContextRRC Reconfig

RRC ACK Context ACKUpdate Bearer

Update ACK


19/48


MME

RRC IDLE HSS

S1-U

LTE-Uu

S5Internet

eNB Serving

GatewayPDN

Gateway

S1-MME

(Control Plane)

IDLE

NO S1 BEARERCell Selection done by UE


TRACKING AREA UPDATE

In this state the MME holds location information for the UE

at least to the accuracy of a tracking area

In this state the UE performs TAU procedures, responds to

paging messages and performs the service request

procedure if there is uplink data to be sent


20/48



LTE-Uu

Internet

Serving

Gateway

PDN

GatewayMME

DL Packet

Notification

Paging

S-TMSI,

Paging

S-TMSI,DL Data

RRC_Connected

Connected

Service Request

S-TMSI


21/48


RRC IDLE Cell Selection

eNB


22/48


RRC IDLE

BCCH

PBCHBCH DL-SCH

PDSCH

SIBs

MIB

Radio Block


23/48


RRC IDLE

20MhzBW

MIBBW = 1.08Mhz

BCCH

BCH

PBCH

MIB

DL-SCH

PDSCH

Logical channels

Transport channels

Physical channels


24/48


RSRP is a RSSI type of measurement. It measures the average

received power over the resource elements that carry cell-

specific reference signals within certain frequency bandwidth.

RSRP is applicable in both RRC_idle and RRC_connected modes

RSRP (Reference Signal Received Power)

Radio

Blockreference signals

Are transmitted inALL radio blocks


25/48


Physical Cell Identity (PCI)

The UE moving towards a new cell and identifies the Physical Cell

Identity (PCI) based on the Synchronization signals

Physical Cell Identity (PCI) = 504

P-SCH S-SCH

P-SCH: for cell search and identification by

the UE -Carries part of the cell ID (one of 3

orthogonal sequences)

S-SCH:for cell search and identification bythe UE Carries the remainder of the cell ID

(one of 168 binary sequences)


26/48


Cell Reselection:

Measuredneighbours

PCI

Best ranked cell

Measurement criteria

S criteriaSuitable

neighbours

R criteria

Re-selection if not serving cell

neighboring cell was ranked with thehighest value R

Srx > Q rxlevmeas (qrxlevmin

Qrelevmin offset)

PCI PCIPCI


27/48


LTE_ACTIVE idle

For a cell to be suitable:

S rx level>0

Srx > Q rxlevmeas (qrxlevmin Qrelevmin offset)

RRC Idle

Cell Selection done by UEBase on UE Measurements

Q rxlevmeas


LTE_ACTIVE idle (Cell Selection)

reference signals

Are transmitted in

ALL radio blocks


28/48


RSRP is a RSSI type of measurement. It measures the

average received power over the resource elements that

carry cell-specific reference signals within certain frequencybandwidth.

RSRP is applicable in both RRC_idle and RRC_connected modes


20MhzBW

REF

BW = 1.08Mhz


29/48


For a cell to be suitable:

S rx level>0

Srx > Q rxlevmeas (qrxlevmin Qrelevmin offset)

Srx = -100 (-80) = -20 (Will not do cell selection)

LTE_ACTIVE idle (Cell Selection)

Q rxlevmeas=-100dBm

Will not do cell selection

Q qrxlevmin =-80dBm

Q rxlevmeas



30/48


Cell Reselection: R-Criterion

Measuredneighbours

Best ranked cell

Measurement criteria

S criteriaSuitable

neighbours

R criteria

Rs = Qmeas,s + Qhysts cell)

Rn = Qmeas,n - Qoffsets,nfor candidate neighbouring cells for cell

reselection

PCI PCI PCIPCI


31/48


Cell Reselection: R-CriterionRs = Qmeas,s + Qhysts (for the serving

cell)

Qmeas,n

Qmeas,s

RSRP

(dBM)

Rs

Rn

Qoffsets,n

Qhysts

Rn > Rs=>cell reselecti

Treselection

the time interval value Treselection,

whose value ranges between 0 and

31 seconds


32/48


HANDOVER

RRC CONNECTED


33/48


MME

Serving

Gateway

S1-MME

(Control Plane)

S1-U

(User Plane)

NAS Protocols

S1-AP

SCTP

IP

L1/L2

User PDUs

GTP-U

UDP

IP

L1/L2

eNB

LTE Functional Nodes- Management Entity(MME

S1-AP UE ID:Two additional temporary

identifiers allocated by eNB

and MME:

- eNB S1-AP UE ID

- MME S1-AP IE ID


34/48


LTE Functional Nodes- X2

User PDUs

GTP-U

UDP

IP

L1/L2

X2-UP

(User Plane)

X2-CP

(Control Plane)

X2-AP

SCTP

IP

L1/L2eNB

eNB

X2

Connected

Mode


35/48


User plane switching in Handover

RLC

RLC

RLCRLC

RLC RLC

X2

Connection


36/48


Handover

IP

L2Ethernet

UDP

GTP -C

L1-SDH

Serving Gateway

MME

IP

L2Ethernet

UDP

GTP -C

L1-SDH

SCTP

IP

S1AP

NAS

L2

(Ethernet)

IP

L2Ethernet

UDP

GTP -U

L1-SDH

MAC

PHY

RLCPDCP

IP

TCP/UDP

User Plane

MAC

PHY

RLCRRC

NAS

Control

DATA

SCTP

IP

S1AP

NAS

L2(Ethernet)

MAC

PHY

RLC

RRC

NAS

Control

S1-

Cont

rol

MME

DIRECTION

Connected Mode Mobility

In LTE_ACTIVE, when a UE moves between two

LTE cells


37/48


2G network operators need to define the

neighbour lists

Also 3G network operators need to define the

neighbour lists but it is possible for UE todetect the new cells outside neighbour list

which makes neighbour list creation simpler.

LTE Functional Nodes-eNodeB


38/48


AUTOMATIC NEIGHBOUR RELATIONS

LTE_ConectedThe UE can detect the intra frequency

neighbours WITHOUT neighour lists

The UE moving towards a new cell and identifies the Physical Cell

Identity (PCI) based on the Synchronization signals

UE MEASUREMENT RORT

WITH PCI

Physical Cell Identity (PCI) = 504

Seving eNodeB

The measurement report contains information about the

PCI and the corresponding RSRP of the candidate cell


39/48



LTE_Connected state

THERE IS NO X2 CONNECTION

Therefore the serving eNodeBrequests the UE to decode the

Global Cell ID from broadcast

channel

UE MEASUREMENT RORT

WITH PCI

Seving eNodeB

The PCI cannot uniquely ID cell there could be thousands of cells

Request for Global cell ID


40/48



The globally unique cell identifier (GID) in LTE consists of

two parts:

PLMN Identity: The identity of the Public Land MobileNetwork. Note that a cell may have multiple PLMN

identities.

CIPL: Unique Cell Identity for a cell within a PLMN

UE MEASUREMENT RORT

WITH PCI

Seving eNodeB

Request for Global cell ID UE to decode the Global Cell ID

from broadcast channel

UE reports Global Cell ID

LTE_Connected state


41/48



whenever a new cell is introduced into the

system it contacts a Operation Support

Systems (OSS) in the network. The

configuration server provides the new cell with

the GID identity and an IP address OR/AND

VLAN ID

NEW CELL

ADDED

Operation Support

Systems (OSS)

GID

IP address

VLAN


42/48


OSS may initiate a network wide re-planning of PCIs

when a conflict is detected.

Serving

Cell

PCI=10

PCI=

6

PCI=

5

PCI=10

Operation Support

Systems (OSS)

neighbor cell

relation (NCR)

6,5,10

neighbor cell

relation (NCR)

10,6

neighbor cell

relation (NCR)

5,10

neighbor cell

relation (NCR)

6,5


43/48



The serving cell may order the mobile to read the GID

This could be done for example:

if the PCI is associated with a cell with handover failures in the past

or

if a central node such as the OSS has requested it.

Or

PCI conflicts

This method makes use

of mobile measurements to update the

neighbour cell relation lists in the cells

and to detect local cell identityconflicts, report the conflicts to the

Operation Support Systems (OSS

PCI=

6

neighbor cell

relation (NCR)5,10


44/48


UE MEASUREMENT RORT

WITH PCI

When a measurement report is received from a mobile it is

handled according to the following scheme:

Is the PCI of the candidate cell already known in theserving cell (i.e. is the neighbour relation already established)?

PCI=50

Yes: Initiate handover decision procedure.

Example

PCI=40

Neighbour Cell Relation (NCR)

PCI VLAN ID IP address

50 20 10.1.1.1


45/48


UE MEASUREMENT RORT

WITH PCI

Is the PCI of the candidate cell already known in the

serving cell (i.e. is the neighbour relation already established)?

PCI=50

neighbor cell relation (NCR)

Example

No: Consider the candidate cell as a NCR list candidate.

Order the UE to report GID. Obtain connectivity information for the

candidate cell and signal to the candidate cell, directly or through the

core network, about a mutual addition to the NCR lists of the two cells.

candidateRequest for Global cell ID

neighbor cell relation (NCR)

40

PCI=40


46/48


Hand over -Inter Frequency

Transmission Gap

Idle period

Minimum one sub-frame

Configured in UE by

Enode BUE needs Inter frequent

Neighbour list


47/48


Questions

How many PCI are there?

What is the function of the MIB?

What physical channel is the MIB transmitted on?

What is the bandwidth of a radio Block?


48/48

Questions

What is the function of the S-TMSI and what allocates it?

The total number of handovers are likely to be higher in LTE than in

UMTS..Why?

What is meant by a VLAN?

Mobilility_LTE

Documents

Transcript of Mobilility_LTE