61048021-LA-RA-URA-guide

Location Area Planning Guidelines for 2G/3G Networks

Nokia Proprietary and Confidential


1 Contents

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1 Contents ................................................................................................................................................. 2

2 Introduction ............................................................................................................................................ 3

3 Registration Area Definitions ................................................................................................................ 5 3.1 Location areas (LA) ............................................................................................................................................... 5 3.2 Routing areas (RA) ................................................................................................................................................ 5 3.3 UTRAN registration areas (URA) ......................................................................................................................... 6 3.4 Cell Area ................................................................................................................................................................ 6 3.5 Service Area (SA) .................................................................................................................................................. 7 3.6 Area Identifiers ...................................................................................................................................................... 7

4 2G/3G Planning Guidelines for LA, RA and URA ................................................................................ 8

2 (9) © Nokia Networks OyNokia Proprietary and Confidential

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2 IntroductionMobility Management (MM) of the core network (CN) is maintaining the UE location in UMTS network .In GSM MM is completely handled between MS and NSS(VLR/HLR), in 3G also RNC is partially handling some MM functions.

UMTS contains 4-level location definitions:

1. Location Area (LA) in CN Circuit Switched (CS) domain

2. Routing Area (RA) in CN Packet Switched (PS) domain

3. UTRAN registration area (URA) in RAN (RNC)

4. Cell area

In CS Idle mode, CN knows the locations of a UE with the accuracy of LA.

In PS Idle mode, CN knows the locations of a UE with the accuracy of LA/RA.

In connected mode (CS-connected or PS-connected) UE is known from CN by SRNC. In 3G There is no LA or RA update when UE is in connected mode, see picture down..

Picture 1: Different Update procedures in GPRS and 3G

The RNC maintains registration of the current URA for each UE. Like LA and RA, the URA identity is stored to USIM.

Location Area update is done between UE-RNC-MSC/VLR (one or many MSC/VLR). Routing Area update is done between UE-RNC-SGSN (one or many SGSN). Cell update and URA update is done between UE and RNC.

LA, RA or URA size affects the amount of Paging traffic (on PCH in DL) and other common channel traffic (mainly on RACH in UL and FACH in DUL)


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MM

RR RR BSSGb BSSGb

MM

RA Update

UE BSC SGSN

MM

RRC RRC RANAP RANAP

MM

LA Update

UE RNC MSC

MM

RRC RRC RANAP RANAP

MM

RA/ LA Update

UE RNC SGSN

GPRS

3G PS MM

CS MM

Standby/ Idlestate

MM

RR RR BSSGb

RA Update, cell update

UE BSC

MM

RRC RRCRANAP RANAPURA and cell

updating,Handover

UE RNC SGSN

MM

RRC

UE

Ready/ MM-connectedstate

Handover

MM

RANAP

MM

MSC

RRC RANAP

RNC

BSSGb

MM

SGSN

MM

RR RR BSSGb BSSGb

MM

RA Update

UE BSC SGSN

MM

RRC RRC RANAP RANAP

MM

LA Update

UE RNC MSC

MM

RRC RRC RANAP RANAP

MM

RA/ LA Update

UE RNC SGSN

GPRS

3G PS MM

CS MM

Standby/ Idlestate

MM

RR RR BSSGb

RA Update, cell update

UE BSC

MM

RRC RRCRANAP RANAPURA and cell

updating,Handover

UE RNC SGSN

MM

RRC

UE

Ready/ MM-connectedstate

Handover

MM

RANAP

MM

MSC

RRC RANAP

RNC

BSSGb

MM

SGSN


• With increasing sizes of LA, RA or URA, traffic on the PCH will also increase. Paging messages intended for UE’s not camping in the same cell as a specific UE will cause extra traffic in the cell that the UE is camping on if both cells belong to the same registration area.

• The bigger the registration area, the higher the probability that extra PCH traffic is produced in a cell and the higher the PCH traffic in that cell.

• With increasing sizes of LA, RA and URA, the RACH and FACH traffic caused by location update, routing area update and URA update will decrease.

Picture 21. Areas with relations


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cell

cell

cell

cell

LA

RA

RA

URA

URA

URA

URAcell

cell

cell

cell

cell

cell

cell

cell

cell

cell

cell

cell

PLMN Area including BSS and RAN


3 Registration Area Definitions

3.1 Location areas (LA)

A LA consists of a set of cells with a size of at minimum one cell and at maximum an MSC/VLR area. A LA further has the following characteristics:

• When crossing the border of an LA, the CS idle UE has to perform a location (LA) update procedure.

• The LA is used by only the CS (circuit switched) domain of the CN (core network).

• The CN uses a TMSI to identify an UE within a LA. A TMSI is reassigned with a location update procedure and has to be unique within a LA.

• A RNC may include many LA’s or a LA may span over many RNC areas; in this last case, the RNC’s have to be connected to the same MSC/VLR.

LAC is broadcasted to UE in system information messages, in BCCH. LAC is read by UE in idle mode. LA update is performed by UE in CS-idle mode only (not in CS-connected or CS-detached mode).

Also periodic LA update is possible, but as a default it is not used.

Parameter used

• WCEL: LAC (location area code): range 1..65535, step 1

3.2 Routing areas (RA)

A RA has to be a subset of a LA and cannot span upon more than one LA. Furtheremore a RA has the following characteristics:

• A RA has a size of at minimum one cell and at maximum a SGSN area.

• The RA is used by only the PS (packet switched) domain of the CN.

• The CN uses a P-TMSI to identify an UE within a RA. A P-TMSI is reassigned with a routing area update procedure and has to be unique within a RA.

• When crossing the border of a RA, the PS idle UE has to perform a routing (RA) update procedure.

• A RNC may include many RA’s or a RA may span over many RNC areas but not over many LA’s; in the latter case, the RNC’s have to be connected to the same SGSN.

RAC is broadcasted to UE system information meaasge, in BCCH. It is read by UE in idle mode. RA update is performed by UE in PS-idle mode only with one exception that


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UE shall also initiate RA update in PS- connected mode when RAI in MM system information change after SRNS relocation. In this case, the new RNC sends new MM system information to UE via UTRAN MOBILITY INFORMATION message. Not used in PS-detached mode.

Also periodic RA update is possible, default value is 54 min.

Parameter used

• WCEL: RAC (routing area code): range 0..255, step 1

3.3 UTRAN registration areas (URA)

A URA is an area known only in the UTRAN, but not at CN level. The followings further characterize an URA:

• URA area is used inside UTRAN, but not at CN level• Each cell in the network is assigned at least one URA identifier (URAid) Overlapping URA’s are possible

• Overlapping URA’s reduces the number of URA updates for a given UE• URA consist of number of cells belonging to one RNC• URA is used to avoid high amount of cell updates for high mobility UEs. UE will

change state from CELL_PCH state to URA_PCH state based on certain parameters defined in RNC. only URA updates instead of cell updates

URA update is a RRC procedure. URA_id is broadcasted to UE in System Information message, send on BCCH. It is read and used in connected mode in URA_PCH state.

URA_update is done either periodically or by URA reselection in case there has been URA change. The default value for periodic update is 30 min.

Parameter used

• WCEL: URAId, range 1…65535, step 1, Each cell can belong to 8 different URAids. • WCEL: URAidlist

3.4 Cell AreaA cell is the smallest entity in the UTRAN, it is not known in the core network.

Cell update is a RRC procedure. Cell ID is broadcasted to UE in System Information message, send in BCCH. It is read in idle mode, CELL_FACH, CELL_PCH and URA_PCH state.

A cell update takes place if the UE leaves the cell border while it is in CELL_FACH or CELL_PCH state. Also cell update can happen in CELL_DCH state if the criteria for radio link failure is met.


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Cell Update is done also to notify UTRAN after re-entering service area in the CELL_FACH or CELL_PCH state, or during paging response.

Cell Update is done also periodically. The default value for periodic update is 30 min. Same timer used as in URA_update.

3.5 Service Area (SA)

Service Area is used for location services (LCS) and cell Broadcast (BC) services (not implemented in RAN1.5). They are not as such related to LA or RA . In Ran1.5 the max accuracy of SA is the cell level, In RAN2.1 the accuracy is better -inside the cell.

There is no Service Area update message send between UE and RAN.

Service Area Broadcast feature (RAN2.0) enables information provider to submit short messages for broadcasting to a specified Service Area within the PLMN. These messages could be used for informing of, for example, PLMN news, emergencies, traffic reports, road accidents, delayed trains, weather reports, theatre programmes, telephone numbers or tariffs

The Service Area Identifier (SAI) identifies an area consisting of one or more cells which belong to the same Location Area (LAI).

The Service Area Identifier is composed of the PLMN Identifier, the Location Area Code (LAC) and the Service Area Code (SAC).

The SA planning rule is different for LCS and BC purposes. A cell may belong to one or two Service Areas. In the case that it belongs to two Service Areas, one is applicable for the BC and the other is applicable for the LCS. The broadcast (BC) requires that Service Area consist of one cell.

• For LCS purposes, 1 SAC is 1 Antenna (same for all carriers within the sector) or including many cells depending on the operator

• For BC purposes, 1 SAC is 1 UTRAN cell

Parameter used

• WCEL: SAC, range 1…65535, step 1

3.6 Area IdentifiersSeveral identifiers are needed to identify neighbour cells:

• UTRAN Cell Identifier = Global RNC Identifier (GlobalRNCid) and the Cell Identifier (CI).

• PLMN Identifier (PLMNid) consists of Mobile Country Code (MCC) and Mobile Network Code (MNC)

• Location Area (LAI)=PLMN Identifier + Location Area Code (LAC)

• Routing Area = Location Area (LAI) + Routing Area Code (RAC)


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• Service Area Identifier (SAI) = SAC + LAC +PLMNid

A neighbour cell is identified with following combination:

Neighbour info for UTRAN cell: MCC + MNC + RNC ID + CI + LAC + RAC

Neighbour info for GSM cell: MCC+MNC+LAC+CI+BCCH+BSIC

4 2G/3G Planning Guidelines for LA, RA and URA

Initially the assumption was that the criteria for planning LA and RA areas is closely aligned with methodology used in a GPRS network. In a GPRS network the main limiting factor in dimensioning a Routing area is the demand on the CCCH caused by paging and routing area update messages.

Location areas and Routing areas should never run close to and parallel with major roads and railways, since the ‘ping ponging’ will create a heavy update-messaging load. Similarly routing areas that run perpendicular to major roads will create excessive upadate messaging on the cells serving that area.

In the beginning the LA & RA areas could be defined as such that the RA and LA update will happen at same place. One RA area could be then one RNC area, like one LA area is one BSC area.

URA area is smaller than LA/RA area because of the possibility to have high amount of paging traffic. To minimise the paging traffic an estimation is to use 10-20 sites per one URA, and adding second URA for those cells at URA boundary area. By doing so URA update will be avoided in URA boundary.

SA is used for Location Based Services (LCS) and Broadcast Services (BC). The planning rule is different for these services.

Summary of the planning rules:

1. CI (2G & 3G)


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Use different CI codes for 2G and 3G cell for easy identification purposes within same PLMN.

2. LA (2G & 3G)

The initial size of this is one BSC and one RNC area. Use different LA code for 2G and 3G cells.

3. RA (GPRS & 3G)

The initial size of RA is LA area. Use different RA code for 2G and 3G cells.

4. URA (3G only)

This is done only for 3G cells. Use 10-20 sites per one URA area, add second URA for cells at URA boundary area to avoid URA updates.

5. SA

The SA concept is fully used in RAN2 releases, where the following rules could be used:

• For LCS purposes only (in RAN1.5), 1 SAC is 1 antenna (same for all carriers within the sector) or including many cells depending on the operator.

• For BC purposes, 1 SAC is 1 UTRAN cell, this is only possible with RAN2.0. Also other SAC code is needed for LCS. The content of the codes could be similar.

Picture 32: Example of Area definitions


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UMTS RAN

MSC/VLR3G

GSM/GPRS BSS Iu (ps)-interfaceIu (cs)-interface

GSM/GPRS BSS

Operator 1,PLMN1

3G HLR/AUC

MGW

LA_2G=1RA_2G=1

Intranet

2G/3G SGSN

GPRS/3G Backbone

Iu (ps)-interface

UMTS RAN

LA_3G=2RA_3G=2

URA_area: same code for 10-20 3G cells, in URA boundary use two codes/3G cell

CI for 2G and 3G cells different when Co-siting is used

LA_2G=3RA_2G=3LA_3G=4RA_3G=4

• LA and RA is needed foreach 2G and 3G cell, in case of co-siting, different CI, LA and RA valueis needed even if the area size is same.Assumtion here is that eachBSC/RNC is one LA area =RA areaCI for 2G and 3G cells could besame, but its easier to identify thecells if CIs are different

3G SGSN

UMTS RAN

One Uraid/cell in this area

Two Uraids/cell in this area

(URA_boundary)

One Uraid/cell in this area

URA_id=10

URA_id=10,11

URA_id=11

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61048021-LA-RA-URA-guide