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UTRAN Paging Concepts

Sireesha Panchagnula

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Background

Paging Performance Improvement in GERAN. UTRAN paging research for future use. Apply lessons learnt from GERAN to UTRAN. Detailed document on UTRAN Paging Concepts at

http://docs.eng.t-mobile.com/inforouter/docs/~D460521

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UMTS vs. GERAN Paging

Factors not available in GERAN that make UMTS paging different UTRAN UE States in RRC connected mode Both CN and UTRAN can originate paging procedures Paging co-ordination DRX implementation Paging for system information updates

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UTRAN UE States

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RRC connected UE states

CELL_DCH Uses Dedicated channel, known on a cell level.

CELL_FACH Uses common channels, Known on a cell level.

CELL_PCH Receives on Paging channel, changes to CELL_FACH to transmit data. UE known on a cell level. Cell Update procedure informs network about its location.

URA_PCH Receives on Paging channel, changes to CELL_FACH to transmit data. UE known on a cell level. URA Update procedure informs network about its location.

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CELL_PCH vs. URA_PCH

UE is in CELL_PCH or URA_PCH - when it is not connected to the CS CN. CELL_PCH, URA_PCH - UE keeps a signaling connection to the CN but

has no radio resources. UE uses lesser power, and can be reactivated faster in the CN when

needed. Currently Ericsson supports URA_PCH but not CELL_PCH Currently Nokia support CELL_PCH but not URA_PCH. Disadvantage of CELL_PCH state – Overhead from high number of cell

updates. CELL_PCH URA_PCH based on an inactivity or excessive number of

cell updates

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Paging co-ordination in UMTS

Paging co-ordination - Network can send paging messages for CS services on the same channel as used for PS services.

Example of Paging co-ordination in UMTS

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UMTS Paging characteristics

UMTS Paging characterized by Originating Node – RNC or CN Paging Type 1 or Paging Type 2 Message Radio resources used for paging Paging Area

Paging Record - page intended for a specific UE Pages originated by CN or UTRAN converge at the RNC. RNC schedules paging records into a Paging Type 1 message (UE

is in idle, CELL_PCH or URA_PCH) or a Paging Type 2 message (UE is in CELL_FACH or CELL_DCH).

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UMTS Paging characteristics

UE State

RRC Connected

Paging Type

Resources Used

Originating Node

Paging reason Paging Area

Idle State No Type 1 PICH and SCCPCH (carrying PCH)

CN Terminating service LA / RA

UTRAN System Information updates

CELL_DCH Yes Type 2 DPCCH (carrying DCH)

CN Terminating service from a CN that UE is not connected to

Specific UE

CELL_FACH Yes Type 2 SCCPCH (carrying FACH) and PRACH (carrying RACH)

CN Terminating service from a CN that UE is not connected to

Specific UE

CELL_PCH Yes Type 1 PICH and SCCPCH (carrying PCH)

CN CS Terminating service Last known cell

UTRAN Allow UE to trigger cell update procedure, System Information Updates

URA_PCH Yes Type 1 PICH and SCCPCH (carrying PCH)

CN CS Terminating service Last known URA

UTRAN Allow UE to trigger cell update procedure, System Information Updates

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Paging signaling flows

CN originated paging in Idle Mode

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Paging signaling flows

CN originated paging in CELL_DCH or CELL_FACH mode

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Paging signaling flows

UTRAN originated paging in CELL_PCH / URA_PCH

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Paging channels

PICH and SCCPCH (carrying PCH) are used to carry Paging Type 1 message for UEs in idle, CELL_PCH and URA_PCH mode.

Mobiles listen first to PICH on their turn, and if they get a positive indication, listen to the corresponding SCCPCH 2 ms later.

Fixed relation between each PICH and the corresponding SCCPCH.

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Paging Groups or Indicators

Np = 18, 36, 72 or 144 paging groups or paging indicators (PI) per cell. PICH has 288 bits to carry PI. # bits representing one PI = 288/Np. More Paging groups => Less # of bits representing PI => high

probability of erroneous transmission => PICH sent with higher power. Less Paging groups => More # of bits representing PI => less

probability of erroneous transmission => PICH sent with lower power. Less Paging groups => High chance that UE listens to PICH without

a page in associated SCCPCH. PI for a specific UE can be calculated based on its IMSI. In Ericsson – Np is hard coded to 18. In Nokia – Np is parameter controlled.

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Discontinuous Reception

DRX - Mobiles listen to PICH only in certain paging occasions, which helps increase battery life.

Paging occasions for a specific UE are calculated as

(IMSI mod DRX cycle length) + n * DRX cycle length, n = 0, 1, 2… DRX cycle length = 2k * 10 ms; k is CN domain DRX cycle length

coefficient. Typical values of DRX cycle length are 320 ms or 640 ms.

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Paging for System Information Updates

RNC sends paging message to a UE in idle, CELL_PCH and URA_PCH to inform about available updates to System Information.

Then UE reads the BCCH for the new system information.

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Paging Repetition in Ericsson UTRAN

Ericsson - Depends on the UE state, originating node. CN page repeated by UTRAN irrespective of response –

parameter controlled. UTRAN page repetition is time supervised. If RNC timer expires -

page is repeated once. Timer is hard coded. UTRAN repeats page for the same system information update

information with maximum possible DRX cycle length a specified number of times – parameter controlled.

Nokia - Repetition only for CELL_PCH state Page can be repeated up to a maximum of 2 times – parameter

controlled. Parameters set interval between repetitions.

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Factors affecting UTRAN paging

Similar concepts as in GERAN. Periodic LA update based on RNC parameter T3212 - avoids

unnecessary paging of mobiles that have lost coverage. IMSI Attach/Detach procedure helps avoid unnecessary paging

attempts. UE sends a ‘Detach’ message when it is powered off. CN knows that

the UE is inactive, it will not send any pages to this UE. UE performs LA registration with IMSI attach if switched on in the

same LA as switched off , or normal LA update otherwise.

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LA, RA and URA

Location Area is where a UE is paged for CS service. Routing Area is where a UE is paged for PS service. URA – UTRAN Registration Area exists only in the UTRAN and is

completely unknown to the CN. URA can’t span over RNC borders. URAs within an RNC can overlap. Each cell can belong to a maximum of 4 URAs. URA can span over LA/RA borders. UEs in URA_PCH perform periodic URA updates and no periodic

LAU/RAU.

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LA, RA and URA

LA design guidelines The LA borders whenever possible should be designed to occur in low

traffic and low mobility areas. The location area borders should be perpendicular to main traffic flow, so

as to avoid ping pong between LAs. 1 LA per RNC at initial deployment.

RA design guidelines RA = LA.

URA design guidelines Set URA = LA at initial deployment.

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Glossary

Term or Acronym Definition

CN Core Network

CS Circuit Switched

DCH Dedicated Channel

DRX Discontinuous Reception

FACH Forward Access Channel

GERAN GSM Edge Radio Access Network

IMSI International Mobile Subscriber Identity

LA Location Area

PCH Paging Channel

PI Paging Indicator

PICH Paging Indicator Channel

PS Packet Switched

P-TMSI Packet Temporary Mobile Subscriber Identity

RA Routing Area

RNC Radio Network Controller

RNTI Radio Network temporary Identity

SCCPCH Secondary Common Control Physical Channel

TMSI Temporary Mobile Subscriber Identity

UE User Equipment

UMTS Universal Mobile Telecommunications Systems

URA UTRAN Registration Area

UTRAN UMTS Terrestrial Radio Access Network

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Thank You