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UTRAN Paging Concepts
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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