UTRAN Paging Concepts
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UTRAN Paging ConceptsSireesha Panchagnula
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 athttp://docs.eng.t-mobile.com/inforouter/docs/~D460521
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
UTRAN UE States
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.
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
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
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).
UMTS Paging characteristicsUE State RRC ConnectedNo
Paging TypeType 1
Resources UsedPICH and SCCPCH (carrying PCH) DPCCH (carrying DCH) SCCPCH (carrying FACH) and PRACH (carrying RACH) PICH and SCCPCH (carrying PCH) PICH and SCCPCH (carrying PCH)
Originating NodeCN UTRAN CN
Terminating service System Information updates Terminating service from a CN that UE is not connected to Terminating service from a CN that UE is not connected to
LA / RA
CS Terminating service Allow UE to trigger cell update procedure, System Information Updates CS Terminating service Allow UE to trigger cell update procedure, System Information Updates
Last known cell
Last known URA
Paging signaling flowsCN originated paging in Idle Mode
Paging signaling flowsCN originated paging in CELL_DCH or CELL_FACH mode
Paging signaling flowsUTRAN originated paging in CELL_PCH / URA_PCH
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.
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.
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.
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.
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.
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.
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 cant 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.
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.
GlossaryTerm or AcronymCN CS DCH DRX FACH GERAN IMSI LA PCH PI PICH PS P-TMSI RA RNC RNTI SCCPCH TMSI UE UMTS URA Core Network Circuit Switched Dedicated Channel Discontinuous Reception Forward Access Channel GSM Edge Radio Access Network International Mobile Subscriber Identity Location Area Paging Channel Paging Indicator Paging Indicator Channel Packet Switched Packet Temporary Mobile Subscriber Identity Routing Area Radio Network Controller Radio Network temporary Identity Secondary Common Control Physical Channel Temporary Mobile Subscriber Identity User Equipment Universal Mobile Telecommunications Systems UTRAN Registration Area UMTS Terrestrial Radio Access Network