Signaling Procedures

8/2/2019 Signaling Procedures

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Mobile Communication Division RNE_Fund_17_05E04.ppt / Edition 04/ Page 1 ACS/ SR2

Signal ling Procedures

SignallingProcedures

UPLINK)

DOWNLINK

BSC

BSS

MSCMSC

A-Interface

Abis-

Interface

Air In terface


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GSM Signalling Procedures

t Call setup

n Mobile originated call setup

n Mobile terminated call setup

t Location updatet Handover

n Synchronous HO (Intra Cell / Co Site)

n Asynchronous HO (Inter Cell)

t Call release

n Call release by MSn Call release by network

LocationArea B

LocationArea A

Ring-Ring...


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Purpose of Logical Channels (1)t BCH - Broadcast Channel

n FCCH Frequency correction channel

n SCH Synchronisation channel for frame synchronisation

n BCCH Broadcast control channel to transmit system information

t CCCH - Common Control Channel to setup Signall ing Channeln RACH (UL) Random access channel SDCCH channel request message of

mobile

n AGCH (DL) Access grant channel acknowledge access request andassign a SDCCH to MS

n PCH (DL) Paging channel BTS transmits paging message within location

areat DCCH - Dedicated Contro l Channel for Signall ing

n SDCCH Signalling (call setup, SMS, location update, authentication...)


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Purpose of Logical Channels (2)t TCH - Traffic Channel to transmit Speech or Data

n Full rate and half rate traffic channels

t Associated Channels

n FACCH associated with TCH for signalling

l Signalling after TCH setup (end of call processing, handover ....)

l Steals up to 24 TCH timeslots of a 26 multiframe (stealing flag)

n SACCH associated with SDCCH or TCH to transmit

l DL: sysinfo messages and commands for TA and PC

l UL: Measurement reportl 1 timeslot per 26 Multiframe


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Mobile Originated Call Setup (1)

t Radio Link Establishment - Establish Links between

n BSS and MS (SDCCH)

n BSS and MSC (SCCP link: Signalling Connection Control Part)

t Authentication and Ciphering

n Authenticate MS identity

n Ciphering optional

t TCH assignment

n Assign TCHn Release SDCCH

Ring-Ring...


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Mobile originated call setup (2) - Radio Link EstablishmentMS BTS BSC MSC

RACH

AGCH

SDCCH

SDCCH

channel request(rn, est. cause)

channel req.

(Meas. TA, rn) allocation ofSDCCH channel

channel activation(TA/ SDCCH/Pwr)

Initiatephysicallayer

resourceschannel act. ackn.

Immediate assignment

commandIm. ass. cmdrn , fn,TA,SDCCH

SABM (service request)

UA (service request)

Establishment

indication

SCCP Connection

Request

SCCP ConnectionConfirm

MS

switchesto SDCCH


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Mobi le or iginated call setup (3) - TCH AssignmentMS BTS BSC MSC

SDCCHsetup message(called party nr.)

Authentication and Cyphering

SDCCHcall proceeding

assignment requestchannel type + cm

TCH

allocationalgorithm (int. level)

physical contextrequest

physical context

confirm: TA + Pwr

channel activationTCH+ TA+ cipher+DTX+ Pwr

SACCH

TA+ Pwr+ Sysinfo

channel activation

acknowledge

assignment cmd

assignment cmd

SDCCH

Release

SDCCHSwitch to

TCH


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Mobi le or iginated call setup (4) - TCH AssignmentMS BTS BSC MSC

FACCHSABM

FACCHUA

establish indication

Assignment Complete: to in itiate release of SDCCH

FACCH

Set swit ching pathbetween Abis and

A interface resources,Establish LAPDmconnection for TCH

FACCH

FACCH

FACCH

ALERTING

CONNECT

CON NECT ACKNOW LEDGE

TCH

CALL ESTABLISHED CONVERSATIO N PHASE


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BSSBSSBSSBSS

BTS

BSCBTS

BSSBSSBSSBSS

BSSBSSBSSBSS

BTS

BSCBTS

MSCMSC

6

65

32

HLRHLRHLRHLRVLRVLRVLRVLR

PP

SS

TT

NN

----

II

SS

DD

NN

((

7

1. Initial Address Message (IAM)2. Interrogation3. MSC address of subscriber4. Initial Address Message (IAM)

5. Get subscriber data

6. Paging command7. Paging of subscriber

8. Access to BSS9. Call establishment

BT

S

BSCB

TS

BSSBSSBSSBSS

8

GMSCGMSC

14

6

6

9

Mobile terminated call (1)


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Mobile terminated call (2)

t Follows the same basic procedures as MS originated call

t Differences are:MS BTS BSC MSC

PCH

Paging message

TMSI/ IMSI + cell l ist

Paging command

TMSI/ IMSI paginggroup + channel

MS listensto messages

of its paginggroup

Paging request

TMSI / IMSI

RACHchannel request(rn, est. cause)

channel req.(Meas. TA, rn)

allocation ofSDCCH channel

RADIO LINK AND ESTABLISHMENTPROCEDURE

AUTHENTICATION AND CYPHERINGASSIGNMENT PROCEDURE FOR TCHring toneuser answers

alertconnect

connect acknowledge

FACCH


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Location Update (1)

BSSBSSBSSBSS

BTS

BSCB

TS

BSSBSSBSSBSS

BTS

BSCBTS

BSSBSSBSSBSS

BTS

BSCBTS

VLRVLRVLRVLR

MSCMSC

HLRHLRHLRHLR

VLRVLRVLRVLRMSCMSC

1

Old location area

New location area and new MSC area

3

25

6

4

8

8

7

9

1. MS enters a new Location Area

2. MS recognizes new LAI(Location Area Index)

3. Access to BSS

4. Location update request

5. Location update i nfo6. Response7. Subscriber data inscription8. Response

9. Delete subscriber data

LAI

LAI


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Location update (2)t Always ini tiated by MS - performed in idle mode

n Periodic location update (timer transmitted on BCCH)

n MS moving in new location area (LAI transmitted on BCCH)

t Air interface messages

n RACH (UL): channel request

n AGCH (DL): imediate assignment CMD (SDCCH)

n SDCCH (UL): location update request (IMSI / TMSI)

n SDCCH (UL/DL): authentication / ciphering

n Subscriber data insertion to new VLR (update request of BSS)

n Data in previous VLR is deletedn SDCCH (DL): location update accept/ reject message (new TMSI)

n SDCCH (UL/DL): channel release procedure


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Synchronous and Asynchronous HO


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Synchronous internal TCH HOMS Target BTS MSCBSCServing BTSSACCH

measurementreport

measurementresult

HO detection

HO alarmTarget cell

evaluation

physical context

request

physical context

confirm: TA/ Pwrchannel activationTA+ cipher+ DTX+ power+ channel

channel activation acknow ledge

Target BTSactivates TCH

FACCH

Handover cmd: HO ref+ Pwr+ cell desc. + TA+ cipher+ channel

releasewith

serv

BTS access burst (TA = 0) handover detection

SABM establ . i ndi cation

UAhandover complete handover performed

recalculationof TA


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Asynchronous external HO

t After MS releases connection of serving BTS

n Synchronisation with target BTS required using FCCHand SCH

n Since TA value of target BTS is unknown: MScontinuously sends access bursts until it receives thephysical information message

n Target BTS receives access burst and calculates TA

n Target BTS sends physical information message onFACCH


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Radio Link ControlPower ControlHandover


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Radio Link Control Process

t Cell Selection / Reselection in Idle Mode

t Power Control

t Handover

t Radio Link Supervision


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Cell Selection / Reselection

tMS in idle mode

t Cell Selection

n Condition for cell selectionRXLEV > RXLEV_ACCESS_MIN

n Selection of strongest cell

t Cell Reselection

n MS moving from cell A to cell B

n Within location area (LA) : reselection ifRXLEV(B) > RXLEV(A)

n Different LAs: reselection ifRXLEV(B)> RXLEV(A)+ CELL_RESELECT_HYSTERESIS

LocationArea BBSC 2

LocationArea A

BSC 1

selection

reselection


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PC & HO Algorithm - Connected Mode

Coverage Hole

Interfered area

LocationArea BBSC 2

Location

Area ABSC 1

12

3

4

5t Intercell / Intracell

t Emergency / Better Cell

t Internal / Externalt Synchronous / Asynch.


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HO Categories (1)

t Intercell / Intracell

n Intercell:

Handover between two channels of adjacent cells

n Intracell:Handover between two channels of same cell

t Emergency / Better Cell

n Emergency: triggered to rescue the call(bad level, quality, interference etc.)

n Better cell: triggered to improve overall performance

lPBGT HO: interference reduction

l Directed retry: load reduction

Intercell

Better cell

IntracellEmergency

Interfered area


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Handover Categories (2)

t Internal / External

n Internal: target and serving cell belong to

same BSC BSC controlled HO

n External: target and serving cell belong to differentBSC MSC controlled HO

t Synchronous / Asynchronous

n Synchronous: same clock (cosited BTS)

l Simplified protocol: no need to synchronise and recompute TA

l Intracell HO or HO between sectors

n Asynchronous: different clock (different sites)l Synchronisaion and recomputation of TA

B

TS

BSC1

B

TS

MSCMSC

BT

S

BSC2external

internal


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Radio LinkMeasurements

Active channelpreprocessing

PC & HOthresholdcomparison

HO candidatecell evaluation HOdecision +execution

PCcommand

General Behaviour


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Radio Link Measurements

t Input for PC and HO

n RX_LEV, RX_QUAL in UL and DL direction

n Timing advance and cell load

UPLINK

MeasurementReport (SACCH)

DOWNLINK

RXLEV_DLRXQUAL_DL

RXLEV_ULRXQUAL_UL

Timing AdvanceBSC Abis

measurementresult (UL/ DL)

Cell Load

BTS


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Preprocessing

t SlidingAveraging and Weighting

n To avoid wrong decisions due to fading

n BSS Parameter: averaging windows and weighting parameter

Example: A_LEV_PC, W_LEV_PC

X

XX

XX

X

X

X X

XX

X

X

Measurement

Samples

480ms

Averaging W indow = 4 SACCH frames

time


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Threshold comparison

t Triggering of HO

n Compare preprocessed values to predefined thresholds to trigger

PC command (increase or decrease power)

HO candidate cell evaluationn BSS Parameter: thresholds, e.g.

L_RXLEV_UL_PL_RXQUAL_HHO_MARGIN(A, B)

Preprocessed

measurementsamples

Threshold

comparision(PC & HO)

Powercontrol

command

Handoverbut to whichtarget Cell?


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Candidate Cell Evaluation

t Target cell selection based on raw list = declared neighbour cells

t Preselection of raw list by specific conditions (e.g. RXLEV_MIN)

t Sorting of remaining candidates to determine top ranked candidate

servingcell

1

2

3

4

5

6Candidate raw list = cell 1 to cell 6Preselected candidates = cell 2 to cell 4Top ranked candidate = cell 3


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Radio Link Supervision (Alcatel specific)t In case no measurement reports are available

Input for PC and HO algorithm not available

t Step 1: Radio Link Recovery Procedure

n Increase MS and BTS power to maximum after defined period

t Step 2: Detection of Link Lossn If no improvement define link as lost after defined period

t BSS Parameter

n EN_RL_RECOV

n N_BSTXPWR_M

nRADIO_LINK_TIMEOUT_BS

UPLINK

MeasurementReport (SACCH)

Signaling Procedures

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