Huawei - Access failures troubleshooting work shop

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

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Huawei WorkshopTroubleshooting Access Failures

May 17th, 2011


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Contents

• Call Setup Procedure (step by step & all protocols)

• General Causes of failures

• How to chase and to solve specific access failures:

RRC Access Failure Troubleshooting.

Paging Access Failure Troubleshooting

RACH Access Failure Troubleshooting

Page 2


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Mobile Terminated Call Setup Procedure (I)

Page 3

UE Node B RNC MSC / VLR MGW

RRC3. PCH: PCCH: PAGING TYPE 1 <TM>

RRC

2. PAGINGRANAP RANAP

RRC4. RACH: CCCH: RRC CONNECTION REQUEST <TM>

RRC

1. IAMISUP

5. RADIO LINK SETUP REQUEST

6. RADIO LINK SETUP RESPONSE

9. DOWNLINK SYNCHRONISATION

12. SYNCH IND

7. ESTABLISHMENT REQUEST (AAL2)

8. ESTABLISHMENT CONFIRM (AAL2)

Start RX

NBAPNBAP

NBAPNBAP

ALCAP

ALCAP

ALCAP

ALCAP

DCH-FPDCH-FP

L1 L1

Start TX

11. FACH: CCCH: RRC CONNECTION SETUP <UM>RRCRRC

14. DCCH: RRC CONNECTION SETUP COMPLETE <AM>RRCRRC

10. UPLINK SYNCHRONISATIONDCH-FP DCH-FP

13. RADIO LINK RESTORE INDICATIONNBAPNBAP

Can be either RRC

Connection setup (to this cell

and or inter freq to another

one when DRD) or Reject.

Here the Node-B will start

RL with DL transmission

Here the UE will start to send

the PRACH and wait for AICH

and then send RACH message

Here the UE will do DL synchronization (using N312=1,

T312=1, N313=20 andT313=3) . Then the UE will start UL TX

transmission and the Node-B will detect UL SYNCH (based on

N_INSYNCIND=8, N_OUTOFSYNCIND=8,TRLFAILURE=20)

Here the RNC will

perform a DRD decision

and CAC decision for

RRC


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Mobile Terminated Call Setup Procedure (II)

Page 4


28. RAB ASSIGNMENT REQUESTRANAP RANAP

26. DT [ CALL CONFIRMED ]RANAP RANAP

25. DCCH: ULDT [ CALL CONFIRMED ] <AM>RRCRRC

24. DCCH: DLDT [ SETUP ] <AM>RRCRRC

RANAP RANAP

15. DCCH: INITIAL DT [ PAGING RESPONSE ] <AM>RRCRRC

RANAP RANAP

RRCRRC

RRCRRC

19. SECURITY MODE COMMANDRANAP RANAP

20. SECURITY MODE COMMAND

21. SECURITY MODE COMPLETE

22. SECURITY MODE COMPLETE

16. SCCP CONNECTION RQ [

INITIAL UE MESSAGE

[ PAGING RESPONSE ] ]

27. BINDING ID, SPEECH

CODE TYPE, B PARTY

ROUTE

RANAP RANAP18. COMMON ID

23. DT [ SETUP ]

17. SCCP CONNECTION CONFIRMSCCP SCCP

SCCP SCCP

Here the RNC will

perform a DRD decision

and CAC decision for

RAB


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Mobile Terminated Call Setup Procedure (III)

Page 5


46. DT [ CONNECT ACK ]

46. DCCH: DLDT [ CONNECT ACK ] <AM>

RANAPRANAP

RRCRRC

39. DCCH: ULDT [ ALERTING ] <AM>

40. DT [ ALERTING ]

RANAP RANAP

RRCRRC

42. DCCH: ULDT [ CONNECT ] <AM>

43. DT [ CONNECT ]RANAP RANAP

RRCRRC

37. RAB ASSIGNMENT RESPONSERANAP RANAP

41. ACM

ISUP

47. ANS (CONNECT)ISUP

36. DCCH: RADIO BEARER SETUP <AM>

38. DCCH: RADIO BEARER SETUP COMPLETE <AM>

RRC

RRCRRC

RRC

29. ESTABLISHMENT REQUEST ( AAL2 )

30. ESTABLISHMENT CONFIRM ( AAL2 )

ALCAP

ALCAP ALCAP

ALCAP

33. ESTABLISHMENT REQUEST (AAL2)

34. ESTABLISHMENT CONFIRM (AAL2)

ALCAP

ALCAP

ALCAP

ALCAP

31. RADIO LINK RECONFIG PREPARE

32. RADIO LINK RECONFIG READY

NBAPNBAP

NBAPNBAP

44. OPEN CONNECTION

35. RADIO LINK RECONFIG COMMITNBAPNBAP

Terminating UEs

are considered to

be in a call after CC

Connect ACK

Originating UEs are

considered to be in a

call after CC Connect

message


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General Causes of failures (I)

• RF Reasons

• Radio Parameter Problems

• Miscellaneous causes

Page 6


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General Causes of failures - RF reasons (II) Poor DL coverage. The “fake coverage” phenomenon (the user sees the 3G icon on the screen in

idle but cannot connect to any service). The cause could be overshooting cells but also excessive

values of Qqualmin like -22 dB. Solution: Adjust the antenna azimuth and down tilt, add repeaters and

RRUs, add micro cells. Any user should get a better signal than EcIo = -18 dB.

Lack of Dominance (no clear Best server): Continuous change of best server leads to

RRC failures and RAB failures.Solution: Establish a best server everywhere. Clear dominance.

Poor UL coverage: The UE has not enough TX power to communicate with Node-B (even when

there is low UL traffic on the cell). Solution: Adjust the antenna azimuth and down tilt, add repeaters,

reduce CPICH power.

Strong UL interference: Due to external interference or high UL traffic (the cell shrinking

phenomenon). The UE will not be able to increase to more than 21 dBm for the preamble power and the

RACH will fail - or synch will fail later. Solution: Up to operator‟s decision (implement more tilt ,CPICH

power reduction, chase external source of interference or increase the number of Node-Bs to cope with

traffic)

Strong DL interference: Usually due to overshooting cell, external interference, high DL traffic

on this cell and surrounding cells. The UE will miss the AI message for RACH and will fail to establish a

call - or will fail to get synch in DL. Solution: Improve best server area (strong dominance)

RF radiating system problems: Antenna‟s footprint not touching the ground properly: sites with over 120 m height and tilts around 3 degrees. More than 3/4 of the

antenna pattern will not be touching the ground with a decent level of signal. Most calls are handled on side lobes.

RF jumpers (feeding the antennas with RRU signal) are too long (should be no more than 3 meters, we‟ve seen cases in --- with 10

meters of ½” jumpers). This definitely leads to high noise factors and call setup failures. Also UL and DL coverage is very much

limited.

Missing neighbours: Leads to call setup failures due to poor signal.

Page 7


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Poor DL coverage. The “Fake coverage” phenomenon (user gets the 3G icon on his screen in idle but either cannot pass an RRC or a

RAB). Cause is overshooting cells but also excessive values of Qqualmin like -22 dB. Solution: Adjust the antenna

azimuth and down tilt, add repeaters and RRUs, add micro cells, improve best server, change Qqualmin. Any user

should get a better signal than EcIo=-18 dB. If this level cannot be achieved it is better to display ” no service” on.

user screen.

Page 8

When -16>EcIo>-2 then RRC_SR>95%When -18>EcIo>-16 ; 95%>RRC_SR>80%When -22>EcIo>-18 ; 80%>RRC_SR>20%

User experience: 3G icon,3G signal

bars, great service accessibility. User „s

perception: Very Positive.

User experience: 3G icon,3G signal

bar, good service accessibility. User „s

perception: Positive.

User experience: 3G icon, no 3G bar, no

service accessibility. User „s perception:

Very negative.

Qqualmin PRO CONS Comments

-22 dB

• User always see the 3G icon

on his phone‟s screen (although

it‟s a “fake” coverage the user

does not always attempt to use

the service)

•Maximum traffic possible

• Bad customer experience but less

NW signalling.

•Not all call attempts are counted

(not a clear perception of

accessibility).

Will grab all extreme

traffic leading quickly into

DL Power congestion and

accessibility issues.

-18 dB

• The user will not always have

the 3G Icon on his phone‟s

screen (but when icon is

present service is 100%

accessible)

• Potential traffic decrease

• Great and real customer

experience but increased signalling

(coverage lost);

• All “Call attempts” are counted

(better performance perception of

accessibility) due to this RRC_SR

KPI may (or may not) be

improved.

No more “fake coverage”.

Decrease in DL Power

Congestion.

-20 dB Qqualmin=-20dB is suggested as a trade-off solution by Huawei.


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General Causes of failures – Radio Parameter Problems(II)

Page 9

• Excessive values in object UCELLSELRESEL: Examples: Qqualmin<-18, IDLESINTRASEARCH ≠ 127,

IDLEQHYST2S>1, IDLEQHYST1S>3.

• Improper settings of access parameters: No discrepancies found in UCELLACCESSRESTRICT

• Inappropriate settings of preamble power ramp step and retransmission times: Current set of

parameters is NOK (PREAMBLERETRANSMAX=20, CONSTANTVALUE-20, PowerRampStep=2, Mmax=8).

• Inappropriate setting of adjacent cells for UINTRAFREQNCELL: Qoffset1sn, Qoofset2sn out of the

range (-4dB;+4dB). Wrong settings for Sintra (like 0 dB), Sinter( also like 0 dB).

• Inappropriate settings of synchronization parameters: Synch and Out-Of-Synch parameters for UL

(N_INSYNC_IND=8, N_OUTSYNC_IND=8,and T_RLFAILURE=20), DL (T312=1, N312=1, N313=D20 ,T313=3 and

N315=D20). Please remember that call re-establishment is activated for both UL and DL (great KPIs but acceptable user

perception)

• Unsuitable power allocation rate for DL common channel: No discrepancies found (PSCHPower,

SSCHPower, BCHPower , MaxFachPower, PCHPower, AICHPowerOffset, PICHPowerOffset)

• Unsuitable initial power of uplink and downlink dedicated channel: No discrepancies found for UL

(DPCCH_Initial_Power = PCPICHPower - CPICH_RSCP + Uplink interference + DefaultConstantValue) and DL initial SIR

target

• Unsuitable setting of uplink Initial SIR target value of dedicated channel: No discrepancies found for

DL initial SIR Target

• Inappropriate setting of adjacent cells for UINTERFREQNCELL:• When 1900 and 850 MHz have significant azimuth difference why there is DRD just towards one 1900 cell and

not for the other 1900 cell as well?

• Why Qoffset1sn, Qoofset2sn are out of the range (-4;+4) on top of the IdleQhyst1s >2?


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General Causes of failures –Miscellaneous causes(II)

Page 10

•Transmission issues (fluctuating PATH, high BER, reduced capacity, routers down in the IP

cloud).

•Alarms on cells, on Node-Bs, on RNC, on transmission

•Planning issues: traffic not properly shared between layers and NodeB, lack of a clear best

server( no dominance), paging congestion due to LAC splitting issue.

•Radio Congestion:

• CE

• DL Power

• UL Power

• R99 Codes

• Iub bandwidth

• SPU bottleneck

• WMPT board bottleneck


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How to identify and solve different issues?

Page 11


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Page 12

RRC Access Failure Troubleshooting (I)Is cell/NodeB/RNC configuration the correct one? YES NO Should be done daily (automatically and network wide) based on a defined template.

Where there any alarms on investigated cells (or any of it's

neighbouring cells, intra or inter) ?YES NO

Every morning there should be an email with cells unavailable on previous day and

duration of unavailability.

Is it a repetitive failure or a "one time" event? YES NO If one time event, please wait one more day before to conclude. Could be a social event

If a repetitive failure (according to KPI values in the past) is it a slowly

degradation (with traffic increase) or an event one (degraded

seriously from a specific moment)?

YES NOIf event one, go back to that day and see what was changed at that time and reconsider

that change

Is the SHO factor less than 50%? YES NO If not, please review its best server area, tilt, azimuth and CPICH power

Is this cell having full overlapping with other neighbouring cells? ( i.e.

there's no direction user can move without having good coverage). Is

any user, in any indoor environment within the footprint of this cell,

able to get a decent RSCP and EcIo?

YES NOIf no review your targeted coverage and accept current limitations and constraints due

to location and/or number of Node-Bs.

Is the height of the antenna less than 100m? YES NO If No, please do not expect a good RRC Success rate.

Is the total tilt of the cell more than 3 degree downtilt? YES NO

If no (and footprint is on a plain terrain) please take immediate actions to increase downtilt.

Antenna RF pattern is hardly touching the ground, users are handled on side lobes. DL

Power issues will occur.

is the cell Idle sintrasearch=127? YES NO If no, please do not expect a good RRC Success rate.

is the cell idleQoffset1sn<4? YES NO If no, please do not expect a good RRC Success rate with idleQoffset1sn>4dB

is the cell Idle idleQoffset2sn<2? YES NO If no, please do not expect a good RRC Success rate with idleQoffset2sn>4dB

is the cell idleQhyst1<4? YES NO If no, please do not expect a good RRC Success rate with idleQhyst1>4dB

is the cell idleQhyst2<2? YES NO If no, please do not expect a good RRC Success rate with idleQhyst2>4dB


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Page 13

Date---- RNC1 RNC2 RNC3 RNC4

Sum of VS.RRC.AttConnEstab.Sum 6154003 7115377 5397822 1920647

Sum of Cell.RRC.Att.Fail 46702 73768 87275 12471

Sum of VS.RRC.Rej.Redir.Service 0 0 0 0

Sum of VS.RRC.Rej.ULIUBBand.Cong 0 0 0 0

Sum of VS.RRC.Rej.ULPower.Cong 14 10 0 0

Sum of VS.RRC.Rej.DLPower.Cong 135 118 1965 290

Sum of VS.RRC.Rej.DLIUBBand.Cong 0 0 0 0

Sum of VS.RRC.Rej.ULCE.Cong 1144 1352 721 507

Sum of VS.RRC.Rej.DLCE.Cong 822 11 0 0

Sum of VS.RRC.Rej.Code.Cong 12 41 372 0

Sum of VS.RRC.Rej.RL.Fail 30 50 419 0

Sum of VS.RRC.Rej.TNL.Fail 0 0 0 0

Sum of VS.RRC.FailConnEstab.Cong 2343 1552 3070 802

Sum of VS.RRC.Rej.Sum 2373 1602 3489 802

Sum of VS.RRC.SetupConnEstab 6151630 7113775 5394333 1919845

Sum of VS.RRC.FailConnEstab.NoReply 44006 71818 83566 11667

Sum of RRC.SuccConnEstab.sum 6107301 7041609 5310547 1908176

Conclusion: Most RRC failures (over

90%) are due to RRC no reply. For

RRC issues, focus on overshooting

cells first (to solve No reply), second

on congested cells.

Here are most of

the RRC failures

occurring

indicating poor

UL coverage

(overshooting)

RRC Access Failure Troubleshooting (II)


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Page 14

RRC Access Failure Troubleshooting (III)

Identify if RRC failures for a cell are due to SPU : (check

ADD NODEB command to find the SPU for a cell/Node-B) .

Identify top N cells (more than 2000 RRC

attempts per day and success rate is less

than 98%)

SPU board is the issue when

(VS.RRC.SuccConnEstabCPU /

VS.RRC.AttConnEstabCPU)

<97% (daily stats)

Solution: Open a ticket to TAC (should not

happen after SPH226)

Identify if more than 10% of the failures for a cell are due

to congestion :

YES

NO

YESSolution: On the RNC LMT, run the PING IP command to the IP of the NodeB

during failing hours. If packet loss rate is greater than 0.1% please contact

transmission engineers (to troubleshoot or upgrade)

VS.RRC.Rej.ULIUBBand.Cong

VS.RRC.Rej.DLIUBBand.Cong

VS.RRC.Rej.ULPower.Cong

Check configuration(ULTOTALEQUSERNUM=160;

NBMULCACALGOSELSWITCH=ALGORITHM_SECOND). Solution: Increase

ULTOTALEQUSERNUM to 180. If still failing: add carrier or reduce/balance traffic to

other layers/cells.

VS.RRC.Rej.DLPower.Cong

Check configuration :UPCPICH and MAXTXPOWER should be at least 10 dB

between the 2 values. DLOLCTRIGTHD=95.DL_UU_OLC=0.

Solution1:add carrier or reduce/balance traffic to other layers/cells

Solution2: change NBMDLCACALGOSELSWITCH=ALGORITHM_THIRD

VS.RRC.Rej.ULCE.Cong

Solution per cell: change ULTTICREDITSFRESTHD from SF8 to 4SF4.

CE resources for admission is in congestion status the new admitted 2ms

HSUPA terminals will be mapped onto the 10ms TTI radio bearer. 2ms

TTI HSUPA users whose bit rate is below the threshold of TTI

reconfiguration(800Kbps) will be reconfigured to 10ms TTI

Solution per RNC: decrease ULGBR from 32 to 16 for specific services

VS.RRC.Rej.DLCE.CongSolution per cell: ???

Solution per RNC: decrease DLGBR from 64 to 32 for specific services

VS.RRC.Rej.Code.CongSolution per cell is to activate Code reshuffling algo: in object

UCELLALGOSWITCH change CELL_CODE_LDR to 1

Identify if more than 10% of failures for a cell are due to

RL.Failure :VS.RRC.Rej.Rl.Fail

Solution 1: If failures correlated with VS.IUB.FailRLSetup.NoReply

then it is WMPT board congestion( add UTRP Board)

Solution 2: run the PING IP command on the IP of the NodeB to detect congestion

on the IuB.

Solution 3: If failures correlated with RLM.FailRLSetupIub.Cong then it is WBBP

board congestionGO TO NEXT SLIDE

NO


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Page 15

RRC Access Failure Troubleshooting (IV)


TNL (Transport Network Layer) :VS.RRC.Rej.TNL.Cong

Solution 1: Recheck configuration( IPPATHs of Nodeb has same capacity

of transmission one;same for pair one)

Solution 2: Run the PING IP command on the IP of the NodeB to detect

congestion on the IuB.


FACH congestion :

YES

NO

YESSolution 1: (After SPH226) MOD UCELLALGOSWITCH: CellId=xxxxx,

RsvdPara1=RSVDBIT5-1; (will improve CS success rate, will degrade PS success rate)

Solution 2: Offload traffic

VS.RRC.AttConnEstab.Msg

>>

VS.RRC.AttConnEstab.Sum

VS.CellFACHUEs>25 Solution: Offload traffic

VS.CRNCIubBytesFACH.Tx or

VS.CRNCIubBytesPSR99.CCH.Tx

are flat in time( limited)

Solution1: Offload traffic

VS.MaxRTWP - VS.MeanRTWP >

10 dB

Solution 1: reduce HSUPA traffic

Solution 2: Offload traffic

Solution 3: Check external interference

Check missing neighboursSolution 1: Add important Neighbours

Solution 2: Increase tilt to avoid risky overlaping footprints

If RRC Estab SR for whole

RNC<99% and UU no reply is

major cause

Solution 1 per RNC : modify RRC estab type to be on DCH

SET URRCESTCAUSE:RRCCAUSE=TERMCAUSEUNKNOWN,

SIGCHTYPE=DCH_3.4K_SIGNALLING, EFACHSWITCH=OFF;

Take care as this will improve the RRC SR but will increase DL Power

Solution 2 per RNC : stop SRB over HSDPA when DRD could be

present SET UFRCCHLTYPEPARA, SRBCHLTYPE=HSUPA,

SRBCHLTYPERRCEFFECTFLAG=TRUE


VS.RRC.FailConnEstab.NoReply :

NO

FROM PREVIOUS SLIDE

YES

Please ask for HUAWEI support if after all those steps a

cause for poor RRC failure could not be found

NO

FACH Channel utilisation>80% Solution1: Offload traffic


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Page 16

•.

Here are most of

the RRC failures

occurring

indicating poor

UL coverage

(overshooting)

Top offending cell in xxx area with more than 10.000 RRC

attempts per day: cell yyyyy

Data cellID=yyyyy

Sum of VS.RRC.AttConnEstab.Sum 73083

Sum of Cell.RRC.Att.Fail 17110

Sum of VS.RRC.Rej.Redir.Service 0

Sum of VS.RRC.Rej.ULIUBBand.Cong 0

Sum of VS.RRC.Rej.ULPower.Cong 0

Sum of VS.RRC.Rej.DLPower.Cong 163

Sum of VS.RRC.Rej.DLIUBBand.Cong 0

Sum of VS.RRC.Rej.ULCE.Cong 0

Sum of VS.RRC.Rej.DLCE.Cong 0

Sum of VS.RRC.Rej.Code.Cong 0

Sum of VS.RRC.Rej.RL.Fail 0

Sum of VS.RRC.Rej.TNL.Fail 0

Sum of VS.RRC.FailConnEstab.Cong 163

Sum of VS.RRC.Rej.Sum 163

Sum of VS.RRC.FailConnEstab.NoReply 16944

Sum of VS.RRC.SetupConnEstab 72920

Sum of RRC.SuccConnEstab.sum 55973

RRC_SR 76.59%


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Page 17

•.

Here are most of

the RRC failures

occurring

indicating poor

UL coverage

(overshooting)

Data cellID=yyyyy


















RRC_SR 92.91%

2nd offending cell in xxx area with more than 10.000 RRC

attempts per day: cell yyyyy


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Page 18

•.

Here are most of

the RRC failures

occurring

indicating poor

UL coverage

(overshooting)

Data cellID=yyyyy


















RRC_SR 93.41%

3rd offending cell in xxx area with more than

10.000 RRC attempts per day: cell yyyyy


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Page 19

•.

Here are most of

the RRC failures

occurring

indicating poor

UL coverage

(overshooting)

4th offending cell in xxxx area with more than

10.000 RRC attempts per day: cell yyyyy

Data cellID=yyyyy


















RRC_SR 95.23%


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Page 20

Paging Access Failure Troubleshooting-(I)-

case of one SCCPCH

2 Physical channels:

– PICH (Paging Indicating Channel): This is just to inform the UE that it needs to initiate an RRC Connection request. Those are the details for this channel.

– SCCPCH (Secondary Common ControlPhysical Channel). It carries paging messages themselves as well as packet messages for mobiles in cell FACH.


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Page 21

Paging Access Failure Troubleshooting-(II)

-case of two SCCPCH

2 Physical channels:

– PICH (Paging Indicating Channel): This is just to inform the UE that it needs to initiate an RRC Connection request. Those are the details for this channel.

– 2nd SCCPCH (SecondSecondary CommonControl PhysicalChannel). It carries only paging messages themselves.

2nd SCCPCH


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Paging Access Failure Troubleshooting-(III)

PICH timing in relation to P-CCPCH and S-CCPCH (extras from 3GPP 25.211-700) :

Paging

indicator

Paging

message

(3 IMSI or

5 TMSI)

Paging

ocassion


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Paging Access Failure Troubleshooting-(IV)PICH channel parameters:

• SF 256 used all the time.Each UE looks for a particular PICH timeslot according to several parameters broadcasted on SIBs :

• PI number of paging indicators per radio frame. 3GPP allows values 18,38,72,144. It is broadcasted in Sysinfo5: PI-countperframe

• SFN of the P-CCPCH where the PICH frame started. The SFN is known by UE immediately after synchronization with P-CCPCH. SFN range is from 0 to

4096.

• K number of S-CCPCH and can be found in Sysinfo5 . Usually 1 or 2 ( same like in GSM combined or non-combined BCCH).

• DRX cycle. UE will use the DRX=min (DRXPS,DRXCS). DRX cycle is broadcasted in Sysinfo1: cn-DRX-CycleLengthCoefficient (2 values broadcasted,

one for each CN domain)

• IMSI known from U-SIM.

• Frame offset =Ts-ccpch,k –Tpich (see previous slide). Ts-ccpch,k = Tk 256 chip, Tk {0, 1, …, 149} and can be found in Sysinfo5: and it is called timming offset. For particular UTRAN timming offset=0(S-CCPCH and P-CCPCH are time aligned). Tpich = 7680 chips as a fix value forced by 3GPP.

• A paging indicator set to “1” indicates that the UE should read the S-CCPCH of the corresponding frame.

• Total number of chips in one 10msec radio frame is 38400. PICH channel can transmit (38400/256) 150 indicator modulation symbols or (150X2) 300 bits. Only the

first 288 of these are used, leaving the last 12 bits undefined

• More details in 3GPP specs: 25.211-700 and in 25.331-710 RRC protocol specification

•

PO= {(IMSI div K) mod (DRX cycle length div PBP)} * PBP + n * DRX cycle length + Frame Offset

Where n = 0,1,2… as long as SFN is below its maximum value ,for FDD PBP=1

PI = DRX Index mod Np Where DRX Index = IMSI div 8192

If we consider particular settings:

DRXcycle=7=>128 frames

Frame offset =-7860 chips

PBP=1

K=1 (there„s only one S-CCPCH that carries PCH)

PI=Np=36

PO= (IMSI)mod128+ n* 128 -7860 chips

PI=(IMSI/8192) mod36


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Paging Access Failure Troubleshooting-(V)

••

PICH frame structure :

• A group of bi=1 means there‟s a paging and UE should read it‟s very first paging occasion.

• A group of bi=0 means there‟s no paging and UE could go back to idle till next paging indicators.

• More bits inside a PI means a greater probability to decode the paging indicator but less capacity of the paging channel and power

consumption for UE. Less bits means a lower probability for the UE to decode the paging indicator but longer battery life of the UE. Best

solution is a mid-way one: PI=36.


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Paging Access Failure Troubleshooting-(VII)

•From all this information what do you need to know?:

• there can be several places where paging could get congested: Iu interface, IuB

interface, RNC boards, or PCH interface . PICH channel is the only channel that

is never congested!

• Check with CN how many paging repetitions have, how do they page: by IMSI or

by TMSI. If first paging fails how many repetitions? Last paging is network wide or

LAC wide only?

• --- is currently facing PCH channel load: all smart phones are in cell PCH state. In

this state can only receive paging but can not transmit any data. Any paging for a

UE it is sent specifically to that cell. How RNC knows where is such an UE? By

cell update!. Every time UE changes the cell in cell PCH there is a cell

update+cellupdate confirm, utran mobility information confirm. That means that

the RNC is aware about new location of the UE.

• How much is the paging success now in --- network?

• What solutions we have to offload the PCH channel?:

• LAC split.

• Page by TMSI

• Reduce ping-pongs (and reselections)

• Improve best server area and reduce overlapping


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•Why are RACH parameter VERY important? Because it impacts strongly user experience (also

called E2E=end-to-end user experience)

RACH Access Failure Troubleshooting (I)

Enough performance

counters

No performance

indicators. Only

estimation by RTWP,

load of the RACH

channel etc..


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Page 27

RACH Access Failure Troubleshooting (II)

Uplink/UE/PRACH Preamble 1

Message part…. ….

Max_TX_power_on_PRACH

Preamble n

Preamble_Retrans_Max :

MMax

The answer on AICH must be a specific positive

response for the specific RACH sent

Parameters for RACH/PRACH:

•NBO1( 0 NBO1min NBO1 NBO1max ) is the time between 2 ramping power of the preamble within the same preamble cycle.

•Preamble_Retrans_Max is the maximum number of preamble that can be sent in a cycle.

•Mmax is the maximum number of preamble cycles.

•Preamble_Initial_Power = Primary CPICH TX power – CPICH_RSCP + UL interference + Constant Value

•Constant value is an initial value to start the first preamble power usually is -24.

•UL interference is the latest value broadcasted by the NodeB in SIB7. Ue needs to decode this value before being able to transmit RACH.

•Power_Ramp_Step is the how much the preamble power should be increased after each No ack received on AICH.

•Power offset P p-m = Pmessage-control – Ppreamble, measured in dB, between the power of the last transmitted preamble and the control part of

the random-access message.

•AICH_Transmission_Timing is the time when the RACH message must be transmitted after positive AICH was received( there are other

parameters too)

RACH is a common type transport channel in the uplink. RACHs are always mapped one-to-one onto physical channels (PRACHs), i.e. there is no physical

layer multiplexing of RACHs, and there can only be one RACH TrCH and no other TrCH in a RACH CCTrCH. Service multiplexing is handled by the MAC

layer. In one cell several RACHs/PRACHs may be configured. If more than one PRACH is configured in a cell, the UE performs PRACH selection

NB01

Preamble_Initial_Power :

Power_Ramp_Step :Pp-m :

AICH_Transmission_Timing

RACH message mandatory parameters:

-UE identity( IMSI,IMSI+LAI, TMSI, IMEI-when no USIM is inserted)

-RRC establishment cause (31 causes)

-radio bearer ID( AS or NAS, UM or TM or AM)

-release5 indicator

-measurements results on RACH(like EcNo of the serving cell).


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RACH Access Failure Troubleshooting-(III)

•

From all this information what do you need to know?:

• Current RACH parameters are not optimal: allows the UE to increase

the power 20 dBm more than the RTWP(CONSTANTVALUE=-20,

PREAMBLERETRANSMAX=20, POWERRAMPSTEP=2). Due to this

RTWP increase, due to this RACH increases and so on(it creates an

avalanche effect). Better have longer call setup time for one UE (RACH

failures due to missing NB relations of overshooting cells) instead of

having entire cell shrinked due to one UE not being able to transmit

RACH message.

• Missing neighbours, lack of best server area and poor UL coverage

influence a lot the RACH success rate.

• Cell radius is now at 29.000 km. Make sure there are no UE from a

larger distance(path distance) else will fail on RACH.

• Spreaders inside the Node-B are limited. Multipath ( long distance) is

not good for resource consumptions and so RACH messages might be

missed.


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Preliminary conclusions

• Most attempt failures are related to planning

• Plenty of attempts failures not recorded within the performance

file (When EcIo is worse than -18 very few RACH “reach” the

Node-Bs)

Page 29

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Huawei - Access failures troubleshooting work shop