Huawei - Access failures troubleshooting work shop

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
Security Level:
www.huawei.com
Huawei Workshop
Troubleshooting Access Failures
May 17th, 2011

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

Mobile Terminated Call Setup Procedure (I)
Page 3
UE Node B RNC MSC / VLR MGW
RRC
3. PCH: PCCH: PAGING TYPE 1 <TM>
RRC
2. PAGING
RANAP RANAP
RRC
4. RACH: CCCH: RRC CONNECTION REQUEST <TM>
RRC
1. IAM
ISUP
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 SYNCHRONISATION
DCH-FP DCH-FP
13. RADIO LINK RESTORE INDICATION
NBAPNBAP
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

Mobile Terminated Call Setup Procedure (II)
Page 4
28. RAB ASSIGNMENT REQUEST
RANAP 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 COMMAND
RANAP 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 RANAP
18. COMMON ID
23. DT [ SETUP ]
17. SCCP CONNECTION CONFIRM
SCCP SCCP
SCCP SCCP
Here the RNC will
perform a DRD decision
and CAC decision for
RAB

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 RESPONSE
RANAP 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 COMMIT
NBAPNBAP
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

General Causes of failures (I)
• RF Reasons
• Radio Parameter Problems
• Miscellaneous causes
Page 6

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

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.

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?

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

How to identify and solve different issues?
Page 11

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential 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 NO
If 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 NO
If 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

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)

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
YES
Solution: 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.Cong
Solution per cell: ???
Solution per RNC: decrease DLGBR from 64 to 32 for specific services
VS.RRC.Rej.Code.Cong
Solution 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 congestion
GO TO NEXT SLIDE
NO

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
YES Solution 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 neighbours
Solution 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

•.
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%

•.
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

•.
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

•.
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%

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 Control
Physical Channel). It
carries paging messages
themselves as well as
packet messages for
mobiles in cell FACH.

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 (Second
Secondary Common
Control Physical
Channel). It carries only
paging messages
themselves.
2nd SCCPCH

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

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

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.

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

•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..

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).

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.

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

Huawei - Access failures troubleshooting work shop

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