ps irat success rate

Report
Ps irat(u2g) optimization
INTRODUCTION
PS IRAT (UMTS to GSM ) Success Rate
The KPI defines the success rate for PS Inter RAT cell change attempts for UE on
dedicated channel. During Inter-RATCC from UTRAN to GPRS, UE on DCH, the
Handover evaluation function triggers this function to indicate that we need to make
handover to a GSM cell.
PS IRAT SUCCESS RATE =
pmNoOutIratCcSuccess/pmNoOutIratCcAtt
Flowchart for IRATCC from UTRAN to GPRS
STEPS FOR PS IRAT OPTIMIZATION
› To start with , Neighbour List Tuning has to be done. Prominent 2G neighbours should be
added and Far-off neighbours should be deleted.
› 3G cells with very low number of 2G relations have to be identified . It is preferred to have
atleast 7 gsmrelations per utrancell.
› Proper Selection Priority for gsmrelations has to be given based on 2G-2G Handover
Matrix ,Tier and distance.The colocated 2G cell, 2G cells of the same site and TIER 1
neighbours should be given selection priority as 1, selection priority as 2 to TIER 2
neighbours and so on.
› The 2G definitions like LAC , CI, BCCH, BSIC have to be checked if they are defined correctly
in the RNC/MSS or not.
› To check 2G definitions in the RNC, we can use following command line in the RNCget externalgsmcell = GSM Cell Name
This has been illustrated with an example in the next slide
BSIC=nccbcc = 21
Identifying worst gsmrelations
› After all neighbour tuning, checking cell definitions has been done , it has to be checked if the
IRAT failure is occuring for some particular gsmrelations. Observing trends of
pmNoOutIratCcSuccess and pmNoOutIratCcAtt per utrancell per gsmrelation can help in finding
such worst gsmrelations
› After the worst gsmrelations identification has been done , we should check the packet channel
allocation attempts and packet channel allocation failures .The 2G counters for finding the same
are:
PCHALLATT for Number of packet channel allocation attempts and PCHALLFAIL for Number of
packet channel allocation failed
› Hard Blocking and Soft Blocking in the worst gsmrelations have also to be checked .High packet
channel failure implies 2G congestion.
CONGESTION IN 2G CELLS
The counter pmNoOutIratCcReturnOldCh has also to be verified. This counter provides the
total number of the PS Inter-RATCC attempts for UE on DCH where the UE returns to old
channel. It is stepped for Inter-RATCC from UTRAN to GPRS, UE on DCH. The counter is
increased when the “Cell change order from UTRAN failure” RRC message is received from the
UE. ONE REASON FOR RETURN TO OLD CHANNEL (i.e 3G) IS HIGH PDCH ALLOCATION
FAILURE.
To improve PS IRAT in such cases, following actions might be taken:
1.2G congestion has to be resolved which can be done by allocating more PDCH channels . In
cases of extreme congestion, additional TRXs may be installed.
2.3G parameters can be retuned to trigger IRAT from 3G to 2G only when 3G coverage becomes
very poor and 2G radio conditions are very good. The parameters to be tuned have been
explained in the upcoming slide.
Optimizing 3G parameters
› By lowering the value of the parameters like serviceOffest2dEcNo and serviceoffset2dRscp we
can delay the compress mode and can avoid unnecessary compress mode .The counters
pmcmattdlhls and pmcmsuccdlhls can be used to find the number of HLS attempts and success
respectively. The value of the parameter ‘gsmthresh3a’ can also be increased to trigger IRAT only
when 2G radio conditions are very good. This will reduce PS IRAT attempts and will also improve
PS IRAT success rate. An example of the parameter settings is:
gsmthresh3a can be increased to -90
serviceOffest2dEcNo to -3
serviceoffset2dRscp to -5
(The setting of these parameters may vary from network to network)
› However ,it is advisable to change service offsets only for following UeRC states:
64/64,128/128,64/128 and 128/64
› If the PS IRAT remains poor even after tuning the above parameters and adding additional PDCH
, then NEGATIVE INDIVIDUAL OFFSET can be set for some particular worst gsm relations.
However, this will affect CS IRAT as well so care should be taken of.
› The ICM bands in 2G have also to be checked.
ICM band
ICM BAND-INTRODUCTION
If ICM is active, GPRS/EGPRS Channel Administration can use the ranking of channels into
interference bands as helpful information when selecting channels from the circuit switched
domain to be configured as dedicated or on-demand PDCHs. When a PDCH is reconfigured to a
TCH, the channel is placed in the interference band it was in before it was allocated as PDCH. Idle
Channel Measurements are not performed on PDCHs . For idle channel measurement there are
four object types for FR/HR and OL/UL i.e Overlaid and Underlaid. In these object types there are
counters for the accumulated number of idle channels in each interference band viz. ITFUSIBi
,ITHUSIBi,ITFOSIBi ,ITHOSIBi i as 1,2,...,5.
RELATED KPIs
ITFOSIB1 + ITHOSIB1 = OL ICM 1, ITFOSIB2 + ITHOSIB2 = OL ICM 2,
ITFOSIB3 + ITHOSIB3 = OL ICM 3,ITFOSIB4 + ITHOSIB4 = OL ICM 4,
ITFOSIB5 + ITHOSIB5 = OL ICM 5, ITFUSIB1 + ITHUSIB1 = UL ICM 1
, ITFUSIB2 + ITHUSIB2 = UL ICM 2 , ITFUSIB3 + ITHUSIB3 = UL ICM 3 ,
ITFUSIB4 + ITHUSIB4 = UL ICM 4 , ITFUSIB5 + ITHUSIB5 = UL ICM 5
Correlating icm band with PS IRAT SUCCESS
RATE
If ICM Band is showing high value in ICM Band 4 (which is above -98 dBm) and ICM Band 5(which
is above -88dBm) , then there is definitely some source of external interference in the 2G cell and
this may also cause PS IRAT FAILURE in the cells. A spectral scan using Spectrum Analyser should
be done in high interference cells. We can also use Band Pass filter or CDMA filter to resolve the
issue.
The screenshots below show two cells of Aircel J&K where ICM Band 4 and ICM Band 5 are
showing high values and corresponding PS IRAT Success rate are also very low. Its probable that
because of external interference in the 2G cell, the PS IRAT attempts are not becoming successful.
2G PARAMETER-ICMSTATE
› The parameter ICM STATE also needs to be checked. ICM STATE is a parameter defined in the
BSC that sets the idle channel measurements to ACTIVE, PASSIVE or NOALLOC. NOALLOC means
that the idle channel measurements are used for statistics only, and not for channel allocation.
RECOMMENDED VALUE
Some additional 3G parameters and counters that can be checked for PS IRAT optimization
have been explained in the next few slides.
Parameter- gsmAmountPropRepeat
› This parameter decides how many times RNC will command UE to re-attempt
cell change to the GSM cell repeatedly based on the same measurement
report excluding the first attempt. A few UEs under such circumstances
contribute highly in the of count of pmnooutiratccatt and may cause low PS
IRAT Success Rate.
› So the parameter gsmAmountPropRepeat which is generally set to 4 can be
reduced to 2 or 1.This will reduce IRAT attempts and will also improve PS IRAT
success rate.
› The functionality of this parameter can be well understood from the flowchart
given in the next slide
EVENT 3a
Parameter - fachMeasOccaCycLenCoeff
› Fach Measurement Occasion Cycle Length coefficient - A factor used when the UE performs
inter-frequency and inter-system measurements. The UE uses this parameter to calculate the
interval length in order to determine the repeating cycle of the measurement.
› Value mapping:
0 : not broadcasted in SIB 11.
1 : not used.
2 : not used.
3 : used when inter frequency and GSM neighbors.
4 : used when inter frequency or GSM neighbors.
5 - 12 not used.
If fachMeasOccaCycLenCoeff is set to 0, the parameter is not sent in system information and the
UE is not allowed to leave the SCCPCH in order to perform measurements on other frequencies
and RATs and if fachMeasOccaCycLenCoeff is set to a value 4,the UE performs inter-RAT
measurements during FACH occasions .
It is recommended to change this parameter to 4 if is set to 0.
Pdf Counter-PMPROPAGATIONDELAY
› The pdf counter –pmPropagationDelay can be used to observe samples of a cell . If a cell is
serving at a very long distance, then phsical optimization may also help to reduce the number of
PS IRAT attempts.
› Example: After downtilting the cell UBB071Z(BHURNC1-Aircel),the irat attempts reduced from as
high as >100 to <10, and all samples were then observed from distance less than 1.5 km
PRE
Samples coming from more than 10 km
No samples from far range
POST
Issue of Rau rejection/failure
› The “RAU Rejection” during IRAT HO may also cause low PS IRAT handover success rate.
› The occurances of RAU rejection can be known from SGSN trace or from the
Drive test log files .The TEMS DT files shows Rauting Area Update Failure/Reject
RAU REQUEST
INSTANCE OF RAU REJECTION WHILE UE IS IN 2G
•IN 2G: L3 MSG : DETAILS SHOW : The mobile station does not support the PS Handover. If such issues
are observed, there is a high probability that the issue is mainly from the core side and it needs to be
checked.
UETR, UEH TRACING
FAILED IRAT CELL CHANGE
›
›
›
›
›
›
›
›
›
›
›
›
Timestamp lh UE RBS RNC CN Prot Message
------------------------------------------------------------------------------------------------------------------------[02:20:18.653]01,2385 <<--------<< (RRC) cellChangeOrderFromUTRAN (rrcTID=0) (targetIRAT:BSIC/BCCH=10/48)
[02:20:18.787]01,2385
(MEAS) TRANSPORT_CHANNEL_BER (0:2)
[02:20:18.849]01,2385
(MEAS) TRANSPORT_CHANNEL_BER (0:2)
[02:20:19.008]01,2385
(MEAS) UL_DCH_BLER (nrOfTransportBlocks=5) (nrOfFaultyTransportBlocks=0)
[02:20:19.025]01,2385 >>--->> (NBAP) DedicatedMeasurementReport (tID=16859L) (RNC.CCID=23) (measID=1) (RL-SetID=0) (sIRErrVal=-18.5dB)
[02:20:19.037]01,2385 >>--->> (NBAP) DedicatedMeasurementReport (tID=16860L) (RNC.CCID=23) (measID=300) (rL-ID=0)
(txCodePwrVal=18.5dBm)
[02:20:19.827]01,2385
(MEAS) TRANSPORT_CHANNEL_BER
[02:20:19.849]01,2385
(MEAS) TRANSPORT_CHANNEL_BER
[02:20:19.925]01,2385 >>--->> (NBAP) RadioLinkFailureIndication (tID=16861L) (RNC.CCID=23) (RL-SetID=0)
(cause:radioNetwork/synchronisation-failure)
[2011-11-03 02:20:38.656] 000800/RncLmUePT(UEH_EXCEPTION) ../src/UehIratCcUtranGsmC.cpp:1481 TRACE1:ExceptionCode = 512;
TIMER cellChangeTimerId has expired; InterfaceTimout (Internal); CN; RRCConRel; Dropped Call Release Pending; callProc =
UehProcIndIRATCellChange; UeRef = 2385; IMSI = 404371140260784; cellId = 50001; cellFroId = 0; S-RNTI = 35153; RLs in DRNC = 0;
Best RL in DRNC: No; conntype = uehPacket64Hs targetConnType = uehNotValid
RNC is sending CC order to Ue but not receiving RAU update from Ue, due to missing Access & sync to
target 2G cell . UETR snap shows IRAT CC [cellChangeOrderFromUTRAN] and the unsuccessful
UEH_EXCEPTION :ExceptionCode = 512; TIMERcellChangeTimerId has expired.
THANK YOU

similar documents