1_importante speech dcr analysis_revc

Speech DCR Analysis

Telefonica Spain

Ericsson Internal | 2012-09-14 |

› In the last months, speech drop rate is constant increasing on Telefonica Spain network

› Next slides contains the updates on the current analysis being done

› Different behavior seen on different regions, so analysis is done in a separate way

Introduction


– Degradation of 0.2 points – Degradation on both UMTS 900 and UMTS 2100 (increase start

mainly on W21):

Madrid


– For the step on W21, the following RNCs contribute: › ALTAVISTA-01› ALTAVISTA-02› ATOCHA-03› ATOCHA-01 (aunque tb hay un escalón en W12)› SIMANCAS-01 (aunque tb hay un escalón en W17)

– Other RNCs that also have a degradation step:› DELICIAS-01 – W27› LUCRECIA-02 – W28› MANOTERA-01 – W24› MANOTERA-02 – W14

– Ericsson proposes for troubleshooting:› ATOCHA-03 – W21› DELICIAS-01 – W27

Madrid


– Degradation of 0.15 points– Degradation mainly on U900 (big step on W25) and U2100 F1

Barcelona


› For the step on W25, it can be seen a correlation between RSSI increase and Speech DCR during W25 and W36:

RSSI - BCN


› IRAT degradation of both zones is mainly presented on U900 band (failures due to physical channel failure):

IRAT degradation - MAD


› IRAT degradation of both zones is mainly presented on U900 band (failures due to physical channel failure):

IRAT degradation - BCN


› Degradation seen on (PERU and VICALVAR present congestion on HS):

IUR degradation - mad


› Degradation seen on (GUELL and BOTEROS present congestion on HS):

IUR degradation - bcn


› Some correlation seen between SHO Success and Speech DCR, worthy to troubleshoot

› Degradation seen on W21 (but also in the beginning of the year have bad values and Speech DCR was not degraded):

SHO - MAD


› The next slides contain the troubleshooting done for RNCs with significant degradation on SHO Success Rate.

SHO – MAD troubleshooting


› Correlation of SHO failures with ADM failures

RNC-M-ATOCHA-02


› Correlation of SHO failures with ADM failures since W35

RNC-M-Albeniz-02


› Responsible for big degradation step on SHO since W33 is utrancell OPORTO_FUTBOL_280603701_01, with 0% of success rate. Probably this is a dummy cell that is causing SHO failures and drops.

RNC-M-Albeniz-02


› No real correlation between SHO Failures and ADM Failures

RNC-M-Albeniz-03


› Main responsible for big degradation step on SHO since W36 are utrancells PHABANA with 0% of success rate.

RNC-M-Albeniz-03


› Correlation between SHO Failures and ADM Failures since W35

RNC-M-albeniz-01


› Main responsible cells for SHO degradation:

RNC-M-albeniz-01


› No correlation between SHO Failures and ADM Failures

RNC-M-atocha-01


› Responsible for big degradation step on SHO since W33 are utrancell sOPORTO_FUTBOL_280603701 with 0% of success rate. Probably this is a dummy cell that is causing SHO failures and drops.

RNC-M-atocha-01


› No clear correlation between SHO Success and Speech DCR, although at RNC level, there are some significant correlation (see next slide)

SHO - BCN


SHO - BCN


Ueh exception analysis - mad

Important contribution of MRAB in total number of drops


Ueh exception analysis - mad

Although most of the drops are not in SHO and IRAT, there is a significant amount of drops due to these procedures.


Ueh exception analysis – rnc-m-atocha-01

Important to tune SHO/RCS Parameters


Ueh exception analysis – rnc-m-atocha-03

Important to tune RCS Parameters


› The following slides contain proposals in order to tune Radio Connection Supervision timers on:

– Layer 1 - Physical– Layer 2 – RLC– Layer 3 – SHO

Rcs parameters change proposal


L1 Timer (UE side)

N313 : number of consecutive “out of sync” after that Ue starts t313

“Out of sync” generation is Ue dependant, generally when the Ue measures a SIR < target SIR.

T313: After n313 consecutive “out of service”, the UE starts T313 and doesn’t stop it doesn’t

Measure an “in Sync” that is SiR> SIR Target

Timer for Radio Link Failure in DL = n313*10 (ms)+ t313 . After this timer expiry the call is

Dropped


L1 Timer (proposed value)• Actual Telefónica Settings:

N313=100

T313=3

DL Radio Link Failure = 3 (sec) + 100*10 (ms) = 4 seconds.

This means that after 4 seconds Ue exits the DCH state and stays in Idle; there is no possibility to recover the call for the RNC.

• For Radio Link Failure in uplink Teflefónica has the DchRcsLost=5 (sec) and RLfailureT=1 (sec) noutSyncInd=10

That means DchRcsLost+ RLfailureT + nOutSyncInd*0.01= 6,1 seconds.

So uplink and downlink RLF timers are unbalanced

It is recommended to align them to a value that is enough robust. Proposed values:

RadioLinkFailureT = 20 (2 sec)

T313 = 5 sec

N313 = 200

So UL and DL will be balanced to 7 seconds for total L1 supervision


L2 TimersUE RNCActive set update (1 or 2 RLC PDUs)

RLC

RLC

Signaling (rrc) messages associated with speech (and other RABs) are made

of RLC PDUs. If they are not received by the peer entity (don’t get an “ack”

by RNC / UE), may due to bad radio radio condition, they are retransmitted;

The total timer of retransmission is:

Timerpoll*(MaxDat-1)+TimerRST*(MaxRST-1)

Consider that if this total time expiries, the UE goes into Idle , while on the RNC

Side, it drops the call (maximum number of RLC retransmission reached)

Ericsson Internal | 2012-09-14 | Page 33

L2 Timers• Current Telefónica settings for SRB:

Timerpoll (both sides RNC and Ue)=160

MaxDat(both sides RNC and Ue)= 40

rncMaxRST = 1

UeMaxRST= 0 (means 1)

rncTimerRST=550

UeTimerRST= 10 (means 550)

Current in Telefónica Total L2 timer (both UL or DL)= Timerpoll*(MaxDat-1)+TimerRST*(MaxRST-1)= 160*(39)+ (1-1)(550) = 6,24sec < 7,1 sec (L1 proposed supervision timers)

Even if L1 = 6,1s, L2 should be greater enough to make L2 supervision algorithm more robust

In Ericsson opinion L2 supervision timers need to be made more robust (longer timeouts) to handle temporary bad radio, and it is suggested to set them enough higher than L1 timers and less than L3 timers


L2 Timers : proposed values- On RNC side there is no limit on maxDat, so use that to increase the timeout

- On UE side maxDat is limited, set it to the max value (15) and then increase timerPoll to get the timeout length wanted.

UeRC=2 / UeRcRb=2,3,4 (UeRc=speech and DCH 2,3,4 associated with speech)

UeTimerPoll = RncTimerPoll= proposed = 240

In this case the RLC supervision timing will last

In RNC 240*39 = 9,36 seconds

In Ue 240* 39 = 9,36 seconds

The proposal to change them not only on pure speech (uerc=2, ueRcRb=2,3,4), but also for Speech + Ps 0/0, and to all active multiRab associated with Speech.


L3 Timers•L3 Timers start when a rrc procedure takes place (i.e. Radio Bearer / Radio Bearer Setup complete - active set / active set update complete)

•The more classical example is L3 soft handover procedure

Active set update

UERNC

Iu relase request to the CN (internal System release triggered)

tRrcActiveSetUpdate=5 seconds

Rrc connection relase “unspecified”

After sending an rrc active set update, if the RNC doesn’t receive an active set update complete by the UE within timer: tRrcActiveSetUpdate the call is dropped , even if the Ue should recover the L1 or the L2 levels. So L3 timers (in particular the soft handover) should expiry only after the L1 and L2 timers have expiried (Ue / RNC has had all time considered useful to recover The connection)

5 sec


L3 Timers proposed value

•Actual value of tRrcActiveSetUpdate in Telefónica = 6 seconds

•Proposed value= 10 seconds.


› The following checks were performed, but no correlation with speech dropped call was found:

– Downtime– # Cells integrated– Total number of RAB Attempts– Correlation between IRAT Failures and high interference on 2G– Prop Delay checks:

› Check done on Madrid downtown and no significant impact found, next step to check on regions with big penetration of U900

Other Checks performed


– Cell level analysis– Prop Delay impact on DCR on U900– GPEH analysis focused on Terminal Type Impact– Choose one/two RNCs and implement Parameters change Proposal– Check SHO Degradations on BCN RNCs– Study SHO Parameters and check possible parameter changes– Optimizaton Tools trial:

› IRAT Neigbours› Intra-Frequency Neigbours› R99 power paremeters

Next steps

1_importante speech dcr analysis_revc

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