HS Load Distribution Between 2 Carriers

HS Load Distribution between 2 carriers

Wataniya

Hussein RidaGSDC LebaNon

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the footer area Hussein Rida WATANIYA 2ND CARRIER DEPLOYMENT 2010-04-172

abstract

› Wataniya (Kuwait) has started deployment of second carrier on its network (132 Sites).

› The traffic was unloaded between F1 and F2, where most of the load was on F1, and effectively there was high HS load on F1 and very low HS load on F2.

› Wataniya wants to distribute load on both carriers to utilize effectively both frequencies and thus higher throughput and higher download volume.

› They have tried to use IFLS to distribute the load, but it was not effective, since the R99 load is not reaching 50%, and basically IFLS is not active on most of the sites.

› This KO describes a new strategy based on IDLE Mode behavior to allow distribution of traffic on both Carriers.

› Speech traffic was minimized on F2 using Directed Retry to allow more utilization for HS on F2.

› The KO also includes statistics that show HS load increase on F2 reaching 46%.

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Table of contents

› Idle Mode Behavior and Parameters.› Load Sharing Feature.› Directed Retry to GSM.› 2nd Carrier Strategy.› Deployment Strategy: 3 Profiles.› New parameter’s implementation and statistics.› Ways Forward.› Conclusion.› Abbreviations.› References.› Business Object Reports.

IDLE Mode Behavior and Parameters

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Cell Selection (S-Criteria)

› For a UE to select a cell, the S-criteria should be met. The S-criteria is described as follows:

- Squal = CPICH - qQualMin > 0Measurement on Ec/No

AND- Srxlev = CPICH - qRxLevMin - Pcompensation > 0

Measurement on RSCP

Pcompensation = max(maxTxPowerUL – P;0) - Pcompensation is used to compensate for UE’s that

cannot send at the configured Maximum UL power.

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S-Criteria Parameters

Parameter Range , Default Value

Description

qQualMin Range: -24 to 0, Default=-18 (dB)

› Minimum Required quality level for a cell.› Increasing qQualMin, makes EcNo

conditions of a cell more strict for a UE to camp on in Idle Mode.

qRxLevMin Range: -119 to -25, Default=-115 (dBm)

› Minimum required RX level in the cell.› Increasing qRxLevMin reduces the cell

radius, allowing nearby UE’s to camp on when having good Cpich_RSCP

maxTxPowerUL Range: -50 to 33, Default=24 (dBm)

› Maximum UE transmission power on the RACH when accessing the system.

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Cell Reselection (R-Criteria)

› A UE needs to make a cell reselection when:– The cell on which it is camping is no longer suitable (S criteria are

not valid anymore).– When the UE finds a stronger cell.

› During Cell reselection, the suitable cells are ranked according to the R-Criteria and the highest ranked cell is reselected. (Suitable cells are cells that meet the S-Criteria). The R ranking is according to:

- R(serving) =Qmeas(s) + qHyst(s)- R(neighbor) = Qmeas(n) - qoffset(s,n)- Measurements are done on either EcNo or RSCP based on

the parameter qualMeasQuantity.

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Cell Reselection (R-Criteria)

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R-Criteria ParametersParameter Range ,

Default ValueDescription

qHyst1 Range: 0 to 40, Default=4

› The hysteresis value to avoid ping pong Effect .It is used when measurements are done on CPICH_RSCP.

› When Increasing qHyst1, we delay the cell reselection to another cell.

qHyst2 Range: 0 to 40, Default=4

› Same as qHyst1, but it is used when measurements are done on CPICH_EcNo.

qoffset1 (s,n) Range: -50 to 50, Default=0

Default=7 (for gsmRelation)

› The offset between the 2 cells when measurements are done on CPICH_RSCP.

› When Increasing qOffset1(s,n) the cell n will be given a lower rank

qoffset2 (s,n) Range: -50 to 50, Default=0

› Same as qOffset1(s,n), but it is used when measurements are done on CPICH_EcNo.

qualMeasQuantity Default=CPICH_EC_NO

› Determines if measurements will be done based on EcNo or Rscp

tReselection Range: 0 to 31, Default=2 sec

› Time-to-trigger for cell reselection

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IDLE mode measurement

› A UE in idle mode starts measurements on neighbor cells when:– Intra-freq neighbour measurement› CPICH_EcNo (S) ≤ qQualMin + sIntraSearch

– Inter-freq neighbour measurement› CPICH_EcNo (S) ≤ qQualMin + sInterSearch

– GSM neighbour measurement› CPICH_EcNo (S) ≤ qQualMin + sRatSearch› or› CPICH_Rscp (S) ≤ qRxLevMin + sHcsRat

› The decision when to start Inter/Intra/GSM measurements is based only on quality (EcNo).

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Idle mode measurementParameter Range ,

Default ValueDescription

sIntraSearch Range: 0 to 27, Default=0

0 : not sent

1 : -32 dB

2 : -30 dB

...

27 : 20 dB

› The decision on when measurements on intra-frequencies shall be performed.

› When 0, UE always makes intra-frequency measurements.› When it increases, the intra-frequency measurements is

faster which could lead to an earlier cell reselection.

sInterSearch Range: 0 to 27, Default=0

0 : not sent

1 : -32 dB

2 : -30 dB

...

27 : 20 dB

› The decision on when measurements on inter-frequencies shall be performed.

› When 0, UE always makes intra-frequency measurements.› When it increases, the intra-frequency measurements is

faster which could lead to an earlier cell reselection.

sRatSearch Range: -32 to 20, Default=4

› The decision on when measurements on GSM frequencies shall be performed.

sHcsRat Range: -105 to 91, Default=-105

› RAT specific threshold in the serving cell used in the inter-RAT measurement rules

Load Sharing Feature

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Inter-Frequency Load Sharing› At call set-up

– RRC Connection Establishment for all RABs– Channel Switching from FACH to DCH Mode

› Triggered by Downlink Transmitted Carrier Power

› The feature is activated in an RNC by setting the parameter loadSharingRrcEnabled to TRUE.

› The attribute loadSharingCandidate TRUE/FALSE specifies whether the target cell is a load-sharing neighbor of the source cell

f1 f1f1 f1

f2 f2

Reference: WCDMA Functionality

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Inter Frequency Load Sharing

› When the Load of a cell is more than 50%, IFLS execution starts.– LOAD defined as:

Total non-HS Carrier power

(pwrAdm*maximumTransmissionPower)

– Total non-HS Carrier Power can be get from the PDF counter: “pmTransmittedCarrierPowerNonHS”–Maximum Transmission Power is the value of RBS Parameter

maxDlPowerCapability.

Note: pwrAdm is the parameter that defines the power admission threshold

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Load Sharing - Example

DL Load =5W9W

= 55.5%1Check SourceCell DL LOAD > 50%?

2 Check SourceCell(S)“Remaining Pwr”

100% - DL Load(S) - LoadSharingMargin

3 Check TargetCell(N)“Remaining Pwr”

100% - DL Load(N) - LoadSharingMargin

100% - 3W - 5% 9W

= 61.6%

Remaining Pwr(N) -

Remaining Pwr(S) 4

>50%

>20%

= 35.5% 100% - 55.5% - 10%

= 27.1% Target Cell has 20% more “remaining pwr”

ExecuteLoadSharing

AND

y

y

loadSharingMargin = 5%

CellA-F2

CEllA-F3

pwrAdm=90% (Available Pwr = 9W)

Remaining pwr = 4W 10W RRU

Remaining pwr = 6W 10W RRU

Used Pwr= 5W

Used Pwr= 3W

LoadSharing

setup

source

Target

loadSharingMargin = 10%

› loadSharingMaring is used to make the Remaining Resource of a cell lower that is actually is.

Reference: 2nd Carrier Deployment (Japan) (P7)

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Load Sharing Parameters

Parameter name

Level Range Default Parameter Description

loadSharingRrcEnabled

RNCFALSE = 0TRUE = 1

0 An RNC-wide flag for turning on the feature.

loadSharingCandidate

UtranRel

FALSE = 0TRUE = 1

0

A UtranRelation attribute that indicates if a target cell is a load sharing neighbor of the source cell.In order to set the value to TRUE (i.e. to define the target cell as a candidate for IFLS), the target cell and the source cell must belong to the same RBS (both must refer to the same IubLink MO) and must have different frequencies (frequencyRelationType for this UtranRelation = INTER_FREQ). This also implies that it is only possible to set the value to TRUE when the target is a UtranCell and not when it is an ExternalUtranCell.

loadSharingMargin

Cell 0..100 0A cell-specific parameter that specifies the amount of resource excluded from load-sharing use.

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Ineffective IFLS at low Load

› IFLS is a very efficient feature to distribute the Load between two different carriers. – This includes all types of RAB’s (speech, Video, R99 PS, HS …)

› IFLS is activated only when the Power load is 50% of the power admission. The load considered is only non-HS Load (control Channel, CS, R99 PS)

› In Wataniya’s network the non-HS load is less than 50% of power admission, though there is a demand on HS.

› This leads to that all HS requests are kept on one carrier, and thus the users’ HS throughput is reduced.

› Ultimately, we need to distribute the HS users equally among different carriers which will lead in an increase in both cell and user throughput.

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How to Distribute (HS) traffic at low load

› Reducing pwrAdm can solve the problem, but the overall capacity is reduced.

› Another way to distribute the HS users on both carriers is by distributing users among different carriers when they are in IDLE Mode.

› This means the users in IDLE mode will be camping on one of the 2 carriers based on IDLE mode parameters. When an HS call is established, the call shall remain on its initial carrier.

Directed Retry To GSM

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Directed Retry to GSMApplicable for Voice

WCDMA

GSM

AdmissionControl

Reference: WCDMA Functionality

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DIRECT retry to gsm› The feature enables speech users in a WCDMA network to be redirected to GSM at call

set up, in case the utilization of cell resources does not allow the user to be admitted in the WCDMA network.

› Directed Retry to GSM is triggered during the establishment of a speech Radio Access Bearer, when the core network has sent a RAB assignment request to UTRAN and the admission control function in UTRAN rejects the request due to lack of available radio resources.

› Based on operator configured UTRAN-GSM cell relations, the Directed Retry function evaluates if a directed retry to GSM should be tried. If the result of this analysis is positive, UTRAN rejects the RAB request and informs the core network about the reason for the rejection and the identity of the new target cell, and initiates a handover to GSM.

› The operator can only define one GSM target cell per UTRAN source cell for Directed Retry, and since new measurements take more time than is available in a directed retry situation, the target cell selection will be based on connection quality of the active set at the time of the last handover evaluation. Going top-down in this list of quality ranked active set cells, and checking for GSM cell relations, the Directed Retry function will chose the GSM cell belonging to the first such relation it finds. Only GSM cells to which the UE has access will be considered. At failure to hand-over to GSM, no other candidate cell will be proposed and the call will be dropped. UE capabilities are taken into account when the directed retry decision is taken.

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Directed Retry to GSM

Directed retry to GSM– At call set-up - RAB Establishment for voice– Triggered by Downlink Transmitted Carrier Power

– The feature is activated in an RNC by setting the parameter loadSharingDirRetryEnabled to TRUE

– One GSM target can be defined for each WCDMA cell via the cell parameter directedRetryTarget

– loadSharingGsmThreshold specifies the minimum load at which off-loading to GSM begins: ex 80% of pwrAdm

– loadSharingGsmFraction specifies the percentage of Directed Retry candidates to be diverted to GSM while the cell load is above the specified load threshold

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Directed Retry to GSM Parameters

Parameter name

Level Range Default Parameter Description

loadSharingDirRetryEnabled

RNCFALSE = 0TRUE = 1

FALSEIndicates whether the Load Sharing via Directed Retry to GSM function has been enabled in the RNC.

directedRetryTarget

CellFALSE = 0TRUE = 1

The Default Value is Empty

Reference to the ExternalGsmCell MO, containing the specification of this Load Sharing via Directed Retry target cell.

loadSharingGsmFraction

Cell0 to 100 100

Defines percentage of Speech calls that can be directed to GSM after the loadSharingGsmThreshold has been exceeded.If the value of loadSharingGsmFraction is set to 0, this means no voice calls subject to Directed Retry should be directed to GSM (no voice calls aredirected to GSM).If the value of loadSharingGsmFraction is set to 100, this means that ALL of the voice calls proposed for Directed Retry should be directed to GSM (all voice calls that are proposed for directed retry are directed to GSM).

loadSharingGsmThreshold

Cell 0..100 75

Defines percentage of the guaranteed non-handover admission limit (pwrAdm) above which Directed Retry should be invokedIf the value of loadSharingGsmThreshold is set to 100 then this means that the threshold at which voice calls are directed to GSM is 100 % of pwrAdm. Therefore no voice calls should be moved to GSM until the admission threshold pwrAdm is reached.If the value of loadSharingGsmThreshold is set to 0 then this means that the threshold at which voice calls are directed to GSM is 0 % of pwrAdm.

2nd Carrier Strategy

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2nd Carrier Deployment Strategy

HS/R99

HS/R99

GSM

1nd Carrier

› Both 1st and 2nd carrier are HS capable as a requirement for Wataniya.

› In the coming strategy we will consider 3 scenarios:–Cluster 2nd carrier. –Border/Isolated 2nd carrier.–No Co-GSM Sites.

2nd CarrierHS/R99 (F2)

HS/R99 (F1)

GSM GSM

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F2 F2 F2

F1 F1 F1

GSM GSM GSM

Inter-Freq

Cell Reselection

Intra-FreqLoad-SharingLoad-Sharing

IRAT HO

Directed Retry to GSM(for speech only)

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› Idle Mode Strategy:› Carrier selection will be based on best

quality. This will reduce CPM in dedicated mode› Reduce Idle mode coverage of second

carrier and limit Camping on it only for UE’s that are near the site.

F2 F2 F2

F1 F1 F1

Cell Reselection

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› When reducing the idle mode coverage for 2nd carrier (by increasing qRxLevMin), UE’s that are at the edge of the cell will camp on 1st carrier.

› For UE’s that are near the site, they will camp on 2nd carrier since the quality of second Carrier is better than 1st carrier.

› In this way, we can control the absorption of UE’s in F2 and effectively load distribution between carriers.

Cell selection /reselection on F2

Cell selection /reselection on

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2nd Carrier Deployment StrategyCluster 2nd carrier› CPM and HHO:– Traffic is pushed to GSM from F1 when low

coverage or bad quality–Allow UE’s to do IFHO from F2 to F1 during

poor coverage/quality (for speech and R99).› hsToDchTrigger on F2 isON at poor

quality to avoid HS call drop.

F2 F2 F2

F1 F1 F1

GSM GSM GSM

Inter-Freq

IRAT HO

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2nd Carrier Deployment StrategyCluster 2nd carrier› Inter-frequency Load Sharing:– Load Sharing Between Co-Cell carriers (F1 F2) to balance the traffic.–Not very Effective due to the low load on CS

and R99 traffic.

F2 F2 F2

F1 F1 F1

Load-SharingLoad-Sharing

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Directed retry to GSM (DR)

› To offload second carrier from speech, Directed Retry 2 GSM feature is activated on F2 cells for the sites that have co-GSM.

› The parameter settings are set aggressively to Direct all speech users to GSM whenever feasible.

› For sites with no co-GSM, F2 shall not suck too much UE’s in idle mode to prevent having high speech utilization. This is achieved by varying the idle mode parameters.

F2 F2 F2

F1 F1 F1

GSM GSM GSM

Directed Retry to GSM(for speech only)

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DR to GSm Vs. serviceOffset2dto Offload Speech› The DR to GSM is used to offload speech users from F2 per

Wataniya’s requirements.› This is required since the Idle Mode behavior parameters will distribute

UE’s on both carriers regardless of the needed service; this means that speech users are also distributed on both carriers, which is an undesired effect.

› Another solution to offload speech traffic on F2 was to redirect speech calls from 2nd carrier to first carrier at call establishment by allowing Inter-frequency HO at call setup. This can be achieved by reducing the “serviceoffset2dRscp/Ecno” for speech UERC, and thus allow earlier IFHO for speech.

› Effectively, the speech users on 2nd carrier will directly go to CPM and will initiate an IF HO, where as the non-speech RAB’s will be kept on 2nd carrier.

› The drawback of this solution is that speech will be directed from F2 to F1 and also from F1 to GSM.

Deployment Strategy: 3 Profiles

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Deployment Strategy: 3 Profiles

Cluster Border

Sites with No co-GSM

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Parameter Profiles

New parameter’s implementation and statistics

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New Parameters implementations

Cluster # Change Date

Cluster 1 10-May-10

Cluster 2 4-May-10

Cluster 3 5-May-10

Cluster 4 11-May-10

Cluster 5 12-May-10

Cluster 6 9-May-10

Cluster 7 6-May-10

Cluster 8 6-May-10

Cluster 9 10-May-10

Cluster 10 11-May-10

Cluster 11 9-May-10

Cluster 12 12-May-10

› There are 12 clusters on the network, and the last cluster’ parameters were changed on the 12th of May 2010.

› The sequence of changes on clusters was based on geographical area.

› After implementing the new parameter profiles on F2 cells over all the network, there were an increase in traffic on F2.

› There were some variations in load on F2 between different clusters depending on the number of border/isolated sites and the number of sites where DR was not enabled due to non existence of co-GSM.

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Statistics

› There was an increase in:–RRC requests–Speech Establishment attempts (these are redirected to GSM

whenever possible).–PS/HS establishment attempts.– The KPI’s show the accessibility remained as good as before any

change.

› Speech retainability is not affected much.› HS payload on F2 increased up to 46%.– F2 is now handling 37% of the total payload. (previously it was

24%).

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RRC attempts/success on F2

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Speech attempts/success/DR on f2

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PS attempts/success/DR on f2

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hS attempts/success/DR on f2

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Speech Retainability

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Speech Retainabiltiy

› Speech Retainability is not affected on F2 (nor on Network level), but now it is more sensitive if there are any cells that have high number of call drops.

› Since DR is activated on F2, most of the speech attempts are forwarded to GSM.– This leads to a decrease in total speech call end (up to half).

› So if one (or few) cell(s) had a high number of call drops, the CDR on all F2 will be affected, and there will be a big impact on it.

› For example, on 13/5/2010, there were 686 call drops on all F2 cells making the CDR at 0.75%.– 9 cells (some of them with no DR) which are having high UL contributed with 135 call

drop. If these cells are taken out, the CDR becomes 0.65%, which is an improvement on CDR.

› Before the parameters’ changes, these cells didn’t have a big impact on the network level, because the total number of releases was much higher than now, and thus such cells CDR was hidden by other good performing cells.

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Speech Retainability

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HS Volume increase on f2

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HS volume on F1 and F2

HS Volume (in MB) on F1 cells on Friday 23/4/2010 and Friday 14/5/2010 HS Volume (in MB) on F2 cells on Friday 23/4/2010 and Friday 14/5/2010

› HS traffic increased a little on both Carriers.› HS volume increased on F2 by 46%› HS volume on F2 is 37% of the total volume.– This value will increase when more clusters are added, and reducing the

number of Border sites.

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Ways forward

› When more clusters in F2 will be added and number of border cells will be reduced, HS load will increase more on F2.

› If for specific cells HS load needs to be pushed more on F2, you can reduce qRxLevMin up to -87dBm, but this will suck more speech users, and if DR is On, they will sent on GSM, which might cause GSM congestions.

› When new F2 sites are added, make sure that the nearby cells’ profiles are set properly.

› If DR is available on more sites, speech on F2 will be much reduced.

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Conclusion

› After implemeting the new parameters profiles, there was an increase of 46% of HS load on F2.

› Speech load was reduced on F2 by directing most speech calls on F2 to GSM.

› Accessibility and retainability were not affected by the new changes.

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Abbreviations

› CPM Compressed Mode.› CS Circuit Switched Services.› DR Directed Retry to GSM.› IFHO Inter-Frequency Hand-Over.› IFLS Inter-Frequency Load Sharing.› IRAT HO Inter Radio Technology Hand-Over.› HHO Hard Hand-Over.› HS(DPA) High Speed (Downlink Packet Access).› PS Packet Switched Services.› RAB Radio Access Bearer.› RRC Radio Resource Controller.› UE User Equipment.

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References

› WCDMA Functionality.› KO: “2nd Carrier Deployment (Japan) (P7)”.› Alex: RAN P7.1.4 Library.

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Business object reports

General_CMP_IRAT_IFHO_ KPIsGeneral KPIs

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HS Load Distribution Between 2 Carriers

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