Inter Frequency Load Sharing

Inter frequency Load Sharing

Load Sharing - Introduction

• Load sharing improves the performance of a Radio Access Network by pooling together resources from different parts of the WCDMA network.

• There are two load-sharing features in the WCDMA RAN: – Inter-Frequency Load Sharing

– Directed Retry to GSM (not discussed in this presentation).

• Inter-Frequency Load Sharing diverts incoming traffic from a heavily loaded cell in one WCDMA carrier to a another WCDMA carrier with a lighter load (speech and packet calls can be diverted).

• Directed Retry to GSM is a one-way diversion from WCDMA to GSM (speech calls with no on-going packet connections).

• There is no inter-operability issue between the two load sharing features. It is possible for a speech call to be first directed from one WCDMA frequency to another and then further redirected to GSM later. Whether that would happen depends on the cell load and the parameter setting at the time.

Inter-Frequency Load Sharing

WCDMA RAN by pooling all the traffic among different carriers depending on the load.

• It provides means to:

– Increase the trunking

efficiency

– Remove any long-term

load imbalance

between the different

carriers

– Steer traffic from one

WCDMA carrier to

another in an

asymmetric way

IFLS – Cell Load

• Cell load is defined as the ratio between the downlink transmitted carrier power and the admission limit, as given by the cell parameter pwrAdm:

• For load sharing purpose, the total resource of a cell is the fraction of the total transmission power up to the admission limit as given by the cell parameter pwrAdm. Load sharing decisions are made based on the amount of remaining resource in the cell:

remaining resource = 1 – cell load – excluded resource

• The calculation are done taking in consideration only non-HSDPA traffic (CS and PS R99). Time Cel l Lo a d 50% pwrAdmPwr IFLS Active PwrAdm power tx load cell _  _

The Downlink Transmitted Carrier Power is retrieved using the Downlink Transmitted Carrier Power Monitor within the Capacity Management function

IFLS – How it works

1. The mobile starts a RRC connection establishment procedure (NO

distinction in RRC cause is made) 2. If the cell load of the service cell is

higher than 50%, then the target cell is evaluated (load-sharing neighbour). The call will be direct to the cell with more resources.

3. If the target cell is chosen, the UE will not be instructed directly to go to the target cell, but it will be told to scan for a suitable cell in the frequency of the target cell (Redirection Info

Information Element in the RRC Connection Reject message)

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IFLS – Functionality Step by Step

1. Ue tries to establish a RRC connection.

2. IFLS evaluates the remaining-resource off the serving cell based on:

remaining resource = 1 – cell load – excluded resource (the amounts are

in percentage). Excluded resource are specified by the parameter loadSharingMargin.

3. If the remaining resource < 50% then an evaluation of the target cell is

performed. If the remaining resource of the target cell is more than the service cell then RRC Connection Reject with redirection to the second carrier is sent back to the Ue.

4. Ue scan for a suitable cell in the frequency of the target cell (2nd _carrier).

It can select the target cell or other cell depending of the ranking. This is done in this way to overcome the possible coverage mismatches.

Free Resource = R[2] Power/ pwrAdm 33% 100% DL power in use 100% Free Resource = R[1] Power/ pwrAdm 33% Second Carrier First Carrier L[1] < 50 % -> Don’t do anything Second Carrier Free Resource = R[2] Power/ pwrAdm 33% L[2] = 33% -- L[1] = 60% L[1] > L[2] 

Select Second Carrier

100% DL power in use 100% Free Resource = R[1] Power/ pwrAdm First Carrier 60% Layer 2 Layer 1 Lo a d Cell 2 Lo a d Cell 1

> = <

?

IFLS – Examples

-> Compare the load with the load sharing candidate

Free Resource = R[2] Power/ pwrAdm 33% 100% Second Carrier DL power in use 100% Second Carrier Free Resource = R[2] Power/ pwrAdm 33% Free Resource = R[1] Power/ pwrAdm 100% First Carrier 60% loadSharingMargin (10%) L[2] = 33% + 10% = 43% L[1] = 60% L[1] > L[2] 

Select Second Carrier

DL power in use 100% Free Resource = R[1] Power/ pwrAdm First Carrier 60% DL power in use 100% Second Carrier Free Resource = R[2] Power/ pwrAdm 33% Free Resource = R[1] Power/ pwrAdm 100% First Carrier 60% loadSharingMargin (40%) L[2] = 33% + 40% = 70%

L[1] = 60%, L[1] < L[2] => Stay in First Carrier

DL power in use 100% Free Resource = R[1] Power/ pwrAdm First Carrier 60% DL power in use 100% Second Carrier Free Resource = R[2] Power/ pwrAdm 33% Free Resource = R[1] Power/ pwrAdm 100% First Carrier 60% loadSharingMargin (70%) L[2] = 33% + 40% = 103%

L[1] = 100%, L[1] < L[2] => Stay in First Carrier

But R[1]=0, second evaluation w/o margin

L[1] = 100%, L[1] < L[2] (33%) => go 2nd _Carrier DL power in use 100% Free Resource = R[1]=0 Power/ pwrAdm First Carrier 100%

IFLS – Coverage Mismatch

• Coverage mismatch happens when the coverage of the service cell is different than the coverage of the target cell in the 2nd _carrier.

• Ideally, both coverage should match. However, this does not represent a problem by itself because Ue has to reselect to the best cell in the 2nd

carrier. In Hot Spot deployment could be a problem.

• When Ue reselect to a cell different than target cell, it could be reject by Admission Control since the selected cell was not evaluated by load

sharing.

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Watch for load in cell X

Hot Spot -Potential Issue

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IFLS – Considerations

• Load-sharing neighbors must be defined before any load-sharing action can take place. They are specified by neighbor-cell relations. The

attribute loadSharingCandidate (TRUE or FALSE) specifies whether the target cell is a load-sharing neighbor of the source cell.

• For Inter-Frequency Load Sharing to work properly, there should be no more than one neighbor per carrier for each source cell. Note that this is

assumed but not enforced.

• Because of the co-location requirement, load-sharing neighbors are assumed to be served by the same RBS. Load sharing between cells served by different RBS’s (even if they are co-located) are not allowed, and attempts to configure such neighbors will fail.

• UE will always try to be set up in the cell of the second access attempt, regardless of the resource situation.

IFLS - PARAMETERS

Parameter

Comment

loadSharingRrcEnabled

A RNC parameter used to turn on the feature.

Setting: True or False.

loadSharingCandidate

A UtranRelation attribute that indicates if a target cell is a load sharing neighbor of the source cell.

Setting: True or False.

loadSharingMargin

A cell-specific parameter that specifies the amount of resource excluded from load-sharing use. Expressed as a percentage.

Default = 0, Range = 0..100.

The higher the value, the more loaded a cell will appear (artifical load to conserve resources).

IFLS – Parameters Details

loadSharingRrcEnabled _{Indicates whether the}

Inter-Frequency Load Sharing function has been enabled in the RNC

RNC 0 0=FALSE ₁ MOC Name RncFunction Node Id RNC

Parameter Description Indicates whether the Inter-Frequency Load Sharing function has been enabled in the RNC.

Data Type BooleanVals MOM Range

Length Range Default Value FALSE Valid Values FALSE = 0 TRUE = 1

loadSharingCandidate _{Identifies whether the target}

cell is an inter-frequency load sharing candidate of the source cell

UtranRelation _{0 N/A 1,0} MOC Name UtranRelation Node Id RNC

Parameter Description Identifies whether the target cell is an inter-frequency load sharing candidate 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. Unit: N/A Resolution: N/A Data Type BooleanVals MOM Range

Length Range Default Value FALSE Valid Values FALSE = 0 TRUE = 1

NOTE: 1 for the overlay cell, 0 for the other cell

loadSharingMargin _{Offset added to the DL power}

of the cell at inter-frequency load sharing evaluation. Unit: 1 %

UTRANCELL _{0 0 ?} MOC Name UtranCell Node Id RNC

Parameter Description Offset added to the DL power of the cell at inter-frequency load sharing evaluation.

Unit: 1 % Resolution: 1 Data Type long MOM Range 0..100 Length Range Default Value 0

IFLS - Scenario: 1900 on 850

Define IFLS to F1 in co-site

ON F1:

• Define ILFS to F2 in co-site

• Define IRAT only on F1

GSM

UMTS F1 UMTS F2

IFLS

IFLS - Scenario: 850 on 1900

Define IFLS to F1 in co-site

• Define IRAT on F2 ON F1:

• Define ILFS to F2 in co-site

• Define IRAT on F1 outside overlaid area

GSM UMTS F1 UMTS F2 IFLS IRAT IRAT PRACTICAL USE:

-Even load between two carrier. -Steer traffic to a prefer carrier -Divide HS traffic from R99 traffic