Inter Frequency Load Sharing

Inter frequency Load Sharing

UMTS on 2nd Carrier

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.

Load Sharing - Diagram

Inter-Frequency Load Sharing

• IFLS improves the efficiency of a 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

GSM

WCDMA F1

WCDMA F2

Load Sharing

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

Ce

ll L

oa

d

50%

pwrAdmPwr

IFLS Active

PwrAdm

powertxloadcell

__

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)

f1

f2

Time

Cell

Lo

ad

50%

pwrAdmPwr

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%


Power/ pwrAdm

33%

Second Carrier

First Carrier

L[1] < 50 %

-> Don’t do anything

Second Carrier


Power/ pwrAdm

33%

L[2] = 33% -- L[1] = 60%

L[1] > L[2]

Select Second Carrier

100%



Power/ pwrAdm

First Carrier

60%

Layer 2

Layer 1

Lo

ad

Cell 2 Lo

ad

Cell 1

> = <

?

IFLS – Examples


Power/ pwrAdm

33%

100%


Free Resource =R[1]

Power/ pwrAdm

60%

Second Carrier

First Carrier

L[1] > 50 %

-> Compare the load with the

load sharing candidate


Power/ pwrAdm

33%

100%

Second Carrier


Second Carrier


Power/ pwrAdm

33%


Power/ pwrAdm

100%

First Carrier

60%

loadSharingMargin (10%)

L[2] = 33% + 10% = 43%

L[1] = 60%

L[1] > L[2]

Select Second Carrier



Power/ pwrAdm

First Carrier

60%


Second Carrier


Power/ pwrAdm

33%


Power/ pwrAdm

100%

First Carrier

60%


L[2] = 33% + 40% = 70%

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



Power/ pwrAdm

First Carrier

60%


Second Carrier


Power/ pwrAdm

33%


Power/ pwrAdm

100%

First Carrier

60%


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


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.

f1

f2

f1

f1

f2

Ideal situation

Watch for load in cell X

Hot Spot -Potential Issue

f2 f2 X

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 PARAMETER

DESCRIPTION LEVEL DEFAULT

VALUE

ATT

VALUE

RECOMMENDED

VALUE

INFO

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

On F2:

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

IRAT

IFLS - Scenario: 850 on 1900

On F2:

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

Documents

Inter Frequency Load Sharing