Minimum Rate Proportional Fair Scheduler.pdf

Minimum Rate Proportional Fair Scheduler

USER DESCRIPTION

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Copyright

Ericsson AB 2011. All rights reserved. No part of this document may bereproduced in any form without the written permission of the copyright owner.

Disclaimer

The contents of this document are subject to revision without notice due tocontinued progress in methodology, design and manufacturing. Ericsson shallhave no liability for any error or damage of any kind resulting from the useof this document.

Trademark List

All trademarks mentioned herein are the property of their respective owners.These are shown in the document Trademark Information.

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Contents

Contents

1 Introduction 11.1 Basic Characteristics 11.2 Benefits 11.3 Additional Information 2

2 Feature Operation 32.1 Network Requirements 32.2 Feature Operation Sequence Diagram 32.3 Process Steps 3

3 Parameters 53.1 Introduced Parameters 53.2 Affected Parameters 5

4 Network Impact 74.1 Capacity 7

5 Associated Features and Affected Functions 95.1 Prerequisite Features 95.2 Affected Features 95.3 Related Features 95.4 Affected System Functions 9

6 Performance 116.1 KPIs 116.2 Counters 116.3 Events 11

7 O&M Information 13

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Introduction

1 Introduction

This document describes the Minimum Rate Proportional Fair Schedulerfeature and its main benefits and impacts in the LTE RAN.

1.1 Basic CharacteristicsFeature Identity:

FAJ 221 0920, Minimum Rate Proportional FairScheduler

Replaces: N/A

Dependencies

This feature requires the following RAN features to be active:

QoS-Aware Scheduler

This feature affects no other features.

1.2 BenefitsThis section describes the benefits of this feature.

The Minimum Rate Proportional Fair Scheduler feature allows system sharingof RAN, RBS, and baseband resources between different radio bearers. Itprovides a trade off between user fairness and system performance. Thisfeature makes it possible to benefit from the fact that different users experiencedifferent radio conditions at a certain time. By prioritizing users experiencinggood channel quality, a higher throughput can be achieved, compared to theResource Fair algorithm. However, to avoid some users being allocated toofew or no resources due to poor channel quality, fairness is provided by alsotaking into account the average rate in scheduler prioritization.

In many scenarios, cell capacity can be increased by using the low fairnessversions of the proportional fair scheduling algorithms. These algorithmsincrease the share of the resources given to users with good channelconditions. This leads to an overall increase in capacity.

The feature also helps in giving a consistent cell edge throughput with theminimum rate Quality of Service (QoS) characteristic. The basic concept is thatflows experiencing a bit rate lower than their configured minimum bit rate will beprioritized before flows that have a bit rate above their configured minimum rate.

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1.3 Additional InformationMore information about this feature and related topics can be found in thefollowing documentation:

QoS-Aware Scheduler

Scheduler

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Feature Operation

2 Feature Operation

This section describes the Minimum Rate Proportional Fair Scheduler feature inmore detail, including network configuration requirements and operation flows.

2.1 Network RequirementsThe following must be fulfilled at feature activation:

The QoS-Aware Scheduler feature must be activated.

The Minimum Rate Proportional Fair Scheduler feature license must bepresent.

2.2 Feature Operation Sequence DiagramThe high level flow for scheduling described in Scheduler applies also when theMinimum Rate Proportional Fair Scheduler is active except that the scheduleris enabled to make prioritization based on the estimated channel quality andaverage rate.

2.3 Process Steps

2.3.1 Configuration

The feature allows selecting a preferred scheduling algorithm per QoS ClassIndicator (QCI). There are five Proportional Fair scheduling algorithms for theoperator to select from:

Equal Rate

Proportional Fair High

Proportional Fair Medium

Proportional Fair Low

Maximum C/I

If the Maximum C/I scheduling algorithm is used, the scheduler focuses onallocating resources to users with good channel conditions to maximize cellcapacity. If the Equal Rate scheduling algorithm is in use, the scheduler aimson providing an equal average bit rate for the flows in the cell. For the otherthree settings, the scheduler provides a balance between the cell capacityand cell edge throughput. The names Proportional Fair High, Proportional

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Fair Medium, and Proportional Fair Low indicate the amount fairness of thescheduling algorithm.

The feature also includes setting a minimum bit rate for QCIs that are configuredfor one of the Proportional Fair scheduling algorithms. The minimum rate forUplink (UL) and Downlink (DL) can be set independently and are configuredfor each QCI by the operator.

2.3.2 Operation

The Proportional Fair Scheduling concept is based on the scheduler havingan overview picture of the channel quality of the users in the cell and theaverage rates of their flows. Therefore, the scheduler monitors channel qualityfrom User Equipment (UE) reported Channel State Information (CSI) andmeasurements performed in the RBS. Also, the average rate is calculatedbased on previous transmissions for the flows. When resources are dividedamong users, the prioritization is based on a weighted measure of the channelquality and average rate.

In addition to the above, the scheduler maintains a configured minimum bit rateof the flows. If the average rate of a flow is lower than the configured value ofminimum bit rate, the scheduler will prioritize assigning radio resources to thatflow higher than flows for which the rate is above its minimum bit rate.

When the Minimum Rate Proportional Fair Scheduler feature is applied, it isnot recommended to configure a mix of bearers with different proportionalfair and resource fair scheduling algorithms in the same cell unless that thecorresponding QCIs are also configured to use absolute priority and havedifferent levels of priority. Configuration of absolute priority is described inQoS-Aware Scheduler.

Setting a high value of the minimum bit rate or enabling minimum bit rate fora too great number of users, or both, may have a large negative impact onbearers configured without a minimum bit rate.

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Parameters

3 Parameters

This section describes parameters introduced by the Minimum RateProportional Fair Scheduler feature, and parameters affected by activatingthe feature.

3.1 Introduced ParametersTable 1 and Table 2 describe the parameters introduced by the feature.

Table 1 Introduced Parameters in MO PfsParameter DescriptionfeatureStatePfs Indicates whether the licensed feature UL and DL Proportional

Fair Scheduling with minimum rate scheduling is ACTIVATED orDEACTIVATED

keyIdPfs License key ID for the UL and DL Proportional Fair Schedulingwith minimum rate scheduling feature

serviceStatePfs Indicates if the UL and DL Proportional Fair Scheduling withminimum rate scheduling feature is operable or inoperable.

PfsId The value component of the Relative Distinguished Name (RDN).licenseStatePfs Indicates whether the licensed state of feature UL and DL

Proportional Fair Scheduling with minimum rate scheduling isENABLED or DISABLED, if a valid license key is installed for thefeature

Table 2 Introduced Parameters in MO QciProfilePredefinedParameter Description

ulMinBitRate UL minimum bit rate

The scheduler will attempt to achieve minimum bit rate for allbearers before giving any user a higher rate. This parameterwill only be used if one of the five Proportional Fair schedulingalgorithms has been selected.

dlMinBitRate DL minimum bit rate

The scheduler will attempt to achieve minimum bit rate for allbearers before giving any user a higher rate. This parameterwill only be used if one of the five Proportional Fair schedulingalgorithms has been selected.

schedulingAlgorithm Specifies which scheduling algorithm is to be used for a certainQCI

3.2 Affected ParametersThe implementation of this feature affects no parameters.

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Network Impact

4 Network Impact

This section describes how the Minimum Rate Proportional Fair Schedulerfeature impacts the network functions and capabilities.

4.1 CapacityThis section provides information on the impact of the feature on networkcapacity.

The Proportional Fair Medium setting should give a good trade off betweencell edge throughput and capacity at high load, that is, in cases where thebandwidth is shared between users, due to opportunistic scheduling. The highfairness settings offer more emphasis on cell edge throughput while the lowfairness variants offer more emphasis on cell capacity.

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Associated Features and Affected Functions

5 Associated Features and AffectedFunctions

This section describes how the Minimum Rate Proportional Fair Schedulerfeature affects other features and functions.

5.1 Prerequisite FeaturesTable 3 lists prerequisite features to the Minimum Rate Proportional FairScheduler feature, that is, they must be active prior to introducing the MinimumRate Proportional Fair Scheduler feature.

Table 3 Prerequisite FeaturesFeature Description

QoS-Aware Scheduler Changes to the parameters schedulingAlgorithm,dlMinRate, and ulMinRate takes effect only if the servicestate for QoS-Aware Scheduler is operable.

5.2 Affected FeaturesThis feature affects no other feature.

5.3 Related FeaturesThis feature is not related to any other feature.

5.4 Affected System FunctionsTable 4 lists features that are related to the Minimum Rate Proportional FairScheduler feature.

Table 4 Related FeaturesFeature Description

Scheduler When there is no license available for the Minimum RateProportional Fair Scheduler feature, the system scheduler setsto RF(1) as default.

(1) Resource Fair

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Performance

6 Performance

This section describes performance indicators, counters, and events associatedwith the Minimum Rate Proportional Fair Scheduler feature.

6.1 KPIsTable 5 lists the main Key Performance Indicators (KPIs) associated with theMinimum Rate Proportional Fair Scheduler feature.

Table 5 KPIsKPI Description

Downlink Throughput Data volume for each time unit in the DL

Uplink Throughput Data volume for each time unit in the UL

More information can be found in Key Performance Indicators.

6.2 CountersTable 6 lists the counters associated with the Minimum Rate Proportional FairScheduler feature.

Table 6 CountersCounter Description

pmRadioThpVolDl Total successfully transferred data volume on MAC(1) level inthe DL

This counter includes possible padding bits. In bytes.

pmRadioThpVolul Total successfully transferred data volume on MAC level in the ULThis counter includes possible padding bits. In bytes.

pmRadioThpResDl Total amount of physical resources used for transmission in theDL

Both successful and unsuccessful transmissions are counted.

pmRadioThpResUl Total amount of physical resources used for transmission in theUL

Both successful and unsuccessful transmissions are counted.

(1) Medium Access Control

6.3 EventsThis feature has no associated events.

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O&M Information

7 O&M Information

This section provides Operation and Maintenance (O&M) information for theMinimum Rate Proportional Fair Scheduler feature.

Activating the Minimum Rate Proportional Fair Scheduler feature requires thatthe corresponding license is installed. More information on handling licensescan be found in License Management. The Minimum Rate Proportional FairScheduler feature is activated by setting the featureStatePfs parameterto ACTIVATED. The operation state of the Minimum Rate Proportional FairScheduler feature can be checked using the serviceStatePfs parameter.

The operator can select a preferred scheduling algorithm for each QCI using theschedulingAlgorithm parameter. A minimum bit rate may be configured fora QCI that is using Proportional Fair Scheduling. There is one parameter for DLand one for UL minimum bit rate, that is, dlMinBitRate and ulMinBitRate.The configured minimum bit rate only takes effect for QCIs for which absolutepriority (refer to QoS-Aware Scheduler) is not enabled.When using the lower fairness algorithms, "Proportional Fair Low" and"Maximum C/I", it is recommended to configure a minimum bit rate to avoidstarvation of UEs experiencing poor channel quality. When using the minimumbit rate for this purpose, a suggested range for the setting is 100-200 kbps.

For UL, the same scheduling algorithm will apply for each Logical ChannelGroup (LCG). The value for the schedulingAlgorithm parameter for theLCG is selected from the logical channel with the highest priority among theactive ones in the group. Furthermore, the UL minimum bit rate used forthe logical channel group is the sum of the ulMinBitRate parameters ofthe active logical channels in the group. Therefore, at radio bearer setup orradio bearer release, if there is a change of highest priority logical channel,the parameters of the LCG are changed accordingly. The ulMinBitRateparameter for the LCG is also recalculated.

For DL, the scheduler has the full view of the logical channels and the valuesof schedulingAlgorithm and dlMinBitRate parameters apply as theyare configured.

Note: Reconfiguration of MOM parameters schedulingAlgorithm,dlMinRate, or ulMinRate takes effect when a new bearer is setup.At that instance, the changes also take effect for all existing bearershaving the same QCI. An exception to this is made in UL where thelogical channel which corresponds to the changed QCI is the logicalchannel from which the LCG draws its parameter values, in this casethe new parameter values will apply to existing bearers when theycome back in synchronization.

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toc1 Introduction1.1 Basic CharacteristicsDependencies1.2 Benefits1.3 Additional Information

2 Feature Operation2.1 Network Requirements2.2 Feature Operation Sequence Diagram2.3 Process Steps2.3.1 Configuration2.3.2 Operation

3 Parameters3.1 Introduced Parameters3.2 Affected Parameters

4 Network Impact4.1 Capacity

5 Associated Features and Affected Functions5.1 Prerequisite Features5.2 Affected Features5.3 Related Features5.4 Affected System Functions

6 Performance 6.1 KPIs6.2 Counters6.3 Events

7 O&M Information

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Minimum Rate Proportional Fair Scheduler.pdf