3G Capacity Management

HOW TO INVESTIGATE LOW HS THROUGHPUT

Agenda• HS cell throughput

– Formulas and Counters description

• Site configuration

– Parameters description

• Number of users

– Counters description

• Alarms

• Radio conditions

• Iub utilization

– Counter’s description

• Accessibility

– Counters description

HS cell throughput

• There is 2 kinds of HS cell throughput:

– Scheduled cell throughput

– Served cell throughput

• Relation between Scheduled and Served cell throughput

– Served Cell throughput = Scheduled cell throughput * Scheduling ratio

• Where Scheduling ratio is the percentage of time that HS subframes have been sent (with data or empty) during a specified period.

formulas

• Scheduling ratio =

Where measurement time = number of ROP * 15 * 60 [s]

• Scheduled cell throughput =

• Served cell throughput =

HS throughput counters: pmNoActiveSubFramesSpiXX

• Description– The number of subframes (2 ms), for scheduling priority class XX (XX= *0, …, 15+ ),

containing high-speed data transmitted by the RBS

• Condition– Increased by one when a subframe containing high-speed data is transmitted by the

RBS.

• MO Class– HsDschResources

HS throughput counters: pmNoInactiveRequiredSubFramesSpiX

X• Definition

– The number of subframes, for scheduling priority class XX (XX= *0, … 15+), in which no data is transmitted although there is user data to be sent in the validated PQ.

• Condition– Increased by one when a subframe is transmitted when data is scheduled for priority

queue.


HS throughput counters: pmSumTransmittedBitsSpiXX

• Definition– The number of transmitted bits at MAC-hs level per scheduling priority class XX (XX= *0, …

15]), including retransmission.

• Condition– Each whole transmitted MAC-hs kilobit, including retransmissions, increases the counter

by one.

• Unit– 1 Kilobits


HS throughput counters: pmSumAckedBitsSpiXX

• Definition– The number of MAC-hs bits received and acknowledged by the UE per scheduling priority

class XX (XX= *0, … 15+).

• Condition– Each whole MAC-hs kilobit received and acknowledged by the UE increases the counter

by one.

• Unit– 1 Kilobits.


Site configuration• Verify the site configuration (HS parameters) with the configuration supported by the

customer.

• The HS parameters are:

RBS parameters RNC parameters

dynamicHsPdschCodeAdditionOn codeThresholdPdu656

maxNumHsPdschCodes numHsPdschCodes

maxNumHsdpaUsers numHsScchCodes

flexibleSchedulerOn hsdpaUsersAdm

supportOf16qam

numHsCodeResources

maxHsRate

RBS parameters: dynamicHsPdschCodeAdditionOn

• Definition– Used as a switch to turn, the Dynamic Code Allocation feature, on or off by setting its

value to true or false.

• Precondition

– To set its value to true, the license key for Dynamic Code Allocation must be activated.

• MO Class– RbsLocalCell .

RBS parameters: maxNumHsPdschCodes

• Definition– It is the maximum number of HS-PDSCH codes allowed per cell. Its value can vary

between 5 and 15.

• MO Class– RbsLocalCell

RBS parameters: maxNumHsdpaUsers

• Definition– It is the maximum number of HSDPA users allowed per cell. Its value can vary between 1

and 96.

• MO Class– RbsLocalCell

RBS parameters: flexibleSchedulerOn

• Definition– Used as a switch to turn, the Flexible Scheduler feature, on or off by setting its value to

true or false.

• Precondition

– To set its value to true, the license key for Flexible Scheduler must be activated.

• MO Class– NodeBFunction

RBS parameters: supportOf16qam

• Definition– Used as a switch to turn, the HSDPA 16QAM feature, on or off by setting its value to true

or false.

– If supportOf16qam = True , so the capability of the UE decides whether 16 QAM or QPSK is used.

– If supportOf16qam = False, so 16 QAM support is not set.

• Precondition– To set its value to true, the license key for HSDPA 16QAM must be activated.

• MO Class– NodeBFunction

RBS parameters: numHsCodeResources• Definition

– It indicates how many processing resources on the TXB that shall be loaded with HSDPA software. An HSDPA processing resource supports a number of HS-DPSCH codes. The number of supported HS-DPSCH codes depends on how many cells that uses the HSDPA processing resource.

– Its value can vary between 0 and 3.

• Disturbances– Changing this attribute can affect traffic (drop calls). The TXB is restarted if the

configuration requires new loading of the TXB. For that, it is recommended to soft block the TX board (or the whole site if there is only one TX board) before changing this parameter.

• MO Class

– TxDeviceGroup

RBS parameters: maxHsRate

• Definition– It indicates the maximum HSDPA bit rate over the Iub

• maxHsRate = 15 * number of E1s

• Unit– 0.1 Mbps

• MO Class

– IubDataStreams

RNC parameters: codeThresholdPdu656• Definition

– It is a threshold for determining when to use the RLC PDU size = 656 bits for UEs with HS-DSCH physical layer category 7 to 10

– Its value can vary between 0 and 15 (default value = 6)

• Values– codeThresholdPdu656 = 0, this mean that always use the RLC PDU size = 656 bits

– codeThresholdPdu656 = 15, this mean that never use the RLC PDU size = 656 bits

– codeThresholdPdu656 < numHsPdschCodes, so the 656 bits is used

– codeThresholdPdu656 > numHsPdschCodes, so the 336 bits is used

• MO Class– Hsdsch

RNC parameters: numHsPdschCodes

• Definition– It determines the minimum number of codes of SF=16 reserved for the HS-PDSCH

• Disturbances

– Changing this attribute may affect ongoing traffic

• When the number of codes is incremented, all traffic is released from the cell

• When the number of codes is decreased, traffic is not released in the cell, but the Hs-dsch throughput may be affected.


RNC parameters: numHsScchCodes• Definition

– This parameter decides the maximum number of HS-SCCH that may be transmitted at the same time (in the same TTI). Since each separate user has a separate HS-SCCH, this also sets the maximum number of UEs that can receive data at the same time when using the HSDPA code multiplexing.

• Disturbances

– Changing this attribute may affect ongoing traffic

• When its value is incremented or decreased, all traffic within the cell is released.


RNC parameters: hsdpaUsersAdm

• Definition– It is an admission limit for the number of users assigned to the HS-PDSCH/HS-SCCH in

the cell.

• MO Class– UtranCell

Number of Users per cell

• The number of users per cell has a big impact on the cell throughput– More the number of users using different services (HS, PS, …) increase, more the cell

resources are distributed between more users, and then the cell throughput decreases.

• Average HS users =

• Average PS users =

ish hRabEstablestPsHsAdcpmSamplesB

EstablishsHsAdchRabpmSumBestP

bEstablishachPsIntRapmSamplesF

ablishsIntRabEstpmSumFachP

Number of users counters: pmSumBestPsHsAdchRabEstablish

• Definition– It is the sum of all sample values recorded during a ROP for the number of A-DCH radio

bearers established in the cell carrying HS-DSCH in the active set.

• Condition– Values are read periodically from an internal level counter and added to this counter.

– The level counter maintains the current number of A-DCH radio bearers established in the cell carrying HS-DSCH in the active set for which this cell is the best cell.

• Sampling rate = 5 s


Number of users counters: pmSamplesBestPsHsAdchRabEstab

lish• Definition

– It is the number of samples recorded within the ROP for

pmSumBestPsHsAdchRabEstablish.


Number of users counters: pmSumFachPsIntRabEstablish

• Definition– It is the sum of all sample values recorded during a ROP for the number of established PS

RABs in state FACH. Incremented in the best cell in the active set.

• Condition– Values are read periodically from an internal level counter and added to this counter.

– The level counter maintains the current number of established PS RABs in state FACH for which this cell is the best cell in the active set.

• Sampling rate = 5 s


Number of users counters: pmSamplesFachPsIntRabEstablish

• Definition

– Number of samples recorded within the ROP for pmSumFachPsIntRabEstablish.


Alarms

• Any alarm (transmission problem, hardware problem, license problem …) can affect the site performance and then affect the site throughput.

• To check the alarms, we can use the command “lga” on Moshell which shows all the alarms history.

• To check the alarms on a specific date (for example 1-February-2010), we can use the following command:

– lga | grep 2011-02-01

Radio conditions

• The radio conditions (CPICH Ec/No, CPICH RSCP, CQI …) have an impact on cell throughput.

• Bad radio conditions means:– Bad CPICH Ec/No, Bad CPICH RSCP (bad coverage)

– Pilot pollution

– Bad CQI (Channel Quality Indicator)

• Bad radio conditions have a negative influence on cell throughput

Iub utilization• The Iub congestion is one of the limiting factors of the HS throughput.

• To check the Iub utilization, we must check the following counter: pmCapAllocIubHsLimitingRatioSpiXX (XX = *0 … 15+)

• Definition– This counter indicates in what degree the HSDPA traffic in downlink for Scheduling Priority

Indicator (SPI) XX is limited by the Iub/Iur interfaces, between SRNC and RBS. – A high value indicates that these interfaces limit the HSDPA traffic in a high degree.

• Unit = 1%

• MO Class– IubDataStreams

Accessibility

• The accessibility is also a limiting factor of the HS throughput.• The two counters that shows the HS accessibility are:

– pmNoRabEstablishSuccessPacketInteractiveHs

– pmNoRabEstablishAttemptPacketInteractiveHs

• If the number of HS RAB success is very low comparing to the number of HS RAB attempt, investigate the cause of this low success rate which could be (Iub

congestion, lack of codes, lack of power, lack of CE … ).

Accessibility counters: pmNoRabEstablishAttemptPacketInteractiveHs

• Definition– It is the number of RAB establishment attempts for the PS Interactive RAB containing

HS-DSCH.

• Condition– It is incremented by one when a RANAP RAB Assignment Request message is received

from the CN with RABs to be set up or modified, after successful RAB mapping to PS Interactive and successful HS-DSCH cell selection.

• MO Class

– UtranCell

Accessibility counters: pmNoRabEstablishSuccessPacketInteractiveHs

• Definition– It is the number of successful RAB establishments for the PS Interactive RAB containing

HS-DSCH.

• Condition– It is incremented by one after sending the RANAP RAB Assignment Response message to

the CN, indicating a successful establishment of a PS Interactive RAB mapped on HS-DSCH.


HSDPA Performance with IBS

Capacity limiting FactorsA WCDMA RAN system has several different resources that are to be looked into to

assess capacity limiting.

Since each user is allocated some of these resources, the usage of these resources

increases with the number of connections in the cell.

Examples of such resources are :

1. Power

2. Air Interface Speech Equivalents (ASE)

3. Downlink channelization codes

4. RBS Hardware (CE’s)

Monitor counter pmNoReqDeniedAdm:

– Incremented when radio admits the connection, but some other resource is unavailable. This could be Iub, CE, or some other processing resource

Power

A fundamental property of WCDMA is that coverage can be traded for capacity.

DL Tx carrier power – is a resource which is shared among the common and dedicated channels.

primaryCpichPower is reference for all channels in the system and is therefore controlling the cell size

Trade-off:-Increasing the CPICH power result in a decrease in capacity

-Decrease in the CPICH power result in an increase in capacity

DL Tx Carrier Power Monitor•The purpose of the admission check on Tx carrier power is to prevent users from overbooking the RBS.

beMarginDlPwr =10 pwrAdm =75

pwrAdmOffset =10

To increase cell capacity it can be considered to increase pwrAdm:However

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Performance Monitoring

Some useful counters which can help monitor the DLpower resources:

– pmTransmittedCarrierPower: To estimate the utilization of the MCPA with respect to the admission limit.

– pmNoFailedRabEstAttemptLackDlPwr: To detect admission rejects due to DL power.– pmNoOfSwDownNgAdm: To detect soft congestion in the cell. Soft congestion is triggered

either due to lack of transmitted carrier power, DL channelization codes or hardware.– pmNoOfTermSpeechCong, pmNoOfTermCsCong: To monitor the number of users released due

to congestion resolution action– pmNoSystemRabRelease: Dropped call counters can be used to detect quality problems due to

overloading of MCPA

ASE

• Estimates the air interface resources usage in a cell (both in uplink and downlink)

• The ASE of a RL is expressed in the equivalent # of speech RBs which generate the same amount of air interface load.

DL ASE

Purpose: to avoid running the system close to the downlink pole capacity and thereby prevent power rushes on the DL.

• Recommended to disable DL ASE admission control and rely on Tx Carrier Power as it is a better measure of the DL air interface load.

• Disabling aseDlAdm will decrease the risk for unnecessary admission denials and allow for increased capacity.


Some useful counters which can help monitor the DL ASE resources:

– pmSumOfSampAseDl: To estimate how close a cell is to the DL ASE admission limit

– pmNoFailedRabEstAttemptLackDlAse: To identify cells in which admission rejections due to DL ASEs occur

– pmFailedDchChSwitch: To detect failed channel switches. This may be an indication of DL ASE shortage

UL ASE

Purpose: to avoid excessive UL load which could lead to inferior coverage and UE power rushes.

• Increasing aseUlAdm can result in increased capacity. However, should be monitored closely as UL ASE is the only mechanism available for preventing excessive UL noise rise.


Some useful counters which can help monitor the UL ASE resources:

– pmSumOfSampAseUl: To estimate how close a cell is to the UL ASE admission limit

– pmNoFailedRabEstAttemptLackUlAse: To identify cells in which admission rejects due to UL ASEs occur

– pmAverageRssi: To detect excessive noise rise as a result of an increase of aseUlAdm

– pmTotNoRrcConnectReqSucc: To detect uplink coverage problems

DL Channelization CodeThe monitoring of this resource is based on tracking the amount of the downlink code tree in use

and to avoid users overbooking code resources

beMarginDlCode =5 dlCodeAdm =80

Reserving 20% of the code tree for handover legs

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Some useful counters which can help monitor the DL code resources:

– pmNoFailedRabEstAttemptLackDlChnlCode: To detect admission rejections due to DL channelization codes

– pmNoOfSwDownNgAdm: To detect soft congestion in the cell. Soft congestion is triggered either due to lack of transmitted carrier power, DL channelization codes or hardware

– pmNoSystemRabRelease: Dropped call counters can be used to detect quality problems due to overloading of DL channelization code tree.

RBS Hardware

• The available RBS hardware is a limited resource due to, for example, the amount of installed hardware or licensing restrictions.

• The total number of capacity credits available in the RBS, is the minimum of the amount installed hardware and the amount activated by the software license key.

• Channel Element (CE) is the required baseband processing capacity and hardware for one speech bearer (AMR12.2 kbps) connection.

• Ericsson’s definition of a Channel Element is linked to Dedicated Channel (DCH) resources of the RBS. Processing capacity required for common signaling channels and certain radio network functionality is NOT included in the definition of a Channel Element


• Some useful counters which can help monitor the CE resources:

– pmNoFailedRabEstAttemptLackDlHw: Number of failed RAB establishment attempts due to lack of DL hardware resources

– pmNoFailedRabEstAttemptLacUllHw: Number of failed RAB establishment attempts due to lack of UL hardware resources

– pmNoFailedRabEstAttemptLackDlHwBest: Number of failed RAB establishment attempts due to lack of DL hardware resources, for the best cell in active set

– pmNoFailedRabEstAttemptLackUlHwBest: Number of failed RAB establishment attempts due to lack of UL hardware resources, for the best cell in active set

– pmUlCredits: Total consumed RBS UL credits– pmDlCredits: Total consumed RBS DL credits


• CE shortage:– Characterised by poor accessibility for all RAB types (usually during busy hour),

and equally across all sectors.

– High count of pmFailedAfterAdm

– Alarms:

• UplinkBaseBandPool_UlHwUsageExceedsUlLicenseLevel

• DownlinkBaseBandPool_DlHwUsageExceedsDlLicenseLevel

• Monitor CE usage and determine consistent CE utilization above 60%.

IMPROVING CAPACITY

2nd Carrier• Main driver:

– Improve capacity• Second carrier added at hot spots where capacity increase is most

needed.– Improve HSDPA performance

• As R99 power rises, HS power available declines. As HS power declines, the total HS throughput declines in a linear manner.

2nd carrier

RURALURBAN SUBURBAN

Premium HSDPA

HSDPA & R99 R991st carrier R99

HSDPA & R99 R991st carrier

2nd Carrier - Load Sharing• 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

IFLS diverts incoming traffic from a heavily loaded cell in one WCDMA carrier to a another WCDMA carrier with a lighter load

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

2nd Carrier - Alternatives

• Shortage of DL Codes for Speech:

– Turn on Dynamic Code Allocation and reduce the number of codes reserved for HSDPA

– Limit number of PS R99 users

• Shortage of Power for Speech:

– Increase Admission Threshold from 75% to 85%

– Limit number of PS R99 users

• Limit # of 384 users:

– The parameter sf8Adm can be used to configure the maximum number of allowed radio links with spreading factor = 8 (384 kbps)

– Allows for more lower bit rate users

2nd Carrier - Alternatives

• Adjust BLER targets:– Increasing the target BLER, less power will be required for a radio bearer– Lead to increase of # of simultaneous connections– Increased capacity at the expense of more lost speech frames (quality).

• Shortage of DL codes for HSDPA:– Turn on Dynamic Code Allocation– Turn on code multiplexing to allow several users to be served simultaneously in one 2 ms TTI

• Dynamic Code Allocation:– With 15 codes available for HS, few or no codes are left for R99. With this feature, it is possible to

reserve only a limited set of HS codes from the RNC.– DCA de-allocates HS codes when more DCH codes are needed and adds more HS codes when

resources are available.

Other capacity improvement areas

• Areas where capacity can be gained through optimization:

– Antenna system

– SHO / SrHO overhead

– Radio Links replacement

Antenna system• Antenna direction:

– GSM: no impact to DL capacity by serving users on side lobes

– WCDMA: substantial capacity gains by serving traffic hotspots within main lobe

• Antenna height:

– Avoid high antenna heights

– Difficult to confine coverage

– Suburban: served within 2 tiers

– Urban: served within 1 tier

Antenna system

• Antenna gain:

– High gain antenna

– Increase capacity gains

• Antenna type:

– Wide horizontal beam widths lead to greater overlapping and higher SrHO overload

– Narrower 60-65 degree antennas will result in capacity gains

Soft/Softer handover overhead

• Trade off between Soft/Softer HO and system capacity

• Soft/Softer HO:

– Several radio links

– More DL channelization codes

– More DL power

• Reducing S/SrHO overhead can improve system capacity

Radio link replacement

• Monitor RL replacements

• pmNoTimesRlRepInActSet incremented when cell removed from AS

• High value indicates pilot pollution

• Combining soft-softer overhead stats with RL replacement rates provide a powerful aid to assess the severity of power exhaustion

• Improving these metrics will lead to increased capacity

Conclusion – how to improve capacity

• Good Radio Network Dimensioning/Design• Power of CCHs are set accordingly• Admission parameters are tuned properly• Limit interference in network• SHO areas are not too large• Not too many neighbours defined• BLER Quality target is set properly • Limit the number of 384 users• Use of high gain antennas• Additional channel elements• Dynamic code allocation• Second Carrier where needed• IFLS & directed re-try to GSM

3G Capacity Management

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