Upload
nandha-gopal
View
196
Download
6
Embed Size (px)
DESCRIPTION
3G Capacity
Citation preview
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
Counters 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.
MO Class HsDschResources
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
MO Class HsDschResources
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.
MO Class HsDschResources
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.
MO Class Hsdsch
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.
MO Class Hsdsch
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
MO Class UtranCell
Number of users counters: pmSamplesBestPsHsAdchRabEstab
lish Definition
It is the number of samples recorded within the ROP for
pmSumBestPsHsAdchRabEstablish.
MO Class UtranCell
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
MO Class UtranCell
Number of users counters: pmSamplesFachPsIntRabEstablish
Definition
Number of samples recorded within the ROP for pmSumFachPsIntRabEstablish.
MO Class UtranCell
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.
MO Class UtranCell
HSDPA
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 (CEs)
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 MonitorThe 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
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.
Performance Monitoring
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.
Performance Monitoring
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
Performance Monitoring
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.
Ericssons 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
Performance Monitoring
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
Performance Monitoring
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