


Load Control

• Load Control Functions

• Radio Interface Load

• BTS Measurements


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Load Control Functional Overview• LC is a cell based RRM Function, utilising cell specific:

• thresholds set by RNP,

• load measurements,

• AC, PS & LC algorithms.

• Main functions of LC are:• to maximise capacity,

• preventive load control,

• overload control.

• LC performs the function of load control in association with AC & PS

• LC Updates load status using resource measurements & estimations provided by AC and

PS

• Continuously feeds cell load information to the other RRM functions, e.g. PS and AC

• SHO LC in RNC consists of MS specific part and cell specific part. The UE specific part isthe controlling entity between the cell specific entities (LC, AC and PS)

LC

ACACAC

PSPSPS

RMRMRM

RNC



Load Control Functional Overview

RRM in RNC

LC

AC

PS

Load changeestimations

Load changeestimations

Scheduling period

CCH load measurement

period

BS

Radio Resource Indication Period

RL measurement reporting period

parameters

parameters

measurements

estimations

when changed Load change info

Load status request

Load status

NRT load

measurements

1

2

3

3



LC includes the following load status reports and load control parameters:Parameters related to the LC, which are common for AC, LC and PS:

• PrxTarget [dB], PtxTarget [dBm]

• PrxOffset [dB], PtxOffset [dB]

• PrxNoise [dBm]

Cell load status, including the load measurement results:

In the Radio Resource Indication Message:

• PrxTotal [dBm]

• PtxTotal [dBm]

• RACH load (# of received RACH preambles during the measurement period)

In the Radio Link Measurement Report:

• PtxAverage [dBm]

Estimated cell load:

• PrxNc [dBm], PtxNc [dBm] – updated by LC• PrxRTinacitive [dBm], PtxRTinacitve [dBm] – updated by LC

• PrxNRT [dBm], PrxNRT [dBm] – updated by PS

• Lrt – updated by AC

• Lnrt – updated by PS

Load Control Functional Overview

1

2

3



Load Control

• Introduction/Functions• Radio Interface Load




Load Estimation Methods

Throughputbased threshold

Wideband powerbased threshold

W i d

e b a n

d p

o w

e r

l e v

e l

I t o t a l

( c o

v e r

a g e

)

Own cell load factor

(capacity)

i=0.5i=0

i=1

own

oth

I I i =



Througput Based Load Estimation

• The downlink load of the cell can be estimated by using the sum of the downlink allocated bitrates as follows

• The uplink load of the cell can be estimated by using the sum of the load factors of the usersconnected to this cell.

max

1

R

R N

j

j

DL

∑==η

∑=

⋅+= N

j

jUL load i1

)1(η

Max. allowed throughtput of the cell




Power Based Load Estimation- Nokia way

• The downlink load of the cell can be estimated by dividing the total downlink transmissionpower, Ptx_total by the maximum Node B transmission power Ptx_BTS,max.

• The uplink fractional load can be estimated with Prx_noise

, the background and receiver noiseand Prx_total, the total received power, according to this formula:

max, _

_

BTS tx

totaltx

DLP

P

=η

NRP

P

totalrx

noiserx

UL

111

_

_ −=−=η

NRP

P

P

PP

P

PP

totalrx

noiserx

totalrx

noiserxtotalrx

totalrx

ownrxothrx 111

_

_

_

_ _

_

_ _ −=−=

−=

+=η




Radio Interface Load

• The BTS measures the total received power (PrxTotal ) and the total transmitted power(PtxTotal ) on cell basis

• The BTS reports PrxTotal and PtxTotal of each cell to the RNC by sending RADIO

RESOURCE INDICATION message periodically (RRIndicationPeriod )

• LC updates cell load status for each cell based on RADIO RESOURCE INDICATION

• LC updates non-controllable UL (PrxNC) and DL (PtxNC) load in cell (see AC)

• AC and PS algorithms work on the current cell load status provided by LC

• Denying call admission (AC) and throttling back NRT traffic (PS) are the overloadactions

• After scheduling PS provides LC with PrxNRT, PtxNRT & LNRT estimates

• After admitting RT RAB, AC provides LC with NC load increase estimate




System Noise

• System noise (PrxNoise ) is the sum of all stationary noises;• thermal noise• interference caused by spurious emissions of other systems,• noise cause by additional equipment such as repeaters

• PrxNoise can vary place to place and even time to time

• PrxNoise (-101.9dBm) is a RNP parameter whose setting affects the capacity of cell• PrxNoise too low: overestimation of cell load and can lead to unnecessary call blocking

• PrxNoise too high: underestimation of cell load and can lead to overload situation




Derivation of Prx_noise Figure = 101.9dBm

• Thermal Noise density [dBm/Hz] is defined as:

⇒where k is Boltzman's constant [1.38*10^-23] and T is the temperature in Kelvin[T=300 kelvin]

⇒Therefore, thermal noise density is approx. -173.83 dBm/Hz

• Receiver noise figure [dB]⇒equipment specific values which are assumed to be 6dB (4dB + 2dB tolerance) at

the BS and 8dB at the MS• Receiver Noise Density [dBm/Hz]

⇒Receiver noise density is the sum of the thermal noise density and the receivernoise figure.

⇒BTS receiver noise figure = 4dB + 2dB tolerance⇒Thermal Noise density [dBm/Hz] + Receiver noise figure [dB] = Receiver NoiseDensity [dBm/Hz] = -173.83 dBm/Hz + 6dB = -167.83dBm/Hz

• In order to calculate the Noise power of the receiver (minimum baseband signalstrength at the receiver i.e. the receiver sensitivity for the non loaded network), the

receiver noise density has to be scaled to the WCDMA carrier bandwidth⇒Receiver Noise Power [dBm] = Receiver Noise Density [dBm/Hz] +

10log10(3.84*106) = -167.83 + 65.84 = -101.99 dBm

)001.0

(*10 _ _ kT

Log Density NoiseThermal =

Uplink

RECEIVING END BSThermal Noise Density dBm/Hz -173.83

BTS Receiver Noise Figure dB 6.00

BTS Receiver Noise Density dBm/Hz -167.83

BTS Noise Power [NoW] dBm -101.99

Uplink

RECEIVING END BS

Thermal Noise Density dBm/Hz -173.83

BTS Receiver Noise Figure dB 6.00

BTS Receiver Noise Density dBm/Hz -167.83

BTS Noise Power [NoW] dBm -101.99




PrxNoise Autotuning Algorithm

• RNC provides tools to measure unloaded system noise, PrxUnloaded, and tools toadjust PrxNoise parameter based on these measurements

• PrxTotal = PrxUnloaded when own cell is considered unloaded (or very low load);

Own Cell;LRT ≤ Unloaded RT and

LNRT ≤ Unloaded NRT

Unloaded RT and Unloaded NRT are hidden hardcoded RNC parameters (value settingsfor NRT: 1 %, RT: 2 %)

LRT and LNRT are fractional UL load factor for own cell RT (AC estimates) & PS users (PSestimates)

• RNC calculates averaged PrxUnloaded values using a mean filter to removetemporary interference peaks

• PrxNoise is updated by the autotuning algorithm based on PrxUnloaded

• PrxNoise autotuning step size is limited by PrxNoiseMaxTuneAbsolute parameter• Maximum autotuning is 20dB




UL Preventive & Overload Thresholds

Prx Target [dB]

PrxTarget [dB] + PrxOffset [dB]

r x

Overloaded Area

Marginal Load Area

Feasible Load Area

load factor

t o t a l r e c e

i v e d p o w e r

P

T o

t a l [ d B ]




UL Preventive Thresholds

Preventive threshold = PrxTarget

• Prx Target is relative to the system noise, it gives an upper threshold for the noise rise

• Target threshold defines the optimal operating point of the cell load, up to which PS &

AC can operate normally and is calculated from the UL loading (η) value:

• If cell load exceeds these limits then AC & PS move to PREVENTIVE STATE function

• New RT RABs are blocked, and PS can't schedule more NRT bit rates in the cell

PrxTarget range : 0...30 dB, step 0.1 dBdefault : 4 dB

(e.g. in CHT project, 30dB to effectively disable UL Load Control due to PHS spurious interference)

( ) [ ]dB Log η −⋅− 110 10PrxTarget =




Overload threshold = PrxTarget + PrxOffset • Overload Threshold defines the limit when the cell is considered to be overloaded

• If load in the cell exceeds these limits then AC & PS move to OVERLOAD STATE function

• New calls are blocked, and PS starts to decrease NRT bit rates in the cell

PrxOffset range : 0...6 dB, step 0.1 dBdefault : 1 dB

UL Overload Thresholds




DL Preventive & Overload Thresholds

Ptx Target [dBm]

Ptx Target [dBm] + PtxOffset [dB]

t o t a l t r a n s m i t t e d

p o

w e r

P t x

T o t

a l [ d B m ]

Overloaded Area

Marginal Load Area

Feasible Load Area

load factor

Cell Maximum




DL Preventive Thresholds

Preventive threshold = PtxTarget • Target threshold defines the optimal operating point of the cell load, up to which PS &

AC can operate normally

• If cell load exceeds these limits then AC & PS move to PREVENTIVE STATE function• New RT RABs are blocked, and PS can't schedule more NRT bit rates in the cell

PtxTarget range : -10...50 dBm, step 0.1 dBdefault : 42 dBm (WPAB) / 45dBm (WPAD)

• Default value depends on the cell max TX power (WPAB=43dBm (20W); WPAD=46dBm(40W)): in case the cell max power is 43 dBm, the PtxTarget should be 42 dBm and if cellmax power is 46dBm, the PtxTarget should be 45dBm.

DL O l d Th h ld




DL Overload Thresholds

Overload threshold = PtxTarget + PtxOffset • Overload Threshold defines the limit when the cell is considered to be overloaded

• If load in the cell exceeds these limits then AC & PS move to OVERLOAD STATE function

• New calls are blocked, and PS starts to decrease NRT bit rates in the cell

PtxOffset

range : 0...6 dB, step 0.1 dBdefault : 1 dB

The default value is given for 20W WPAB and 40W WPAD!




Load Control

• Introduction/Functions• Radio Interface Load





Prx and Ptx Total Measurements

P r x

T

o t

a l

/ P

t x

T o

t a

l

Frame average measurements

Frame Prx and Ptx Totalmeasurements

∑=

14

0

// TotalPTotalP txrxtxrx

0 141 2 ...




Alpha Trimmed Filter

P

r x

T o

t a

l /

P t

x T

o t a

l

Ptx/Prx MeasAveWindow

1. Frame average measurement values are sortedinto frames consisting of Ptx/Prx MeasAveWindow values

2. (Ptx/Ptx MeasAveWindow ∗ Ptx/Prx Alpha )lowest and highest values are removed

3. (Ptx/Ptx MeasAveWindow ∗ (1-Ptx/Prx Alpha))values remain

4. Remaining values are used by the BTS for averagePrx/Ptx Total calculation and are sent to the RNCevery RRIndPeriod

E l




Prx/PtxMeasAveWindow = 10

Prx/PtxAlpha = 0.2

Frame averages are sorted into groups consisting of 10 values

2 lowest and 2 highest values are excluded (0.2 ∗10)

Final P rx_total & P tx_total averages are calculated using 6 remaining values

( )

∑

∑

=

−

+=

=

−

=

8

3

_

)1(

1

_

6

1

21

1

k

k totalrx

NoFrames

NoFramesk

k totalrx

yP

y

NoFrames

Pα

α α

( )

∑

∑

=

−

+=

=

−=

8

3

_

)1(

1

_

61

21

1

k

k totaltx

NoFrames

NoFramesk

k totaltx

yP

y NoFrames

Pα

α α

Example

Frame average measurements

Prx/Ptx

P




Parameters

• Prx/PtxMeasAveWindow • The parameter defines the number of frames used for long term averaging at the

BS of the short term (frame based) averages of Prx/PtxTotal measurements

range : 10...200 frames, step 1 framedefault : 10 frames (during one RRI period when RRI=500 ms)

• In case the measured values are fluctuating very much, the averaging period couldbe made longer to get better PS performance

• Prx/PtxAlpha

• Defines the type of measurement filter used for the total received wideband power

(PrxTotal) in a cell. If the value is 0, pure sliding window mean filter is used and ifthe value is 0.5, sliding window median filter is used. If the value is between 0 -0.5, trimmed mean filter is used

range : 0... 0.5, step 0.05 default : 0

R di R I di ti P i d





…

BTS Measurements

RRI Period

R di R I di ti P i d





•RRIndPeriod

•The parameter defines the reporting period of the RADIO RESOURCE INDICATIONmessages, which are used for cell based load measurements.

range : 0...2000 ms, step 100 ms default : 500ms

• The BTS informs the RNC about the current load at the radio interface from theradio resource point of view and the load of every RACH in each cell.

• For that purpose the BTS sends periodically a Radio Resource Indication messageto the RNC

• In the Radio Resource Indication message the BTS reports periodically:• the total uplink interference power of the cells• the total transmitted power of the cell,• and RACH load (average number of RACH received per radio frame)

RACH M t




• A BTS measures RACH load of cell, and reports it to the RNC using the RADIORESOURCE INDICATION message

• RACH load includes following measurements:

• RACH load: Averaged number of received RACH preambles per radio frame during thereporting period

• RACH decoded messages: Averaged number of all decoded RACH messages per radio frameduring the reporting period

• Successfully decoded messages: Averaged number of successfully decoded RACH messagesper radio frame during the reporting period

• Reporting is controlled by parameters RRIndicationPeriod & RACHLoadIndicationPeriod which the BTS receives in the CONFIGURATION DATA message

RACH Measurements

RACH Measurements




• RACHLoadIndicationPeriod

• The parameter defines the reporting period of the PRACHs in a BTS. The BTS may

report load figures to the RNC in every Nth (N=1-20) NBAP Radio ResourceIndication message. Value 0 of the parameter means that the BTS does not reportthe load information for RACH.

range : 1...20, step 1 default : 1

RACH Measurements

C ti B d M t




Connection Based Measurements

• A base station measures:

• transmission power of one carrier• one scrambling code• one channelisation code

and averages it during the reporting period. BTS reports transmitted code powers using dedicateRADIO LINK MEASUREMENT REPORT message.

• Reporting is controlled by RLMeasRepPeriod parameter, which the BTS receives from

the RNC in the CONFIGURATION DATA message.

• These measurement reports are used as an input for defining initial power for PS and AC

• The report affects the accuracy of PS and AC initial power definition





• RLMeasRepPeriod

• range : 0...2000 ms, step 100 ms default : 500 ms

• Bigger value decreases Iub signalling load, smaller value increases accuracy

• Value 0 = OFF


04 LoadControl 2006 Partner

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