gsm_optimization-module2.pdf

Page 1© Copyright 2001, Wireless Facilities Inc.

Prepared By:Advanced Technology Group

in collaboration withRF Engineering

Contact:[email protected]

GSMRadio Network Optimization


Outline

Module 1

• Introduction

• Optimization Guideline

• Logical Channel Structure

• Idle Mode Operation

• Radio Resource Management

• Intelligent Overlay - Underlay

• Intelligent Coverage Enhancement

• Dynamic Hotspot

• Techniques to Reduce Interference


Outline (Continued)

Module 2

•Network Management System (NMS)

•Measurements

• Power Control (PC)

• Handover (HO)

• Frequency Hopping (FH)

• Directed Retry & Intelligent Directed Retry

• Queuing


Network Management System(NMS)


Contents of NMS

Database for BSC Measurements andobservation statisticsFault ManagementPerformance ManagementConfiguration ManagementSecurity ManagementAccounting ManagementRadio Network ManagementTransmission Network ManagementSystem Management


Contents of NMS

Database for BSC Measurements andobservation statistics

Counters, Statistics, MeasurementsMostly stored for 2 weeks in databaseAdditional Off-line Database need

Fault ManagementAlarm collection and storageAlarm acknowledgementAlarm Statistics and managementAlarm History and monitoringScheduled loop testing


Contents of NMS

Performance ManagementAdministration of BSS MeasurementsPM Data Post ProcessingTextual Data Representation (Observations)Performance Measurements Database Contents (DB)Thresholds for measurementsBSS Radio Resource Online Display (Observation)BSS Radio Measurement Online Display (BSC -Observation)


Contents of NMS

Configuration ManagementHardware Configuration ManagementSoftware Configuration ManagementObject creation and deletionNew features/upgradesConsistency ChecksLogical interconnection schemes to show variousNEs, subsystems and functional blocks at each site.


Contents of NMS

Security ManagementPassword authentication of OMC and NMS usersLogging of OMC/NMS attemptsAutomatic log-offIs achieved using both user- and device-related accessauthorization mechanisms included in the softwareand the smart cards with coded user identifiers.

Accounting ManagementCollection of billing information for the servicesprovided.Negotiation with other networks on the basis ofsharing revenues.


Contents of NMS

Radio Network ManagementPlanning Data TransferDownloading ParametersRouting Area IP ManagerLAPD Link Manager

Transmission Network ManagementBTS Access Report

System ManagementAuthority ManagerDatabase FunctionsUser Group ProfilesNetwork Editor


NM tools (Cell Doctor)

Cell Doctor is an optional tool for NOKIA NMSand provides:

Fault Management ReportsConfiguration Management ReportsPerformance Measurement ReportsBenchmark and Analysis


Radio Link Measurements



In GSM, the MS uses the BS Identity Code (BSIC) todistinguish between neighboring BSs.The measured signal level value (RXLEV) and signalquality level value (RXQUAL) parameters are used forthe purpose of inter-cell and intra-cell Handovers.Inter-cell Handover from the serving cell to a neighborcell occurs when RXLEV and/or RXQUAL is low in theserving cell and better in the neighbor cell.Intra-cell Handover from one channel/time slot toanother channel/time slot in the same cell occurs whenRXLEV is high but RXQUAL is low.



The MS monitors the signal strength of neighbor BSs andmaintains a list of six strongest non-serving BSs. A newBS is selected from the list if:

The path loss criterion for the serving BS is not met for 5seconds.The signaling link with the serving BS fails.The serving BS becomes barred.Non-serving cell access signal is greater than that of the servingBS for 5 seconds, and by at least theCELL_RESELECT_HYSTERSIS value in dB.


Measurement Processing

MS downlink measurements of serving andneighboring (NBR) cells

Idle Mode MeasurementMS decodes BCCH of serving cell, every 30 sec., and BCCHof NBR cells every 5min (pre synchronize and decode theBSIC).The list of 6 best NBR cells is updated every 60 sec, and if anew NBR cell appears on the list, MS has to decode its BCCHwithin 30 sec.



Dedicated Mode MeasurementMS has limited time to conduct measurements since MS istransmitting and receiving data from serving cell.MS measures NBR cells after transmitting and beforereceiving the next frame.MS gets a list of NBR cells on BCCH (System Info 5).During Idle slot (slot #25 of traffic multi-frame), MS hasmore time to decode and measure NBR cells’ signals. MSpre-synchronize with the frequency of NBR cell and decodeBSIC.MS has to pre-synchronize and decode BSIC of NBR cellsonce every 10 sec. MS needs to decode New NBR on the listwithin 5sec.



MS sends the measurements of the 6 NBR cells to the BTSevery SACCH period (480 msec). BTS pre-process the dataand forwards it to the BSC. Final processing is done at theBSC.BTS averages UL&DL measurement over 1, 2, 3 or 4 SACCHperiod set by parameter btsMeasAver(1…4 SACCH).Averaging and sampling of measurements in the BSC iscontrolled by parameters ho/pcAveragingLev/QualDL/UL.The parameters have windowSize(1…32 SACCH) andweighting(1…3) as arguments. Weighting parameterdetermine how samples are averaged and weighted due toDTX.msDistanceAveragingParam(1…32 SACCH) is the averagingparameter used to trigger HO due to distance.Averaging is done every SACCH period by using a slidingaveraging window.


Averaging and Sampling

HoThresholdLevDL = 33 (-77 dBm) WindowSize = 5, Weighting = 1Px = 3, Nx = 4btsMeasAver = 1 (no pre-processing in BTS)

30 2550 3545 40 1520 10

480 ms AVERAGE=40 P=0

AVERAGE=35 P=0

AVERAGE=30 P=1

AVERAGE=25 P=2

AVERAGE=20 P=3

Handover trigger



Fast Handover Averaging MethodSuitable for micro cells where fast HO decision isrequired.Can be used in call setup phase (SDCCH) by enablingenaFastAveCallSetup (y/n)Can be used after power control by enablingenaFastAvePC (y/n)Can be used in the beginning of a new TCH byenabling enaFastAveHO (y/n)The method is always used in NBR cellsmeasurements



After PC command, PC comparison is started againbut HO comparison is continued and onlymeasurement before PC are initialized.

0 1 1 1 0

0 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0

0 1 1 1 0

0 0 0 0 0 0 1 1 1 0 1 0 0 0 0 0

PC

HO

PCHO

New Ave.

Old Ave.

Px 4

Nx 6

Px 4

Nx 6



BSC capacity is related to number of adjacent NBRcells processed simultaneously in the BSC. ParameterallAdjacentCellsAveraged (Yes/No), is used to specifyif all NBR should be averaged or just the 6 best ones.“No” means 6 best NBRs.BTS sends to the BSC 6 best NBR measurements, the rest is beinggiven a zero result. Good adjacent cells without measurementresults “zero value” can still be taken into account (up to 7 zeros)with the parameter numberOfZeroResults (0…7).numberOfZeroResults zero samples can be omitted whenaveraging measurement results in choosing NBR cells.


Averaging with DTX and weighting

DTX is allowed just on TCH (only for speech call, not fordata call)“SUB”- measurement results are reported when DTX isused

AV_RXLEV_UL_PC = 2x35 + 1x42 + ... + 2x35 2+1+2+2+1+1+1+2 = 36

Sample: 1 2 3 4 5 6 7 8DTX used: 0 1 0 0 1 1 1 0uplink level: 35 42 33 36 39 40 39 35

ExamplepcAveragingLevULwindowSize= 8weighting= 2

DTXMode 0 MS may use DTX1 MS shall use DTX2 MS shall not use DTX

Parameter ValueBTS


RXLEV and RXQUAL parameters

The RXLEV and RXQUAL values used in GSM are listed below:

RXLEV dBm

0 < -110

1 -110 to -109

2 -109 to -108

3 -108 to -107

. .

62 -49 to -48

63 > -48

RXQUAL BER (%)

0 < 0.2

1 0.2 to 0.4

2 0.4 to 0.8

3 0.8 to 1.6

4 1.6 to 3.2

5 3.2 to 6.4

6 6.4 to 12.8

7 > 12.8

Signal level values Quality level values


Power Control (PC)


Objectives

Power Control reduces the overall systeminterference and increases spectral efficiency. Italso prolongs MS battery life.Uplink/Downlink PC

The BTS can independently control the power level of eachuplink and downlink time slots.Power Control for downlink and uplink are performedindependently. Measurements are performed by MS andBTS respectively.Power Control can be performed on all downlink channelsexcept BCCH (MS continuously measures serving andNBR cells’ BCCH).Power Control is performed on all uplink channels.


PC scheme is controlled by BSC

The PC scheme is controlled by the BSC which,compares MS and BTS measurements with relevant PCthresholds and calculates the power level increase ordecrease and communicates it to both MS and BTS.Power level can be changed on a variable or fixed stepsof 2, 4 or 6 dB increments every 60 ms. If two fixed stepswere not enough to reach the target level, the variablestep size is used.Power control can be enabled/disabled on a cell by cellbasis by parameter PowerCtrlEnabled (Y/N).


Transmission powers (Parameters)

Max and Min MS transmission powers are defined on a cellby cell basis (serving cell) and are determined by parametersmsTxPwrMax and msTxPwrMin (33dBm, step sizes of 2dB).

MS typical range for GSM1900 is 0 ~ 30dBm.Maximum and Minimum transmission power of the BTS aredetermined by BsTxPwrMax and BxTxPwrMin.The BTS attenuation factor is 0 to 30 dB from maximumtransmitter power with step sizes of 2dB.BTS PC is enabled with PowreCtrlEnabled(Y/N)Timer PowerControlInterval(0…31s) defines the minimuminterval between the changes in the RF power level. It is usedto prevent unnecessary repetitive PC changes in the BTS/MS.


PC and HO

The Power Control algorithm is closely coupledwith the Handover algorithm.The BSC will try to increase the power level of theMS as it moves farther away from the BTS. After itmakes a determination that the quality of thecommunication link can no longer be improved byincreasing MS’s transmit power, it starts theHandover process.Handover has always priority over Power Control.


PC: Signal’s Level and Quality

Power Increase(Bad Quality)

Power Increase(Bad Level)

Power Decrease(Good Quality)

Power Decrease(Good Level)

RXLEV

RXQUAL

pcLowerThresholdLevUL/DL pcUpperThresholdLevUL/DL

pcUpperThresholdQual UL/DL

pcLowerThresholdQual UL/DL

RxQual = 0

RxQual = 7


PC Algorithm

MS/BTS Increase due to LEVELPC increase can be based on a fixed or variable power step size.powIncStepSize (2, 4 or 6 dB) determines fixed step increase ofMS/BTS power.pcLowerThresholdsLevUL/DL (-110…-47dBm, Px, Nx) determinesthe lower threshold value for triggering power control.Trigger PC if: AV_RXLEV_UL/DL_PC <=pcLowerThresholdsLevUL/DL for Px(1…32) out of Nx (1…32).If: RXLEV_UL/DL + 2 × PowIncrStepSize* <=

pcLowerThresholdsLevUL/DL then go to variable power increase step size:

PWR_INCR_STEP = pcLowerThersholdsLevUL/DL -RXLEV_UL/DL (The actual RxLEV not the averaged value).

else:powIncrStepSize (2, 4 or 6 dB)

* If 2 fixed steps are not enough to reach target, use variable step size.


PC Algorithm

MS/BTS Increase due to QUALITYpcLowerThresholdsQualUL/DL (0…7, Px, Nx) is compared withAV_RXQUAL_UL/DL_PC.Trigger PC If: AV_RXQUAL_UL/DL_PC >=pcLowerThresholdsQualUL/DL for Px (1…32) out of Nx (1…32).

Calculation of MS/BTS power increase due to Quality?Insufficient Quality can be due to low signal or interference. BSCcalculates one step size due to low signal and one due tointerference and selects the larger step.1) Interference Step Size:

PWR_INCR_STEP = [1+Max(0,Qa)] × PowIncrStepSizeWhere Qa = RXQUAL_UL/DL - pcLowerThresholdsQualUL/DLRXQUAL_UL/DL is the current actual value (not the averaged value)


PC Algorithm

2) Low signal Level Step Size:If: AV_RXLEV_UL/DL_PC + 2 × PowIncrStepSize >=

pcLowerThresholdsLevUL/DL Then: PWR_INCR_STEP = pcLowerThersholdsLevUL/DL -

RXLEV_UL/DLThe actual RXLEV is used and not the averaged value.

For quality PC, the BSC always applies a variable step size.


PC Algorithm

BTS Decrease due to LEVELTrigger PC if: AV_RXLEV_DL_PC >= pcUpperThresholdsLevDL forPx(1…32) out of Nx (1…32).Parameter VariableDLStepUse (Yes/No) indicates if variable stepsize is used for DL power decrease.Parameter OptimumRxLevDL(-109…-47 dBm) indicate optimumDL signal level which ensures adequate speech/data quality withminimum DL interference. Parameter is controlled on a transceiverby transceiver basis.If: RxLev_DL - 2 × PowDecrStepSize* >= pcUpperThresholdsLevDL

then use variable power decrease step size:PWR_DECR_STEP = MIN[(RXLEV_DL - PcUpperThersholdsLevDL), 10]

else:powDecrStepSize (2, 4 or 6 dB)



PC Algorithm

BTS Decrease due to QUALITYTrigger PC if: AV_QUAL_DL_PC =< pcUpperThresholdsQualDLfor Px(1…32) out of Nx (1…32)

The BSC will determine DL power decrease based on twoalternative algorithms:

1) Based on Non defined optimum downlink RF Signal Level If: RxLev_DL - 2×PowDecrStepSize* >= pcUpperThresholdsLevDL

then variable power decrease step size.PWR_DECR_STEP = MIN[(RXLEV_DL -PcUpperThersholdsLevDL),10]

else:powDecrStepSize (2, 4 or 6 dB)



PC Algorithm

2) Based on Defined optimum downlink RF Signal Level.DL BTS power decrease is based on:

– AV_RXQUAL_DL– Quality Threshold for BTS decrease: pcUpperThresholdsQualDL– Optimum DL RF signal level: OptimumRxLevDL(-109…-47 dBm)– Current DL signal level: RXLEV_DL

PWR_DECR_STEP = MIN[PwrDecrLimit, MAX(A, B)]PwrDecrLimit, A and B are some parameters defined in thesystem.A margin of 6dB is used in the formulas to prevent a powerdecrease due to quality to trigger a power increase due to level(pwrLowerThresholdLevDL).


PC Algorithm

Formula for reference:– PWR_DECR_STEP = MIN[PwrDecrLimit, MAX(A, B)]– PowDecrLimit/Band0-2 is the maximum size of the variable

power decrease step:» PwrDecrLimitBand0 (0…38dB) indicates max size of power

decrease step when BTS power is decreased due to quality andthe average BER is better than 0.2%.

» PwrDecrLimitBand1 (0…38dB) indicates max size of powerdecrease step when BTS power is decreased due to quality andthe average BER is between 0.2 - 0.4%

» PwrDecrLimitBand2 (0…38dB) indicates max size of powerdecrease step when BTS power is decreased due to quality andthe average BER is worst than 0.4% (quality band from 2 to 7).

– A = MAX(0, RXLEV_DL - OptimumRxLevDL) reduces theBTS power to the Optimum level defined by parameterOptimumRxLevDL (-109…-47dBm).


PC Algorithm

– B = [PwrDecrQualFactor + MAX(0,Qa)] × PowRedStepSize» PwrDecrQualFactor indicates whether power decrease takes

place when: RXLEV_DL < OptimumRxLevDL &&AV_RXQUAL_DL_PC = PcUpperThresholdsQualDL.

» PwrDecrQualFactor (2…4) ensures that B is always > 0.» Qa = pcUpperThresholdsQualDL -

AV_RXQUAL_DL_PC takes into account the distancebetween the B

(2…4)


PC Algorithm

MS Decrease due to Signal Level

Trigger PC if: AV_RXLEV_UL_PC >= pcUpperThresholdsLevDL for Px(1…32) out of Nx (1…32)

If: RXLEV_UL - 2× PowDecrStepSize* >= pcUpperThresholdsLevUL then go to variable power increase step size:

PWR_DECR_STEP = RXLEV_UL - PcUpperThersholdsLevUL else:

powDecrStepSize (2, 4 or 6 dB)



PC Algorithm

MS Decrease due to QUALITYTrigger PC if: AV_RXQUAL_UL_PC =<pcUpperThresholdsQualUL for Px(1…32) out of Nx (1…32)

The BSC will determine DL power decrease based on twoalternative algorithms:

1) Based on OptimumRxLevUL = “not used”If: RxLev_UL - 2 × PowRedStepSize* >= pcUpperThresholdsLevULthen go to variable power increase step size:

– PWR_DECR_STEP = RXLEV_UL - PcUpperThersholdsLevUL else:

powDecrStepSize (2, 4 or 6 dB)* If 2 fixed steps are not enough to reach target, use variable step size.


PC Algorithm

2) Based on OptimumRxLevUL = used (on TRX by TRX basis)UL MS power decrease is based on:

– UL signal quality: AV_RXQUAL_UL– Quality Threshold for MS decrease: pcUpperThresholdsQualUL– Optimum UL RF signal level: OptimumRxLevUL (-109…-47 dBm)– Current UL signal level: RXLEV_UL

Formula for reference:– PWR_DECR_STEP = MIN[( MIN(PwrDecrLimit, MAX(MAX(0,

RXLEV_UL - OptimumRxLevUL) , (PwrDecrQualFactor +MAX(0,Qa)) × PowRedStepSize))), 10]

– Qa = PcUpperThresholdsQualUL - AV_RXQUAL_UL_PC– PowDecrLimit/Band0-2 is the maximum size of the variable power

decrease step, as described earlier.


Summary

Measurements are done by the BTS and the MS andprocessed by the BSC

Power control tries to keep the received level and receivedquality within specific ranges by changing the BTS and MStransmit powers.For quality power control, the calculation involves both leveland quality.For power decrease, the parameter optimumRxLevUL/DL isused to calculate the UL/DL transmit power that leads to anoptimum receive level at the BTS/MS.


Handover


There are two types of Handover in GSMInternal handover

External handoverThe handover is internal if the serving and target BTSsare located within the same BSS. In this case the BSCcan perform handover without the MSC involvement.This is also called intra-BSS handover.

Handover decisions are made by the Radio ResourceManagement (RRM) in the BSC.

The handover is external if the serving and target BTSsdo not reside in the same BSS. In this case the MSCperforms the switching task between two BTSs.

External handover can be classified as intra-MSC or inter-MSChandovers.

Handover in GSM


There are three main categories of Handover:Radio Resource Handover

Imperative Handover

Traffic HandoverHandover is considered Radio Resource if it relates to:

The Level, where the signal level is below the Handoverthreshold level

The Quality, where the signal quality is below the Handoverthreshold quality

The Interference, where the interference level is above theHandover threshold interference level

The Power Budget Handover

The Umbrella Handover

Handover categories


Handover threshold level, Handover threshold quality andHandover threshold interference are three definedparameters for both uplink and downlink.

Power Budget Handover: Ensures that the MS is always handed over to the cell with theminimum path loss.BSC evaluates neighboring cells’ radio link properties, in regulartime intervals, to find a target cell.Is only performed between cells of the same category, e.g., Microto Micro.

Handover categoriesHandover categories


Umbrella Handover:Can be enabled/disabled

Is executed in regular time intervals

Considers MS’s power class, and some other definedparameters, in choosing the neighboring cells as Handovertarget cells, e.g., Macro cells for vehicular and portable MSs andMicro cells for handheld MSs.Fast moving MSs are handled by Umbrella Handover withinMacro cells. If MS is moving slowly, a Handover to lower layers,i.e. Micro cell, is triggered.

Umbrella Handover has priority over Power BudgetHandover.



Handover is considered Imperative if it relates to:MS-BTS distance

O&M order to empty cell

Directed-Retry

Rapid-Field-DropTurn-Around-Corner

In Traffic Handover, in order to share load among cells,MSC request BSC to perform Handover.In both Imperative and Traffic Handovers, target cellsare ranked based on their link quality. Priorities are notconsidered.



Handover Priorities

1. Uplink and downlink Interference2. Uplink quality3. Downlink quality4. Uplink level5. Downlink level6. Distance7. Rapid Field Drop8. Slow moving MS9. Better cell i.e., Periodic check (Power Budget HO or

Umbrella HO)


Handover Algorithm

First condition in all Handover cases:1. AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, A) Where: A = msTxPwrMax(n) - P

P = depending on MS Classmark

Except for Umbrella Handover:1a. AV_RXLEV_NCELL(n) > hoLevelUmbrella(n)

The additional condition:2. PBGT > hoMarginPBGT(n) where: PBGT = ((msTxPwrMax - msTxPwrMax(n)) - (AV_RXLEV_DL_HO -

AV_RXLEV_NCELL(n)) - (btsTxPwrMax - BTS_TXPWR))

2a. PBGT > hoMarginLev/Qual(n) where: PBGT = (AV_RXLEV_NCELL(n) - AV_RXLEV_DL_HO) -

(btsTxPwrMax - BTS_TXPWR)

If enableHoMarginLevQual = Y


Target Cell Selection

BTS sends the measurements and list of best candidates to the BSC.BSC selects cells which meet radio link requirements.BSC can handle up to 16 (Intra-BSC) to 32 NBR target cell evaluation.BSC verifies candidates’ load with parameter btsLoadThreshold(0…100%)BSC decrease priority of overloaded cells, specified by parameterhoLevPriority(0…7), by another paramater hoLoadFactor(0…7).After load check, priority comparison between candidates is made.Candidate with highest priority is selected as target cell. For equalpriority cells, selection is based on best signal strength.Minimum interval between HO requests related to the same connectionis set by parameter MinIntBetweenHoReq (0…31s)Minimum time MS must wait after HO failure before new attempt tothe same connection is set by parameterMinIntBetweenUnsuccHoAttempt (0…31s)


Handover due to Level

Parameter hoThresholdsLevUL/DL (Px, Nx) is used for triggeringLevel HO.Candidate selection by BSC:

Equation-1 is used.If enableHoMarginLevQual = N, Use Equation-2

Else, Use Equation-2a with hoMarginLev.Priority and Load are both considered.

hoThresholdLevUL/DL -110 … -47 dBmpx 1 … 32nx 1 … 32

Parameter Value

rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 … 43 dBmhoMarginLev(n) -24 … 24 dB

HOC

ADJC


Handover due to Level

Equations 1 and 2a are used if parameter enableHoMarginLevQual is set “Yes”

2 dB

hoMarginLev = 4 dBTrigger for Handover due to Level

A

B

=> Since 2dB < 4 dB, cell B is not selected as candidate for HO due to level

Threshold (Lev)-95 dBm


Parameter hoThresholdsLevUL/DL (Px, Nx) is used for triggeringQuality HO.Candidate selection by BSC:

Equation-1 is used.If enableHoMarginLevQual = N, Use Equation-2

Else, Use Equation-2a with hoMarginLev.Priority and Load are both considered.

hoThresholdQualUL/DL 0…..7px 1 … 32nx 1 … 32

Parameter Value

rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 ..... 43 dBmhoMarginQual(n) -24 … 24 dB

HOC

ADJC

Handover due to Quality


Handover due to Quality

Equations 1 and 2a are used if parameter enableHoMarginLevQual is set “Yes”

2 dB

hoMarginQual = 0 dBTrigger for Handover due to Quality

A

B

=> Cell B is selected as potential candidate for HO due to Quality since 2 dB > 0 dB


Parameters hoThresholdsLevUL/DL (Px, Nx) andhoThresholdsInterferenceUL/DL (Px, Nx) are used for triggeringInterference HO.Candidate selection by BSC:

Priority for InterCell / Intracell HO selected at BSC independently forUL / DLPriority InterCell HOQuality HO if any candidate, If not IntraCell HOPriority IntraCell HO

hoThresholdInterferenceUL/DL -110…..-47 dBmpx 1 … 32nx 1 … 32

enableIntraHoInterfUL/DL Y / N

Parameter Value

hoPreferenceOrderInterfUL/DL INTER / INTRA

HOC

BSC

Handover due to Interference


Handover due to Interference

Equations 1 and 2a are used if parameter enableHandoverMarginQual is set “Yes”

hoThresholdQual = 4hoThresholdInterferenceDL = -85 dBmhoPreferenceOrderInterfDL = intra

Trigger for Handover due to Interference

A

B

- Field strength higher than threshold- Bad quality=> interference=> intra cell Handover

Threshold (Interf Lev) -85 dBm


Power Budget Handover

Periodic Check (hoPeriodPBGT) is used for triggeringCandidate selection:

Equation 1 & 2 are usedPriority and Load Considered

Multi-Layered NetworkTypically used between cells of the same "Layer"

hoPeriodPBGT 1 ... 63 (SACCH Period)enablePwrBudgetHandover Y / N

Parameter Value

rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 … 43 dBmhoMarginPBGT(n) -24 … 24 dB

HOC

ADJC


Power Budget Handover

Equations 1 and 2 are used Serving Cell: Best Adjacent Cell:

AV_RXLEV_DL_HO = -90 dBmmsTxPwrMax = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)BTS_TX_PWR = 42 dBm = (16 W)hoMarginPBGT(n) = 6 dB

PBGT = [(msTxPwrMax- msTxPwrMax(n)) - (AV_RXLEV_DL_HO - AV_RXLEV_NCELL(n)) - (btsTxPwrMax - BTS_TXPWR)]PBGT = [(33dBm-33dBm)-(-90 - -80)-(42dBm-42dBm)] = 10 dB

Second condition: 10 dB > 6 dB ⇒ Handover!

AV_RXLEV_NCELL(n) = -80 dBmrxLevMinCell(n) = -99 dBmmsTxPwrMax(n) = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)

AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max [0, msTxPwrMax(n) - msTxPwrMax]-80 dBm > [-99 dBm + (33 dBm - 33 dBm)] ⇒ First condition: -80 dBm > -99 dBm

1.

2.


Umbrella Handover

ExampleGSM MS class 4 (33 dBm)

gsmMacrocellThreshold = 35 dBmgsmMicrocellThreshold = 33 dBmmsTxPwrMax(n) = 33 dBm

hoLevUmbrella = -85 dBmhoThresholdLevDL = -90 dBm

6 dB

UmbrellaHandover

A

B-90 dBm

Handover dueto Level

Macro cell

Micro cell

-85 dBm

UmbrellaHandover

Handover dueto Level

Periodic Check (hoPeriodUmbrella ) is used for triggeringCandidate selection:

Equation 1a is usedPriority and Load Considered

Multi-Layered Network


Combined Umbrella and PBGT Handover

macrocells

microcells

UMB,RR

PBGT,RR

PBGT,RRUMB,RR

UMB umbrella HORR radio reason HOPBGT power budget HO

If enablePowerBudgetHo = Yes & enableUmbrellaHo = YesPower Budget Handover to cells of the same layerUmbrella Handover to cells of different layer

Parameters to be used:gsmMacrocellThreshold, gsmMicrocellThresholdmsTxPwrMax, msTxPwrMax(n)MS classmark


IHO - Rapid Field Drop

Parameter hoThresholdRapidLevUl is used for triggering RFD HO.Rx_Lev_UL (Not averaged/only UL)

Candidate SelectionOnly Chained adjacent cellEquation 1 only/no priority

Multi-Layered Network MS

Chained CellServing

Cell

Rapid Field Drop Handover.

.1st2nd

-93 dBm

Serving CellhoThresholdRapidLevUl = - 93 dBm

hoThresholdRapidLevUlN (px) = 2chainedAdjacentCell = Yes

Example


IHO - Enhanced Rapid Field Drop

In case of DDE (Deep Dropping Edge), the averaging window sizesand power budget period are reduced:

Level downlink window sizeLevel uplink window sizeAdjacent cell’s averaging window sizeHandover period power budget

A MS moves away from cell site,the signal is dropping gradually

A MS turns a corner,the signal drops rapidly

Sign

al L

evel

Time Figure 7 Signal Strength of a Fast Moving MS

MS moves away from cell site,the signal is dropping gradually

MS turns a corner, thesignal drops faster thanmoving in straight line

Sign

al L

evel

TimeFigure 8 Signal Strength of a Slow Moving MS


IHO - Enhanced Rapid Field Drop

Example

ddeWindow = 3 SACCH (n = 3)ddeThresholdLev = 10

the BSC compares the most recent measurement of sample 8 (multiframe k)with the measurement of sample 5 (multiframe k-n).

DDE_LEVEL = RXLEV(k- ddeWindow) – RXLEV(k) = -69 dBm – (-83 dBm) = 14 dB

Sample 1 2 3 4 5 6 7 8Signallevel

-71dBm

-68dBm

-70dBm

-71dBm

-69dBm

-70dBm

-75dBm

-83dBm


BSC Initiated TRHO

Network’s load can be more efficiently distributed by reducingpower budget margins between heavy loaded and less loaded cells

=> more trunking efficiency => more capacityCapacity of the regular layer can be released and performance ofIUO is increased => Quality + capacity

Ping-pong handovers are avoided due to AMH penalty system => quality

Handover

+0 dB +4dB +6 dB


BSC Initiated TRHO

New algorithm:1. AV_RXLEV_NCELL(n) > TRHO_TARGET_LEVEL(n) + Max(0, (MS_TXPWR_MAX_CELL(n)-P))2. PBGT (n) > AmhTrhoPbgtMArgin & PBGT(n) < HOMArginPBGT

AmhUpperLoadThreshold 0…100%AmhMaxLoadOfTgtCell 0…100%amhTrhoGuardTime 0…120 sec

AmhTrhoPbgtMargin -24dBm ….. +24dBm

Parameters Values

HOC

BSC


IUO Load control

During a very light load, only regular frequencies are used. Thusadditional handovers are avoided => increases quality

super-reuse TRXsuper-reuse TRX


Multi-layer Load control

In the night time, when the load is very small, and the speed of theMSs can be very fast, the MSs can be kept in the macro cell layer,

avoiding additional handovers between different layers => quality

G S M /m acroG S M /m acro

D C S /m icroD C S /m icro


Timers

MinIntBetweenHoReq is the minimum time between consecutivehandovers related to the same connections.

MinIntBetweenUnsuccHoAttempt is the minimum time betweenhandover attempts after a failure

Is applied differently in Intercell / Intracell handovers

minIntBetweenUnsuccHoAttempt 0 ... 30 (seconds)minIntBetweenHoReq 0 ... 30 (seconds)

Parameter Value

HOC


Frequency Hopping (FH)


Frequency Hopping

FH is used in GSM to improve the system’s performanceand quality in the multipath fading environment and toreduce the required S/N ratio.GSM uses Slow FH in which the hopping rate is lessthan the message bit rate.

In GSM the operating frequency is changed only with everyTDMA frame.The hopping rate is 216.7 hops per second which corresponds toa frame duration of 4.615 sec.

The mobile transmits at different frequencies fordifferent time slots. A frequency synthesizer is used tochange and settle on a new frequency within a fractionof one time slot (577 µs).


Frequency Hopping

FH provides frequency diversity to overcome Rayleighfading which may cause fades of 40 to 50 dB deep on thereceived signal.FH also provides interference diversity (interferenceaveraged over multiple users).FH reduces the S/N ratio required for an acceptableQoS, from 12 dB for a non-hopping radio link to 9 dB(approx.), improving the overall network’s capacity.Different hopping algorithms can be assigned to the MS

Cyclic HoppingRandom Hopping


Frequency Hopping

In the Mobile Station, in FH mode, only three time slotsare available to transmit, receive and monitor while in theBTS all eight time slots are capable of transmitting andreceiving to support eight MSs in one frame.The Broadcast Channels (BCH) comprising of FCCH, SCHand BCCH are not allowed to hop. All dedicated channeltypes can hop (TCH/SDCCH/FACCH/SACCH).Two different implementation schemes of SFH are used inBSs which are RF hopping and base-band hopping.Hybrid hopping is a combination and compromise of thetwo implementation schemes.


Base-band Hopping

B= BCCH TSL. It does not hop.

TSL 1….7 of all TRXs hop over (f1,f2,f3,f4)

BB hopping on 4 TRXs. Also the BCCH TRX is hopping except on RTSL-0.The call is hopping over TRXs (TRXs keep the same frequency as planned)


RF Hopping

B= BCCH TSL. TRX does not hop.

Non BCCH TRXs are hopping over the MA-list (f1,f2,f3).

RF hopping in 2-TRX cell. The BCCH TRX cannot hop because the BCCHfrequency must be continuously transmitted in a cell.Other TRXs will physically change frequency along a specified MAL.


Parameters

Base-band Hopping

hoppingSequenceNumber1 (TS 0) 0 ... 63(0 = cyclic, 1 ... 63 = pseudorandom)

hoppingSequenceNumber2 (TS 1 ... 7) 0 ... 63(0 = cyclic, 1 ... 63 = pseudorandom)

btsIsHopping BB (BaseBand Hopping) RF (Radio Freq. Hoping) N (No Hopping)

CA = Cell AllocationMA = Mobile AllocationMAIO = Mobile Allocation Index OffsetHSN = Hopping Sequence Number

General Parameters

TRX 1TRX 2TRX 3

0 1 72 TS

TRX 4

B f 1f 2f 3f 4

BTS

BTS


Parameters

TRX 1

TRX 2

TRX 3

TRX 4

MAL(f3,f4..fn)

0 1 72 TS

B f 1

MAL MAL MAL

BSC

mobileAllocationList 1 ... 124 (GSM) mobileAllocationId 1 … 128

usedMobileAllocation 1 … 128hoppingSequenceNumber1 0 … 63(0 = cyclic, 1 ... 63 = pseudorandom)

BTS

General Parameters

RF Hopping


Flexible MAIO Management

Allows More Flexible RF HoppingEnables Frequency Sharing, i.e. sharing an MA list between thesectors at the same site.Longer MA lists possible.Minimised interference.

New MAIO Step ParameterWhen used together with MAIO offset, no successive MAIOswill be allocated for TCHs sharing the same MA list.


MAIO Step

BCCH

Sector HSN MAIO Offset TRX MAIO, same for all RTSLs within the TRX

1 TRX-1 BCCH, not hopping

1 N

TRX-3 2

TRX-4 4


2 N

TRX-7 8

TRX-8 10


3 N

TRX-11 14

TRX-12 16

0

6

12

HSN same for all sectors

TRX-2 0

TRX-6 6

TRX-10 12

MA = f1, f2, f3, f4,....

MA list can includeadjacent frequencies

MAIO step

2

2

2Nor co-channelsneither adj. channelsused simultaneously ifnumber of frequencies> 2*number of TRXs

Hopping Freq'sBand allocation:

Operator can also set the MAIO step size

Operator can set the lowest MAIOs for the cells


MAIO Step

BCCH

Band allocation:

MA list

Hopping frequenciesHopping frequenciesMAIO Offset

MA list and BCCH need planning

MA list possibly shorter -> reduced gain

MA list and BCCH need planning

MA list possibly shorter -> reduced gain

BCCH Hopping Freq's

Band allocation:

MA list

No need for MA list planning

BCCH frequencies planned as usual

No need for MA list planning

BCCH frequencies planned as usual

MAIO Offset + Step


Flexible MAIO benefits

One MA list per siteOne MA list can contain a continuous band No risk of co-channel nor adjacent channel being usedsimultaneously within a siteSingle MA/HSN possible -> only BCCH frequency planningMore tighter reuse possible and thus more capacity can be achieved


Directed Retry &Intelligent Directed Retry


DR Algorithm

When no TCH is available in the serving cell, TCHcan be allocated in an adjacent cell

Mobile Originated and Mobile Terminated CallsIt is actually handover from SDCCH to TCH.

Imperative Handover (equation 1 only)Candidates ranked based on radio properties.

Queuing can take place in source cell, not in targetcell.

BTS A

Call Setup (SDCCH)

BTS B

Traffic (TCH)

rxLevAccessMin


DR Algorithm

AssignmentRequest

minTimeLimitDR

maxTimeLimitDR

Time DR not allowed : improves the reliability of the measurements of adjacent cells and gives the queuing process time

DR allowed


Parameters

Parameters Value

drInUse Yes/NoMinTimeLimitDR 0 … 14 (sec.)MaxTimeLimitDR 1 … 15 (sec.) BTS


Directed retry improvement

DR: to avoid the loss of a call in call-setup if theaccessed cell is congestedimprovement: new criterion in candidate cellselectiondrThreshold > RxLEV_MIN

SDCCH

TCH

congested


Directed retry improvement

Parameters

Parameters Value

drMethod 0: Improvement not in use1: Threshold evaluation method

drThreshold -47 … -110 dBm

BTS

ADJC


Intelligent Directed retry

Based on Directed Retry : Target Cell selection dependsupon

Classmark of the MS or MS PriorityAdjacent Cell Type

Subscribers Classified in GSM or MCNBased on Classmark ( bitmap in BSC associates classmarks toGSM/MCN )Based on MS Priority ( bitmap in BSC associates MS Priorities toGSM/MCN )Criterion defined in the BSC

DR and IDR enabled/disabled independently on a percell basis.



GSM subscriber

congestionmicro cells (MCN cells)

DRcongestion

macro cell (GSM cell)

micro cells (MCN cells)

MCN subscriber

IDR

• No TCH Available on Accessed Cell• GSM or MCN subscriber ?

• MCN => IDR in Use in the Cell ?• Yes => Directed Retry Only to MCN Cells • No => Reject Call

• GSM => DR in Use in the Cell ?•Yes => Directed Retry (any Cell) • No => Reject Call

• No TCH Available on Accessed Cell• GSM or MCN subscriber ?

• MCN => IDR in Use in the Cell ?• Yes => Directed Retry Only to MCN Cells • No => Reject Call

• GSM => DR in Use in the Cell ?•Yes => Directed Retry (any Cell) • No => Reject Call



Parameters

Parameters Value

IdrUsed Yes/NoCellType GSM/MCN

adjCellType GSM/MCN

BTS

ADJC


Queuing


Queuing and Radio Resources

Purpose• To avoid rejecting call set-up or handover attempt by waiting for the release of a suitable traffic channel

Queuing Environment

• Queuing is a BTS specific procedure (controlled by the BSC)

• Each BTS has a queue of its own• Individual queue parameters and queue management for each

BTS• Only traffic channels are queued

• Call attempts and Handovers are in the same queue• The maximum queue length is relative to the number of traffic

channels


Queuing and Radio Resources

• The maximum queuing time can be set individually for bothqueue types

• Different priorities according to queue type (Call/Ho) and/orMS priority

Prioritization: The placement in the queue is determinedby:• Queue Type (Priority)

• Call Setup

• Handover attempt (non-urgent)

• Urgent Handover Attempt

• MS Priority Level


Queuing Management

A Queuer is removed from the queue when:

No suitable channel is released within queuing time limit => timer expires

Higher priority subscriber (queue type and/or MS priority)replaces a queuer when the queue is full

The queuing TRX/TSL is blocked (call release)

Queue size is reduced due to removing TRX’s


Queuing and Handover

Internal inter-cell HandoverRanked list is produced by the Handover algorithm and passedto RR managementMaximum sixteen cells as alternative target cellsThe best candidate with free traffic channel is selectedIf all BTSs in the list are congested

queuing possibility is checked in the candidates according toranking

External inter-cell HandoverThe BTS identified by the MSC in a HANDOVER_REQUESTmessage is used as queuing target

- Averaging and processing for HO continues during queuing- The timers for hoPeriodPBGT or for hoPeriodUmbrella are stopped during queuing

Documents

gsm_optimization-module2.pdf