GSM Optimization

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Wireless Facilities Inc.

© Copy Right 2001, WFI

Page 1© Copyright 2002, Wireless Facilities Inc.

Prepared By:Advanced Technology Group

in collaboration withRF Engineering

Contact:[email protected]

Module 3

GSMRadio Network Optimization

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GSM_Module 3: Outline

• Power Control

• Discontinuous Transmission (DTX)

• Frequency Hopping (FH)

• Intelligent Underlay & Overlay (IUO)

• Intelligent Coverage Enhancement

• Dynamic Hotspot

• New techniques to reduce interference

• Queuing

• Introduction

• Optimization Process

• Idle Mode Operation

• Radio Link Measurements

• Radio Resource Management

• Directed Retry & Intelligent Directed Retry

• Handover

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Introduction

Ø Network optimization phase begins after siteshave been commissioned and integrated into thenetwork.

Ø The optimization process would involven System performance measurements

n Analysis of measurement data

n Refining system parameters to achieve optimumperformance

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Optimization Goals

Ø Optimization is performed in order to:n Ensure that system operation is in accordance with

designè to move measured network performance closer toward

predicted and desired performance objectives.è the prediction is refined with measured network performance

data collected during the optimization process.

n Tune system parametersèHandoff parameters, neighbor lists, switching system

parameters, etc.

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Optimization Goals (cont.)

n Control the introduction of users into the network

èBy gradually introducing users to the network, performanceunder real-world conditions can be determined and thenoptimized.

èAs optimization progresses, these users are given access tolarger sections of the network.

èAt the end of the optimization process, enough users shouldbe utilizing the network to make the transition to commercialservice virtually seamless.

n Quantify problems with the network and identifysolutions to those problems

èEngineers enabled to quickly isolate problems, correctlydetermine and implement solutions to those problems andquickly test the solution.

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Optimization Steps

Ø Site’s pre-testn This is prior to site turn-on and includes checking

design predictions, parameter settings, physicalconnections, antenna configurations, drive test routeselections, etc.

Ø Site’s functional testn After the pre-test has been completed and the site

has been turned on, the site is tested to verify that itis functioning properly. This includes checkingtransmitted power, basic call processing, test mobileperformance, etc.

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Optimization Steps (cont.)

Ø Cluster optimizationn Optimization undertaken at this early stage is coarse

and typically focuses on interference reduction,coverage verification, and handoff performance.

n Adjustments may not only be required to the switchparameters, but also to RF site configurations such asantenna orientations and downtilts.

n Optimization procedures can be performed ondifferent clusters in parallel, as clusters becomeready.

n Experience gained at this stage will be fed back intothe design specification and RF engineering process inorder to design more effective sites later in theprocess.

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Optimization Steps (cont.)

Ø System optimizationn Testing is performed on the adjacent clusters as a

system, with new clusters being added after theyhave passed cluster optimization. In this manner, thewhole network is built up piece-by-piece.

n Optimization undertaken at this stage is verydetailed, and fine parameter adjustments are made totruly maximize network performance.

n As more clusters pass system optimization, moreusers can be added and given access to the newareas.

n Eventually, the complete network will be active andoptimized with users placing calls throughout. Thenetwork is then ready for launch.

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Optimization Tools

Ø Network optimization tools have been developed toassist engineers in the complex optimization task.

Ø Specialized hardware for performance data collectionfacilitates rapid collection of large amounts ofinformation upon which network diagnoses andcorrections can be made.

Ø Advanced software tools enable optimization engineersto efficiently organize and process this vast amount ofdata in order to make the best and most accuratediagnosis in the shortest amount of time

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• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






• Handover

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Optimization Guidelines

Clusterization

System Wide

Parameters

Drive test routes

Specifications

Organization

Site are grouped intoclusterCluster may consist of 10to 20 sites

Data fill parameters includingneigborlist and frequencies assignment

Drive test are mutuallyagreed upon by allenvolved parties

Service quality parametersare mutually accepted byall envolved parties

RF Optimization point of contactPoint of contact on OMC-BTower crew point of contactI&C (Instrument & control) point ofcontact

InitialVerification

OMC-B verifiessoftware

I&C verifies hardware

OptimizationDrive test

Network Reconfigured

System Acceptance

Test

Failed

Passed Failed

passed

-Call setup-Frequency verification-Time slot qualityverification-Intra site handoververification (betweensectors of same site)

Ant tiltAnt Az.Ant ModelSystem wide parameters(including Neighbor list andfrequency retune)

NETWORK OPTIMIZATION

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Optimization Process

Ø Radio Network Optimization Process

n Data Collectionn Problem Identificationn Problem Resolutionn Implementation of Changesn Monitoring of Changesn Documentation

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Data Collection

Ø Data Collection Concept:n Problem Identificationn Problem Solving

Ø Methods of Data Collection:n Drive Testn OSS / Equivalent Sourcen Customer Care/ Trouble Reports

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Data Collection - Drive Test

Ø Drive tests should be planed carefully ahead of time.Drive-routes must meet the following conditions:n Follow normal traffic routesn Cover the low signal areasn Cover the high population areas

Ø Drive tests should be performed on regular basis.

Ø Switch can also provide measurement data,Uplink/Downlink, by setting up CTR (Cell TrafficRecording). CTR provides a record of events (handover,call setup, dropped call, etc.) and a complete set ofmeasurements such as RXQUAL and RXLEV.

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Data Collection - OSS

Ø In order to assess Service-Quality, certain parametersshould be collected from the BSC. Useful parametersare:

n Number of handover attempts per cell and per BSCn Number of handover completion per cell and per BSCn Number of call attempts per cell and per BSCn Number of call completion per cell and per BSCn Number of blocked calls per cell and per BSCn Dropped call percentage per cell and per BSC

Ø BSC counters are used for traffic-monitoring and event-detection purposes.

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Data Collection - Trouble Reports

Ø Although it is sometimes difficult to determinethe actual problem from the customer report,the problem area can be identified.

Ø After identifying the problem, performanceengineers should investigate all possibilities ofthe root cause.

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Problem Identification and Resolution

Ø General network issues include:

n Coveragen Interferencen Capacityn Multipathn Functionalityn Handover Failuren Call Droppingn Call blocking

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Problem Identification and Resolution (cont.)

Ø Coverage problem is usually due to power limitations,obstructions, foliage and defective H/W.

Ø Interference is usually due to cell spacing, overshootingor improper frequency planning.

Ø Capacity analysis is the study of Erlang, utilization, GoSand feature-loading . Busy hour is the reference point forthis study.

Ø Multipath interference occurs when delay-signal exceedsfour to five symbol periods and the main-path to delay-path ratio is less than 15dB.

Ø Functionality problems are usually due to defective MS,RBS or Telco line(s).

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Problem Identification and Resolution (cont.)

Ø Handover problems are usually due to:Ø Neighbor ListØ Handover ParametersØ Interference / High Noise LevelØ Path Imbalance / Power Measurement Module

Ø Call dropping is usually due to:n Missing Neighborsn High Interferencen Low RSSIn Equipment

Ø Call Blocking is usually due to resource availability, aswell as non-uniform distribution. Solutions are:n Channel-Addn Off-Loadingn Underlay/Overlay

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Change-Orders / Implementation

Ø Change-Orders should be released by RF toOperations.

Ø Change-Orders should be implemented properlyto correct / optimize the network.

Ø RF should verify the effect of recent changes bymonitoring traffic performing drive tests.

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Documentation

Ø Documentation:n Allows cross-referencing problems and solutionsn Allows back-trackingn Facilitates performance reporting

Ø Problems and solutions should always bedocumented in detail with the followinginformation:n Problem Typen Date & Locationn Down-Time Durationn Root Causen Problem Status

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Initial Site testing & Verification

Ø Call Setup Check

Ø “Intra Site” Handover Check

Ø Coverage Check

Ø Frequency / BSIC / Time Slots Check

Ø Antenna Orientation Check

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Key Performance Factors (KPF)

Ø Call Success RateØ Handover Success RateØ Signal Quality (FER, BER)Ø TCH Availability RateØ Non-Blocking TCH Rate (GoS < %2)

n A Different weighting factors can be given to each of KPFsn Totally Network/Client Dependentn General Performance of the network rather than single factors

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Main features/parameters to check

Ø Periodic Consistency Check

Ø Frequency Planning CheckØ Drive Test & Analyzing Layer 3 MessagesØ Cell Access ParametersØ Handover ParametersØ Power Control ParametersØ Frequency Hopping Parameters (HSN, MAIO)Ø Optional FeaturesØ Site Configuration Recommendations (Antenna Type

Change, Antenna Height Change, BTS Equipment/Filter Change,Antenna Orientation Change, Downtilt)

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• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






• Handover

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Idle Mode Operation

Ø When?n When the MS is switched ONn When there is no dedicated connection

Ø Why?n To camp on the best suitable cell

Ø Why to camp on a specific cell?n For MS to receive system information from the NW on DLn For MS to be able to initiate a call whenever neededn For the NW to be able to locate the MS when there is a MT

call/SMS

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Idle Mode Operation

Ø Access/Mobility management

Ø PLMN selection

Ø Cell selection and reselection

Ø Location update

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Access/Mobility management

Ø ACCESS/MOBILITY MANAGEMENTn notAllowedAccessClases (0…9, 11…15) indicates which

mobile classes can’t have access to the cell.n plmnPermitted (0…7) broadcast on the BCCH. MS will report

measurement of permitted PLMN.

Ø Location Informationn LocationAreaId = MCC + MNC + LAC

èCountry ⇒ MCC is the Mobile Country CodeèOperator ⇒ MNC is the Mobile Network CodeèArea in the PLMN ⇒ LAC is the Location Area Code

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Access/Mobility management (cont.)

Ø Parameter: baseStationIdentityCode - “BSIC”:

BSIC = NCC (0…7, fixed for every PLMN) + BCC (0…7,BTS color code)n In the same area, Cells with same BCCH frequencies should

have different BSIC. BSIC is used to separate co-channels usedin different BTS. In other word, if cells A and B have identicalBCCH and BSIC, a NBR cell to A or B can confuse the two cells ifA and B are not isolated from a propagation perspective.

n In order to identify NBR cells, MS decodes BSIC and includes theinfo together with the BCCH frequency in the measurementreport.

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Access/Mobility management (cont.)

LAC1 LAC2

F1, BSIC1

F1, BSIC2

MNC - Operator

MCC - USA

F1, BSIC2

F1, BSIC3

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PLMN Selection

Ø An operational network in GSM is called PLMN (Public Land MobileNetwork).

Ø A GSM customer has a subscription relationship with a single PLMN.This specific PLMN is called home PLMN of the subscriber.

Ø The home PLMN is set as the PLMN to try at the switch on.

Ø A change of PLMN can occur only when the user decides so, orwhen the MS finds out that the serving PLMN can no longer providenormal service (because the MS is leaving the PLMN coverage area).

Ø In those cases the MS will search for cells in the whole spectrum, tofind which PLMNs cover the location.

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PLMN Selection (cont.)

Ø The PLMN selection is done in either manualmode or automatic mode.n The automatic mode is based on the existence of

preferred PLMN list which is stored in the SIM. ThePLMNs are tried starting with:èHome PLMNèEach PLMN that has been stored in SIM in priority orderèOther PLMNs with received signal strength above –85dBm.

n In manual mode the list of PLMNs the MS has foundas potential candidates for providing normal service ispresented to the user.

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Cell selection in Idle Mode

Ø Two methods:n (a) Normal cell selectionn (b) Stored list cell selection (optional)n If no suitable cell found with method (b) then (a) is tried

Ø Suitable cell to camp onn Cell is in the selected PLMNn Cell is not barredn Cell is not in a forbidden location area for national roamingn C1 >0n If there is no normal priority cell then low priority cell

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Cell selection in Idle Mode (cont.)

ØRadio Criteria

C1 = (A - Max(B,0))

s A = Received Level Average - p1s B = p2 - Maximum RF Output Power of the Mobile

Stations p1 = rxLevelAccessMin: Min. received level at the MS

required for access to the systems p2 = msTxPowerMaxCCH: Max. Tx power level which

an MS may use when accessing the system

Averaging 3-5 Sec.

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Parameters

Ø Parameter: RxLevAccessMin (-110…-47 dBm)

n Minimum signal strength required by the MS to get service froma specific cell in idle mode.

Ø Parameter: CellReselctHysteresis (0…14 dB)

n A margin used in cell reselection when NBR cell is in a differentLAC. It prevent ping pong location update which consumesSDCCH capacity:

F Rxlev_Cell_A > Rxlev_Cell_B + CellReselectHysteresis

Ø Parameter: msTxPwrMaxCCH (13…43 dBm)

n MS maximum transmit power when accessing the system.

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Cell Reselect Hysteresis

cellReselectHysteresisThe nominal LA border

L1

L2

The real LA bordercellReselectHysteresis (0 … 14 dB)

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Cell selection in Normal Operation

Search all RF CH and sort by RxLev

Search for FCCH to verify if BCCH

BCCH?

Decode BCCH data

Suitable Cell?-Correct PLMN-Cell not barred “CELL_BAR_ACCESS=0”-C1 > 0-Location not forbidden for national roaming

If no Normal Cell found? camp on lower priority cell

Camp On Cell

Tune to next

Frequency

in the List

No

No

No

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Cell Re-selection

Ø MS will calculate the C1 and C2 for the serving cell,every 5 s.

Ø MS will calculate the C1 and C2 for the six best neighborcells, every 5 s.

Cell re-selection is needed if:n Path Loss criterion C1 < 0 for cell camped on , for more than 5

seconds.n Any of the NBR have a higher C1 after 5 sec.n There is a DL signaling failure.n Cell becomes Barred.n There is a better cell with C2 criterion.n Random access attempts is still unsuccessful after

maxNumberRetransmission repetitions.

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Cell Re-selection based on C2 Criteria

Ø Used in GSM Phase 2 (for Dual band and layered systems)

Example: single band system with macro and micro layers. Fastmoving MS can be for example kept on the macro layers and slowmoving mobiles on the micro layer.

Parameter: cellReselectParamInd(Yes/No) if C2 parameters aresent to MS. cellBarQualify (Yes/No) control if cell baring can beoverridden.

Parameter: PenaltyTime (20…640 s) time delay before finalcomparison is done between 2 cells.

Parameter: TemporaryOffset (0…70 dB) temporary offset in dBduring PenaltyTime of received signal strength.

Parameter: CellReselectOffset (0…126 dB) offset in dB to cellreselection

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Cell Re-selection based on C2 Criteria (cont.)

Ø C2 calculation:n C2 = C1 + cellRselectOffset - temporaryOffset x

H(penaltyTime - T) when penaltyTime < 640.OR:n C2 = C1 - cellReselectOffset when penaltyTime = 640.

Where:n H(x) = 1 when x >= 0n H(x) = 0 when x < 0n A timer “T” is started for each cell in the list of the 6 strongest

cells as soon as it is placed on the list. T is reset to 0 whenremoved from the list.

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Cell Re-selection based on C2 Criteria (cont.)

timepenaltyTime

C1cellReselectOffset

cellReselectOffset

C2

C2

temporaryOffset

dBC2 when penaltyTime = 640C2 when penaltyTime < 640

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IMSI Attach/Detach

Ø MS is indicated as inactive in the Network to avoiduseless paging. Parameter: IMSIAttachDetach (Yes/No)n IMSI detach procedure may be invoked by a MS if the MS is

deactivated.n No response is returned from the Network in this case.

Ø IMSI attach procedure complements IMSI detach toindicate that The MS is active in the network.

Ø The IMSI attach procedure is used only if the IMSI wasdeactivated while the MS was in "idle updated" state andthe stored LAI is the same which is sent on the BCCH ofthe current serving cell.

Ø IMSI attach is performed by using the location updatingprocedure. The LOCATION UPDATING REQUESTmessage shall indicate IMSI attach.

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Location Update

Ø MS initiates procedure by sending LOCATION UPDATINGREQUEST message to the network and starts a timer.

Ø The authentication procedure is initiated by the networkupon receipt of the LOCATION UPDATING REQUESTmessage from the MS.

Ø The ciphering mode setting procedure is initiated by thenetwork, if a new TMSI has to be allocated.

Ø If the location updating is accepted by the network aLOCATION UPDATING ACCEPT message is transferred tothe Mobile Station.

Ø MS stores the received location area identification (LAI),stop the timer, reset the attempt counter and set theupdate status to "updated".

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Location Update (cont.)

Ø If the LOCATION UPDATING ACCEPT message contains an IMSI, theMS shall delete any TMSI. If it contains a TMSI, it should replace theold TMSI and send a TMSI REALLOCATION COMPLETE to theNetwork.

Ø After that, the mobile station shall wait for the network to releasethe RR-connection.

Ø In normal cases, the mobile station will enter the "idle, updated"state after the release of the RR-connection. In this state it shall :n Perform normal location updating when a new location area is enteredn Perform periodic updating controlled by “timerPeriodicUpdateMS

(0.0…25.5hours)”n Perform IMSI detachn Perform IMSI attach if activated in the same location arean Respond to paging

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• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






• Handover

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Radio Link Measurements

Ø In GSM, the MS uses the BS Identity Code (BSIC) todistinguish between neighboring BSs.

Ø The measured signal level value (RXLEV) and signalquality level value (RXQUAL) parameters are used forthe purpose of inter-cell and intra-cell Handovers.

Ø 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.

Ø Intra-cell Handover from one channel/time slot toanother channel/time slot in the same cell occurs whenRXLEV is high but RXQUAL is low.

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Radio Link Measurements (cont.)

Ø 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:n The path loss criterion for the serving BS is not met for 5

seconds.n The signaling link with the serving BS fails.n The serving BS becomes barred.n Non-serving cell access signal is greater than that of the serving

BS for 5 seconds, and by at least theCELL_RESELECT_HYSTERSIS value in dB.

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Measurement Processing

Ø MS downlink measurements of serving andneighboring (NBR) cells

n Idle Mode MeasurementèMS decodes BCCH of serving cell, every 30 sec., and BCCH

of NBR cells every 5min (pre synchronize and decode theBSIC).

èThe 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.

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n Dedicated Mode MeasurementèMS has limited time to conduct measurements since MS is

transmitting and receiving data from serving cell.èMS measures NBR cells after transmitting and before

receiving the next frame.èMS gets a list of NBR cells on BCCH (System Info 5).èDuring Idle slot (slot #25 of traffic multi-frame), MS has

more time to decode and measure NBR cells’ signals. MS pre-synchronize with the frequency of NBR cell and decodeBSIC.

èMS has to pre-synchronize and decode BSIC of NBR cellsonce every 10 sec. MS needs to decode New NBR on the listwithin 5sec.

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èMS 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.

èBTS averages UL&DL measurement over 1, 2, 3 or 4 SACCHperiod set by parameter btsMeasAver(1…4 SACCH).

èAveraging and sampling of measurements in the BSC iscontrolled by parametersho/pcAveragingLev/QualDL/UL. The parameters havewindowSize(1…32 SACCH) and weighting(1…3) asarguments. These parameters determine how samples areaveraged and weighted due to DTX.

èmsDistanceAveragingParam(1…32 SACCH) is theaveraging parameter used to trigger HO due to distance.

èAveraging is done every SACCH period by using a slidingaveraging window.

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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

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Ø Fast Handover Averaging Methodn Suitable for micro cells where fast HO decision is

required.n Can be used in call setup phase (SDCCH) by enabling

enaFastAveCallSetup (y/n)n Can be used after power control by enabling

enaFastAvePC (y/n)n Can be used in the beginning of a new TCH by

enabling enaFastAveHO (y/n)

n The method is always used in NBR cellsmeasurements

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..





n 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..





n BSC capacity is related to number of adjacent NBRcells processed simultaneously in the BSC. ParameterallAdjacentCellsAveraged (Yes/No), is used tospecify if all NBR should be averaged or just the 6best ones. “No” means 6 best NBRs.

n BTS sends to the BSC 6 best NBR measurements, the rest isbeing given a zero result. Good adjacent cells withoutmeasurement results “zero value” can still be taken into account(up to 7 zeros) with the parameter numberOfZeroResults(0…7). numberOfZeroResults zero samples can be omittedwhen averaging measurement results in choosing NBR cells.

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Averaging with DTX and weighting

Ø DTX is allowed just on TCH (only for speech call, not fordata call)

Ø “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 Value

BTS

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




RXLEV and RXQUAL parameters

Ø 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..





• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






• Handover

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Traffic Channel Allocation

Ø After a request including the preferred TCH rateis received, the BSC determines the type of TCHresource to be allocated. This is based on thefollowing:n the A interface circuit that the MSC has allocated for

the calln the given list of preferred speech codecs by MSn the speech codecs’ support of the BTSn the TCH configuration on the BTSn the resource situation in the BTS

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Idle Channel Interference

Ø The BTS measures and reports on the uplinkinterference of the radio channels which havebeen idle during the whole measurement period.

Ø Idle TCHs are classified into five interferenceclasses

Ø RR Management algorithm assigns a channelfrom the lowest possible interference class

Parameters Value

interferenceAveragingProcess 1 ... 32 (SACCH Period)

boundary 1-5 -110 ... -47 (dBm) (boundary0/5 fixed)

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Idle Channel Interference

40 7

=> TS4 will be selected!

Interference Level (dBm)-47

-90

-95

-100

-105

-110

Boundary5

Boundary4

Boundary3

Boundary2

Boundary1

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




TRX Prioritization in TCH Allocation

Ø The advantages of using the BCCH carrier forcall set up:n It would not increase interference in the network.n BCCH channels are planned to be the least interfered

ones.

Ø The advantage of using the TCH TRX for callset up:n The hopping gain.

Ø It is possible to set priority between the TCHTRXs and BCCH TRX.

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




TRX Prioritization in TCH Allocation

Parameters Value

TrxPriorityInTCHAllocation 0 … 2where: 0 = no preference1 =BCCH preferred2 =Beyond BCCH preference

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




FACCH Call Setup

Ø When an idle SDCCH is not available for therequestn BSC tries to allocate a TCH for signaling instead of an

SDCCH.n After the signaling is finished the channel mode is

modified as TCH and the call continues on the samechannel.

Parameters Value

pagingAnsOnFACCH Y/NrestablishOnFACCH Y/NemerCallOnFACCH Y/NordinaryCallOnFACCH Y/N

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..





• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






• Handover

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Directed Retry (DR) Algorithm

n When no TCH is available in the serving cell, TCH canbe allocated in an adjacent cellèMobile Originated and Mobile Terminated Calls

n It is actually handover from SDCCH to TCH.è Imperative Handover (equation 1 only)èCandidates ranked based on radio properties.

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

BTS A

Call Setup (SDCCH)

BTS B

Traffic (TCH)

rxLevAccessMin

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DR Algorithm (cont.)

AssignmentRequest

minTimeLimitDR

maxTimeLimitDR

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

DR allowed

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




DR Parameters

Parameters Value

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

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DR Improvement

n DR helps network to avoid the loss of a call in call-setup if the accessed cell is congested

n DR improvement: introduces new criterion incandidate cell selectionèdrThreshold > RxLEV_MIN

SDCCH

TCH

congested

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




DR Improvement (cont.)

Ø Parameters

Parameters Value

drMethod 0: Improvement not in use1: Threshold evaluation method

drThreshold -47 … -110 dBm

BTS

ADJC

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Intelligent Directed Retry (IDR)

Ø Based on Directed Retry : Target Cell selection dependsuponn MS Classmarkn MS Priorityn Adjacent Cell Type

Ø Subscribers Classified in GSMn Based on Classmark (bitmap in BSC associates classmarks to

GSM subscriber)n Based on Priority (bitmap in BSC associates MS Priorities to GSM

subscriber)

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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Intelligent Directed Retry (cont.)

GSM subscriber

congestionmicro cells (MCN cells)

DR

congestion

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

macro cell (GSM cell)

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




IDR Parameters

Ø Parameters

Parameters Value

IdrUsed Yes/NoCellType GSM/MCN

adjCellType GSM/MCN

BTS

ADJC

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..





• Power Control





• Dynamic Hotspot


• Queuing

• Introduction






•Handover

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Ø There are two types of Handover in GSM

n Internal handover

n External handover

Ø The 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.n Handover decisions are made by the Radio Resource

Management (RRM) in the BSC.

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

handovers.

Handover in GSM

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Ø There are three main categories of Handover:

n Radio Resource Handover

n Imperative Handover

n Traffic Handover

Ø Handover is considered Radio Resource if it relates to:

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

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

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

n The Power Budget Handover

n The Umbrella Handover

Handover categories

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Ø Handover threshold level, Handover threshold qualityand Handover threshold interference are three definedparameters for both uplink and downlink.

Ø Power Budget Handover:n Ensures that the MS is always handed over to the cell with the

minimum path loss.n BSC evaluates neighboring cells’ radio link properties, in regular

time intervals, to find a target cell.n Is only performed between cells of the same category, e.g.,

Micro to Micro.

Handover categoriesHandover categories

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Ø Umbrella Handover:

n Can be enabled/disabled

n Is executed in regular time intervals

n Considers MS’s power class, and some other defined parameters,in choosing the neighboring cells as Handover target cells, e.g.,Macro cells for vehicular and portable MSs and Micro cells forhandheld MSs.

n 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.

Ø Umbrella Handover has priority over Power BudgetHandover.


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Ø Handover is considered Imperative if it relates to:

n MS-BTS distance

n O&M order to empty cell

n Directed-Retry

n Rapid-Field-Dropn Turn-Around-Corner

Ø In Traffic Handover, in order to share load among cells,MSC request BSC to perform Handover.

Ø In both Imperative and Traffic Handovers, target cellsare ranked based on their link quality. Priorities are notconsidered.


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Review: 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Target Cell Selection

Ø BTS sends the measurements and list of best candidates to the BSC.Ø BSC selects cells which meet radio link requirements.Ø BSC can handle up to 16 (Intra-BSC) to 32 NBR target cell evaluation.Ø BSC verifies candidates’ load with parameter btsLoadThreshold

(0…100%)Ø BSC decrease priority of overloaded cells, specified by parameter

hoLevPriority(0…7), by another paramater hoLoadFactor(0…7).Ø 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.

Ø Minimum interval between HO requests related to the sameconnection is set by parameter MinIntBetweenHoReq (0…31s)

Ø Minimum time MS must wait after HO failure before new attempt tothe same connection is set by parameterMinIntBetweenUnsuccHoAttempt (0…31s)

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Handover due to Level

Ø Parameter hoThresholdsLevUL/DL (Px, Nx) is used fortriggering Level HO.

Ø Candidate selection by BSC:n Equation-1 is used.n If enableHoMarginLevQual = N, Use Equation-2 Else, Use Equation-2a with hoMarginLev.n 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Ø Parameter hoThresholdsLevUL/DL (Px, Nx) is used fortriggering Quality HO.

Ø Candidate selection by BSC:n Equation-1 is used.n If enableHoMarginLevQual = N, Use Equation-2 Else, Use Equation-2a with hoMarginLev.n 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Ø Parameters hoThresholdsLevUL/DL (Px, Nx) andhoThresholdsInterferenceUL/DL (Px, Nx) are used fortriggering Interference HO.

Ø Candidate selection by BSC:n Priority for InterCell/Intracell HO selected at BSC independently for

UL/DLn Priority InterCell HOn Quality HO if any candidate, If not IntraCell HOn Priority 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Power Budget Handover

Ø Periodic Check (hoPeriodPBGT) is used for triggeringØ Candidate selection:

n Equation 1 & 2 are usedn Priority and Load Considered

Ø Multi-Layered Network

Ø Typically 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Review: 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.

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Umbrella Handover

ExampleGSM MS class 4 (33 dBm)

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

hoLevUmbrella = -85 dBmhoThresholdLevDL = -90 dBm

6 dB

Umbrella

Handover

A

B-90 dBm

Handover dueto Level

Macro cell

Micro cell

-85 dBm

UmbrellaHandover

Handover dueto Level

Ø Periodic Check (hoPeriodUmbrella) is used for triggeringØ Candidate selection:

n Equation 1a is usedn Priority and Load Considered

Ø Multi-Layered Network

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Combined Umbrella and PBGT Handover

macrocells

microcells

UMB,RR

PBGT,RR

PBGT,RRUMB,RR

UMB umbrella HORR radio reason HOPBGT power budget HO

Ø If enablePowerBudgetHo = Yes & enableUmbrellaHo = Yesn Power Budget Handover to cells of the same layern Umbrella Handover to cells of different layer

Ø Parameters to be used:n gsmMacrocellThreshold, gsmMicrocellThreshold

n msTxPwrMax, msTxPwrMax(n)

n MS classmark

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




IHO - Rapid Field Drop

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

Ø Candidate Selectionn Only Chained adjacent celln Equation 1 only/no priority

Ø Multi-Layered Network MS

Chained Cell

Serving Cell

Rapid Field Drop Handover

..

1st

2nd

-93 dBm

Serving CellhoThresholdRapidLevUl = - 93 dBm

hoThresholdRapidLevUlN (px) = 2chainedAdjacentCell = Yes

Example

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




IHO - Enhanced Rapid Field Drop

Ø In case of DDE (Deep Dropping Edge), the averaging window sizesand power budget period are reduced:n Level downlink window sizen Level uplink window sizen Adjacent cell’s averaging window sizen Handover 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




IHO - Enhanced Rapid Field Drop

Example

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

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

Ø 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




BSC Initiated TRHO

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

=> more trunking efficiency => more capacityØ Capacity of the regular layer can be released and performance of

IUO is increased => Quality + capacity

Ø Ping-pong handovers are avoided due to AMH penalty system

=> quality

Handover

+0 dB +4dB +6 dB

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Review: BSC Initiated TRHO

ØNew 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

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




IUO Load control

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

super-reuse TRXsuper-reuse TRX

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-Notes:…………………………………….…….…………………………………………………...………………………………….………………………………………………………………………………………………………………….……………………………………………………………..




Multi-layer Load control

Ø 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

GSM/macroGSM/macro

DCS/microDCS/micro

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Timers

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

Ø MinIntBetweenUnsuccHoAttempt is the minimum time betweenhandover attempts after a failuren Is applied differently in Intercell / Intracell handovers

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

Parameter Value

HOC

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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Objectives

Ø Power Control reduces the overall systeminterference and increases spectral efficiency. Italso prolongs MS battery life.

Ø Uplink/Downlink PCn The BTS can independently control the power level of each

uplink and downlink time slots.n Power Control for downlink and uplink are performed

independently. Measurements are performed by MS andBTS respectively.

n Power Control can be performed on all downlink channelsexcept BCCH (MS continuously measures serving and NBRcells’ BCCH).

n Power Control is performed on all uplink channels.

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PC scheme is controlled by BSC

Ø 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.

Ø Power level can be changed on a variable or fixed stepsof 2, 4 or 6 dB increments every 60 ms. If two fixedsteps were not enough to reach the target level, thevariable step size is used.

Ø Power control can be enabled/disabled on a cell by cellbasis by parameter PowerCtrlEnabled (Y/N).

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Transmission powers (Parameters)

Ø Max and Min MS transmission powers are defined on a cell bycell basis (serving cell) and are determined by parametersmsTxPwrMax and msTxPwrMin (33dBm, step sizes of2dB).

MS typical range for GSM1900 is 0 ~ 30dBm.Ø Maximum and Minimum transmission power of the BTS are

determined by BsTxPwrMax and BxTxPwrMin.Ø The BTS attenuation factor is 0 to 30 dB from maximum

transmitter power with step sizes of 2dB.Ø BTS PC is enabled with PowreCtrlEnabled(Y/N)Ø Timer PowerControlInterval(0…31s) defines the minimum

interval between the changes in the RF power level. It is usedto prevent unnecessary repetitive PC changes in the BTS/MS.

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PC and HO

Ø The Power Control algorithm is closely coupled with theHandover algorithm.

Ø The BSC will try to increase the power level of the MS asit moves farther away from the BTS. After it makes adetermination that the quality of the communication linkcan no longer be improved by increasing MS’s transmitpower, it starts the Handover process.

Ø Handover has always priority over Power Control.

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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

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PC Algorithm

Ø MS/BTS Increase due to LEVELn PC increase can be based on a fixed or variable power step size.

powIncStepSize (2, 4 or 6 dB) determines fixed step increaseof MS/BTS power.

n pcLowerThresholdsLevUL/DL (-110…-47dBm, Px, Nx)determines the lower threshold value for triggering powercontrol.

n Trigger PC if: AV_RXLEV_UL/DL_PC <=pcLowerThresholdsLevUL/DL for Px(1…32) out of Nx (1…32).

n If: RXLEV_UL/DL + 2 ×× PowIncrStepSize* <= pcLowerThresholdsLevUL/DL then go to variable

power increase step size:èPWR_INCR_STEP = pcLowerThersholdsLevUL/DL -

RXLEV_UL/DL (The actual RxLEV not the averaged value).

else:èpowIncrStepSize (2, 4 or 6 dB)

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

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PC Algorithm

Ø MS/BTS Increase due to QUALITYn pcLowerThresholdsQualUL/DL (0…7, Px, Nx) is compared with

AV_RXQUAL_UL/DL_PC.n Trigger PC If: AV_RXQUAL_UL/DL_PC >=

pcLowerThresholdsQualUL/DL for Px (1…32) out of Nx(1…32).

Ø Calculation of MS/BTS power increase due to Quality?n Insufficient Quality can be due to low signal or interference. BSC

calculates one step size due to low signal and one due tointerference and selects the larger step.

n 1) Interference Step Size:èPWR_INCR_STEP = [1+Max(0,Qa)] ×× PowIncrStepSize

èWhere Qa = RXQUAL_UL/DL - pcLowerThresholdsQualUL/DL

èRXQUAL_UL/DL is the current actual value (not the averaged value)

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PC Algorithm

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

pcLowerThresholdsLevUL/DL

Then: PWR_INCR_STEP = pcLowerThersholdsLevUL/DL -RXLEV_UL/DL

è The actual RXLEV is used and not the averaged value.

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

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PC Algorithm

Ø BTS Decrease due to LEVELn Trigger PC if: AV_RXLEV_DL_PC >=

pcUpperThresholdsLevDL for Px(1…32) out of Nx (1…32).n Parameter VariableDLStepUse (Yes/No) indicates if variable step

size is used for DL power decrease.n Parameter OptimumRxLevDL(-109…-47 dBm) indicate optimum

DL signal level which ensures adequate speech/data quality withminimum DL interference. Parameter is controlled on a transceiverby transceiver basis.

n If: RxLev_DL - 2 × PowDecrStepSize* >=pcUpperThresholdsLevDL then use variable powerdecrease step size:è PWR_DECR_STEP = MIN[(RXLEV_DL - PcUpperThersholdsLevDL), 10]

else:èpowDecrStepSize (2, 4 or 6 dB)


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PC Algorithm

Ø BTS Decrease due to QUALITYn Trigger PC if: AV_QUAL_DL_PC =<

pcUpperThresholdsQualDL for Px(1…32) out of Nx (1…32)

Ø The BSC will determine DL power decrease based on twoalternative algorithms:n 1) Based on Non defined optimum downlink RF Signal Level If: RxLev_DL - 2××PowDecrStepSize* >=

pcUpperThresholdsLevDL then variable power decrease stepsize.èPWR_DECR_STEP = MIN[(RXLEV_DL -

PcUpperThersholdsLevDL),10]



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PC Algorithm

n 2) Based on Defined optimum downlink RF Signal Level.èDL 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

èPWR_DECR_STEP = MIN[PwrDecrLimit, MAX(A, B)]èPwrDecrLimit, A and B are some parameters defined in the

system.èA margin of 6dB is used in the formulas to prevent a power

decrease due to quality to trigger a power increase due tolevel (pwrLowerThresholdLevDL).

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Review: PC Algorithm

èFormula for reference:– PWR_DECR_STEP = MIN[PwrDecrLimit, MAX(A, B)]

– PowDecrLimit/Band0-2 is the maximum size of the variable powerdecrease step:

» PwrDecrLimitBand0 (0…38dB) indicates max size of power decrease step whenBTS power is decreased due to quality and the average BER is better than 0.2%.

» PwrDecrLimitBand1 (0…38dB) indicates max size of power decrease step whenBTS power is decreased due to quality and the average BER is between 0.2 - 0.4%

» PwrDecrLimitBand2 (0…38dB) indicates max size of power decrease step whenBTS power is decreased due to quality and the average BER is worst than 0.4%(quality band from 2 to 7).

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

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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 intoaccount the distance between the pcUpperThreholdsQualDL and theaverage quality that triggered the PC. The distance is multiplied by thepower reduction step size PowDecrStepSize (2…4).

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PC Algorithm

Ø MS Decrease due to Signal Level

n Trigger PC if: AV_RXLEV_UL_PC >= pcUpperThresholdsLevDL for Px(1…32) out of Nx (1…32)n If: RXLEV_UL - 2×× PowDecrStepSize* >=

pcUpperThresholdsLevUL then go to variable power increasestep size:èPWR_DECR_STEP = RXLEV_UL - PcUpperThersholdsLevUL


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

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PC Algorithm

Ø MS Decrease due to QUALITYn Trigger PC if: AV_RXQUAL_UL_PC =<

pcUpperThresholdsQualUL for Px(1…32) out of Nx (1…32)

Ø The BSC will determine DL power decrease based on twoalternative algorithms:n 1) Based on OptimumRxLevUL = “not used”

è If: RxLev_UL - 2 ×× PowRedStepSize* >=pcUpperThresholdsLevUL then go to variable power increase stepsize:

– PWR_DECR_STEP = RXLEV_UL - PcUpperThersholdsLevUL

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

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PC Algorithm

n 2) Based on OptimumRxLevUL = used (on TRX by TRXbasis)èUL 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

èFormula 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.

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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Discontinuous Transmission (DTX)

Ø The DTX aims at increasing the system efficiency through adecrease of the interference level, by inhibiting the transmission ofthe radio signal when not required.

Ø If the transmitter is silent during the speech pauses, the powerconsumption in the MS is decreased as well as the amount ofemitted radio power.

Ø When DTX uplink and downlink is used, there is an improvement ofthe C/I in the system. This improvement can be utilized for a tightercell planning, especially when frequency hopping is used. It will alsosave battery life in the MS.

Ø DTX is not used on a BCCH carrier.

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DTX (cont.)

Ø In a speech connection, the Voice Activity Detector in thetranscoder or MS detects whether a traffic frame consists of speechor of background noise.

Ø If a frame consists of only noise, the transmitter sends one SilenceDescriptor (SID) frame, and then the transmission is stopped. Afterthat, one new SID frame is sent each SACCH period, until speech isdetected again.

Ø The active speech flow is of one frame of 260 bits each 20 ms,while the inactive speech flow is of one such frame each 480 ms.

SF SF SF SF SF SF SF SID No TX SID SIDNo TX

20ms 480 ms

SF = Speech FrameSID = Silence Indicator

SACCH period

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DTX (cont.)

Ø DTX mode may slightly deteriorate the quality oftransmission, in particular when used twice along a path,mobile to mobile call. So it can be activated on a call percall basis by the network.

Ø Used in conjunction with frequency hopping, DTX cangive an improvement of approximately 3dB in the C/I forthe TCH channels.

Ø The recommended setting for DTXU and DTXD are asfollows:

Parameter Default value Recommended Value

DTXU 2 1

DTXD OFF ON

DTXU is the uplink parameter and states whether the MS shall (DTXU=1) or shallnot (DTXU=2) use DTX. With DTXU=0 the MS may use DTX which means thatMSs in battery saving mode shall use DTX.

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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Frequency Hopping

Ø FH is used in GSM to improve the system’s performanceand quality in the multipath fading environment and toreduce the required S/N ratio.

Ø GSM uses Slow FH in which the hopping rate is less thanthe message bit rate.n In GSM the operating frequency is changed only with every

TDMA frame.n The hopping rate is 216.7 hops per second which corresponds to

a frame duration of 4.615 sec.

Ø 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 µ s).

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Frequency Hopping (cont.)

Ø FH provides frequency diversity to overcome Rayleighfading which may cause fades of 40 to 50 dB deep onthe received signal.

Ø FH also provides interference diversity (interferenceaveraged over multiple users).

Ø FH reduces the S/N ratio required for an acceptable QoS,from 12 dB for a non-hopping radio link to 9 dB(approx.), improving the overall network’s capacity.

Ø Different hopping algorithms can be assigned to the MSn Cyclic Hoppingn Random Hopping

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Frequency Hopping (cont.)

Ø 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.

Ø The Broadcast Channels (BCH) comprising of FCCH, SCHand BCCH are not allowed to hop. All dedicated channeltypes can hop (TCH/SDCCH/FACCH/SACCH).

Ø Two different implementation schemes of SFH are used inBSs which are base-band hopping and RF hopping.

Ø Hybrid hopping is a combination and compromise of thetwo implementation schemes.

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ANT

TS handler transmitter f0




TRX 1

TRX 2

TRX 3

TRX 4

filtercombiner

Bus for routing of bursts

Base-band Hopping

Ø Each transmitter is assigned with a fixed frequency. Attransmission, all bursts, irrespective of which connection,are routed to the appropriate transmitter of the properfrequency. The mobile is hopped around the transmittersand receivers.

Ø The advantage with this mode is that narrow-band lowloss filter combiners can be used.

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Base-band Hopping (cont.)

B= BCCH TSL 0 (f1). 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)

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TS handler transmitter f0 . . . fn

TS handler

TS handler

TS handler

TRX 1

TRX 2

TRX 3

TRX 4

transmitter f0 . . . fntransmitter f0 . . . fn

transmitter f0 . . . fn

ANThybridcombiner

ANThybridcombiner

RF Hopping

Ø One transmitter handles all bursts that belong to a specificconnection. In contrast to base-band hopping, the transmitter tunesto the correct frequency at the transmission of each burst.

Ø The advantage of this mode is that the number of frequencies thatcan be used for hopping is not dependent on the number oftransmitters. It is possible to hop over a lot of frequencies.

Ø The disadvantage with synthesizer hopping is that wide-band hybridcombiners have to be used. This type of combiner has approximately3dB loss making more than two combiners in cascade impractical.

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RF Hopping (cont.)

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.

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Hopping Algorithms

Ø Cyclic frequency hopping: the frequencies are changed,once every TDMA frame, in a consecutive order (e.g.…,f1,f2,f3,f4,f1,f2,f3,f4,…).

Ø Random frequency hopping: a random hopping sequenceis implemented as a pseudo-random sequence. 63independent sequences are defined. Hopping SequenceNumber (HSN) will specify which of the 63 sequences tobe used (e.g. …,f1,f4,f4,f3,f1,f2,f4,f1,…).n The random hopping mode is superior for averaging the co-

channel interference. Random hopping is the hopping mode ofchoice for high capacity networks.

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Hopping Algorithms (cont.)

Ø Orthogonal hopping sequence: for each transceiver, inthe same channel group, in the same cell, they will beassigned with the same HSN, i.e. they hop in the sameway.n In order not to interfere with each other, they must not use the

same frequency at the same time.n The problem is solved by using an offset in the hopping

sequence, referred to as Mobile Allocation Index Offset (MAIO).Two transceivers bearing the same HSN but different MAIO willnever use the same frequency in the same TDMA frame

(e.g., …,f1,f4,f4,f3,f1,f2,f4,f1 ,… …,f2,f1,f1,f4,f2,f3,f1,f2,… …,f3,f2,f2,f1,f3,f4,f2,f3,… …,f4,f3,f3,f2,f4,f1,f3,f4,…).

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FH 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 1

TRX 2

TRX 3

0 1 72 TS

TRX 4

B f 1

f 2

f 3

f 4

BTS

BTS

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FH Parameters (cont.)

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

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Flexible MAIO Management

Ø Allows More Flexible RF Hoppingn Enables Frequency Sharing, i.e. sharing an MA list between the

sectors at the same site.n Longer MA lists possible.n Minimised interference.

Ø New MAIO Step Parametern When used together with MAIO offset, no successive MAIOs will

be allocated for TCHs sharing the same MA list.

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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's

Band allocation:

Operator can also set the MAIO step size

Operator can set the lowest MAIOs for the cells

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MAIO Step (cont.)

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

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Flexible MAIO benefits

Ø One MA list per site

Ø One MA list can contain a continuous band

Ø No risk of co-channel nor adjacent channel being usedsimultaneously within a site

Ø Single MA/HSN possible -> only BCCH frequencyplanning

Ø More tighter reuse possible and thus more capacity canbe achieved

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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IUO

f3

f3

f3

f3

f1

f1

f1

f1f2

f2

f2

f2

Ø Regular BCCH-TRXØ Super-reuse TRXØ Different frequency reuse

patternsØ Super reuse frequencies form

the underlay network wherefrequencies are reused veryintensively to produce theextended capacity

Ø Selection between regular/super-reuse TRXs based on C/I ratio

Ø Call setup always to regular TRXØ Inter cell HO always to regular

TRX

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IUO (cont.)

Ø Microcells to hot spots (microcellsusing only super frequencies arecalled child cells)

Ø Microcell interference is estimatedby using closest regular TRX as areference (compare C/I basedhandover candidate evaluation)

f3

f3

f3

f3

f1

f1

f1

f1f2

f2

f2

f2

f1

f1

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IUO (cont.)

f1

f1

f1

In order to avoid interference caused bytight frequency reuse, the super reusefrequencies are intended to serve MSwhich are close to the BTS.

f1

f1

f1

Regular frequency is used when themobile is further away from the BTSwhere RxLev would be low and cochannel interference high.

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IUO (cont.)

Super layer (reuse = e.g. 7)

Regular layer (reuse = 12)

Super layer (reuse = e.g. 7)

Regular layer (reuse = 12)Regular layer (reuse = e.g. 12) Regular layer (reuse = e.g. 12)

• Service region of super layer controlled by interference(superReuseGoodCIThreshold)

• Call handed over from super layer to regular layer wheninterference becomes excessive(superReuseBadCIThreshold)

<-------- Interference region ----->

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TCH Assignment to Super-TRX

• When Regular Layer is Congested, TCH Can Be Allocated in the Super Reuse

• Directed Retry

• EnaTchAssignSuper > 0

• EnaTchAssignSuper Defines a Time for BSIC Decoding of Interfering Cells

• Directed Retry to Other Cells ( ? )

• Increased Probability of Congestion on the SDCCH ! --- > Feature to Be Used with Care

SDCCH4 Channels7-8 Channels12 Channels…..


Regular Layer6-7 TSL14 TSL22 TSL…..

Regular Layer6-7 TSL14 TSL22 TSL…..

Super Reuse Layer8 TSL16 TSL24 TSL…..


Call Set-Up

MinBsicDecodeTime



Regular LayerRegular Layer



Set-Up

MinBsicDecodeTime

EnaTchAssignSuper

DR To Other Cells

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Handover causes

Ø Traffic control between regular and super-reusefrequencies

Ø Conventional radio criteria

Ø Other reasons than radio criteria (e.g., traffic handover,umbrella handover)

Ø Regular HO Caused by Radio Criteria(or other reasons)n Intra-cell HO within a regular frequency group

n Inter-cell HO from a regular cell to another regular cell

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IUO Handover Types

Ø Intra-cell HO from a regular TRX to a super-reuse TRX

n DL C/I ratio of the super-reuse TRX is good enough to sustain agood radio link

n Both UL and DL signal quality on the regular TRX are good

n MS-BS distance has not reached the HO threshold

Ø Intra-cell HO from a super-reuse TRX to a regular TRX

n DL interference

n DL signal quality

n Bad C/I ratio

n MS-BS distance has reached the HO threshold

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IUO Handover Types (cont.)

Ø Intra-cell HO within a super-reuse frequency group

n UL interference

NOTE: the parameter EnableIntraHoInterfUL must be enabled.

Ø Inter-cell HO from a parent cell to a child cell

n Same as Intra-cell HO from a regular TRX to a super-reuse TRX

n As a Power Budget HO

Ø Inter-cell HO from a child cell to a parent cell

n Same as Intra-cell HO from a super-reuse TRX to a regular TRX

n As an imperative handover

Ø HO from a dedicated control channel to a super-reuse TRX

n intra-cell and inter-cell (child-cell)

n set EnaTchAssSuperIUO to “yes”

n Directed Retry is essential

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Improvements

Inter Super-reused Layer Handovern In order to minimize the number of imperative handovers

without degradation of service quality, a handover betweensuper reused layers (an intra-cell handover) is performedwhen the regular TRX is congested

n Other super reuse TRX has to fulfill the C/I requirement

Two options:

1) Handover between thesuper reused layers ifRegular TRX is congested

2) Handover between thesuper reused layers if C/Iof the target super isgood

SDCCH

REG TRX

SUPER 1

SUPER 2

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Intelligent Frequency hopping (IFH)

f1f1BCCH BCCH

TCH TCH TRX-1TRX-2

TCHTCH

TCHTCHTRX-3TRX-4

Regular layer

Super-reused layer

f2f3

f2f3

f4f5f6

f4f5f6

RF Hopping

BCCH BCCH

TCH TCH TRX-1TRX-2

TCHTCH

TCHTCHTRX-3TRX-4

f1f2

f1f2

f4f5

f4f5

BB Hopping

ØImproved radio spectrum efficiencyØAdds the benefits of interference averaging by frequency

hopping to the capacity gains of IUO to further boostperformanceØFrequency hopping combined with IUO means capacity increase

by controlled C/I and decreased reuse patternØApplicable for both Radio Frequency and Base Band Hopping

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IFH (cont.)

Ø Intelligent Frequency Hopping is an optional feature.

Ø Both layers of a sector can be set hopping separately byusing regular hopping mode and super hopping mode.

Ø In RF hopping both layers, overlay (regular) andunderlay (super), shall have their own mobile allocation(MA) attached.

Ø The parameters for this feature can be modified onlywhen the frequency hopping for intelligent underlayoverlay is on.

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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ICE

PWR_INCR_STEP = (

where

Qa = RXQUAL_DL - PcLo

HIGH POWER TRX• The call is always started from high power TRX

• When the signal level exceeds the Upper_threshold, the call is handedover to low power TRX

PWR_INCR_STEP = (

where

LOW POWER TRX• When the signal level goesbelow the Lower_threshold, orbad DL quality exists the callis handed over to high powerTRX

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ICE Handover Support

Ø Handovers between layers are based on DL RxLevel orDL RxQuality

Ø The transceivers are divided into regular (high power)and super-reuse (low power) TRXs as in IUO

Ø Frequency Hopping can be used. Both layers have theirown Mobile Allocation (IUO + FH is needed)

Ø BCCH recovery can be handled by using feature"Preferred BCCH TRX"

Ø "TCH assignment to super-reuse TRX" and "Direct accessto Super-reuse TRX" can be used together with thisfeature

Ø The performance of the handovers, absorption of thelayers, etc. can be measured by using IUO measurement

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Parameters

Parameter Value

superReuseEstMethod AVE / MAX / ICE/NONE

-47 … -110 (dBm)superReuseGoodRxLevelThreshold

Rxlevel

-47 … -110 (dBm)superReuseBadRxLevelThreshold

Rxlevel

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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Dynamic Hotspot

n Controls the traffic load of a frequencyhopping radio network on the basis ofinterference

n Achieves a higher radio network capacityin a network in which frequencies arereused tightly

n Makes it possible to reuse hopping TRXfrequencies effectively without qualitydegradation

Result:

The quality of frequency hopping network is kept good and the number of dropped calls is kept low

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Benefits

Ø Enables the usage of very tight frequency reuse of hoppingTRXs without quality degradation and dropped calls

Ø BSC limits traffic intensity in those areas where theinterference intends to increase above acceptable level

Ø With unequal traffic distribution some cells can dynamicallyhandle more traffic than the others when the traffic intensityin the other cells is relatively lower

Ø BSC monitors the level of quality from the neighboring cellsand the load of the accessed cell

Traffic

Cell

Maximum traffic loadwhen trafficis evenly divided andinterferencelimited

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Dynamic Hotspot

If load of accessed cell < Limitreserve TCH

otherwise verify Soft Blocking

Probability of getting a channel depends on:prob(BTS1), prob(BTS2),prob(BTS3) and prob(BTS4)

If load of accessed cell < Limitreserve TCH

otherwise verify Soft Blocking

Probability of getting a channel depends on:prob(BTS1), prob(BTS2),prob(BTS3) and prob(BTS4)

Quality Good Quality Sufficient Quality Bad Quality

Q1 Q2 Q3

Probability 1 P1 P2 P3 0

BTS1

BTS2BTS3

BTS4

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Dynamic Hotspot

BadQual Limit

SignalQual Limit1

SignalQual Limit2

GoodQual Limit

o

P1

P2

P3

1

TCH PROBABILITY 1

TCH PROBABILITY 2

TCH PROBABILITY 3

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Dynamic Hotspot

Ø Dynamic HotSpot is applied in following situations:n During a calln During an internal inter-cell handovern During an external handovern During an underlay-overlay handover

Ø Dynamic HotSpot is not applied in the followingsituations:n Intra-cell handover (except underlay-overlay handover)n TCH is allocated from a non-hopping TRXn Internal inter-cell handover is performed because of bad signal

quality

Ø Dynamic HotSpot is an optional feature

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Parameters

Parameter Value

softBlockingStartReg 0…255

BTS

interferedCell 0 (no interference)1 (interference on regular frequencies)2 (interference on super-reuse frequencies)3 (interference on regular and super-reuse frequencies) ADJC

softBlockingStartSup 0…255

badQualityLimit 0…100 (%)

goodQualityLimit 0…100 (%)

signalQualityLimit1, 2 0…100 (%)

tchProbability1, 2, 3 0…100 (%)

BSC

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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New techniques to reduce interference

Ø The efficient use of spectrum and thereforetechniques to reduce the interference andenhance the system capacity are of primeinterest.

Ø There are some approaches in GSM that can beused for this purpose:n Channel borrowing or effective channel management.n Advanced antenna technology

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Channel Borrowing Techniques

Ø Dynamic Channel Allocation (DCA)n In DCA a central pool of channels is used. A channel is

borrowed from the pool by a BS for use on a call andreturned to the pool when the call is completed. All BSshave access to the whole channel set.

n The basic DCA has a self-organizing channel assignmentalgorithm based on dynamic real-time measurements ofinterference levels.

n These measurements are usually performed at the MS inorder to reduce the computational load and the complexityof the system.

n Several variation of DCA have been proposed and some ofthem have been implemented. Adaptive Channel Allocation(ACA) significantly increases the capacity of a TDMAsystem as compared to the traditional Fixed ChannelAssignment (FCA).

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Ø Hybrid Channel Assignment (HCA)n In HCA, some channels are permanently assigned to each

BS, as in FCA, and others are kept in a central pool forborrowing as in DCA.

n Channel Locking is used to prevent an increase in co-channel interference. It means that BSs within therequired minimum channel reuse distance from a BS thatborrows a channel can not use the same channel.

n Channel locking has some disadvantages including thelimit on the number of available channels to borrow andsystem complexity.

n Another disadvantage is the difficulty in maintaining co-channel reuse distance at the minimum required valueeverywhere in the system.

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Ø Channel Borrowing Without Locking (CBWL)n In CBWL, each BS is allocated channels as in FCA. If all

channels of the BS are occupied and a new call arrives,channel borrowing is used.

n The borrowed channel cannot be used by the originallending BS but can still be used in any nearby co-channelBSs.

n In CBWL, only a fraction of the total channels of thesystem need to be accessible to each BS.

n The CBWL can be employed in existing cellular systemswithout additional infrastructure cost.

n Unlike cell splitting, CBWL does not require new BSs andadditional antenna towers to increase system capacity.

n Simulations show that CBWL provides better channelutilization than a conventional system with FCA, DCA orHCA.

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Smart Antennas

Ø Another way to reduce interference is to use a smart orintelligent antenna.

Ø A smart or intelligent antenna refers to a group of coreRF technologies that control directional antenna arraysby means of sophisticated Digital Signal Processing(DSP) algorithms.

Ø Smart antennas belong to two basic classes:n Switched beam in which the antenna combines signals according

to a fixed number of beam patterns.n Adaptive in which the antenna picks out the desired signal amid

a field of interfering signal/thermal noise and self-regulates itsperformance to satisfy some pre-assigned criteria.

Ø In TDMA based systems, the use of adaptive antennaswould be considerably beneficial to coverage, capacity,signal quality and the portable terminal transmit power.

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• Introduction






• Handover

• Power Control





• Dynamic Hotspot


• Queuing

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Queuing and Radio Resources

Ø Purposen To avoid rejecting call set-up or handover attempt by waiting

for the release of a suitable traffic channel

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

n Each BTS has a queue of its own

n Individual queue parameters and queue management for eachBTS

n Only traffic channels are queued

n Call attempts and Handovers are in the same queue

n The maximum queue length is relative to the number of trafficchannels

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Queuing and Radio Resources

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

n Different priorities according to queue type (Call/Ho) and/or MSpriority

Ø Prioritization: The placement in the queue is determinedby:n Queue Type (Priority)n Call Setupn Handover attempt (non-urgent)n Urgent Handover Attemptn MS Priority Level

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Queuing Management

Ø A Queuer is removed from the queue when:

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

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

n The queuing TRX/TSL is blocked (call release)

n Queue size is reduced due to removing TRX’s

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Queuing and Handover

Ø Internal inter-cell Handovern Ranked list is produced by the Handover algorithm and passed

to RR managementn Maximum sixteen cells as alternative target cellsn The best candidate with free traffic channel is selectedn If all BTSs in the list are congested

èqueuing possibility is checked in the candidates according toranking

Ø External inter-cell Handovern The BTS identified by the MSC in a HANDOVER_REQUEST

message is used as queuing target

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

stopped during queuing

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