ud75_Multiband Operation

OPEN INFORMATION USER DESCRIPTION 1(12)KI/ERA/SVN/NRA LARS KLOCKAR8508775842000-10-24D 75/1553-HSC 10312Uen ERA/SVN/NRAC (Lennart Blixt)Uppgjord —Prepared Datum —Date Rev Dokumentnr —Document no Godkänd —Approved Kontr —Checked Tillhör/referens —File/reference EUser Description,Multiband Operation Copyright ©Ericsson Radio Systems AB 2000.All rights reserved.No part of this document may be reproduced in any form without the written permission of the copyright holder.Disclaimer Trademarks Contents Page 1Introduction 22Glossary 22.1Concepts 22.2Abbreviations and Acronyms 23Capabilities 24Technical description 34.1General 34.2Power and frequency capability of an MS 34.3Broadcast of measurement frequencies 44.4Measurement reporting 44.5GPRS 44.6Related Counters 44.7Main changes in Ericsson GSM system R8/BSS R8.055Engineering guidelines 55.1General 55.2Traffic control by sufficient SS threshold,active mode 55.3Traffic control by sufficient SS threshold,idle mode 65.4GPRS 75.5Load dependent traffic distribution 85.6Neighbour relations 85.7Subscriber differentiation 95.8Classmark 3Messages 96Parameters 96.1Main controlling parameters 96.2Parameters for special adjustments 106.3Value ranges and default values 117References 12SEIF v2.3,1IntroductionAn operator with licenses to operate both in the GSM900and1800frequencyband can choose to have the GSM900network and the GSM1800networkcombined into the same network.Each cell in a multiband network has frequencies from only one frequencyband.The Multiband operation feature allows cell re-selection,assignmentand handover between the GSM900cells and the GSM1800cells.With the Multiband Operation feature it is also possible to have GSM900and/or GSM1800cells together with GSM1900cells,supported by the sameBSC.However,it is not possible to perform cell re-selection,assignment orhandover between GSM1900and the other bands.2Glossary2.1ConceptsE-GSM Extended GSM900band including the Primary GSM900bandand the G1.G1Extension band defined for GSM900at880-890MHz(uplink)and925-935MHz(downlink).P-GSM Primary GSM900band defined at890-915MHz(uplink)and935-960MHz(downlink).2.2Abbreviations and AcronymsCLS Cell Load SharingGPRS General Packet Radio ServiceHCS Hierarchical Cell StructurePBCCH Packet Broadcast Control ChannelSS Signal Strength3CapabilitiesA combined GSM900and GSM1800network provides a very efficientsolution for building a cost efficient high capacity network together withgood coverage.The radio waves on the900MHz and1800MHz frequency band have differentpathloss characteristics.GSM900cells generally have a larger range thanGSM1800cells.If cells from the different frequency bands can be joined intoone single network,GSM900cells can be used to cover large areas withlimited traffic density.GSM1800cells can provide additional capacity in highdensity areas.Operators with an existing GSM900network can use theadditional1800MHz band to increase the capacity of their network.Operatorswith an existing GSM1800network may not have full coverage and they canuse GSM900to increase both coverage and capacity.In a multiband network,the system supports cell re-selection,assignmentand handover between GSM900cells and GSM1800cells for multibandMSs.Multiband MSs,and single band MSs(GSM900or GSM1800)canco-exist.This has two benefits:1An operator that is changing the network from a single band(GSM900or GSM1800)to a multiband network is still able toserve the single band MSs on both frequency bands.2A multiband subscriber will be able to use the multiband MS in apure GSM900network as well as in a pure GSM1800network.GSM1900cells must always form a separate network.With GSM900andGSM1800the operator can choose whether to have separate networksor one combined network.4Technical description4.1GeneralA Mobile services Switching Centre(MSC)is able to handle BSCs of differentsystem types,which means that it is possible to have GSM900BSCs,GSM1800BSCs and GSM1900BSCs connected to the same MSC.Correspondingly,a BSC is able to handle cells of different system types,whichmeans that it is possible to have GSM900cells,GSM1800cells and GSM1900cells connected to the same BSC.Each cell must however only containfrequencies related to one system type.A multiband MS is able to receive,transmit and measure on GSM900frequencies as well as on GSM1800frequencies.A multiband MS performsneighbouring cell measurements on GSM900cells as well as on GSM1800cells.Both types of cells are evaluated in the idle mode cell re-selectionalgorithm and in locating.This means that cell re-selection,assignment andhandover can be performed between the frequency bands.A single band MS will not measure neighbouring SS on frequencies it can nothandle.This means that a single band MS will never be allocated a channel inthe wrong frequency band.4.2Power and frequency capability of an MSClassmark3(CM3)contains MS capabilities such as multiband and powercapability of each band,extended-GSM band and multislot.MSs inform thenetwork of their capability during the call set up procedure and at locationupdating.Regarding multiband it is important for the network,besides to knowthe multiband capability itself,to know the MS power capability in the otherfrequency band,not currently used.With parameter ECSC=YES there is a bitin system information3telling the MS to send Classmark Change,containingCM3(and CM2)as soon as possible after access.CM2contains the MSpower capability related to the frequency band on which the MS is residing.The MSC needs to have the CM3information in case of an inter BSChandover.The MSC then transfers the CM3information to the target BSC.If a multiband MS performs an inter-BSC handover,and the MSC does nothave the CM3information,the target BSC will not have the correct informationregarding the power capabilities of the MS.If the handover was between twocells belonging to the same frequency band,the target BSC will treat the MSas a single band MS for the remainder of the call.If the inter BSC handoverwas between two frequency bands,depending on the content of CM2theresult will either be a handover failure,or the target BSC will use incorrectvalues regarding the MS power capability.In order to reduce the load on the A interface(between the BSC and theMSC),the sending of CM3is possible to suppress or delay by parameterCLMRKMSG.For CLMRKMSG=0,the BSC will always transfer the messageto the MSC.For CLMRKMSG=1the message is suppressed in all situations,i.e.the CM3information is never transferred to the MSC.CLMRKMSG=3means that the sending is suppressed at location updating but not at callset-up.Finally it can be delayed even further,until an inter-BSC handover isperformed(CLMRKMSG=2).4.3Broadcast of measurement frequenciesAn MS performs neighbouring cell measurements in idle mode as well as inactive mode.The information about which neighbours that shall be measuredon is broadcasted to all MSs in the cell.A single band MS ignores frequenciesit can not handle.The frequencies of neighbouring cells are given by parameter MBCCHNO,see User Description,Double BA lists.With this parameter GSM900frequencies as well as GSM1800frequencies can be defined as neighbouringfrequencies in a multiband network.4.4Measurement reportingA multiband MS measures the SS from GSM900neighbours as well as fromGSM1800neighbours.It is possible to control how many GSM900cells andGSM1800cells respectively that are reported in the measurement report byparameter MBCR.This implies that not always the six strongest cells will bereported.MBCR determines how many of the decoded neighbours of the otherband that shall be reported,at the expense of neighbours in the current band.If the report is still not full,more neighbours from the other band are included.4.5GPRSThere is no restriction for dualband GPRS.4.6Related CountersIn order to give the operator statistic measurements to adjust parametersfor controlling the traffic between frequency bands to off-load the GSM900cells to a maximum,the object type CELLDUALT is introduced to supportthe following counters:TFDUAL-TRALACC Traffic level accumulator.It gives continuous information on the number of seized channels for dualband MSs.TFDUAL-NDROPNumber of abnormally terminated dualband connections.TFDUAL-CASSALLNumber of assignment complete for all MS power classes.TFDUALAS-SALLNumber of assignment attempts for all MS power classes.The counters are defined per cell and are stepped only for dualband MSs.See User Description,Radio Network Statistics for details.4.7Main changes in Ericsson GSM system R8/BSS R8.0Changes in the Engineering guidelines due to enhanced HCS with8layersand8bands(see User Description,Hierarchical Cell Structures).New counters for dualband MSs(see4.6).5Engineering guidelines5.1GeneralA combined900and1800network depends on the same functionality andplanning principles as a single band network.However,in order to utilise thegiven spectrum efficiently,it is often desired to direct the traffic in accordancewith the distribution of multiband MSs,single band900MSs and1800MSs.Therefore multiband operation makes its own use of other features.Thisengineering guideline is based on the typical scenario of a GSM1800layer implemented on top of a mature GSM900system in order to provideadditional capacity.In that case it is important to give priority to1800cell ina efficient but safe way.Also,more attention must be paid to the numerousneighbour relations.5.2Traffic control by sufficient SS threshold,active modeIn the early stages of a multiband network the presumed high number of1800frequencies and low penetration of multiband phones means large sparecapacity in the1800cells and also low interference.Therefore these cellsshould be favoured whenever they have sufficient SS.This can be done withHCS,Locating and idle mode cell re-selection.The easiest method in active mode is HCS(see User Description,HierarchicalCell Structures).When the900cells and1800cells co-exist the900MHzSS will in general be higher than the1800MHz SS.The natural choice ofcarrier would be the stronger900MHz but with HCS it is possible to direct thetraffic to the higher priority1800MHz frequency band if the SS in that cellis above an absolute SS threshold.Two HCS options are available,one with8layers and8HCS bands andthe other with3layers and no HCS band.The full HCS feature offers thecell two thresholds instead of one.The layer threshold LAYERTHR is usedto limit interference between layers within the same frequency band.Theband threshold HCSBANDTHR is used to prioritise between non interferinglayers.GSM900cells can be specified in one band and GSM1800cell withinanother band.Since each band can consist of layer structures there is onepriority mechanism dealing with multiband and another mechanism usedbetween layers(for example microcells and macrocells)within each band.Since the GSM1800cells are not interfered by the GSM900cells,an1800cell can very well be the serving cell in an area with considerably higher SSfrom the GSM900cells.If the frequency planning within the GSM1800layer is not too aggressive,noise rather than interference limit the GSM1800coverage allowing a low SS threshold.HCSBANDTHR=95is a reasonablelevel for the1800band.Of course a low threshold like-95dBm requires shortSS and quality filters,(E.g.3to5s).The SS may fall quickly and serving cellmust not disappear within the time it takes to complete a handover.More than5s must be allowed due to filtering,time to identify new neighbours andto allow TINIT(see User Description,Locating)to elapse after a possibleprevious handover.A threshold of-95dBm allows time enough to performhandover out in normal urban areas.There are however situations with fastmoving mobiles where the threshold must be higher.In these situations theSS falls a lot more than10dB in the5s before a handover can be performed.The MS will be trapped in the1800cell and drop the connection.This problemhas been seen for example during rapid shifts of height and direction athighway exits.Those kinds of areas must be identified and a threshold of-85dBm or higher should be used in affected cells.The HCS priority is considered already in the assignment stage(see UserDescription,Assignment to Other Cell).If a call set-up is performed in900although1800has sufficient SS,the assignment can be done directly inthe best1800cell provided that CM3is received by the BSC early in theassignment stage.5.3Traffic control by sufficient SS threshold,idle modeTo keep the number of handovers down,a higher priority to1800cellsis desired in idle mode.In cell reselection the C2algorithm(see UserDescription,Idle Mode Behaviour)provides the possibility to apply a CellReselection Offset,parameter CRO,to a high priority cell at cell re-selection.By that the cell becomes favoured a given number of dB in the cell reselection.At low SS it is however dangerous to allow high offsets instead of lettingthe strongest cell be selected.Therefore the use of CRO requires that thefavoured cell cannot be accessed at too low SSs.Parameter ACCMINbecomes important;above which a multiband MS has to camp on1800,evenif the signal is too weak,and below which the MS is not allowed to camp onthe1800band at all.The MS should continuously listen to its paging groupand abandon a cell where paging messages tend to be lost.This leaky bucketbehaviour with common parameter settings,see User Description,Idle ModeBehaviour,gives however no guarantee that the MS selects a strong enoughcell,if possible.From experience it is found that an offset forces the MS tocamp on an1800cell although the cell is too weak to deliver the pagingsproperly.The MS remains silent although there are stronger900cells wherethe pagings would succeed.Call set-up seems to be a smaller problem sincethe MS either change cell after failure or succeeds with call set-up followed by immediate handover or assignment handover out.Below follows three strategies for how to set ACCMIN,associated to three types of situations:1High difference in SS between bands,some1800singleband MSsHigh CRO is necessary which means that ACCMIN1800mustbe high enough to allow e.g.paging.If ACCMIN1800is set tothe lowest safe value instead of the lowest possible value,the 1800coverage area is not decreased noticeable.A safe valuemay differ between networks and MSs but ACCMIN1800=103is a suggestion.Strategy1gives a small discrepancy in theidle and active mode cell borders(unlike strategy3)but this isregarded less important than possible single band1800MSs inthe system,or possible extra coverage added by the1800cells. 2Small difference in SS between bandsIf the SSs of1800and900are almost equal,a small offset of2to4dB can be effective.A few dB offset is excused withoutadjustment of ACCMIN in1800.A small favour to1800iscompensated by less interference and perhaps better uplinkdue to Tower Mounted Amplifier(TMA).3No single band1800MSs,minimum of inter-band handovers It is also assumed that CRO is high.If there are no singleband1800MSs in the system,and if the1800cells provideno additional coverage compared to the GSM900system,ACCMIN1800could be set according to the sufficient SSthreshold in active mode i.e.HCSBANDTHR1800if HCS isused for1800macrocells.Especially when900to1800handovers mean inter-BSC or even inter-MSC handovers,itis advantageous to have about the same cell borders in idleand active mode.5.4GPRSThe GPRS MSs perform an autonomous cell selection in both packet idlemode and packet transfer mode(see User Description,GPRS Cell Selection).For an MS in GPRS mode currently listening to a cell with a PBCCH C31andC32criteria are used to perform the cell re-selection and GPRS mobilesprioritise the bands,but not the layers,in the same order as HCS(see UserDescription,Hierarchical Cell Structures).This solves the task of prioritising inidle mode.In case no PBCCH is configured in the cell C1and C2criteria are used justlike for all circuit switched MSs in Idle Mode.In this case GPRS mobiles willnot see the HCS structure.5.5Load dependent traffic distributionThe traffic load in cells fluctuates over time and some cells may be congested.Also the increasing number of multiband phones may require re-tuning of theHCS thresholds.Ericsson's GSM system has load dependant features fortraffic distribution in order to temporary move traffic from highly loaded cellsto less loaded.In case of congestion,assignment to worse cell(see User Description,Assignment to Other Cell)to the other band would save otherwise lostconnections.It is recommended to allow assignment to worse cell from both1800and900cells.Assignment to worse cell is a method to considerablyincrease the trunking efficiency in the network.AWOFFSET should be highfor the inter-band cell relations due to the non existing interference betweenbands.Since assignment to the other band is only possible for multiband MSs withboth1800and900coverage,not all new call set-ups can be saved by theassignment to worse cell possibility.CLS offers a possibility to off-load a highlyloaded cell before congestion(see User Description,Cell Load Sharing).The creation of spare channels enable single band MSs or multiband MSswithout coverage of the other band to grab resources in highly loaded cells.CLS only moves candidates close to the cell border but in a co-siting situationthis could mean a large fraction of MSs.CLS operates in areas where SSor path loss ranking is used.In combination with HCS that means betweencells belonging to the same band and same layer where both are above orbelow their thresholds.5.6Neighbour relationsIn the case a single band network is expanded to multiband,the existingneighbour lists are probably too long to allow a simple addition of a new layerof cells.In a multiband network there is no room for unnecessary neighbourrelations.Therefore the introduction of multiband often requires a throughoutsurvey of neighbour lists.A missing900neighbour could mean dropped calland a missing1800neighbour could mean less capacity.When1800cells are given high priority,it is important that a handover can beperformed quickly when the SS is below the threshold.With too few defined900neighbours to the1800cell,the MS may be trapped and therefore dropthe connection since HCS allows the cell border to reach deep into a nonco-sited900cell.Therefore the1800to1800relations must be optimised inorder to allow enough1800to900relations.The900to1800relations on the other hand are mainly for capacity and not ascritical.It is enough to add the co-sited1800cells and perhaps a few moreif a need is discovered.Neighbouring Cell List Optimization Expert(seeUser Description,Neighbouring Cell List Optimization Expert(NOX))givesinformation about new neighbour relations that would be suitable to addand information about neighbour relations that are not used and thereforecan be removed.It is recommended to use MBCR=2.It is then possible for an MS to performa handover,or an assignment,to a weak GSM1800cell.5.7Subscriber differentiationAt the same time as traffic is directed to the1800band with its spare capacity,some of these low interfered high quality1800MHz channels can be reservedfor certain privileged subscriber groups.With the use of Differential ChannelAllocation(see User Description,Differential Channel Allocation)a fraction ofthe channels in a cell can be defined as inaccessible for the non privilegedsubscribers.There is a possibility to reserve all channels in a cell for certainsubscribers.Subscribers that are not allowed to access will get the sameresponse as at congestion.Therefore DCA requires assignment to worse cell.Example:It was desired that low paying subscribers in a multiband networkshould only use1800cells while the rest could use both bands.The solutionwith all900TCHs defined inaccessible for some subscribers was satisfactorybut had some drawbacks:1The SDCCH load in900(no CRO)was high since assignmentto worse cell can mean several seconds set-up delay.2The displayed service in idle mode(900)does not alwayscorrespond to actual active mode coverage(1800).3The configuration with900and1800in different BSCs is notpossible but this is not recommended anyway.DCA checks arenot done at inter-BSC handover.5.8Classmark3MessagesIt is important to set parameter ECSC to YES because the multiband versionof Ericsson's GSM system relies on early classmark sending.Without CM3the multiband capability of an MS will be unknown and a missing CM3in targetBSC at handover means that the power class of the MS will be misunderstood.How and when CM3is further delivered to the MSC is controlled by parameterCLMRKMSG.The extra BSC/MSC signalling at call set-up due to CM3ismarginal.Therefore it is recommended to always send CM3to the MSCdirectly(CLMRKMSG=0),at least when the fraction of MSs sendingClassmark Change is small.The other choices may be preferred if MSCsignalling is a bottleneck.To forward CM3at access but not at locationupdating(CLMRKMSG=3)could be a safe way to reduce the load,but moretesting must be done until general recommendations can be given.If nomultislot MSs are expected and E-GSM band is not used,it could be optimalto wait until inter-BSC handover(CLMRKMSG=2)before CM3is forwarded. 6Parameters6.1Main controlling parametersGSYSTYPE is the global system type for the whole BSC.It defines which typeof cells the BSC contains.GSYSTYPE can have four values:•GSM900:All cells in the BSC is of type GSM900•GSM1800:All cells in the BSC is of type GSM1800.•GSM1900:All the cells in the BSC is of type GSM1900•Mixed:The BSC contains cells of more than one typeOnly cells that are supported by GSYSTYPE should be connected.GSYSTYPE must therefore be set to mixed before cells of another bandare connected to the BSC.CSYSTYPE is the cell system type.It can have three values:•GSM900:The cell system type is GSM900•GSM1800:The cell system type is GSM1800.•GSM1900:The cell system type is GSM1900MODE defines whether the BSC is in single or in multi band mode.Theparameter shall be set to MULTI in order to support cell re-selection,assignment and handover between GSM900cells and GSM1800cells.When the parameter is set to SINGLE,each frequency band forms a separatenetwork.MBCCHNO is the list of the neighbouring cells frequencies(see UserDescription,Double BA lists).The parameter is set per cell.ECSC indicates if early classmark sending should be used by the MS.In orderto allow multiband operation the value must be YES.Extended GSM andmultislot also require the value YES.The parameter is set per cell.6.2Parameters for special adjustmentsMBCR defines the number of neighbours from each frequency band that shallbe reported in the measurement report.The parameter can take the valuesbetween0and3,where the different settings mean:0:The multiband mobile station reports the strongest(up to six)identified neighbours irrespective of thefrequency band used in the cells.1:The multiband mobile station attempts to report the strongestidentified neighbour in each frequency band,excluding thefrequency band of serving cell.The remaining positions in thereport are used for neighbours from the serving band.If positionsstill exist,more neighbours of the other bands are included.2:The multiband mobile station attempts to report the2strongestidentified neighbours in each frequency band,excluding thefrequency band of serving cell.The remaining positions in thereport are used for neighbours from the serving band.If positionsstill exist,more neighbours of the other bands are included.3:The multiband mobile station attempts to report the3strongestidentified neighbours in each frequency band,excluding thefrequency band of serving cell.The remaining positions in thereport are used for neighbours from the serving band.If positionsstill exist,more neighbours of the other bands are included.The parameter is set per cell.CLMRKMSG suppresses or delays the sending of frequency and powercapability of a multiband MS from the BSC to the MSC.The parameter cantake the values between0and3,where the different settings mean:0:the sending is neither suppressed nor delayed1:the sending is suppressed in all situations2:the sending is delayed until an inter-BSC handover3:CM3sent at call set-up is not supressed but CM3sent atlocation updating is suppressed except when an inter-BSChandover during location updating is performedThe parameter is a BSC exchange property,and is set per BSC.6.3Value ranges and default valuesTable1Controlling parametersParameter name DefaultvalueRecommendedvalueValue range UnitGSYSTYPE-GSM900,GSM1800,GSM1900,MIXED CSYSTYPE-GSM900,GSM1800,GSM1900 MODE-SINGLE,MULTIARFCN MBCCHNO1to124(GSM900P-GSM)0,975to1023(GSM900G1)512to810(GSM1900)512to885(GSM1800)MBCR020to3ECSC NO YES NO,YES000to3CLM-RKMSG7References1User Description,Double BA lists2User Description,Hierarchical Cell Structures3User Description,Locating4User Description,Assignment to Other Cell5User Description,Idle Mode Behaviour6User Description,Cell Load Sharing7User Description,Neighbouring Cell List Optimization Expert(NOX)8User Description,Differential Channel Allocation9User Description,Radio Network Statistics10User Description,GPRS Cell Selection。