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Open InformationUSER DESCRIPTION 1 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEUser Description, Overlaid/Underlaid SubcellsContents Page1 Introduction . .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 22 Glossary .. ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 22.1 Concepts .. ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 22.2 Abbreviations and Acronyms ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 23 Capabilities . .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 33.1 Increased traffic capacity .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 33.2 Dynamic OL/UL Subcells .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 53.3 BCCH in Overlaid Subcell . ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 63.4 Multi Band Cell ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 64 Technical description .. .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 64.1 General . ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 64.2 Algorithm .. ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 74.3 GPRS/EGPRS Impacts . .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 134.4 Related Counters ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 134.5 Main changes in Ericsson GSM System R10 / BSS R10 ... ... .. ... .. ... ... .. 135 Engineering guidelines .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 145.1 Subcell Load Distribution Active .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 145.2 Subcell Load Distribution Inactive ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 155.3 High Capacity Networks .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 176 Parameters .. .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 186.1 Main controlling parameters . ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 186.2 Additional parameters ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 186.3 Parameters controlling Dynamic OL/UL Subcells .. .. ... .. ... ... .. ... .. ... ... .. 196.4 Value ranges and default values .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 197 References .. .. ... ... .. ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... .. ... ... .. 20A4 XSEIF R2Open InformationUSER DESCRIPTION 2 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceE1 IntroductionThe traffic capacity of a cellular network can be increased by adding morefrequencies or reducing the frequency re-use distance. One approach is toapply a second frequency re-use pattern, using the existing sites, with a tighterfrequency reuse as overlay on the existing pattern. These cells should berestricted in size, making shorter re-use distance possible without causingexcessive co-channel or adjacent channel interference. They are termedoverlaid (OL) subcells, whereas the original cells, now with the OL subcellsassociated, are termed underlaid (UL) subcells. By having more frequenciesper cell, the network capacity is increased.2 Glossary2.1 ConceptsSCLD Subcell load distribution moves connections between thesubcells based on a certain limit of traffic load in the UL subcell.2.2 Abbreviations and AcronymsBCC Base Station Colour CodeBCCH Broadcast Control ChannelBSIC Base Station Identity CodeCHAP Channel Allocation ProfileGPRS General Packet Radio ServiceHSCSD High Speed Circuit Switched DataOL Overlaid (subcell)PDCH Packet Data ChannelSACCH Slow Associated Control ChannelSCLD Subcell Load DistributionSDCCH Standalone Dedicated Control ChannelTA Timing AdvanceTEMS Ericsson GSM Measurement and System Optimisation ToolOpen InformationUSER DESCRIPTION 3 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceETEMS CellPlannerEricsson Cell Planning Prediction ToolTRX TransceiverTSC Training Sequence CodeUL Underlaid (subcell)3 Capabilities3.1 Increased traffic capacityThe fundamental idea with OL/UL subcells is that traffic close to the site ismoved to the OL subcell, while the traffic closer to the cell border is moved tothe UL subcell. By controlling the traffic in this way, the frequencies in theOL subcell can have a tighter reuse.ExampleThe following example shows an application of the basic OL/UL subcell feature.Consider two cells that are located near to each other, cell A containingfrequencies f 1 and f 2 and cell B containing frequencies f 3 and f 4.The traffic intensity in cell A is high. It is decided to assign f 4 to cell A, in orderto solve the capacity problem. However, due to the close vicinity of Cell A andB, this will create interference problems at their respective cell border. In figure1, the solid arrow indicates the carrier signal and the dashed arrow indicates aninterfering signal. Note that only downlink interference from cell B is shown.Open InformationUSER DESCRIPTION 4 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEf1 f2f3f4f4f4f4AFigure 1 The MS using f4 in the vicinity of the cell border experiencesdownlink co-channel interferenceAn OL/UL subcell structure can be used to solve the interference problem.As shown in figure 2, an OL/UL subcell structure is defined for cell A. f 4is assigned to the OL subcell, and f 1 and f 2 to the UL subcell. The totalnumber of frequencies in cell A is still 3. Since f 4 is used in the OL subcell, theconnections using f 4 will experience less downlink co-channel interference,resulting in an improved C/I.Open InformationUSER DESCRIPTION 5 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEf1 f2f3f4f4f4f4AOL ULf4Figure 2 The MSs using f4 are restricted to the OL subcell, where theco-channel interference is limitedThe OL/UL subcell feature can be used to increase the traffic capacity ona system-wide scale. The OL subcell are introduced on a general basisthroughout the network. Due to the smaller size in the OL subcell, a tighterfrequency reuse pattern can be applied to the OL subcell, when comparedwith UL subcell. For example, 3/9 for OL subcells and 4/12 for UL subcells.In this way, the number of frequencies per cell are increased and thus thesystem capacity.3.2 Dynamic OL/UL SubcellsWith ordinary OL/UL subcells (SCLD = OFF), mobile stations within the OLsubcell service area will be served by the OL subcell even if there is a lotof spare capacity in the UL subcell. This is generally undesirable since theOL subcell frequencies (having a tighter re-use pattern and perhaps beingtransmitted at lower output power) may be more vulnerable to interferencethan the frequencies in the UL subcell.To solve this problem Ericsson GSM System offers a feature called DynamicOL/UL Subcells, which aims at keeping the mobile stations connected to theUL subcell. The OL subcell is only used, when the traffic in the UL subcellincreases beyond a certain limit. Secondly, the mobiles closest to the site aremoved to the OL subcell, which means that power control (see User Description,Open InformationUSER DESCRIPTION 6 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEDynamic BTS Power Control and User Description, Dynamic MS PowerControl) are more effective for the OL subcell and less interference is spread.3.3 BCCH in Overlaid SubcellSince the BCCH carrier is non-hopping and does not introduce any of thefrequency diversity or interference diversity gains that hopping channels do, theBCCH carrier should never be used at low signal strength. This would lead tobad perfomance and possibly dropped calls.If Dynamic OL/UL subcells and synthesised frequency hopping is used togetherwith the feature BCCH in Overlaid Subcell, you can improve both the capacityand quality in a tight reuse network, since only mobiles with low pathloss areallowed onto the BCCH carrier. This ensures that the BCCH frequency carriesless interfered traffic and then the BCCH can be planned with a tighter re-use.As a result of this the BCCH can be planned so that it is only carrying traffic atbusy hour. This optimises the utilisation of the BCCH frequency for traffic.Since the hopping channels in the underlaid subcell will be offloaded when theBCCH frequency is used more extensively, the quality is improved on thehopping TCH channels. This will allow more traffic onto these channels. (seeUser Description, BCCH in Overlaid Subcell).Note that the BCCH in the overlaid subcell is still covering the entire celleventhough the TCHs on the BCCH carrier frequency have parameterrestricted coverage.3.4 Multi Band CellIt is possible to configure different frequency bands on different subcells ina subcell structure, in order to have a more integrated network (see UserDescription, Multi Band Cell).4 Technical description4.1 GeneralThe OL and UL subcells share a common Broadcast Control Channel (BCCH),which resides in the UL subcell. Stand Alone Dedicated Control Channels(SDCCHs) may be defined in both OL and UL subcells, but immediateassignment can only be made to the UL subcell. If subcell load distributionis active, SDCCHs can only be defined in the UL subcell. However, this ischanged if the BCCH is used in the overlaid subcell (see User Description,Overlaid/Underlaid Subcells).There is a path loss threshold and a timing advance threshold for each OLsubcell as a criterion to maintain the restricted service area of the OL subcell.Open InformationUSER DESCRIPTION 7 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEAlso, the BTS output power can be set to a different value in the OL subcellcompared to the UL subcell in order to reduce the caused interference.The Dynamic OL/UL subcells feature makes it possible to control the trafficdistribution between the OL and the UL subcell in such a way that the OLsubcell is only used when the traffic load in the UL subcell exceeds a certainthreshold. In addition, the mobiles closest to the site are moved first (from ULto OL subcell).4.2 Algorithm4.2.1 OL/UL subcell change, Subcell Load Distribution inactiveA path loss threshold LOL with a hysteresis LOLHYST and a timing advancethreshold TAOL with a hysteresis TAOLHYST, define the serving area of anOL subcell and control the OL/UL subcell change algorithm in Locating (seeUser Description, Locating).Locating evaluates the conditions for changing subcell every Slow AssociatedControl Channel (SACCH) period and if they are fulfilled a subcell change isrequested. The conditions for changing subcell within a cell are the following:From UL to OL (see figure 3):The downlink path loss L and the filtered timing advance ta shall fulfil thefollowing condition:L ≤ LOL − LOLHYST andta <> LOL + LOLHYST orta ≥ TAOL + TAOLHYSTThe downlink path loss, L, is given by the expression:Open InformationUSER DESCRIPTION 9 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEL = BSTXPWR - rxlev_dlBSTXPWR is the base station output power (at the reference point used byLocating) on all frequencies except the BCCH frequency. It is defined persubcell. If the serving cell is an UL subcell and the currently used channel is onthe BCCH frequency, BSTXPWR is replaced by BSPWR in the expression.BSPWR is the base station output power on the BCCH frequency at thelocating reference point. rxlev_dl (see GSM Technical Specification 05.08) isthe received filtered downlink signal strength value in dBm.If parameter TAOL is set to its maximum value the criterion for changingsubcells is only controlled by the path loss threshold LOL. If parameter LOL isset to its maximum value the criterion for changing subcells is only controlledby the timing advance threshold TAOL. If LOL and TAOL are set to valuessomewhere between their maximum and minimum values, the criterion iscontrolled by both thresholds as described above.4.2.2 OL/UL subcell change, Subcell Load Distribution activeIn every Subcell Load Distribution (SCLD) interval (specified by parameterSCLDTIMEINT) the traffic load in the UL subcells that are active for SubcellLoad Distribution are examined. Each time a maximum number of 16 cells canbe examined, the remaining cells are examined during the next SCLD interval.If the percentage of the total number of idle full rate capable TCHs in an ULsubcell is less than or equal to parameter SCLDLL and the timers of “subcellchange due to bad quality” or “subcell change due to too many intra-cellhandovers” are not activated for the OL subcell, then a subcell change fromthe UL subcell to the OL subcell will be requested, see figure 4. All HSCSD(main and on-demand) channels and all dedicated PDCHs are always countedas busy full rate TCH. On-demand PDCHs are regarded as either idle orbusy depending on the setting of the Exchange property GPRSPRIOUserDescription, Channel Administration.Half rate channels are never counted. Only mobile stations that fulfil thefollowing conditions for LOL and TAOL are allowed to change subcellsL < LOL andta < TAOLMobile stations which have the lowest path loss are selected first. The numberof mobile stations, within a cell, in one SCLD interval, that the BSC will tryto move is given by:int (SCLDLL x (#TCHs )total ) - (#TCHs )idle + 1where int means rounded to the lower integer, #TCHs means the number oftraffic channels, idle or total, in the UL subcell. However, in order to restrictthe network disturbance, the BSC never tries to move more than three mobilestations.Open InformationUSER DESCRIPTION 10 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEAs an example, an UL subcell has a total of 10 TCH and its SCLDLL is set at35%. During a SCLD interval, it has only 1 idle TCH and there is no timeractivated for its OL subcell, therefore, the above criterion are fulfilled and asubcell change, from UL to OL subcell, is requested. From the equation, thenumber of mobiles that will be moved, is int (35% x 10) - 1 + 1 (i.e. 3). Theequation is aiming to return the number of idle TCHs in the UL subcell justabove the SCLDLL limit, i.e. moving the minimum number of mobiles.If the percentage of the total number of idle full rate capable TCHs in the ULsubcell is greater than SCLDUL and the timers of “subcell change due tobad quality” or “subcell change due to too many intra-cell handovers” arenot activated for the UL, a subcell change from the OL subcell to the ULsubcell will be requested. In this case there is no path loss or timing advanceconditions that have to be fulfilled. The mobile stations with the highest pathloss are selected first. The number of mobile stations that the BSC will tryto move is given by:(#TCHs )idle - int (SCLDUL x (#TCHs )total )where int means rounded to the lower integer and the TCHs referred to arethose in the UL subcell. However, the BSC never tries to move more than threemobile stations, within a cell, per SCLD interval.As an example, an UL subcell has a total of 10 TCH and its SCLDUL is setat 55%. During a SCLD interval, it has 9 idle TCH and there is no timeractivated for its UL subcell, therefore, the above criterion are fulfilled and asubcell change, from OL to UL subcell, is requested. From the equation, thenumber of mobiles that will be moved, is 9 - int (55% x 10) (i.e. 4). However, inorder to minimise network disturbance, the BSC will only try to move 3 duringthis interval. The equation is aiming to return the number of idle TCHs in theUL subcell just below the SCLDUL limit, i.e. moving the minimum numberof mobiles, while not exceeding 3.If the number of idle TCHs required for OL to UL subcell change is just onemore than the number of idle TCHs required for UL to OL subcell change therequired number for OL to UL change is automatically increased by one. Thisis to prevent mobile stations from being repeatedly moved back and forthbetween the OL and UL subcell.Open InformationUSER DESCRIPTION 11 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEPercentageof activeTCHsPercentageof idleTCHsSCLDULSCLDLL No subcell change.Subcell change UL to OLSubcell change OL to ULFigure 4 Subcell Load Distribution. When the percentage of idle full ratecapable TCHs in the UL subcell equals or falls below SCLDLL subcell changesfrom the UL to the OL subcell are initiated. When the same percentage exceedsSCLDUL then subcell changes from the OL to the UL subcell are initiated. Inbetween no subcell changes are initiated.Apart from OL to UL subcell change due to Subcell Load Distribution the mobilestation can also be requested to move to the UL subcell because of excessivetiming advance and/or path loss. The following conditions are used:L ≥ LOL + LOLHYST orta ≥ TAOL + TAOLHYSTThis condition is checked by Locating every SACCH period.No SDCCH should be configured in OL subcell, which makes use of SubcellLoad Distribution, since it is only applicable to traffic channels. With SCLDactivated, only assignment to UL is allowed, which makes SDCCH in the OLsubcell inaccessible.Full rate connections as well as half rate connections can be moved by SubcellLoad Distribution. High Speed Circuit Switched Data (HSCSD) connectionscan not be moved, but will remain in the UL subcell.Open InformationUSER DESCRIPTION 12 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceENote that subcell changes that are due to Subcell Load Distribution do notconsider the TINIT timer. However, if the parameters SCLDLL and SCLDULare set appropriately, they will work as an hysteresis for subcell changes dueto subcell load distribution.4.2.3 Handover and assignment to another cellEven if the preferred subcell is OL, in some cases operators would need notto allow direct inter-cell handovers (and assignments to other cells) to the OLsubcell. This is implemented using two new CHAP values (9,10) that arebased on CHAP 0 and CHAP 5, as they represent the most common casesto be considered - BCCH in UL and no Immediate Assignment on TCH.The difference in the CHAPs are for the selection types handling inter-cellhandovers, Assignment to worse cell and Assignment to better cell, in casesof preferred subcell OL. Using these CHAPs, the operator could choose thatin these cases the UL subcell will always be selected (CHAP 9) or always beprioritised (CHAP 10), see User Description, Channel Administration.4.2.4 OL subcell as a last resortNormally, if the UL subcell is preferred and there are no idle channels in theUL subcell, a channel allocation will fail. However, in the event of congestionin the UL subcell it is possible to allocate a channel in the OL subcell as alast resort. This strategy can be chosen through the Channel Administrationfeature by selecting the Channel Allocation Profile 5, 6, 8 or 10 (see UserDescription, Channel Administration).4.2.5 Subcell change due to bad quality and intra-cell handoverIf the criterion for intra-cell handover is fulfilled and the maximum number ofallowed consecutive intra-cell handovers have been executed, a subcell changecan requested to the other subcell, both from the underlaid subcell to theoverlaid subcell and vice versa, based on congestion and the setting of CHAPvalues (see User Description, Intra Cell Handover). At this type of subcellchange, a timer will be set to prevent an immediate subcell change back tothe old subcell. The timer is set to the value of TIHO and the total time duringwhich subcell change will be inhibited becomes TINIT + TIHO.Note that an intra-cell handover can result in a request for a subcell changeafter TINIT, but before TINIT + TIHO has expired.4.2.6 Locating correctionsThe OL subcell and the UL subcell may have different output power. If themobile station is connected to the OL subcell, serving cell measurements arecompensated for the difference in output power between the subcells. This isdone in order to have the same handover borders in the OL subcell as the onesin the UL subcell, see also User Description, Locating.4.2.7 TSC considerationsThe channels in the OL subcell can be assigned a different Training SequenceCode (TSC) from the ones in the UL subcell. The TSC is used by the equaliserOpen InformationUSER DESCRIPTION 13 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEto create a channel model. When configuring an OL subcell network on top ofan existing UL network, it is advisable to reassign the TSCs for the OL subcellsaccording to the OL subcell frequency re-use pattern. Otherwise co-channelsin the OL subcell network might obtain the same TSC, which could makeit difficult for the equalizer to distinguish between these co-channels. TheTraining Sequence Code is set with parameter TSC.4.3 GPRS/EGPRS ImpactsGPRS/EGPRS channels are only allocated in the UL subcell. The reason beingthat the GPRS/EGPRS MS performs cell change by itself, see User Description,GPRS/EGPRS Cell Reselection. Therefore, the system is not controlling thecell change and cannot distribute GPRS/EGPRS MSs between subcells.4.4 Related CountersThe following counters are specifically related to overlaid and underlaidsubcells.Table 1 Statistical Counters for Handover between Overlaid and UnderlaidSubcells (Object Types = CELEVENTS)Counters DescriptionHOAATUL Handover Attempts to Underlaid SubcellHOSUCUL Sucessful Handover Attempts to Underlaid SubcellHOAATOL Handover Attempts to Overlaid SubcellHOSUCOL Sucessful Handover Attempts to Overlaid SubcellIn many situations, e.g. congestion, allocation attempts, connectionestablishment, dropped connections, and etc, there is a corresponding counterfor overlaid to underlaid. For further details, please refer to User Description,Radio Network Statistics.If a cell is not structured in OL/UL subcell, the OL subcell counters are not usedand all the measurements are only done in the UL subcell counters. In the caseof OL/UL subcell, incrementing or decrementing of UL subcell counters, dueto an event in the UL subcell is always done independent of the OL subcellcounters. However, depending on the specific counter pair, incrementing ordecrementing of overlaid subcell counter, due to an event, may or may notaffect the UL subcell counters.4.5 Main changes in Ericsson GSM System R10 / BSS R10Handovers to neighbouring cells’ overlaid subcells are made possibleindependent of the setting of the CS parameter.Two additional CHAP values (9, 10) are introduced.Open InformationUSER DESCRIPTION 14 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEIt is possible to configure different frequency bands in different subcells.The value range of the LOL parameter is extended (0–200).5 Engineering guidelines5.1 Subcell Load Distribution Active5.1.1 Dimensioning of the OL subcellThe difficulty of dimensioning is reduced, when Subcell Load Distribution isactivated (see chapter 5.2.1). This is primarily because the load distributioncan now be controlled by the SCLD parameters, i.e. SCLDLL and SCLDUL,making the setting of TA and pathloss criterion incritical. The cellborder for theOL subcell could be made to coincide with the cellborder for the UL subcellby setting the pathloss and timing advance criteria to the maximum values.Using this setting, the dimensioning is based primarily on the number of TRXsin the OL and UL subcell respectively. There is no trunking loss, as would bethe case, for basic OL/UL subcell, if the OL subcell covered a geographicallysmaller area than the UL subcell.5.1.2 Using BTS and MS Power controlSince the mobiles in the OL subcell generally are closer to the site, it isbeneficial to use MS and BTS power control to reduce interference. Whensubcell load distribution is used, and a subcell change from UL to OL isinitiated, the mobiles closest to the site (lowest pathloss) are moved first, i.e.the mobiles where power control have most impact.One way to use OL/UL and subcell load distribution is to set SCLDLL andSCLDUL to low values, e.g. 20 % and 10 % respectively. The OL subcell isused only when the UL subcell is almost congested, thus taking care of thepeak load. Because of the high load in the cell, the chance of finding mobilesclose to the site is then higher than if the load had been low. Using this settingtogether with power control makes it possible to have an even tighter reuse inthe OL subcell layer.5.1.3 OL/UL subcells together with frequency hoppingThe gain of frequency hopping is reduced with OL/UL subcells. This is becauseof the reduced frequency hopping gain when the available frequencies aredivided between the OL and UL subcell. With Subcell Load Distribution active,frequency hopping can be used, in the following way, assuming that the BCCHplan is good. The OL subcell should have the same cellborder as the ULsubcell. A majority of the available frequencies for the cell are placed in theOL subcell. With this configuration the hopping loss will be minimised whensynthesizer hopping is used in the OL subcell. The OL subcell generally takestraffic closer to the site, which means that BTS and MS power control will havea better effect than if no OL/UL structure were used. The BCCH carrier can notOpen InformationUSER DESCRIPTION 15 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEbe downregulated, but since the UL subcell generally take traffic closer to thecellborder BTS power control would have had little effect.When Subcell Load Distribution is active in the target cell, it is not possible toperform a handover from an OL subcell to another OL subcell (see chapter4.2.3). It is therefore important to dimension the UL subcell, so that it can handleincoming handovers. Also, it is recommended to use Channel Allocation Profile5 or 6 (CHAP = 5 or 6, see chapter 4.2.4) so that the OL subcell can be usedas a last resort if there is congestion in the UL subcell.The possible interactionwith the feature BCCH in Overlaid Subcell introduces new ways of handling theOL/UL feature settings (see User Description, BCCH in Overlaid Subcell).5.2 Subcell Load Distribution Inactive5.2.1 Dimensioning of the OL subcellIn order to protect frequencies in the OL subcell from a low C/I the OL subcellmust be restricted in size. The reduced size will increase C/I in the followingmanner:1 The path loss between interfering cells and the OL subcell increases,i.e. the I part of C/I will decrease.2 The maximum path loss between the serving BTS and the MS in the OLsubcell will decrease, i.e. the C part of C/I will increase. However, in manysituations the BTS output power in the OL subcell must be reduced as wellin order not to cause downlink interference (cell A interfering cell B). Inthis case the downlink C is not increased but the improved C/I comes onlyas a result of a reduced I according to item 1.To determine how small the OL subcell must be made in order to fulfil the C/Irequirements, predictions, using TEMS Cell Planner, or measurements, usingTEMS, may be performed. Normally the OL subcell border has to be moved atleast 5 dB from the original border. In an urban area where C/I fluctuates more,the OL subcell border must be moved even further.Naturally one cannot dimension the OL subcell from C/I considerations alone,one must also make sure that the OL subcell takes traffic. An OL subcell thathas to be made so small that it does not serve any traffic is just a waste ofcapacity. The ideal situation for OL/UL subcells to be applied is a cell wheremuch traffic is generated close to the site. In this case it will be possible to meetthe C/I as well as the traffic requirements.The size of the OL subcell and the number of the TRXs in the OL subcell shouldbe dimensioned in a way that the OL subcell gets congested before the ULsubcell. This is because traffic can "spill over" from the OL subcell to the ULsubcell at congestion in the OL subcell.Note that the channels in the OL subcell will be allocated before the channelsin the UL subcell when subcell load distribution is not used. This means thatthe channels in the UL subcell will be saved for mobile stations that cannotuse the OL subcell.Open InformationUSER DESCRIPTION 16 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceE5.2.2 Path loss thresholdThe path loss threshold LOL is the most important threshold and should alwaysbe used. It guarantees a minimum level of received signal strength for the MSsin the OL subcell and will in most situations also restrict the size of the OLsubcell. In some cases also the timing advance threshold is required to restrictthe OL subcell size, see chapter 5.2.3.The following example illustrates how LOL can be determined:In an existing cell, one of the frequencies causes and suffers from co-channelinterference. It is believed that much of the traffic is generated close to the site.It is decided to split the cell into one OL/UL subcell pair and allocate the badfrequency to the OL subcell. Suppose, with reference to predictions usingTEMS Cell Planner, we wish to reduce BSTXPWR, from 42 dBm to 36 dBm andthat the OL subcell border is also to be moved 8 dB from the original border.Measurements with TEMS show that handovers between the UL subcell and itsneighbours occur at approximately - 90 dBm, which gives:LOL = 42 - ( - 90) - 8 = 124.The recommended value of LOLHYST is 2 dB (default setting is 3). Notethat the hysteresis corridor will be twice as big as the value of LOLHYST. IfLOLHYST = 2 dB the hysteresis corridor will become 4 dB wide.5.2.3 Timing advance thresholdOccasionally the topography of the cell is such that the path loss is particularlylow in certain parts of the cell, for example over water, see e.g.figure 3. Tomaintain the intended small size of the OL subcell even in such cases thereis the additional condition that the timing advance must not be greater thanTAOL in the OL subcell.The resolution of timing advance is one bit period. This means that oneunit of TAOL corresponds to about 550 m. A rough setting of TAOL can beobtained by measuring on a map. If a more accurate setting is desired, TEMSmeasurements of TA along the OL/UL border can be performed.The recommended value of TAOLHYST is 0. This could lead to ping-ponghandovers between the UL and the OL subcell in a small region where theta calculation might be ambiguous. If the ta threshold is used only in smallparts of the cell this will create few problems. If TAOLHYST is set to 1, thehysteresis corridor would become 1 km wide, a value which in many situationswould be too large.5.2.4 OL/UL subcells together with frequency hoppingThe gain of frequency hopping is reduced with OL/UL subcells. The reasonfor this is that when splitting frequencies into OL/UL subcells, the amount offrequencies in each subcell will be reduced. This means that the amount offrequencies over which frequency hopping can be performed is decreased andthus that the gain of frequency hopping is reduced. Frequency hopping is aOpen InformationUSER DESCRIPTION 17 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceEvery important feature providing frequency diversity and interference averaging,see User Description, Frequency Hopping. If the operator has access to a widefrequency band (about 15 MHz or more) the benefits of frequency hopping canbe reaped in both subcells, and a combination of OL/UL subcells and frequencyhopping may be employed.5.2.5 Trunking considerationsWithin a cellular network covered by OL subcells, it is possible to use theavailable channels in both the OL and the UL subcells. However, in thoseparts of the cellular network, which are covered by the UL subcells but not bythe OL subcells, only the channels in the UL subcells are accessible. Thus,trunking efficiency will be reduced in that part of the UL subcells not coveredby the OL subcells. In the area covered by both subcells, there is no trunkingloss, since all channels can be used.The trunking loss can be reduced by allowing channel allocation in OL whenthere is congestion in UL, even if the pathloss and/or timing advance criteriaare not fulfilled for a channel allocation in OL. This is achieved by the featureChannel Administration (see User Description, Channel Administration).5.3 High Capacity NetworksIn a 1/1 or 1/3 (Frequency Load Planning, FLP) networks it is recommended touse OL/UL. As syntesiser hopping must be used in FLP networks, the BCCHfrequency and TCH frequencies are normally placed in different channelgroups. By allocating the TCH channel group to the OL subcell, statistics will becollected separately for the BCCH frequency and the TCH frequencies. This isvaluable when evaluating the performance of a cell.The OL/UL subcell feature will also give an effective tool to distribute the trafficbetween the channel groups. The traffic distribution can be controlled by eitherlimiting the size of the OL subcell with the settings of TAOL and LOL and/or byusing subcell load distribution by settingSCLDLL and SCLDUL. If the BCCHreuse is very tight then the BCCH channels should only to be used as asalvation channel. To achieve this TAOL and LOL should be set to maximumand high values on SCLDLL and SCLDUL should be used. If the BCCH reuseis more relaxed thenSCLDLL and SCLDUL should be set to low values. Thiswill result in that the TCH channel group will only take traffic when the trafficlimit is exceeded in the BCCH channel group. The traffic which will be directedto the OL subcell will be the traffic nearest to the BTS and this will lead to thatthe BCCH channel group will be prioritised at the cell border.It is also recommended to allow channel allocation in OL when UL is congested,(see User Description, Channel Administration), only if the OL subcell is large.Open InformationUSER DESCRIPTION 18 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceE6 Parameters6.1 Main controlling parametersSCTYPE identifies the subcell type, OL or UL, within a cell.LOL is the path loss threshold for the serving area of the OL subcell within acell. This parameter is set per OL subcell.TAOL is the timing advance threshold for the serving area of the OL subcellwithin a cell. This parameter is set per OL subcell.LOLHYST is the path loss hysteresis for the serving area of the OL subcellwithin a cell. This parameter is set per OL subcell.TAOLHYST is the timing advance hysteresis for the serving area of the OLsubcell within a cell. This parameter is set per OL subcell.The OL/UL subcell structure can be created per cell.6.2 Additional parametersBSTXPWR is the base station output power at the reference point forthe locating algorithm (see User Description, Locating) on the non-BCCHfrequencies within a cell. This parameter is set per subcell.BSPWR is the base station output power at the reference point for the locatingalgorithm (see User Description, Locating) on the BCCH frequency within acell. This parameter is set per cell.TSC is the Training Sequence Code for the specified subcell within a cell. Thisparameter is set per subcell, but it is not available for cells without an OL/ULsubcell structure.CS indicates if a cell shares the same site as its neighbour. This parameteris set per neighbouring cell relation.MAXIHO is the maximum number of consecutive intra-cell handovers. Thisparameter is set per subcell.PTIMBQ is the penalty time of the abandoned cell, when bad quality handoveroccurs. This parameter is set per cell.TINIT is the minimum time before handover is allowed on an initial call or afterhandover. This parameter is set per BSC.TIHO is the intra-cell handover inhibition timer, during which intra-cell handoveris not allowed. This parameter is set per subcell.Open InformationUSER DESCRIPTION 19 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceE6.3 Parameters controlling Dynamic OL/UL SubcellsSCLD is used to activate subcell load distribution in a cell. It is set per cell.SCLDTIMEINT defines the cycle time of the subcell load monitoring. It is setper BSC and can only be set in multiples of 100 ms.SCLDLL defines the percentage of idle full rate capable TCHs in the UL subcellat or below which subcell change from the UL subcell to the OL subcell isattempted. It is set per cell.SCLDUL defines the percentage of idle full rate capable TCHs in the ULsubcell above which subcell change from the OL subcell to the UL subcell isattempted. It is set per cell.GPRSPRIO is a BSC Exchange property that controls whether on-demandPDCHs shall be treated as idle or busy when calculating the percentage of idlechannels (see the entire parameter desciption in User Description, ChannelAdministration).6.4 Value ranges and default valuesTable 2 Controlling parametersParameternameDefault value RecommendedvalueValue range UnitSCTYPE - UL, OLLOL - 0 to 200 dBTAOL - 0 to 61 bit periodsLOLHYST 3 2 0 to 63 dBTAOLHYST 0 0 0 to 61 bit periodsBSTXPWR - 0 to 80 dBmBSPWR - 0 to 80 dBmTSC BCC (1) 0 to 7CS NO YES, NOMAXIHO 3 FH: 2, no FH: 3 0 to 15PTIMBQ 10 15 0 to 600 dBTINIT 10 10 0 to 120 SACCHperiodTIHO 10 10 0 to 60 sec(1) Initially, the TSC is defined by the BCC in the BSIC for the cell.Parameters controlling Dynamic OL/UL SubcellsOpen InformationUSER DESCRIPTION 20 ( 20 )EAB/RNR/TG Petter Edström +46858533195 66/1553-HSC 103 12/4 UenEAB/RNR/TGC (Lennart Blixt) 2002-09-24 APrepared (also subject responsible if other) NoApproved Checked Date Rev ReferenceETable 3 Parameters controlling Dynamic OL/UL SubcellsParameternameDefaultvalueRecommendedvalueValue range UnitSCLD OFF ON, OFFSCLDTIMEINT 100 100 to 1000 msSCLDLL 20 0 to 99 %SCLDUL 30 0 to 100 %7 References1 User Description, Locating2 User Description, Channel Administration3 GSM Technical Specification 05.084 User Description, Assignment to Other Cell5 User Description, Intra Cell Handover6 User Description, Frequency Hopping7 User Description, Radio Network Statistics8 User Description, Dynamic BTS Power Control9 User Description, Dynamic MS Power Control10 User Description, GPRS/EGPRS Cell Reselection11 User Description, BCCH in Overlaid Subcell12 User Description, Multi Band Cell