UMTS Planning Issues.ppt

UMTS Radio Planning Issues

*Radio Planning Issues

Planning RequirementsFig 1.CoverageCapacityQuality

Cell Planning


Traditional Cell PlanningFig 2.


W-CDMA Cellular Planning PrinciplesFig 3.Spread signals from same and adjacent cells contribute to interference levels -Good power control required -Capacity of each cell needs planningThis interference remains spread on despreading wanted signal, unless same spreading codes are used, or poor correlation characteristics exist -Code Planning Required.


Soft Handover RegionsFig 4.Mobiles may be served by more than one base station site in soft handover (shaded) areasContinuous coverage should be maintained (if required) under all load conditionsThe combining process enhances the signal in soft handover


Cell BreathingFig 5.Effective range of cell is reduced on higher loading due to interference caused by additional channelsAdjacent cells also breatheSoft handover region reduces

Interference Effects


Interference, Capacity and CoverageFig 6.Need to control:PowerRange (coverage)Processing Gain/Spreading Factor per userOverall loading


Multi-path EffectFig 7.By delaying code generation in the Rake Receiver, multi-path can be used to enhance recovered signal.


Interference SharingFig 8.


LimitationsFig 9.Note that for a 2 Mbps service, three codes would be used


User Data Rates and Number of UsersFig 10.Total capacity (Users x User Rates) is not constant due to dimensioning and also the greater control overhead required for more lower rate users

Reducing Interference / Increasing Capacity


SectorisationFig 11.


Smart AntennasFig 12.Multiple beams can be generated for multiple usersCo-Channel interference in Uplink and Downlink is reducedRange increased due to higher antenna gainCapacity increased due to reduced co-channel interference


Multi-Carrier CellsFig 13.Adjacent channel interference is minimised by co-locating and using same antennas.Different operators using adjacent frequency bands would benefit from co-location to reduce adjacent channel interference


Setting the Carrier SpacingFig 14.Carrier spacing can be set in steps of 200kHz within band to minimise adjacent channel interferenceOperators can minimise adjacent channel interference from their own carriers by co-location (hence spacing can be reduced in order to maximise spacing between operators)


The Layered ArchitectureFig 15.Different Carrier Frequencies may be employed at different layers (hard handovers can be used)Lower range, higher bit rate services may be provided by TDD mode (eg: office environments)

Co-Planning


GSM Co-Planning Range ComparisonsFig 16.


Using Existing 2G SitesFig 17.


Coverage AreasFig 18.

Radio Planning and Simulations


Planning ToolsFig 19.


W-CDMA Planning Considerations - SummaryFig 20.Cellular structure usedSame frequency can be used in each cellCodes need to be planned to prevent co-channel interference (64 groups to choose from)In general, the greater the bit rate per user, the lower the number of users per cellGreater cell range gives reduced capacity (and vice versa) for a given powerThe greater the instantaneous cell usage, the smaller the effective cell range (cell breathing)Interference decreases range and/or capacity for a given powerOverall system noise/interference must be kept as low as possibleInterference reducing techniques may be used Diversity Multi user detection Smart antennas RepeatersIncreased downlink power gives increased capacity only to a certain limitPlanning may use: more than one frequency for capacity or coverage purposes (eg: hierarchical cells) GSM/EDGE to offer more complete coverage around UMTS IslandsTDD mode suited to shorter range (and possibly higher data rates)FDD mode suited to longer rangeAsymmetric services must be planned for

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UMTS Planning Issues.ppt