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3G Radio Network PlanningManaging Cell Breathing
Presented by
Peter GouldConsulting Services Director
Multiple Access Communications [email protected]
IIR Cell Planning Technical Forum, Berkeley Court Hotel, Dublin5 July 2001
Contents
� What is cell breathing?� Load balancing.� Using cell overlap to avoid coverage holes.� Call admission control.� Call blocking.� 3G radio network planning tools.� Network planning example.
What is Cell Breathing?
� In CDMA systems all mobiles can use the same carrier frequency at the same time.
� This means that there will be interference between users in the same cell and in neighbouring cells.
� The CDMA spreading and despreading processes allow this interference to be suppressed to some degree.
What is Cell Breathing?
� The level of suppression is termed the system processing gain.
� The processing gain can be defined as
� The processing gain will vary according to the service.
Period ChipPeriod Bit
Rate Data UserRate ChipCDMA Gain Processing ==
What is Cell Breathing?
� As the loading within a cell is increased, the BS receiver noise floor appears to rise.
� The mobiles must transmit additional power to overcome the increased interference.
� As a result the maximum path loss that can be tolerated within a cell is decreased and the cell effectively shrinks.
Load Balancing
� Cell breathing provides a degree of load balancing.
� As a cell becomes more heavily loaded it becomes smaller.
� This has the effect of shedding users around the cell boundary to more lightly loaded neighbouring cells.
Load BalancingLightly Loaded
Central CellHeavily Loaded
Central Cell
Mobiles on the cell perimeter are shed to neighbouring cells
Planning the Cell Overlap
� However, it is important to plan for sufficient cell overlap to ensure that coverage holes do not develop.
Coverage Hole
Call Admission Control
� The extent of cell breathing can be limited through the use of call admission control (CAC).
� The CAC mechanism is used to decide when a new call can be accepted.
� Schemes that are based on the measured noise rise can be used to set the minimum cell size.
Call Admission Control
� Any new calls will be blocked once the interference reaches a certain level.
05
1015202530
0 20 40 60 80 100Number of Users
Cel
l Noi
se R
ise
(dB) CAC will block calls
once the noise rise reaches 6dB (75% load)
Network Planning
� From this we can see that it is important to consider both network coverage and call blocking when planning a CDMA network.
� Detailed network planning requires a specialised CDMA planning tool.
� These tools use traffic information and propagation predictions to determine the coverage of the CDMA network.
3G Network Planning Tools
Propagation Prediction
Engine
Graphical User
Interface
3G Post Processing
ToolTraffic Data
Service Information
3G Network Planning Tools
� Most 3G network planning tools utilise the �power control loop� method.
� Analytical techniques can also be used, but these are slow when the traffic load is high.
� It is important for the tool to consider call blocking as well as network coverage.
� The tools can also be used to predict the soft-handover regions.
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Planning Example
Using MAC Ltd�s NP WorkPlace Planning Tool and MACcdma Analysis
Tool
Received Signal Strength Prediction
Three-sectored rooftop macrocell
3G CDMA network consisting of five rooftop macrocellular BSs
Two-sectored rooftop macrocell
Service Profile
0.0260.80.05384High-rate data
0.0260.80.15144Medium-rate data
1.0000.50.812.2Speech
Symmetry (UL/DL)
Source Activity
Service Penetration
Bit Rate (kb/s)Service Type
Mobile Transmit PowerSpeech ServiceCDMA post-processing
tool is used to determine the mobile transmit power at each point within the network
Mobile Transmit Power384kb/s Data ServiceThe mobile transmit power
will depend on the service that the subscriber is trying to access.
Call BlockingAs we have seen it is also important to consider call blocking as well as coverage.
Downlink Ec/IoThe quality of the downlink pilot signal should also be analysed.
Traffic MapAs the network subscriber base grows traffic peaks and ridges may occur.
This will have an impact on the mobile transmit power and the call blocking.
MS Transmit Power
Speech Service � uniform traffic
Speech Service � non-uniform traffic
Call Blocking
Speech Service � non-uniform traffic
384kb/s Data Service � non-uniform traffic
Adding MicrocellsReceived Signal Strength for Microcells OnlyMicrocells can be added to
the network to accommodate the traffic peaks.
This will decrease the required mobile transmit power in this area.
MS Transmit PowerWith Microcells
Without Microcells
Call BlockingSpeech ServiceThe addition of the
microcells will also decrease the blocking for the speech service.
However, we must also consider the blocking for the data services.
Call Blocking
144 kb/s Data384 kb/s Data
Call Blocking for 4× Increase in Traffic
Speech384 kb/s Data
Conclusions
� Careful planning is required to ensure that cell breathing does not generate coverage holes in a CDMA network.
� Good traffic forecasts are required.� Call admission control can be used to limit
the extent of cell breathing.� However this will lead to call blocking.� Therefore it is important to consider call
blocking in the network planning process.
