RF Planning Principles and Concepts
Housam Al-Houasmi
16-May -2005
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Soft Capacity
If Outer cells are lightly loaded Centre cell experiences to low interference Margin for capacity increase
Soft Capacity
Equally loaded cells Less interference in the neighboring cells--> higher capacity in the m iddle
Single Frequency Other Mobiles create background noise ! High Interference reduces cell capacity
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Noise Rise & Cell Loading
• All connections generate noise
• More users Higher noise rise
• Cell capacity limited by noise rise
Pole capacity is theoretical maximum cell capacity
OR …… 100% Loading point
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Noise Rise & Cell Loading
Uplink noise rise Design Level……as % of pole capacity
Average: 3dB noise rise 50%
Maximum: 6dB noise rise 75%
Noise rise = - 10 * Log (1 – Load)
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Noise Rise & Cell Loading
Uplink• All handsets typically transmit maximum 21dBm power• Noise rise and cell capacity limited by allowable noise rise
Downlink• Typical 20W downlink power per cell• Users admitted to cell based upon power requirements• Also must be OVSF codes available• Noise rise limited to 20W power transmitted• High data rate user at cell edge may require 5W
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Variable Cell Coverage(Cell Breathing) Range
Loading / Noise Rise
Increase Users in Cell
Increase in Cell loading • Increased noise rise• Reduced DL power per user
Reduction in Range & Coverage holes
Coverage / Capacity Trade-Off
Reduced coverage at high loadingCoverage holes increase at higher rates
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Uplink / Downlink Range
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60
number of voice users
Cel
l ran
ge
(km
)
UPLINK
DOWNLINK
Total DL Pwr / cell = 20W
UL limited
DL limited
• Low load – UL limited
• Increasing load reduces cell range
due to noise rise
• TMA increases UL range (blue dotted line)
• At 20W per cell – DL limited
• DL range then decreases rapidly
• STTD improves Downlink (red dotted line)
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Cell Range / Service Coverage
Cell Range dependant upon:• Data rate • Cell loading• Noise rise• Quality of service
Range limits• UL limited at low load• DL limited at high load
32kbps
64kbps
384kbps
range
load
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ACK
ACK
Initial AccessPilot Power
Control the Power to:Control the Power to: Transmit power as low as possible,
Minimise the interference, but ensure Quality of Service.
Ensure power received at Node B is same for all UEs.
Minimise the “near-far” effect in order to increase the capacity.
Power ControlPower control is THE most important function in a CDMA Power control is THE most important function in a CDMA
systemsystem
CDMA systems are limited by interferenceCDMA systems are limited by interference!!
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F-Factor & Orthogonality
Noise and interference from all other cells
At Node B, Uplink F-factor = noise from own cell Noise from all other cells
DimensioningCalculate capacity of isolated cellEg, f=0.5, then capacity reduced by 50%
100 subs50 subs
Example100 voice subscribers in isolated cellReduced to 50 voice subs per cellIn uniformly loaded network
50 subs50 subs
50 subs50 subs
50 subs
50 subs
Downlink F-factor output from planning tool
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Eb/No Curves
Eb/No values are critical to modelling system performance
Large numbers of curves embedded in modelling tools
Eb/No curves generated based on:
- Bit Rate
- Required BER, BLER, or FER%
- User Speed
- Delay Spread profile (No. of rays)
- Ray imbalance
Voice ITU Vehicular Model A Eb/No vs BER
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Rx Eb/No (dB)
BE
R
3km/hr (2 ant)
50km/hr (2 ant)
120km/hr (2 ant)
3km/hr (1 ant)
50km/hr (1 ant)
120km/hr (1 ant)
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BSNode B
Soft Handover
MS
BSNode B
Soft Handover - UE connected to two or
more cells within SHO threshold window
Softer Handover – UE connected to cells of
same Node B
Produces UL & DL system gain
Gain due to lower Eb/No requirement
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BSNode B
Soft Handover
MS
BSNode B
Overhead on DL power, DL channels
Downlink noise rise and equipment
increases
Typically expect 40% soft handover in a tri-
sector system
Increase in Channel Elements and
Transmission capacity
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Summary Points
Voice and data services• Voice AMR and data up to 384kbit/s • Voice and data users load the system differently• Asymmetric uplink and downlink• Delay tolerant packet data
Variable Cell Capacity• Capacity of a cell is dependant upon RF conditions• Soft – NOT hard blocking• Interference / noise rise limited system• Capacity should not be limited by equipment
Varying Cell Range• Different cell range for Uplink and Downlink• Coverage dependant on bearer rate• Cell shrinkage as loading increases