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