Cell Planning 2

7/30/2019 Cell Planning 2

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FADINGS

signal level (dB)

log (distance)

global mean value

log normal fadinglocal mean valueslow fadingshadowinglong-term fading

rayleigh fadingfast fadingshort-term fading

so many names

to make lifeworst!


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FAST FADING

signal level (dB)

log (distance)

present due to the fact that the mobile antenna is lowerthan the surrounding structures such as trees and buildings.

peak-to-peak distance is ~ lambda/2 (in GSM ~ 17 cm) affects the signal quality and can lead to signal level belowthe receiver sensitivity.

SOLUTIONS: use more power at the transmitter (providing a fading

margin). use space diversity.


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SLOW FADING

signal level (dB)

log (distance)

if we smooth out the fast fading, the signal variationreceived is called the local mean or the slow fading. caused by obstructions near the mobile such asbuildings, bridges and trees and this may cause a rapid

change of the local mean (in the range of 5 to 50 meters). because slow fading reduces the average strengthreceived, the total coverage from the transmitter is reduced.

SOLUTION: fading margin must be used.


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INTERFERENCE

co-channel interference

adjacent channel interferenceCo-channel interference is the term used for the interference in a cellby carriers with the same frequency present in other cells.

Adjacent carrier frequencies, i.e. frequencies shifted +/- 200 kHz with

respect to the carrier, can not be allowed to have too strong signalstrengths either. Even though they are at different frequencies, partof the signal can interfere with the wanted carriers signal and causequality problems.

f1f1

co-channel

wanted carrier

adjacent

carrier


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CO-CHANNEL INTERFERENCE

CI

C

I

C/I > 0 dB

dB Carrier, f1 Interferer, f1

distanceGSM Specification: C/I => 9 dBEricsson Planning Criterion:C/I => 12 dB (without frequency hopping)C/I => 9 dB (with frequency hopping)


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ADJACENT CHANNEL INTERFERENCE

CA

A

C

C/A< 0 dB

dB Carrier, f1 Adjacent, f2f2=f1 +/- 200 kHz

distanceGSM Specification: C/A > -9 dBsince we could not cell plan a negative valueEricsson Planning Criterion:C/A > 3 dB


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ISI

InterSymbol Interference caused by excessive time dispersion. it may be present in all cell re-use pattern.

it can be thought of as a co-channel interference. in this case, the interferer is a time delayed reflectionof the wanted carrier. GSM specification: C/R > 9 dB however, if the time delay is smaller than 15microseconds, i.e. 4 bits or approximately 4.4 km, the

equalizer can solve the problem.

D0

D1

D2


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TRAFFIC THEORY Traffic and Channel Dimensioning

Traffic theory attempts to obtain useful estimates of the numberof channels needed in a cell...

= HOW MANY CUSTOMERS?= HOW LONG WILL THEY TALK?= WHEN?

FACTORS AFFECTING THE CELLULAR SYSTEM CAPACITY: The number of channels available for voice and/or data.

The amount of traffic the subscribers are generating. The grade of service the subscribers are encountering in the system


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The number of channels available for voice and/or data.

Assume 1 cell has 2 carriers:2 x 8 - 2 = 14

14 traffic channels2 physical channels are

needed for signalling


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The amount of traffic the subscribers are generating.

What is traffic? the usage of channels

holding time per time unit

the number of call hours per hour

measured in the unit Erlang (E)


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1 Erlang = 1 call that last 1 hour!

...studies show that the averagetraffic per subscriber during thebusy hour is typically 15 - 20 mE...

Typical actual values:

Philippines (Smart E-TACS)7 mE/subscriber - Metro Manila8 mE/subscriber - Provincial

Malaysia and Sweden25 mE/subscriber


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visualize 15 mE !1 E = 1 hour of use15 mE = ? hour of use

15 mE / 1 E = 0.015~ 1.5% of 60 min = 0.9 min x 60 sec15 mE = 54 seconds of use


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The grade of service the subscribers are encountering in the system.

How much trafficcan one cell carry?

That depends on the number of

traffic channels and the acceptableprobability that the system is

congested, the so called

Grade of Service (GoS)...


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Grade of Serviceis the

Grade of NO SERVICE !

- unsuccessful call set-up- GoS = 2% means

98% can make a call2% blocking probability


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Alien !!!


Erlangs B-Model - loss system

no queues number of subscribers much higher than number of traffic channels no dedicated (reserved) traffic channels Poisson distributed (random) traffic blocked calls abandon the callattempt immediately


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Erlangs B-Model relates: number of traffic channels, n the GoS

the traffic offered, A

Example:2 carriers

14 TCHGoS = 2%from the Erlang Table...Traffic Offered, A = 8.2003 Erlangs


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In GSM, a call goes through two different devices.

TCH & SDCCH

SDCCH procedures: location updating periodic registration IMSI attach IMSI detach call setup SMS (Short Message Services) facsimile other supplementary services

SDCCH TCH


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Ericsson Rule on GoS Dimensioning:

GoSSDCCH


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CHANNEL UTILIZATION (EFFICIENCY)

VS


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CHANNEL UTILIZATION (EFFICIENCY)

VS

To calculate the channel utilization, thetraffic offered is reduced by the GoS (yieldingthe traffic served), and dividing that valueby the number of channels.

Traffic Offered - GoS (Traffic Offered)Channel Utilization =

Number of Channels


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SITE EQUIPMENT

BSC

BTS

Base Station System (BSS)

The BSS consists of a Base Station Controller (BSC) with a numberof base stations connected to it. The BSS is mainly responsible forall radio related functions in the system. In the GSM specifications, thedetonation BTS (Base Transceiver Station) is used for the base station.

site equipment


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SITE REQUIREMENTS

Permits

Access Roads

Material Transport

and Storage Space Requirements

Antenna SupportStructures

AC Mains Supply

Transmission Access

Antenna Feeder Routes


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RBS EQUIPMENT

EricssonNokiaNortelLucent

MotorolaAlcatel


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COMBINERS

transmitter 2

transmitter 3

transmitter n

transmitter 1

combiner

Combiners are needed to enable more thanone transmitter to be connected to one

common transmitting antenna.

In GSM, two different TX combiners can beused -

FILTER COMBINER HYBRID COMBINER


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SENSITIVITY

BTScabinet Feeder & Jumpers ALNA

Without ALNA

RX ref point 2

With ALNA

RX ref point 1

System Cell Planning Worst CaseSensitivity SensitivityGSM900 - 107 dBm - 105 dBmGSM1800 with ALNA - 109 dBm - 107 dBmGSM1800 w/o ALNA - 106 dBm - 104 dBm

Base station receiver sensitivityValid for both Ericssons RBS2000 and RBS200/205

Micro Base Station: Cell Planning Power = 1.6W, 32 dBmWorst Case Sensitivity = - 104 dBm

Base Station


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SENSITIVITY

System MS Power Cell Planning Worst CaseClass Power PowerGSM900 2 39 dBm (8W) 37 dBmGSM900 3 37 dBm (5W) 35 dBmGSM900 4 (handheld) 33 dBm (2W) 31 dBmGSM900 5 (handheld) 29 dBm (0.8W) 27 dBm

GSM1800 1 30 dBm (1W) 28 dBmGSM1800 2 24 dBm (0.25W) 22 dBm

Mobile Station Power Classes

Mobile Station Reference Sensitivity

System MS Type Cell Planning Worst CaseSensitivity Sensitivity

GSM900 Handheld - 104 dBm - 102 dBmGSM900 All other types - 106 dBm - 104 dBmGSM1800 Handheld - 102 dBm - 100 dBm

No loss or antenna gain should be used for the MSs.

MS antenna gain: 0 dBi


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ANTENNAS

Basic Antenna Types

Omnidirectional Antennas Unidirectional Antennas

Special Antennas

Multi Antenna Systems

Diversity

Space Diversity

Polarization Diversity

Antenna Tilt


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DIVERSITY

There is a need for receiver diversity in cellular systemsto improve the uplink.

Space Diversity

TX1/RXA TX1/RXA

BTS Equipment

CommonTX/RXAntenna

dd

Horizontal Separation, dd

for diversity = 12-18 (wavelength)

for isolation = 30 dB = 2 (wavelength)[antennas with 65 degrees beamwidth,

all gain values]


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DIVERSITY


Polarization Diversity using dual-polarized antennas

vertical + horizontal polarization +/- 45 degrees polarization

vertical

array

horizontalarray

antennahousing

connectors

feeders

+45degrees

- 45degrees


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DIVERSITY


Polarization Diversity using dual-polarized antennas

1.5 dB downlink loss

TX1/RXA TX1/RXA

Required isolation >30 dB between

the two antenna parts...


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DIVERSITY


SPACE DIVERSITYVSPOLARIZATION DIVERSITY


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ANTENNA TILT

When the antenna is mounted vertically,the main lobe of the antenna radiationpattern will follow a horizontal linestarting at the centerpoint of the antenna.


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ANTENNA TILT

For reasons, such as co-channel interferenceand time dispersion problems, it can be interestingto tilt the antenna, and let the main lobe point

a few degrees downward.


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NOMINAL CELL PLAN

Traffic and Coverage Analysis

Nominal Cell Plan

Surveys

System Design

Implementation

System Tuning

TRAFFIC DATA

Based on ERICSSON

Initial PlanningSystem Growth

cell database stationlocations

channelallocations


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Cell Planning 2

Documents

Transcript of Cell Planning 2