2 RF Activities (2)

8/12/2019 2 RF Activities (2)

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15/7/05 1Company Confidential

Site Evaluation

Frequency Planning

BTS Installation and Commissioning

RF Coverage Verification

OptimizationCompetitive Comparison

Interference Management

RF Activities in Cellular Systems




Site

Evaluation RF PlanningInstallation

CommissionVerification

Build-Out & Turn-up

Site Roll out Coverage Verification

Optimization Trouble-

shooting

Network

Expansion

Fraud

Detection

In Service

Network Optimization Competitive Comparison

Interference

Management

Continous

RF Activities ApplicationSegments




Coverage Prediction

Frequency Planning

Prediction Tool

Band Clearance

Test Transmission

RF Coverage Verification

Optimization

Troubleshooting

Competitive AnalysisInterference Monitoring

Prediction Tool Modelling

Drive Testing

Commissioning

Maintenance

Trouble Shooting

BTS Testing

Despatch Inspection

Quality Assurance

Troubleshooting

Repairs

MS Testing

Tools

Tools for RF Activities




Search Area

Selection

Site PhysicalQualification

Coverage

Prediction

Band

ClearanceTest

Transmission

Reject

Acquire

Action Steps Site Evaluation




Study of Contour / City Map.

Identifying potential search zones.

Correlating with nearby existing sites.

Drive/Walk through physical Land

Survey.

Search Area Selection




Identifying Potential Sites in Search zone.

Physical verification of the infrastructure. Major obstacles around.

Future potential of major obstacles.

LOS to other sites.

Capturing photographs.

Logging GPS coordinates (Lat,Long,Alt).

Site Physical Qualification




Uses Prediction Software tool to estimate coverage

Software has electrical map and the city contour information

Parameters like frequency,power,antenna parameters,height,

etc are fed to the software

Based on the city model and these parameters the tool

estimates the coverage area .

Data for all sites are fed to estimate the level of interference.

RF Coverage Prediction




WORK

STATION PLOTTER

Prediction Tool

RF Planning




The data available after test transmission is analyzed bythe measurement analysis system.This system consists

of a work station and a plotter.The work station has

software which contains the map of the geographical

area to covered by the network.This map is accurate and

is in terms of earth coordinates. The test transmissiondata is fed to this work station.The work station software

then correlates this data with the map and plots out the

coverage on the map.The coverage level could be preset

in zones of various color like good,average,poor and no-

coverage.With this map representation the sitescapability is determined




Reliability of Prediction Tool

Prediction tool uses either area- to - area or point-to-point prediction models.

Area-to-Area are based on prediction models like HATA,Walfish,etc. These prediction

tools may give a standard deviation from later actual measured coverage in the range

of 12 - 14 dB and above.

Point-to-Point model based prediction tool are specific for a particular terrain and

hence are more accurate and will have a standard deviation of 7-8 dBs and isgenerally accepted.

Prediction tool which deviates from actual measured coverage by 2-3 db over 90%

predicted area is considered to be excellent. This level of accuracy can only be

maintained by consistently modeling the planning tool.

RF Coverage prediction




High cost of installing base stations

Are clear bands really free of interference?

Minimize risk by assessing interference before committing funds

=

Band Clearance




The cost and effort involved in developing cell sites is extremely high. Band

clearing can play a critical role in the site qualification process.

The goal of band clearing is to minimize the risk of interference and tounderstand the signal environment before committing funds to develop the

site. Many factors drive the decision to choose one site over another: real

estate issues, accessibility, maintenance issues, RF propagation, etc.

Risk of interference should be a deciding factor when choosing betweenmultiple candidate sites. Lower risk implies that less time will be spent

combating interference after the network has been turned up. Minimizing

interference will improve network performance and quality of service.

Even when a site has already been committed to, or there is no choice, it iscritical to make the measurements necessary characterize the signal

environment in order to understand the risk and types of interference. This

process will greatly simplify the job of dealing with interference after network

turn-up.




Characterize RF signal environment

In-Band and adjacent bands Long term monitoring

Noise Floor Characteristics

Determine types and sources of potential interference both in

uplink and downlink bands.

Minimize / Understand risk of expensive interference problems

Band Clearance




GP-IB

Spectrum Analyzer

Antenna

PC Controller

System

GPS Receiver

RS-232

Band Clearance




Power Statistics

Estimate Probability of Interference Noise Floor Characteristics

Logging of Signals in the Band

Channel Occupancy

Band Clearance




In order to best understand the signal environment and assess the risk of interference it is

necessary to make statistical measurements of power over a long period of time.

The power statistics are used to estimate the probability of interference in each channel.These probabilities can be used to compare prospective sites based on interference risk.

Since these measurements are channelized they can also be used as an aid in frequency

planning.

The local noise floor can vary from site to site. Various sources of broadband interference will

have an effect on the level of noise at a given location.

Characterization of the noise floor prior to turn-up will help define power settings required to

achieve a desired signal-to-noise ratio. It can also indicate sites where the noise floor may be

excessively high. Noise floor characterization is particularly important for CDMA systems.

Signal logging is done to get a record (frequency and power) of signals present in the band.

Channel occupancy can characterize the usage pattern of signals in the band and possibly

help to define a frequency plan that can work with existing signals.

Again, long-term monitoring is key to getting the best results.




Measure test transmitter signal strength as a

function of location.

Generate Coverage Map

Evaluate foliage and shadowing effects.Help set modeling parameters in RF planning

software.

Calibrate planning software tool.

Test Transmission




1. Test Transmitter 2. Drive System

Two Components

BTS

Simulator

Power

Amplifier

Test Transmission




The typical configuration for a pre-installation RF coverage measurement

system has two major components -- a transportable signal source and a

drive system.

The signal source is placed at the location of the prospective cell site. The

transmitter is elevated to the proposed antenna height of the cell site, often

using a scissor lift or a crane. It may be desirable to execute the drive test

with various antenna heights. Initial measurements are made with a

continuous wave (CW) signal. Typically CW testing provides adequate datafor pre-installation coverage assessment.

In some cases a modulated signal source may be used. A decision must be

made to trade off time to turn-up for a more complete coverage data set. A

modulated signal source also requires a more sophisticated measurementat the receiver to capitalize on the modulation.

The drive system contains a receiver to measure signal strength and a

mechanism for determining location (typically GPS vehicular navigation, or

both).




System Controller

GIS

GP-IB

GPS Receiver

RS-232

RS-232

GSM Test MS

GSM BTS

Receiver

Drive Test System

Test Transmission




Test Transmitter can be Single Channel CW Source; or a GSM

BCH Transmitter

For CW source, Receiver should be preferred in Drive Test

System.

Receiver can do CW measurements accurately, because Mobile

does Channel Power measurement.

For a GSM BCH transmitter, use a different network code, or

preferably activate cell barring, to avoid traffic discrepancies.

Test Transmission




For CW transmission, each measurement value

should be a running average of 50 samples taken over

a distance of 40 wavelengths.

This process, will result into 95% confidence in thepredicted coverage with the CW transmitter, with reference

to the actual coverage later.

Meeting Lee's Criteria




DTS

Tst.Tx

Test Transmission

Test Transmission




Once an approximate site is selected,the test transmission is to

be done.The test transmission as the term states is a processby which a test transmitter ( BTS Simulator ) is temporarily

installed at the site and any of the allotted GSM frequencies is

transmitted. Now this is transmission is received by a Drive Test

System installed in a mobile van which moves around the plan

and gives a plot of signal strength received in the cell.

The received level should be estimated at -85 dbm,which

means a good outdoor coverage and considering on average

15 db indoor margin,this level of outdoor will give somewhat

acceptable indoor coverage




Navigation

Signal Strength

GPS / DR !!!

Mapping

Process

GPS/DR is essential if Prediction tool modeling is to be done

Analysis

Measurement

Test Transmission




This slide depicts a typical configuration for RF coverage

measurements.

The GPS receiver and / or the vehicular navigation system known as

dead reckoning (DR) measures location.

In a CW drive system the signal strength is simply peak power

measured at the transmit frequency. For more sophisticated

modulation types the receiver typically makes an estimate of the bit-error-rate (BER). This is done by comparing a reference signal with the

received signal. The reference signal is constructed to match the

known transmit signal.

The resulting output data is displayed on a map. Often the display isdone in the RF planning prediction tool. This allows for comparison of

the measured coverage to that predicted by the model.




Three types of GPS Receiver's for Navigation

GPS

-- accuracy in the range of 40 - 60 m

GPS with Dead Reckoning-- with Compass and Wheel/Odometer

-- improves performance during signal loss( street canyon)

Differential GPS

-- improves the absolute accuracy ( in few meters)-- Local correction signal is transmitted from a separate Tx.

-- FM receiver with the GPS picks up and applies the correction

Something on GPS




GPS Fix !!

GPS Fix occurs when it gets Satellite Signals.

A reliable GPS should be at least a 8 channel receiver.

2D fix : at least 2 satellite available ( lat,long).

3D fix : at least 3 satellite available (lat,long,alt).

GPS Interface

GPS communicates on the RS232 interface with the PC.

Standard interface protocols are TAIP,TSIP or NMEA.

Something on GPS




F=1

F=2

F=3

F=4,8

F=5,9

F=6,10

F=7

F=1

F=2

F=3

F=4,8

F=5,9

F=6,10

F=7 F=1

F=2

F=3

F=4,8

F=5,9

F=6,10

F=7

F= 1,2,3,4,5,6,7,8,9,10

GSM uses concept of cells

One cell covers small part of network

Network has many cells

Frequency used in one cell can be used

in another cells

This is known as Frequency Re-use

Clusters

Co-Channel ( Re-use ) Cells

Frequency Re-use

Frequency Planning




GSM uses the concept of cells. One cell covers a smallpart of the network. A GSM network will have several

cells. Since a cell has limited area, the frequency used in

this cell can be re-used in some other cell. This is known

as frequency reuse. By using this concept, all cells will

have appropraite frequencies and hence can beincreased, by increasing cell and re-using the

frequencies. The cells which use the same frequency

numbers are known as re-use or co-channel cells.

Adjacent cells should not use the same frequency, as

they would interfere with each other and disturb thespeech.




Objective

Optimum uses of Resources

Reduce Interference

Frequency Planning




A

A

Q = D R

C / Ic = 9 db

Q = Sqrt ( 3 x N )

Co - Channel Re-use factor




Frequency reuse implies that in a given coverage area there are

several cells that use the same set of frequencies.These cells

are called co-channel cells,and the interference betweensignals from these cells is called co-channel interference.An

increase in transmit power and decrease in cell size leads to

this problem . Considering each cell size to be same co-channel

interference becomes the function of the radius of the cell ( R )

,and the distance to the center of the nearest co-channel cell(D). This ratio of D/R is termed as co - channel reuse ratio ( Q )

. By increasing Q the spatial separation between two co-

channels is increased thereby reducing interference.

A small value of Q provides larger capacity by more

reuse,where as a large value of Q provides improvedtransmission quality ,due to a smaller level of co-channel

interference.




Adjacent ARFCN's should not be used in the same cell

It will have no problems in Downlink*, but will have high risk of

uplink interference (due to mandatory uplink power control ).

* If Downlink dynamic power control is not used

- 70 dbm ( C/Ia = 20 )

- 90 dbm ( C/Ia = -20 )

5 dbm

33 dbm

Since all the ARFCN's in a cell are frame

synched, Timeslot numbers will align on

all the ARFCn's

Adjacent-Channel Re-use Criteria




Adjacent ARFCN's can be used in adjacent cells, but as far aspossible should be avoided.

As such separation of 200 Khz is sufficient, but taking into

consideration the propagation effects, as factor of protection

600 Khz should be used*.

In the worst, Adjacent ARFCN's can also be used in adjacent

cells by setting appropriate handover parameters ( discussed

later in optimization)

* Practically not possible in most of the networks due to tight reuse

Adjacent-Channel Re-use Criteria




Omnidirectional Cell

BTS

Sectorial Cell

BTS

Low gain Antennas

Lesser penetration/directivity Receives Int from all directions

Lower implementation cost

High gain Antennas

Higher penetration/directivity Receives Int from lesser directions

Higher implementation cost

Cell Configuration




3,6,9 A

A

B C

3,6,9 B

3,6,9 C

Receives Interference from all directions

Interference in Omni-Cells




A1

A2

A3 36

9

B1

B2

B3 3

9

6

C1

C2

C3 3

69

ReceivesInterference

from lesser

directions.

Sectored Cells




Re-use Patterns ensures the optimum separation between Co-Channels.

Re-use pattern is a formation of a cluster with a pattern of frequency distribution in

each cell of the cluster.

Same cluster pattern is then re-used.

Preferred Re-use Patterns

Omni - Cells : 3 cell, 7 cell, 12 cell, 14 cell, 19 cells etc

Sector - Cells : 3/9 , 4/12, 7/21

Re-use Patterns




A1

A2 A3 B1

B3 C1

C2 C3

A1

A2 A3 B1

B2 B3 C1

C2 C3

A1

A2 A3 B1

B2 B3 C1

C2 C3 A1

A2 A3 B1

B2 B3 C1

C2 C3 A1

B1

B2 B3

A1

A2 A3

B2 C1

C2 C3

C2 C3 C2 C3 C2 C3

A1

3/9 Re-use Pattern




A1

A2 A3 B1

B3 C1

C2 C3

A1

A2 A3 B1

B2 B3 C1

C2 C3

A1

A2 A3 B1

B2 B3 C1

C2 C3 A1

A2 A3 B1

B2 B3 C1

C2 C3 A1

B1

B2 B3

A1

A2 A3

B2 C1

C2 C3

C2 C3 C2 C3 C2 C3

A1

Using ARFCN's 1,2,3,4,5,6,7,8,9 , do the channel allocation for

the below cells using 3/9 pattern

Exercise !!!




Adjacent Channel Interference is very difficult to avoid

within the cluster itself.

1

4

3

2

8 5

7

9 6

Frequency Allocation in 3/9patterns




D1

D3

B1

B3

C1

C2 C3 D1

A1

A2 A3 B1

B2 B3 C1

C2 C3 B1

B2 B3 A1

A2 A3 C1

C2 C3 C1

D1

D2 D3

D2 D3 B2 B3 B2 B3

D2 C1

C3

B2

D2 D3 A1

A2 A3 B1

B2 B3

C2 D1

D2 D3 A1

4/12 Reuse Patterns




Using ARFCN's 1,2,3,4,5,6,7,8,9,10,11,12 do the channel

allocation for the below cells using 4/12 pattern.

D1

D2 D3 C1

C3 B1

B2 B3

C1

C2 C3 D1

D2 D3 A1

A2 A3

A1

A2 A3 B1

B2 B3 C1

C2 C3 B1

B2 B3 A1

A2 A3 C1

C2 C3 C1

D1

D2 D3

B1

B2 B3

C2 D1

D2 D3

D2 D3 B2 B3 B2 B3

A1

Exercise

/ C




1

3 5

2 4 6

7

9 11 12

10 8

4/12 pattern avoids adjacent channels in adjacent cells

4/12 Pattern Channel Allocation

R P C l i



1 / /0 46

Larger reuse patterns give reduction in interference

Re-use patterns becomes more effective with sectorial cell

configurations.

To implement large patterns ( like 4/12, 7/21) , more channels

are required.

So with less resources, the best way to plan is :

1. Use optimum no of channels per cell.

2. Thus, increase the pattern size.

Reuse Patterns Conclusion

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