RF Activities

Company Confidential 15/7/05 1

Site EvaluationFrequency PlanningBTS Installation and CommissioningRF Coverage VerificationOptimization Competitive ComparisonInterference Management

RF Activities in Cellular Systems


Site Evaluation RF Planning

InstallationCommission Verification

Build-Out & Turn-up

Site Roll out Coverage Verification

Optimization Trouble-shooting

NetworkExpansion

FraudDetection

In Service

Network Optimization Competitive Comparison

InterferenceManagement

Continous

RF Activities Application Segments


C overage P redictio nF requenc y P lannin g

P red ic tion T oo l

B and C learanc eT est T ransm issionR F C overag e V erifica tio nO ptim izationT rouble shootin gC om petitive A nalys isInterfe rence M on itorin gP redictio n T ool M ode llin g

D rive T estin g

C om m issioningM ainte nanc eT rouble S hootin g

B T S T esting

D espatch Inspectio nQ uality A ssuranc eT rouble shootin gR epairs

M S T esting

T ools

Tools for RF Activities


Search Area Selection

Site Physical Qualification

Coverage Prediction

Band Clearance

Test 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


WORKSTATION PLOTTER

Prediction Tool

RF Planning


The data available after test transmission is analyzed by the 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 transmission data 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 sites capability 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 is generally 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 to understand 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 between multiple 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 is critical 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 MapEvaluate 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

PowerAmplifier

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 data for 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 measurement at 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 the predicted 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 process by 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 is done 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=2F=3

F=4,8

F=5,9F=6,10

F=7

F=1

F=2F=3

F=4,8

F=5,9

F=6,10

F=7

F=1

F=2F=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 small part 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 be increased, 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 the speech.


Objective

Optimum uses of Resources

Reduce Interference

Frequency Planning


A

A

Q = DR

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 between signals 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 improved transmission 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 as possible 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


3,6,9A

A

B

C

3,6,9B

3,6,9C

Receives Interference from all directions

Interference in Omni-Cells


A1

A2

A33

69

B1

B2

B3 3

96

C1

C2

C33

69

Receives Interference 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

A2A3 B1

B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3 A1

B1

B2B3

A1

A2A3

B2

C1

C2C3

C2C3 C2C3

C2C3

A1

3/9 Re-use Pattern


A1

A2A3 B1

B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3

A1

A2A3 B1

B2B3C1

C2C3 A1

B1

B2B3

A1

A2A3

B2

C1

C2C3

C2C3 C2C3 C2C3

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

85

7

96

Frequency Allocation in 3/9 patterns


D1

D3

B1

B3

C1

C2C3 D1

A1

A2A3 B1

B2B3C1

C2C3

B1

B2B3 A1

A2A3C1

C2C3 C1

D1

D2D3

D2D3 B2B3

B2B3

D2 C1

C3

B2

D2D3A1

A2A3

B1

B2B3

C2

D1

D2D3 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

D2D3 C1

C3B1

B2B3

C1

C2C3 D1

D2D3A1

A2A3

A1

A2A3 B1

B2B3C1

C2C3

B1

B2B3 A1

A2A3C1

C2C3

C1

D1

D2D3

B1

B2B3

C2

D1

D2D3 D2D3 B2B3

B2B3

A1

Exercise


1

35

24 6

7

9 1112

10 8

4/12 pattern avoids adjacent channels in adjacent cells

4/12 Pattern Channel Allocation


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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