RF Activities in Cellular Systems

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					        RF Activities in Cellular Systems

Site Evaluation
Frequency Planning
BTS Installation and Commissioning
RF Coverage Verification
Competitive Comparison
Interference Management

                      Company Confidential   15/7/05   1
    RF Activities Application

                       Build-Out & Turn-up
    Site                                              Installation
                       RF Planning                                        Verification
 Evaluation                                          Commission

       Site Roll out                                     Coverage Verification

                             In Service

Optimization           Trouble-                   Network              Fraud
                       shooting                  Expansion            Detection

    Network Optimization                             Competitive Comparison


                                  Company Confidential               15/7/05             2
           Tools for RF Activities


Prediction Tool           Drive Testing                          BTS Testing             MS Testing

    Coverage Prediction      Band Clearance                        Commissioning           Despatch Inspection
    Frequency Planning       Test Transmission                     Maintenance             Quality Assurance
                             RF Coverage Verification              Trouble Shooting        Troubleshooting
                             Optimization                                                  Repairs
                             Competitive Analysis
                             Interference Monitoring
                             Prediction Tool Modelling

                                          Company Confidential                 15/7/05                    3
        Reject     Search Area
                                           Site Physical
  Action Steps
                 Site Evaluation           Qualification

   Test               Band                            Coverage
Transmission          Clearance                       Prediction

                    Company Confidential    15/7/05                4
      Search Area Selection

 Study of Contour / City Map.

 Identifying potential search zones.

 Correlating with nearby existing sites.

 Drive/Walk through physical Land

                       Company Confidential   15/7/05   5
Site Physical Qualification

                                      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).

            Company Confidential                     15/7/05                   6
        RF Coverage Prediction

   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.

                              Company Confidential   15/7/05            7
       RF Planning
Prediction Tool

              STATION                          PLOTTER

                        Company Confidential       15/7/05   8
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

                       Company Confidential   15/7/05        9
           RF Coverage prediction
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.

                                     Company Confidential       15/7/05                10
     Band Clearance

   High cost of installing base stations
   Are clear bands really free of interference?
   Minimize risk by assessing interference before committing funds

                             Company Confidential     15/7/05         11
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

                                 Company Confidential    15/7/05            12
Band Clearance

 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

                         Company Confidential   15/7/05       13
  Band Clearance


                                               GPS Receiver

              Spectrum Analyzer


                                                  PC Controller

                Company Confidential           15/7/05            14
Band Clearance

     Power Statistics
     Estimate Probability of Interference
     Noise Floor Characteristics
     Logging of Signals in the Band
     Channel Occupancy

                       Company Confidential   15/7/05   15
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

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.

                                        Company Confidential        15/7/05                16
Test Transmission

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
Calibrate   planning software tool.

                     Company Confidential   15/7/05   17
       Test Transmission

                Two Components
1. Test Transmitter                            2. Drive System

 BTS        Power

                        Company Confidential    15/7/05          18
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
                                Company Confidential   15/7/05            19
    Test Transmission

Drive Test System

                                      GSM Test MS
                                                               GPS Receiver





                                                             System Controller

                    Company Confidential                     15/7/05                   20
           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

   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.

                                   Company Confidential     15/7/05     21
        Meeting Lee's Criteria

   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.

                            Company Confidential   15/7/05       22
      Test Transmission
Test Transmission



                      Company Confidential         15/7/05   23
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

                           Company Confidential   15/7/05           24
     Test Transmission


    GPS / DR !!!


   Signal Strength

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

                          Company Confidential   15/7/05             25
This slide depicts a typical configuration for RF coverage
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.

                            Company Confidential   15/7/05           26
          Something on GPS

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

                               Company Confidential   15/7/05          27
        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.

                               Company Confidential     15/7/05   28
        Frequency Planning

Frequency Re-use                                             F= 1,2,3,4,5,6,7,8,9,10
  GSM uses concept of cells
  One cell covers small part of network                                 F=2
  Network has many cells                                      F=7                F=3
  Frequency used in one cell can be used                                 F=1
   in another cells
  This is known as Frequency Re-use                           F=6,10            F=4,8
                                                       F=2               F=5,9
                                               F=7               F=3             F=2
                                                       F=1               F=7              F=3

                                             F=6,10            F=4,8             F=1
     Co-Channel ( Re-use ) Cells
                                                       F=5,9            F=6,10           F=4,8

                                Company Confidential                 15/7/05                 29
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

                       Company Confidential   15/7/05         30
    Frequency Planning


               Optimum uses of Resources

               Reduce Interference

                        Company Confidential   15/7/05   31
Co - Channel Re-use factor

                                       C / Ic = 9 db


 Q= D                      Q = Sqrt ( 3 x N )

            Company Confidential        15/7/05        32
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

                          Company Confidential   15/7/05         33
    Adjacent-Channel Re-use Criteria
   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 ).

             - 90 dbm ( C/Ia = -20 )

            - 70 dbm ( C/Ia = 20 )
                                                            33 dbm

                                           Since all the ARFCN's in a cell are frame
                     5 dbm                  synched, Timeslot numbers will align on
                                            all the ARFCn's

              * If Downlink dynamic power control is not used

                                     Company Confidential         15/7/05               34
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

                                  Company Confidential         15/7/05             35
        Cell Configuration
    Omnidirectional Cell                                       Sectorial Cell

                             BTS                                                        BTS

   Low gain Antennas                                       High gain Antennas
   Lesser penetration/directivity                          Higher penetration/directivity
   Receives Int from all directions                        Receives Int from lesser directions
   Lower implementation cost                               Higher implementation cost

                                  Company Confidential                  15/7/05              36
Interference in Omni-Cells

C            Receives Interference from all directions


               Company Confidential       15/7/05           37
     Sectored Cells

             3      C1             B3                   3
         6                                                         B1
             9                            6

             A3                                          Receives
                                   3     A1                 Interference
                       6                                    from lesser
                                  9                         directions.

                  Company Confidential        15/7/05                   38
            Re-use Patterns

    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

                                     Company Confidential      15/7/05              39
 3/9 Re-use Pattern

                    A1                          C2             A1     C3            C2
C3        C2              C3

     B1    A3            A2             B1            A3            A2         B1

                    C1        B3                               C1        B3
B3        B2                                    B2                                  B2

     A1                                A1                           C2         A1
               C3        C2                           C3

A3        A2        B1    A3                         A2        B1    A3             A2

     C1                                 C1                B3                   C1
               B3        B2                                         B2

C3        C2        A1        C3                 C2            A1        C3         C2

                              Company Confidential                   15/7/05             40
      Exercise !!!
Using ARFCN's 1,2,3,4,5,6,7,8,9 , do the channel allocation for
the below cells using 3/9 pattern

                     C2        A1                      C2        A1    C3            C2
          C3                           C3

                B1 A3               A2          B1          A3        A2       B1

           B3                  C1       B3                       C1    B3
                     B2                                B2                            B2
                A1                  C2          A1                    C2       A1
                      C3                                    C3

          A3         A2        B1      A3                  A2    B1    A3            A2

                C1        B3                    C1          B3                 C1
                                    B2                                B2

          C3         C2        A1       C3                 C2    A1    C3            C2

                                    Company Confidential                   15/7/05        41
    Frequency Allocation in 3/9

            4                  7

                                              5       8

             6                9

Adjacent Channel Interference is very difficult to avoid
within the cluster itself.

                           Company Confidential       15/7/05   42
 4/12 Reuse Patterns

                    A1                          D2             C1     B3            B2
B3        B2              D3

     D1    A3            A2             B1            C3            C2         D1

                    C1        B3                               A1        D3
D3        D2                                    B2                                  D2

     B1                                D1                           A2         B1
               C3        C2                           A3

B3        B2        A1    D3                         D2        C1    B3             B2

     C1                                 B1                C3                   D1
               A3        A2                                         C2

C3        C2        C1        B3                 B2            A1        D3         D2

                              Company Confidential                   15/7/05             43
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.

               B2        A1    D3               D2          C1    B3             B2
          D1    A3            A2         B1          C3          C2    D1

     D3                  C1    B3                           A1    D3             D2
               D2                               B2
          B1                  C2        D1            A3         A2    B1
     B3        B2        A1    D3                D2         C1    B3             B2

          C1        A3                   B1            C3              D1
                              A2                                 C2
     C3        C2        C1        B3            B2         A1    D3             D2

                                    Company Confidential               15/7/05        44
    4/12 Pattern Channel Allocation


            5                3                       7

                                                9            11

        4                      6                     2

                                                10            8

4/12 pattern avoids adjacent channels in adjacent cells

                         Company Confidential            15/7/05   45
    Reuse Patterns Conclusion

   Larger reuse patterns give reduction in interference

   Re-use patterns becomes more effective with sectorial cell

   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.

                          Company Confidential   15/7/05         46

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