RF PLANNING PROCEDURE
Propagation tool
setup
• Set up the planning tool hardware. This includes the server and or clients which may be UNIX based.
• Setup the plotter and printer to be used.
Terrain, Clutter, Vector data acquisition and setup Procure the terrain, clutter and vector data in the required resolution. Setup these data on the planning tool. Test to see if they are displayed properly and printed correctly on the plotter.
Setup site tracking database
This is done using Project management or site management databases.This is the central database which is used by all relevant department, viz. RF, Site acquisition, Power, Civil engineering etc, and avoids data mismatch.
Load master lease site locations in database
if predetermined friendly sites that can be used are available, then load this data into the site database.
Marketing Analysis and GOS determination
• Marketing analysis is mostly done by the customer.
• Growth plan is provided which lists the projected subscriber growth in phases.
• GOS is determined in agreement with the customer (generally the GOS is taken as 2%)
• Based on the marketing analysis, GOS and number of carriers as inputs, the network design is carried out.
Zoning Analysis
This involves studying the height restrictions for antenna heights in the design area.
Set Initial Link Budget
Link Budget Analysis is the process of analyzing all major gains and losses in the forward and reverse link radio paths. Inputs Base station & mobile receiver sensitivity parameters.Antenna gain at the base station & mobile station.Hardware losses(Cable, connector, combiners etc).Target coverage reliabilty.Fade margins.Output Maximum allowable path loss.
Initial cell radius calculation
Using link budget calculation, the maximum allowable path loss is calculated.Using Okumura hata emprical formula, the initial cell radius can be calculated.Initial cell count estimates Once the cell radius is known, the area covered by one site can be easily calculated.By dividing the total area to be covered by the area of each cell, a initial estimate of the number of cells can be made
INITIAL SURVEY
Morphology Definition
• Morphology describes the density and height of man made or natural obstructions.
• Morphology is used to more accurately predict the path loss.
• Some morphology area definitions are Urban, Suburban, rural, open areas.
• Density also applies to morphology definitions like dense urban, light suburban, commercial etc.
• This basically leads to a number of sub-area formation where the link budget will differ and hence the cell radius and cell count will differ.
Morphology Drive Test
• This drive test is done to prepare generic models for network design.
• Drive test is done to characterize the propagation and fading effects.
• The objective is to collect field data to optimize or adjust the prediction model for preliminary simulations.
• A test transmitter and a receiver is used for this purpose.
• The received signals are typically sampled ( around 50 samples in 40l ).
Propagation Tool Adjustment
• The data collected by drive testing is used to prepare generic models.
• For a given network design there may be more than one model like dense-urban, urban, suburban, rural, highway etc.
• The predicted and measured signal strengths are compared and the model adjusted to produce minimum error.
• These models are then used for initial design of the network.
INITIAL DESIGN
Complete Initial Cell Placement
• Planning of cell sites sub-area depending on clutter type and traffic required.
• Run Propagation Analysis.
• Using generic models prepared by drive testing & prop test, run predictions for each cell depending on morphology type to predict the coverage in the given sub-areas.
• Planning tool calculates the path loss and received signal strength using Co-ordinates of the site location, Ground elevation above mean sea level, Antenna height above ground, Antenna radiation pattern (vertical & horizontal) & antenna orientation, Power radiated from the antenna
Reset Cell Placement( Ideal Sites)
• According to the predictions change the cell placements to design the network for contigious coverage and appropriate traffic.
System Coverage Maps
• Prepare presentations as follows
• Background on paper showing area MAP which include highways, main roads etc.
• Phase 1 sites layout on transparency.
• Phase 1 sites composite coverage prediction
• Phase 2 sites layout transparency.
• Phase 2 composite coverage prediction on transparency.
• If more phases follow the same procedure.
Design Review With The Client
• Initial design review has to be carried out with the client so that he agrees to the basic design of the network.
• During design review, first put only the background map which is on paper. Then step by step put the site layout and coverage prediction.
• Display may show some coverage holes in phase 1 which should get solved in phase 2.
SELECTION OF SITES
Prepare Initial Search Ring
Note the latitude and longitude from planning tool.Get the address of the area from mapping software.Release the search ring with details like radius of search ring, height of antenna etc.
• Set up the planning tool hardware. This includes the server and or clients which may be UNIX based.
• Setup the plotter and printer to be used.
Terrain, Clutter, Vector data acquisition and setup Procure the terrain, clutter and vector data in the required resolution. Setup these data on the planning tool. Test to see if they are displayed properly and printed correctly on the plotter.
Setup site tracking database
This is done using Project management or site management databases.This is the central database which is used by all relevant department, viz. RF, Site acquisition, Power, Civil engineering etc, and avoids data mismatch.
Load master lease site locations in database
if predetermined friendly sites that can be used are available, then load this data into the site database.
Marketing Analysis and GOS determination
• Marketing analysis is mostly done by the customer.
• Growth plan is provided which lists the projected subscriber growth in phases.
• GOS is determined in agreement with the customer (generally the GOS is taken as 2%)
• Based on the marketing analysis, GOS and number of carriers as inputs, the network design is carried out.
Zoning Analysis
This involves studying the height restrictions for antenna heights in the design area.
Set Initial Link Budget
Link Budget Analysis is the process of analyzing all major gains and losses in the forward and reverse link radio paths. Inputs Base station & mobile receiver sensitivity parameters.Antenna gain at the base station & mobile station.Hardware losses(Cable, connector, combiners etc).Target coverage reliabilty.Fade margins.Output Maximum allowable path loss.
Initial cell radius calculation
Using link budget calculation, the maximum allowable path loss is calculated.Using Okumura hata emprical formula, the initial cell radius can be calculated.Initial cell count estimates Once the cell radius is known, the area covered by one site can be easily calculated.By dividing the total area to be covered by the area of each cell, a initial estimate of the number of cells can be made
INITIAL SURVEY
Morphology Definition
• Morphology describes the density and height of man made or natural obstructions.
• Morphology is used to more accurately predict the path loss.
• Some morphology area definitions are Urban, Suburban, rural, open areas.
• Density also applies to morphology definitions like dense urban, light suburban, commercial etc.
• This basically leads to a number of sub-area formation where the link budget will differ and hence the cell radius and cell count will differ.
Morphology Drive Test
• This drive test is done to prepare generic models for network design.
• Drive test is done to characterize the propagation and fading effects.
• The objective is to collect field data to optimize or adjust the prediction model for preliminary simulations.
• A test transmitter and a receiver is used for this purpose.
• The received signals are typically sampled ( around 50 samples in 40l ).
Propagation Tool Adjustment
• The data collected by drive testing is used to prepare generic models.
• For a given network design there may be more than one model like dense-urban, urban, suburban, rural, highway etc.
• The predicted and measured signal strengths are compared and the model adjusted to produce minimum error.
• These models are then used for initial design of the network.
INITIAL DESIGN
Complete Initial Cell Placement
• Planning of cell sites sub-area depending on clutter type and traffic required.
• Run Propagation Analysis.
• Using generic models prepared by drive testing & prop test, run predictions for each cell depending on morphology type to predict the coverage in the given sub-areas.
• Planning tool calculates the path loss and received signal strength using Co-ordinates of the site location, Ground elevation above mean sea level, Antenna height above ground, Antenna radiation pattern (vertical & horizontal) & antenna orientation, Power radiated from the antenna
Reset Cell Placement( Ideal Sites)
• According to the predictions change the cell placements to design the network for contigious coverage and appropriate traffic.
System Coverage Maps
• Prepare presentations as follows
• Background on paper showing area MAP which include highways, main roads etc.
• Phase 1 sites layout on transparency.
• Phase 1 sites composite coverage prediction
• Phase 2 sites layout transparency.
• Phase 2 composite coverage prediction on transparency.
• If more phases follow the same procedure.
Design Review With The Client
• Initial design review has to be carried out with the client so that he agrees to the basic design of the network.
• During design review, first put only the background map which is on paper. Then step by step put the site layout and coverage prediction.
• Display may show some coverage holes in phase 1 which should get solved in phase 2.
SELECTION OF SITES
Prepare Initial Search Ring
Note the latitude and longitude from planning tool.Get the address of the area from mapping software.Release the search ring with details like radius of search ring, height of antenna etc.
Visit friendly site locations.
If there are friendly sites available that can be used (infrastructure sharing), then these sites are to be given preference.If these sites suite the design requirements, then visit these sites first.
Prepare Initial Search Ring
Note the latitude and longitude from planning tool.Get the address of the area from mapping software.Release the search ring with details like radius of search ring, height of antenna etc.Release search rings to project management.If there are friendly sites available that can be used (infrastructure sharing), then these sites are to be given preference.
If these sites suite the design requirements, then visit these sites first.
Select Initial Anchor Site
Initial anchor sites are the sites which are very important for the network buildup, Eg - Sites that will also work as a BSC. Enter Data In Propagation Tool.Enter the sites exact location in the planning tool.Perform Propagation Analysis
Now since the site has been selected and the lat/lon of the actual site ( which will be different from the designed site) is known, put this site in the planning tool and predict coverage.Check to see that the coverage objectives are met as per prediction.
Reset / Review Search Rings
If the prediction shows a coverage hole ( as the actual site may be shifted from the designed site), the surrounding search rings can be resetted and reviewed.Candidate site Visit( Average 3 per ring),For each proposed location, surveys should carried out and at least 3 suitable site candidates identified.
Details
of each candidate should be recorded on a copy of the Site Proposal Form for
that site. Details must include:
•
Site
name and option letter Site location (Lat./Long)• Building Height
• Site address and contact number
• Height of surrounding clutter
• Details of potential coverage effecting obstructions or other comments(A, B, C,...)
Drive Test And Review Best Candidate
In order to verify that a candidate site, selected based on its predicted coverage area, is actually covering all objective areas, drive test has to be performed.Drive test also points to potential interference problems or handover problems for the site.The test transmitter has to be placed at the selected location with all parameters that have been determined based on simulations.Drive test all major roads and critical areas like convention centers, major business areas, roads etc.Take a plot of the data and check for sufficient signal strength, sufficient overlaps and splashes( least inteference to other cells).
Drive Test Integration
The data obtained from the drive test has to be loaded on the planning tool and overlapped with the prediction. This gives a idea of how close the prediction and actual drive test data match.If they do not match ( say 80 to 90 %) then for that site the model may need tuning.
Visit Site With All Disciplines( SA, Power, Civil etc )
A meeting at the selected site takes place in which all concerned departments like RF Engineering, Site acquisition, Power, Civil Engineer, Civil contractor and the site owner is present.Any objections are taken care off at this point itself.
Select Equipment Type For Site
Select equipment for the cell depending on channel requirements.Selection of antenna type and accessories.Locate Equipment On Site For Construction Drawing.Plan of the building ( if site located on the building) to be made showing equipment placement, cable runs, battery backup placement and antenna mounting positions.Antenna mounting positions to be shown separately and clearly.Drawings to be checked and signed by the Planner, site acquisition, power planner and project manager.
Perform Link Balance Calculations
Link balance calculation per cell to be done to balance the uplink and the downlink path.Basically link balance calculation is the same as power budget calculation.The only difference is that on a per cell basis the transmit power of the BTS may be increased or decreased depending on the pathloss on uplink and downlink.EMI Studies
Study of RF Radiation exposure to ensure that it is within limits and control of hazardous areas.Data sheet to be prepared per cell signed by RF Planner and project manager to be submitted to the appropriate authority.
Radio Frequency Plan/ PN Plan
Frequency planning has to be carried out on the planning tool based on required C/I and C/A and interference probabilities.
System Interference Plots
C/I, C/A, Best server plots etc has to be plotted.These plots have to be reviewed with the customer to get the frequency plan passed.
Final Coverage Plot
This presentation should be the same as design review presentation.This plot is with exact locations of the site in the network.Identification of coverage holes.
Coverage holes can be identified from the plots and subsequent action can be taken(like putting a new site) to solve the problem.
RADIO WAVE PROPAGATION:
Isotropic RF Source• A point source that radiates RF energy uniformly in all directions (I.e.: in the shape of a sphere)
• Theoretical only: does not physically exist.
• Has a power gain of unity I.e. 0dBi.
Effective Radiated Power (ERP)
• Has a power gain of unity i.e. 0dBi
• The radiated power from a half-wave dipole.
• A lossless half-wave dipole antenna has a power gain of 0dBd or 2.15dBi.
Effective Isotropic Radiated Power (EIRP)
• The radiated power from an isotropic source
EIRP = ERP + 2.15 dB
• Radio signals travel through space at the Speed of Light
C = 3 * 108 meters / second
• Frequency (F) is the number of waves per second (unit: Hertz)
Wavelength (l) (length of one wave) = (distance traveled in one second)/(waves in one second)
l= C / F
If frequency is 900MHZ then
wavelength l = 3 * 108
900 * 106
= 0.333 meters
dB
• dB is a a relative unit of measurement used to describe power gain or loss.
• The dB value is calculated by taking the log of the ratio of the measured or calculated power (P2) with respect to a reference power (P1). This result is then multiplied by 10 to obtain the value in dB.
– dB = 10 * log10(P1/P2)
• The powers P1 ad P2 must be in the same units. If the units are not compatible, then they should be transformed.
• Equal power corresponds to 0dB.
– A factor of 2 corresponds to 3dB
• If P1 = 30W and P2 = 15 W then
10 * log10(P1/P2) = 10 * 10 * log10(30/15)
= 2
dBm
• The most common "defined reference" use of the decibel is the dBm, or decibel relative to one milliwatt.
•
It
is different from the dB because it uses the same specific, measurable power
level as a reference in all cases, whereas the dB is relative to either
whatever reference a particular user chooses or to no reference at all.• The most common "defined reference" use of the decibel is the dBm, or decibel relative to one milliwatt.
• A dB has no particular defined reference while a dBm is referenced to a specific quantity: the milliwatt (1/1000 of a watt).
• The IEEE definition of dBm is "a unit for expression of power level in decibels with reference to a power of 1 milliwatt."
• The dBm is merely an expression of power present in a circuit relative to a known fixed amount (i.e., 1 milliwatt) and the circuit impedance is irrelevant.}
– dBm = 10 log (P) (1000 mW/watt)
– where dBm = Power in dB referenced to 1 milliwatt
P = Power in watts
If power level is 1 milliwatt:
Power(dBm) = 10 log (0.001 watt) (1000 mW/watt)
= 10 log (1)
= 10 (0)
= 0
Thus
a power level of 1 milliwatt is 0 dBm. If the power level is 1 watt
1 watt Power in dBm = 10 log (1 watt) (1000 mW/watt)
= 10 (3)
= 30
dBm
= 10 log (P) (1000 mW/watt)
The
dBm can also be negative value.If power level is 1 microwatt
Power in dBm = 10 log (1 x 10E-6 watt) (1000 mW/watt)
= -30 dBm
• Since the dBm has a defined reference it can be converted back to watts if desired.
• Since it is in logarithmic form it may also be conveniently combined with other dB terms.
dBmv/m
To
convert field strength
in dbmv/m to received
power in dBm with a 50W optimum
terminal impedance and effective length of a half wave dipole l/p0dBu = 10 log[(10-6)2(1000)(l/p)2/(4*50)] dBm
At 850MHZ
0dBu = -132 dBmà 39dBu = -93 dBm
FREE SPACE PROPAGATION
• Friis Formula
Pr = Pt GtGrl2
(4pd)2
• Propagation Loss
Lp = 10log [4pd / l]2
The square term is the propagation exponent. It is greater than 2 when obstructions exist.
• Propagation Loss in dB
L p = 32.44 + 20Log(d) +20Log(f)
f = MHz
d = km
PROPAGATION MECHANISMS
Reflection• Occurs when a wave impinges upon a smooth surface.
• Dimensions of the surface are large relative to l.
• Reflections occur from the surface of the earth and from buildings and walls.
Diffraction (Shadowing)
• Occurs when the path is blocked by an object with large dimensions relative to l and sharp irregularities (edges).
• Secondary “wavelets” propagate into the shadowed region.
• Diffraction gives rise to bending of waves around the obstacle.
• Scattering
• Occurs when a wave impinges upon an object with dimensions on the order of l or less, causing the reflected energy to spread out or“scatter” in many directions.
• Small objects such as street lights, signs, & leaves cause scattering.
Multipath Propagation
• Multiple Waves Create “Multipath”• Due to propagation mechanisms, multiple waves arrive at the receiver
• Sometimes this includes a direct Line-of-Sight (LOS) signal
Multipath Propagation
• Multipath propagation causes large and rapid fluctuations in a signal.
• These fluctuations are not the same as the propagation path loss.
Multipath causes three major things
• Rapid changes in signal strength over a short distance or time.
• Random frequency modulation due to Doppler Shifts on different multipath signals.
• Time dispersion caused by multipath delays.
• These are called “fading effects.
• Multipath propagation results in small-scale fading.
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