RF Planning

INTRODUCTION TO RF PLANNING

Designing a cellular system - particularly one that incorporates both Macrocellular and Microcellular networks is a delicate balancing exercise.

The goal is to achieve optimum use of resources and maximum revenue potential whilst maintaining a high level of system quality.

Full consideration must also be given to cost and spectrum allocation limitations.

A properly planned system should allow capacity to be added economically when traffic demand increases.

As every urban environment is different, so is every macrocell and microcell network. Hence informed and accurate planning is essential in order to ensure that the system will provide both the increased capacity and the improvement in network quality where required, especially when deploying Microcellular systems.


RF planning plays a critical role in the Cellular design process.

By doing a proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we may encounter in the future and also reduce substantially the cost of optimization.

On the other hand a poorly planned network not only leads to many Network problems , it also increases the optimization costs and still may not ensure the desired quality.

TOOLS USED FOR RF PLANNING

Network Planning Tool

CW Propagation Tool

Traffic Modeling Tool

Project Management Tool


Network Planning Tool

Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage, doing frequency planning automatically, creating neighbor lists etc.

With a database that takes into account data such as terrain, clutter, and antenna radiation patterns, as well as an intuitive graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

– Design wireless networks

– Plan network expansions

– Optimize network performance

– Diagnose system problems

The major tools available in the market are Planet, Pegasos, Cell Cad.

Also many vendors have developed Planning tools of their own like Netplan by Motorola, TEMS by Ericsson and so on.


Network Planning Tool (PLANET)


Propagaton Test Kit

The propagation test kit consists of– Test transmitter.– Antenna ( generally Omni ).– Receiver to scan the RSS (Received signal levels). The receiver

scanning rate should be settable so that it satisfies Lee’s law.– A laptop to collect data.– A GPS to get latitude and longitude.– Cables and accessories.– Wattmeter to check VSWR.

A single frequency is transmitted a predetermined power level from the canditate site.

These transmitted power levels are then measured and collected by the Drive test kit. This data is then loaded on the Planning tool and used for tuning models.

Commonly Graysons or CHASE prop test kits are used.


Propagaton Test Kit


Traffic Modeling Tool

Traffic modelling tool is used by the planning engineer for Network modelling and dimensioning.

It helps the planning engineer to calculate the number of network elements needed to fulfil coverage, capacity and quality needs.

Netdim by Nokia is an example of a Traffic modelling tool.


Project Management Tool

Though not directly linked to RF Design Planning, it helps in scheduling the RF Design process and also to know the status of the project

Site database : This includes RF data, site acquisition,power, civil ,etc.

Inventory Control

Fault tracking

Finance Management


RF PLANNINGPROCEDURES

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.

PRELIMINARY WORK

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.

PRELIMINARY WORK

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.

PRELIMINARY WORK

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.

PRELIMINARY WORK

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.

PRELIMINARY WORK

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 etc.· 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 40 ).

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.

INITIAL DESIGN

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 .

INITIAL DESIGN

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

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.

SELECTION OF SITES

Select Initial Anchor Sites· 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.

SELECTION OF SITES

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,...)

SELECTION OF SITES

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).

SELECTION OF SITES

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.

SELECTION OF SITES

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.

GSM: Logical Channels

RF Planning

Documents

Transcript of RF Planning