CloudRF

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basics

Introduction

RF planning is an art which takes years to master but if done correctly will save time, money, energy and even lives. The number of variables which must be considered to maximise accuracy is potentially infinite if you start worrying about leaves on trees so a practical trade off must be made between the time you take defining variables, learning new software and the lifespan or value of your network(s).

CloudRF is designed around this trade-off. It sacrifices specialist protocol-specific options for simple generic options so it can be used by novices and experts to answer questions ranging from “Where does my repeater cover?” to “Can I reduce my power consumption with a high gain antenna or a lower frequency?”

A link budget is a calculation which computes the received power based upon the transmitter, receiver and link parameters. In it's most basic form you add together the gain values at either end and subtract the path loss in the middle. You can read more about link budgets in the link budget tutorial. A thorough reference for link budgets can be found on Wikipedia.

Planning units

dB, dBm, and dBuV/m are all different values for describing RF coverage.
The decibel (dB) without a reference is just a ratio. For RF planning it is used to describe 'Path loss' across a link and is agnostic to whatever RF power is used. For example, a 2.4GHz signal over 100m has a path loss of 80dB regardless of power output.
You can calculate this quickly with a simple tool like this. dBm is described as 'received power' and is a ratio relative to 1 milliwatt where 1mW = 0dBm. It is the default setting in CloudRF and factors in RF power expressed as a negative value between -1 and -110dBm.
The RF noise floor is described in dBm and is generally near -120dBm. A good signal (eg. 5 bars on your mobile phone) is > -70dBm. An average signal is > -90dBm and a weak signal is < -90dBm. Finally, dBuV/m is decibel micro volts per metre (squared) and is described as 'field strength'. It expresses the RF in volts and is normally used for safety testing and interference measurements.

Transmitter

You can learn a lot about your transmitter from your device's documentation. As a minimum you need to know it's frequency and power output.

Frequency (MHz/GHz)

If the frequency isn't listed in your system's documentation: Google it. Something like a PMR446 handheld radio may list the precise channels it operates on eg. 446.025MHz whereas another system may list a band eg. '2.4GHz' because it occupies multiple channels dynamically. Where precise frequencies are not known you should apply the most accurate frequency you can (2437MHz is in the middle of the 2.4GHz band for example).

RF Power

The RF power can be expressed in both Watts or dBm and is easy to get wrong. Just because your system says it radiates 1 Watt (30dBm) does not mean it does due to inherent losses in the antenna and cabling. You should look for a conservative value when calculating the total effective radiated power (ERP). CloudRF has an automatic ERP calculator so when you enter in 1 Watt and an antenna gain of 9dBi you get 4.8W (36.8dBm) total ERP. Communications authorities restrict power output for different bands so if in doubt, check what your RF ERP really is. This is normally implemented by the equipment vendor so is hard to override without reverse engineering the hardware.
Frequency bandRF limit EuropeRF limit USA
2.4 GHz100mW / 20dBm1000mW / 30dBm
5.8 GHz100mW / 20dBm1000mW / 30dBm

dBm to Watts table

dBmMilliwattsWatts
010.001
11.20.0012
42.50.0025
750.005
10100.01
201000.1
3010001
4010,00010

Antennas

Getting the right antenna is important but don't worry if you're not sure. A common antenna called a dipole exists which serves most basic purposes where the transmitter is radiating in all directions. A mobile phone, walkie talkie, boat and plane all have dipole antennas. An antenna has directional properties in the horizonal (azimuth) and vertical (elevation) planes. A directional antenna (eg. a TV aerial) has a high gain for signals in a given direction, represented as dBi (decibel isotropic) or dBd (decibel dipole). With dBi, a value of 2.14 (0dBd) represents normal gain. This figure is taken from a half wave dipole. A high gain antenna would have a value greater than this. An antenna's radiation pattern can be documented as polar plots of the horizontal and vertical planes. This is what you see in the CloudRF interfaces. Once you've got the right antenna, you should align it correctly (only if it's a directional antenna) using the direction and down-tilt parameters.
Down tilt would be zero if your antenna was parallel to the ground or a positive value if it was pointed downhill. Many high capacity antennas on tall masts have positive down-tilt angles because they are pointed down to serve the closest subscribers. If you wanted to point an antenna up to the top of a hill it would have a negative down-tilt eg. -2 degrees.

Receivers

Knowing your receiver capabilities is vital to get an accurate prediction. The single most important thing to get right when planning is the receiver sensitivity. This value, normally expressed in dBm will make a huge difference. A mobile phone for example has a receiver sensitivity of about -105dBm. A handheld VHF radio is less at around -90dBm. If you are not sure, set this to -80dBm. This will give you a conservative prediction, allowing for fluctuations in the quality of the link referred to as the fade margin. Setting it lower than -90dBm is not recommended if you are unsure.

Environment

The terrain makes a huge difference and thankfully is automatically factored in by the system for you. There are other variables you can control which will affect your coverage.

Terrain conductivity

Depending on where your link is, the ground will affect your potential. Dry ground conducts less well than wet ground. Pick the best match from the selection list. The dielectric values are taken from SPLAT! which in turn are derived from the ITU standard for terrain conductivity. This value has no impact on signals which are greater than a full wavelength above the earth, known as the Minimum Effective Height (MEH).

Radio climate

For signals operating a wavelength or more above the ground, the climate will also affect your potential coverage. Pick the best match from the selection list. This makes only a modest difference to most signals.

Tropospheric scatter

Tropospheric scatter is an atmospheric phenomenon caused by ducts of warm air which can carry a signal much further than normal over the horizon. It should be considered but cannot be practically planned for unless you have a super weather computer which knows when and where there will be warm air ducts. At present, weather super-computers have consistently demonstrated an inability to predict what mother nature has in store.

Clutter

Buildings present a real challenge to RF planning. You can simulate buildings through either an average height value eg. 8m for houses or by importing your own KML layer with large buildings defined. Our legacy competitors emphasise the importance of having accurate clutter data but the accuracy benefit must be traded off against the significant time and cost of doing so. What sales people won't tell you is that perfection is not possible with RF planning - all predictions are estimates based upon limited inputs and are subject to multiple random inputs like the weather or motor traffic. Set an average clutter height of 6m for suburban areas or 2m for rural areas.

Trees

Trees are a big deal but CloudRF is not the sort of software that worries novice users with tedious options about seasons, types of trees or leaf density. For simplicity and peace of mind, a block of trees is regarded as a block of concrete. You can add blocks of concrete trees with the custom clutter layers or simulate a raised canopy with the custom clutter option.

Output

Resolution

Resolution refers to how accurate the prediction is. Values are the number of pixels per degree of latitude so 1200 (default) equates to approximately 90m per pixel (at the equator) and 3600 equals 30m (High accuracy). A higher resolution will take longer to calculate but we've multi-threaded our engine now so you should only wait a few seconds for most calculations. The resolution increases with latitude as the lines of longitude converge towards the earth's poles so the more northern you are the more accurate your predictions are.

Colour schema

The colour scheme you choose is not just cosmetic. The colours represent actual signal values, depicted in a colour key. As well as pre-defined schemas, you can define your own within the 'Custom RGB' option. This allows you to define the signal threshold levels for each colour and is perfect if you want to see just simple 'good' or 'average' maps.

basics.txt · Last modified: 2016/09/01 22:01 (external edit)