Linx explains the considerations for determining and calculating the wireless range of a system, including internal and external factors.

1. Considerations in
Wireless Range

2. What range will my system get?
This is a question frequently asked when
analyzing wireless systems. There are many
factors to take into consideration when
determining wireless range. We will cover:
• Internal Factors
• External Factors
• Calculating Range
(Using the Friis Transmission Equation)

3. Internal Factors

4. Transmitter Output Power
The is the amount of power produced by the transmitter’s output
stage. Essentially, this is how loud the transmitter is.
Receiver Sensitivity
How low a signal level the receiver can pick up and output the data with
an acceptable number of errors. Essentially, this is how well the receiver
can hear.
Mismatch Losses
Power losses that occur inside the product between stages. Nothing is
ever perfectly matched, so some amount of the energy is lost in the
system as heat.
Internal Factors

5. Transmitter & Receiver Antenna Gains
How much the antennas focus the transmitted and received energy in
the direction of each other. There is quite a bit of information behind
this, but a full explanation is beyond the scope of this article. Please see
Application Notes AN-00500 and AN-00501 for more details.
Internal Noise Sources
(Primarily on the receiver side.) Switching power supplies, oscillators
and high frequency logic create ElectroMagnetic Interference (EMI) that
can affect the receiver’s sensitivity. Essentially, it creates noise that
hurts the receiver’s ability to hear the transmitter.
Internal Factors

6. External Factors

7. Radio Signal
The radio signal spreads out as it travels from the transmitter to the
receiver. The farther the signal travels, the weaker it gets. This effect is
frequency dependent, so higher frequency signals get weaker faster.
This is due to the physics of electromagnetic propagation and there is
nothing that can be done about it.
Interference
Interference is always a concern when it comes to wireless range. Other
transmitters on the same frequency in the same area at the same time
will interfere with a transmission in most cases.
External Factors

8. Propagation Path
The path that the signal takes from the transmitter to the receiver. If
there is nothing in the path, then the signal will not be attenuated. If
there is a massive building in the way, then the signal will be attenuated
and get weaker much faster.
Multipath
This refers to the fact that as a transmitted wave spreads out, it can
reflect off of things in the environment. This can be the ground, trees,
buildings, mountains, walls or anything else. The reflected signal can
make its way to the receiver, but will get there later than a part of the
signal that traveled a direct path. Multiple reflections can get to the
receiver from multiple directions. These reflected signals can interfere
with the direct signal and even cancel it out to the point that the receiver
does not pick up any good data.
External Factors

9. Calculating Range

10. • With all of the internal and external factors, it can be difficult to
calculate a system’s wireless range.
• There are some approximations, assumptions and simplifications
that can be made to arrive at a range estimate.
• Basic approach is to not worry about the external factors that can’t
be controlled. This assumes that the antennas are in an area where
there are no external affects, typically called free space.
• To start, we account for how the signal spreads during propagation,
the gains of the antennas and the frequency of operation and we
arrive at the Friis transmission equation.
Calculating Range

12. • This equation is for line-of-sight performance (nothing between
transmitting and receiving antennas).
• Solving for distance (d) gives the most basic way to estimate the
wireless range of the system knowing the rest of the system
parameters.
• Can be modified with mismatch loss and an absorption factor if the
signal is travelling through something other than free space.
• Loss factors can be added if the two antennas are not correctly
aligned.
Calculating Range

13. • Frequently, loss factors are not calculated and a constant 20dB loss
is included. This provides a reasonable approximation of real world
line-of-sight performance.
• Throwing this into the equation and solving distance (d) gives the
following:
• The units used for c need to match the units for d. The conversion for
f from Hz to kHz or MHz can also be added into this term (divide c by
1,000,000 to use MHz, for example).
Calculating Range

14. • The Friis equation provides a reasonable estimate of range for a
wireless RF system but it is just an estimate.
• The real RF world is dynamic and many things affect the signal.
• It is not always practical to model and calculate the effects of the
environment, especially for mobile devices that continuously move
around.
Calculating Range

15. • There are many, many factors (internal and external) to take into
consideration when estimating wireless range.
• Wireless range estimation is generally good to get a feel for how the
product will work.
• Allows different wireless solutions to be compared based on their
specification sheets before a design has begun.
All said and done, there is nothing like getting
out in the field and seeing what really happens.
Wireless Range Summary

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