Linx Technologies has published a white paper titled, "Considerations
for Wireless Range." Author Justin Hopper writes, "One of the first questions one asks when evaluating a wireless
system is 'what range will it get?' The answer to the wireless range question is somewhat complicated. The range
of a wireless system is dependent on several interdependent factors. Some are internal to the design of the product
and some are external. There are ways of estimating the wireless range of a system by taking into account several
factors. The first factors in determining wireless range..."
This article is one of the first entries in
Linx's new Blog.
One of the first questions one asks when evaluating a wireless system
is “what range will it get?” The answer to the wireless range question is somewhat complicated. The range of a wireless
system is dependent on several interdependent factors. Some are internal to the design of the product and some are
external. There are ways of estimating the wireless range of a system by taking into account several factors.
The first factors in determining wireless range are internal to the design of the system.
Transmitter Output Power
Transmitter output power is the amount of power produced by the transmitter’s output stage. Essentially,
this is how loud the transmitter is.
Receiver sensitivity is
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.
and Receiver Antenna Gains
The transmitter and receiver antenna gains are 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-00501 for more
Mismatch losses are 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 Noise Sources
Finally are 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
Looking at external factors, the primary factor that affects wireless range is the
radio signal that spreads out as it travels from the transmitter to the receiver. This means that 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 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
The propagation path is 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.
Finally is something called 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.
Estimating Wireless Range
With all of this,
you can see how it could be difficult to figure out a system’s wireless range. However, there are some approximations,
assumptions and simplifications that can be made to arrive at a range estimate. The most 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.
this equation for distance (d) gives the most basic way to estimate the wireless range of the system knowing the
rest of the system parameters.
This equation can be modified with mismatch loss and an absorption factor
if the signal is travelling through something other than free space. Loss factors can also be added if the two antennas
are not correctly aligned. Measuring all of these factors can be tedious and time consuming and it is still only
valid for a free space environment.
Frequently, these factors are not calculated and a constant 20dB loss
is included. This provides a reasonable approximation of real world line-of-sight performance. Line-of-sight refers
to an environment where there is nothing between the transmitting and receiving antennas, but some loss for multipath
and environmental attenuation.
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).
This 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. Wireless range estimation is generally good enough in these cases to get
a feel for how the product will work. It also allows different wireless solutions to be compared based on their
specification sheets before a design has begun. Still, there is nothing like getting out in the field and seeing
what really happens.
About Justin Hopper
received his BSEE degree from the Georgia Institute of Technology in 1998 with a focus on radio frequency design.
After a few years at Murata Electronics and Panasonic Wireless Design, he came to Linx Technologies in 2003. In
that time he has held a variety of roles spanning design engineering, applications engineering, marketing and sales.
He currently resides in the Tampa, Florida, area and spends his time working on his house and playing with his family.
About Linx Technologies
Linx Technologies makes wireless simple by developing and
manufacturing wireless products that are easy
for engineers of all skill levels to use. The company’s RF modules,
remote controls, antennas and connectors make it easy for engineers to integrate wireless features without the hassle
and expense of engineering RF functionality from scratch.
For customers who need help implementing Linx modules,
Linx offers design services including board layout assistance, programming, certification advice and packaging design.
For more complex RF solutions, Apex Wireless, a division of Linx Technologies, creates optimized designs with RF
components and firmware selected for the customer’s application.
Merlin, OR, US 97532
Phone: +1 800 736 6677
+1 541 471 6256 (outside U.S.)
Fax: + 1 541 471 6251
Posted September 13, 2013