Quality Control for Location-Enabled Devices
A guide to production testing.
QUALITY CONTROL FOR
LOCATION-ENABLED
DEVICES
A guide to production testing
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Challenges for the unfamiliar
The addition of location awareness to all manner of high-volume consumer
products brings with it a number of challenges for manufacturers that
are not necessarily familiar with satellite navigation technology.
And these challenges do not end once the product is
designed and debugged.
When the product moves into production, the challenge becomes how to ensure
that every single unit leaving the factory will perform exactly as it should.
Because any malfunctioning location aware product will very quickly be found
out – as soon as it gives its users an inaccurate fix on their position, or delivers
navigation instructions that are patently wrong.
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Manufacturers of consumer products from cars to
mobile handsets have become all too aware of the
power of the disgruntled user. Online forums and
today's social media provide the dissatisfied
customer with the means to tell the world that
any given product does not do “exactly what it says
on the tin”.
And while such media can offer valuable
opportunities to improve customer interaction, recurring negative comment can
do irreparable damage to any brand's
reputation for reliability.
The
dangers
of
failure
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Quality control
Clearly, the only way to ensure that products released to the market are fit for
purpose is through functional testing at the end of the production
line. And in this respect, the GNSS receiver is no different from any other
function of the end equipment.
The challenge then becomes how best to integrate functional testing of the
GNSS receiver with the other tests performed on the product. And that
means devising a test strategy that will exercise the equipment sufficiently to
prove its correct (or incorrect) functionality in the minimum possible test time.
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Functional testing
As with any functional testing, the operation will involve applying a known
stimulus and observing the response. If the response is within acceptable bounds
the product passes the test; if the response is outside those bounds the product
fails.
The response to the stimulus may simply be a trigger signal or an alarm, or it
may be some variable output that can be measured for the purposes of the test.
But whatever the expected result, it is essential that the stimulus is
accurate and repeatable so that the response can be gauged against a
known standard.
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The tests required
The exact tests required will depend entirely on the intended use of the end
equipment. And while it will not be necessary to exercise all the functions of
the GNSS receiver, the tests need to ensure that the receiver will function as
required when it is used “in anger”.
So while static navigational accuracy may well be the simplest test to perform,
other aspects such as time to first fix (TTFF) or re-
acquisition time might well be important to the overall operation of the
equipment.
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Supplying the stimulus
When integrating GNSS tests with other acceptance tests, the first (and rather
obvious) problem is that the test area is not exactly a GNSS friendly
environment. The roof of the production area will almost certainly block the
ingress of signals from any GNSS system, and there will inevitably be a great
number of interfering RF signals being reflected around the test area.
The first of these problems is relatively easy to solve: the GNSS signals can be
“captured” by an outdoor receiver and relayed to the test area. However, while
relaying “live-sky” signals might seem to offer a cost-effective solution for
production testing of GNSS-enabled equipment, it does have many significant
limitations.
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Don't be fooled
Certainly, if the only test required is for the equipment to recognise the
presence of GNSS signals, then the relayed signals would be adequate for this
purpose. Similarly, if the object of the test is for the equipment to determine its
location from the signals supplied, then the relayed live-sky signals will suffice.
However, the whole ethos of quality control is to
determine whether the equipment produces the
expected response to a known stimulus. Certainly, the
location of the test rig will not change, and so the position calculated by the
GNSS receiver should always be the same.
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But the nature of the “live” signals that are being relayed
will be changing constantly. The relative positions of
the satellites within the constellation will change; the
atmospheric conditions will never be constant; and
other external influences such as interference will not be
consistent. So much for applying a “known” stimulus!
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The reliable alternative
A GNSS simulator provides the ideal alternative to any form of “live” signals for
testing any GNSS receiver. And while the simulator that would typically be used
in characterising the design would need to be a fully-featured multichannel
instrument capable of simulating the signals an entire constellation of satellites,
the simulator used for production testing can be a relatively simple single-
channel unit.
The important aspect here is that the simulator will produce exactly the same
stimulus each and every time. Therefore any variation in the response of the
equipment under test can easily be observed. And if the response falls outside
acceptable bounds then the equipment will be rejected.
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Bringing it all together
Of course, it is highly unlikely that the GNSS receiver will be the only part of the
equipment that requires acceptance testing. So it is important to choose a GNSS
simulator that can be integrated with other test equipment in order to create a
complete functional test system for the whole equipment.
The combined test setup will speed product
throughput, minimising test time and enabling complex “if-then” test
scenarios that can exercise multiple functions in a single software-controlled
test routine.
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Reputation preserved
By integrating simulator-based GNSS receiver testing with other functional
testing as part of a complete quality control procedure, manufacturers can be
confident that their location-enabled products will perform
as designed, helping maintain consumer confidence in their hard earned
brand reputations.
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If you found this article of interest
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You can find more GNSS related technical articles, white papers and eBooks at the
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Visit the Spirent GNSS blog
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Need more information?
gnss-solutions@spirent.com
If you're curious about how the information in this document can benefit you and
your business, please contact Spirent to discuss your particular situation and
explore opportunities.
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