Manufacturers of consumer products routinely perform functional testing on all production output, and it would appear that adding some form of location testing to these production test routines would be sufficient to verify the reliability of the GNSS receiver within the end product. However, it is all too easy to adopt the attitude that the simplest of tests will suffice – particularly when the duration of each test can have a significant impact on productivity.
Although it may be the case that all the other functions of the end product can be assessed with a relatively straightforward go/no-go test, taking such an attitude with a GNSS receiver is fraught with danger. The end user will expect the product to perform adequately under a wide variety of conditions. This means that the receiver will need to be tested not just for an “ideal” situation, but also for adequate performance in the presence of multipath interference, all manner of jamming signals and less than ideal atmospheric conditions.
Key test challenges in a Production line environment
The first obstacle that will be encountered in integrating GNSS receiver testing into a production test setup is pretty obvious. As such tests are performed at the end of the production line, they are inevitably performed indoors. And regardless of whether the equipment is designed to work indoors or outdoors, the roof and walls of the building will introduce variables into the test that will negate its effectiveness. So-called “live-sky” testing is therefore impossible without relaying the GNSS signals from outdoors to the production tester.
It is a relatively simple exercise to capture live GNSS signals and re-radiate them within the production test environment. However, this comes with its own set of shortcomings.
First, radiating any signal in such an environment might have unforeseen consequences on other tests that are performed on the product; and conversely, other RF signals and noise within the production test area may well impact on the integrity of the GNSS signals.
More importantly, though, the inherently dynamic nature of GNSS signals means that while each unit may well be tested in the same physical location (i.e. in the production tester fixture), the relative positions of the GNSS satellites will be different for every unit tested. And, not surprisingly, this makes direct comparison between results unreliable at best.
GNSS tests within a Production line environment
In order to fully assess the performance of a GNSS receiver embedded in any piece of equipment, it is important to work out exactly what response is required. There will be varying degrees of performance required, depending on the end application, but the requirement will be for a combination of navigational accuracy and sensitivity under a wide range of operational conditions. There will also be a requirement for the equipment to work with not just the existing Global Positioning System, but also with the forthcoming enhanced GPS, GLONASS and Galileo systems at the very least.
Some systems may have no direct output. Or, more to the point, the output may only be in the form of an alarm or trigger that is supposed to be produced with proximity to certain co-ordinates. This does not however mean that the performance demands on the receiver are any less arduous. It would however, dictate the pass/fail criteria for the production test.
GNSS test solutions for a Production line environment
Given the inherent variability of any type of live-sky testing, it is logical to seek a more precise and repeatable stimulus against which the performance of an embedded GNSS receiver can be assessed. And this can be supplied in the form of a GNSS simulator.
A multichannel multi-GNSS simulator under software control can produce all the necessary signals required to test the relevant performance criteria of any embedded GNSS receiver in any location-enabled device. Most importantly, it can do so consistently and repeatably for every unit to be tested, ensuring that manufacturing output is 100% fit for purpose.
The tests typically performed on any navigation device are inherently complex, covering the full range of performance criteria from navigational accuracy and sensitivity to acquisition time and immunity to interference. These tests have been designed to ensure the performance of dedicated GNSS receivers, and have been proved over successive generations of personal navigation devices.
Fortunately, once the desired performance of the design has been characterised, the production tests for the end product can be refined into a considerably smaller set of acceptance criteria that can be performed in a relatively short time (as little as 5 minutes).
The SpirentSignal Generator has been designed specifically for high volume production test applications for devices that use commercial GPS/SBAS, GLONASS and/or Galileo receivers. Visit our video library to find out more on how Spirent can help.