How a GNSS Simulator can Help Test the Multipath Performance of GNSS Receivers

Like any form of radio receiver, a global navigation satellite system receiver will be subject to interference from multipath effects arising from the reflection and refraction of its intended satellite signals by both natural and man-made artifacts. However, unlike some radio systems in which a small degree of interference may be tolerable to the end user, multipath interference will have an unacceptable effect on a GNSS receiver, making the output both unstable and inaccurate.

There are several multipath mitigation techniques available to the GNSS receiver designer, but in order both to assess the initial requirement and to measure the effectiveness of the measures taken, extensive testing is required. However, such is the diversity of multipath effects and the factors creating them, it is simply impractical to reproduce any form of meaningful tests using real-world GNSS signals. Therefore, the use of a GNSS simulator in the laboratory offers the only practical solution.

Crucially, a simulator system with suitable software will be able to simulate all the various multipath effects both singly and in combination, enabling designers to assess the true performance of their designs and the effectiveness of their multipath mitigation strategies.

A good GNSS simulator will not only offer the pre-defined models already discussed, but will also give the user complete control of the signals being generated. This control will allow intricate manipulation of the signals at digital baseband, which in turn will allow any effect to be implemented.

Remember, the most important thing is to ensure that you have complete knowledge of your test signals at all times. The moment you stimulate your receiver with an unquantified signal is the moment you introduce unwanted uncertainty into your tests.

With more and more users coming to rely on the accuracy of their global navigation satellite system receivers and increasing numbers of location-based services leveraging this accuracy, it is clear that interference caused by multipath effects cannot be allowed to compromise the accuracy of any GNSS receiver design. Ever-more sophisticated and effective multipath mitigation techniques are becoming available, but it is only by controlled, analytical and statistical testing at all stages of the design process that these techniques can be applied and proven.

Real-world testing can never hope to repeatably replicate all the potential multipath effects that may occur in a limited test timescale, nor can it be expected to provide even a representative sample. And so the use of laboratory-based simulation offers the most reliable, accurate and repeatable test regime to ensure the performance of any GNSS receiver design.

However, not all simulators are born equal, and not all simulation software is made equal. Only by choosing high-quality proven multichannel hardware with software that provides maximum coverage of multipath effects and models can the GNSS receiver designer be sure that his or her design will provide optimum performance under all conditions. And that is the route to end-user satisfaction.

If you want more information on Spirent’s range of GNSS simulators browse our website or get in touch.

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