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How to Ensure Your GNSS-Reliant Device Complies with ETSI EN 303 413

The ETSI EN 303 413 standard requires GNSS device manufacturers test for adjacent band compatibility. Here’s what you’ll need to stay compliant.

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From 13 June 2017, all new and “significantly changed” GNSS-reliant devices launched in the EU must be tested to ensure they are compliant with ETSI standard EN 303 413. This could mean a significant change to your test regime.

Part of the EU Radio Equipment Directive, the new European Telecommunications Standard Institute (ETSI) standard marks the first mandatory testing regulations for GNSS chipset manufacturers and system integrators operating in EU territories who intend to mark their products for European Conformity (CE)

Why a new standard?

The ETSI EN 303 413 standard is designed to make sure GNSS-reliant devices are protected against RF interference in frequency bands adjacent to the GNSS frequency spectrum.

I discussed the history behind the standard in a previous blog, but in summary, this standard is a pre-emptive measure from the EU to ensure adjacent band compatibility between GNSS-reliant products and other RF devices and services continues – even as governments are put under increasing pressure to allow access to parts of the RF spectrum that are close to frequencies used by GNSS

What does the standard include?

The standard specifies a range of testing criteria, including:

  • Noise type and power
  • Injection frequencies (five in total)
  • Received GNSS signal power
  • Allowed degradation of signal

It also includes the type of interference test signal required (an average white Gaussian noise with a 1MHz bandwidth) – and, crucially, the specific measurement parameter: carrier-to-noise ratio (C/N).

Though the standard does not require a specific test methodology, it does provide some testing guidelines. The standard recommends using the following equipment:

  • A GNSS signal generator capable of simulating the GNSS constellations and GNSS signals supported by the Equipment Under Test (EUT)
  • An RF signal generator capable of generating the adjacent frequency signal
  • A filter for ensuring the test is not adversely affected by Out of Band Emissions
  • An RF power combiner for combining the GNSS signal(s) and the adjacent frequency signal
  • A means for recording C/N0 before and after the adjacent frequency signal is applied
  • A way to confirm signal RF power as it enters the EUT

The standard also demands tests are conducted at certain temperature and humidity levels – so a temperature and humidity sensor are also required.

So far, so straightforward for this recommended test setup. The only cause for concern is the means of recording CNR.

Why settle on CNR as the main test parameter?

While there will undoubtedly be a lot of discussion as to the merits of the C/N metric’s suitability for measuring performance degradation of GNSS devices, one point to note is that if each application area had to choose a metric to measure performance degradation, every single one would likely choose a different metric.

C/N offers a single unified metric that will apply across all GNSS devices and use cases. Provided C/N does not degrade by more than 1db during testing, the Equipment Under Test will comply with ETSI EN 303 413.

The only area that could be problematic is the “means for recording C/N”. This may not be easy for some products to do – although in some of these products it may be possible to record the Signal to Noise Ratio (SNR) instead. While this isn’t an equivalent metric, it may allow the C/N and the degradation in C/N to be extrapolated.

When public consultation begins on the standard (very soon the standard will be released for a six month public consultation), one question that could be asked is whether an extrapolation of the SNR back to the C/N value (possibly with some analysis needed) is acceptable or not – and the resulting ramifications for GNSS test regimes.

Beyond ABC – testing spurious emissions

The adjacent band compatibility testing is just one component of ETSI EN 303 413. The standard also includes a spurious emissions test to ensure a device isn’t radiating on unnecessary frequency bands.

The spurious emissions part of the ETSI standard doesn’t include anything most GNSS engineers haven’t seen before. The only noteworthy inclusions are:

  • Devices need to be set to receive only mode
  • The receiver must remain active for the duration of the test
  • Emissions outside of the 30MHz to 8.3GHz need to be identified
  • Both conductive and radiative testing is allowed

The ETSI standard: a first of its kind

I’ve attempted to summarise the key elements of the ETSI standard here to give engineers and device manufacturers a head start on how their testing might need to evolve in the future. I’ll report more details as they come to light, and I’d recommend investigating the standard in further detail.

For more updates on changing legislation and risks to GNSS-reliant devices – or to discuss the new standard with likeminded engineers – you may also like to join the GNSS Vulnerabilities LinkedIn Group.

Or, if you have any further questions on ETSI EN 303 413 compliance and how it might affect your GNSS testing, feel free to talk to the Spirent team.

 
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