The need for a robust Position, Navigation and Timing (PNT) system to complement or back up GNSS in critical infrastructure/critical applications is widely acknowledged. This translates into actions taken by stakeholders to further raise awareness (e.g. radio navigation plans in the US and Europe) and for some, pave the way towards some deployment (e.g. recent Request for Information initiated by the US Department of Transportation for a timing infrastructure independent of GPS). This yields a renewed interest for Extremely Low Frequency (ELF), Very Low Frequency (VLF) and Low Frequency (LF) systems, such as the enhanced Long Range Navigation (eLORAN) or PTB, identified by some as a very relevant candidate to back up GNSS in timing applications.

As the role PNT solutions in safety-critical operations increases, the users’ demands in terms of performance and trust grow past the point in which a single-system approach can meet all requirements. The optimum implementation will be a mix of navigation services that will include space-based global services, terrestrial-based regional services and user-centred systems. Furthermore, wireless communication networks will complement the legacy PNT infrastructure with data dissemination services, as well as with ranging and synchronisation capabilities. For example, existing LF communication systems could be adapted for enabling regional PNT services, exploiting, thus, the
available network of transmitters as well as the benefits of LF signals.

Research and Development (R&D) efforts have been made in order to improve the performance and reliability of PNT systems based on ELF1, VLF and LF signals. Enhancements in the data signalling and broadcast format, and in the propagation models, added to infrastructure upgrades have led to better coverage and higher precision. Further studies showed that these systems could also incorporate signal and message authentication in order to make them more robust against deliberate tampering. The low frequency radio navigation signals are very robust against on-air attacks due to their high power and long wavelength, and given their potential for improvement, are a very attractive candidate for complementing GNSS and for adding security to the PNT landscape.

The understanding of potential benefits and shortcomings of the aforementioned ELF, VLF and LF techniques is not as widespread as for GNSS and more R&D investments are needed to pave a way forward for the solidifying the PNT infrastructure. In this context, it is necessary to investigate these emerging trends in complementary or alternative PNT techniques and bring additional technical perspectives to decision-making process regarding the future of ELF/VLF/LF infrastructure in Europe. Potential developments in
the field will stimulate European industry and will increase the users’ trust in PNT services.

This activity aims at developing an innovative, robust and reliable PNT concept based on ELF, VLF and LF techniques, able to complement GNSS-based services and to provide an alternative in the event of a GNSS outage or service disruption. It will validate the proposed PNT concept by means of a proof-of-concept and benchmark it against legacy GNSS and combined eLORAN/GNSS solutions, in a common framework.

The objectives of the activity comprise:

  • To investigate and report on the need and opportunities of a complementary and/or alternative low frequency PNT concepts and to consolidate the relevant use cases.
  • To review the state-of-the-art relevant for this activity, identify multiple candidate ELF/VLF/LF techniques and system concepts, and assess their benefits and shortcomings (e.g. infrastructure and UE complexity, antenna considerations, security and resilience of the proposed techniques against PNT-specific threats such as interference, jamming and spoofing, etc.).
  • To trade-off and consolidate potential implementations, and to develop a PNT
concept based on at least three innovative ELF/VLF/LF techniques in combination
with (or alternative to) GNSS.
  • To develop a proof-of-concept of the innovative ELF/VLF/LF PNT techniques in combination with (or alternative to) GNSS for critical infrastructure and applications.
  • To test key use cases and scenarios of the combined GNSS/ELF/VLF proposed concept for improved PNT.
  • To assess the achieved performances of the proposed PNT concept with respect to current state-of-the-art of positioning solutions (GNSS and combined eLORAN/GNSS), and derive conclusions and recommendations for future activities.

The outcome of the activity will provide the European industry with a thorough understanding of the potential of ELF, VLF and LF signals for radio navigation and should set the grounds for future R&D activities in the frame of reliable GNSS alternatives for critical infrastructure.