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Positioning, Navigation and Timing in Low Earth Orbit


Low earth orbit (LEO) satellite constellations are promising to revolutionize communications. But building a high-performance LEO service presents a significant challenge.

From 5G and WiFi connectivity to earth imaging and climate monitoring, LEO constellations are opening up new possibilities in a wide range of industries. Amazon’s Kuiper, SpaceX’s Starlink, and the OneWeb constellation are three well-known examples of how this technology area is accelerating. However, what’s perhaps less understood is the dependence of these constellations on positioning, navigation and timing (PNT) data. We are so used to getting our PNT information from space that, perhaps, the consideration that devices in orbit also need to derive that information isn’t immediate.


Many LEO constellations depend on existing GNSS infrastructure to derive PNT information. That information is used in a number of critical ways:

  • Precision orbit determination (POD) for satellites moving at – or in excess of – 7.5 km/s in the most crowded part of space is a crucial function. As well as planning for continuous coverage, this orbit determination reduces the risk level of collision considerably.

  • Precise positioning is central to many of the payloads carried by LEO constellations. Accurately geolocating images taken of earth, for instance, is dependent on that position being reported accurately and reliably.

  • Timing and synchronisation plays a similar role to positioning regarding some satellites. System synchronicity is crucial in timestamping imagery, as well as for transmitting data, and for any time-of-arrival-based signals emitted.

PNT from LEO

As well as a challenge, LEO presents a significant opportunity for PNT. The proximity to earth compared to satellites in MEO orbits means higher power levels are available from LEO satellites, offering possibilities for many applications. For example, combining with MEMS inertial sensors, LEO satellite signals could enable precise indoor positioning. Lower development, launch, and maintenance costs make it an attractive option for total coverage. Lower signal propagation delay also makes it well-placed to offer resilience against the atmospheric delays caused to GNSS signals.

With some LEO PNT systems already moving towards operational capability, and others proposed, this technology is poised to become a great enabler for industries and governments seeking to strengthen their PNT provision.

Enabling Astrocast Satellite IoT

These challenges and opportunities, however, place greater demands on test and development. As has been understood for years in the space industry, sending satellites or devices into space to test their efficacy is not safe or cost-effective. This means testing in the lab – but lab conditions do not naturally mirror the intended environment.

Spirent has been supporting the testing of space-based systems since the early days of GPS in the 1980s. More recently, this tradition has been continued with the support of major and emerging LEO technology through expert knowledge and technological advancement.

Headquartered in Switzerland, Astrocast offers a cost effective, bidirectional and comprehensive Satellite IoT service to tackle global connectivity challenges in remote areas for industries such as maritime, agriculture & livestock, environmental & utilities, land transport, mining, oil & gas, and industrial IoT devices. Its Satellite IoT enables asset tracking and monitoring anywhere, regardless of blind spots without cellular coverage. In order to evaluate and optimize the performance of their network, Astrocast needed to conduct thorough testing of their onboard GNSS receivers – but were being held back by dated and inflexible test equipment.

Read our case study to find out more about how Spirent GNSS simulation technology has helped Astrocast to identify and eliminate issues, saving significant engineering hours and assuring network performance across the coverage area.

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Mia Swain
Mia Swain

Mia Swain is a Product Manager working on simulator products and PNT solutions within the Spirent Positioning Technology business unit. She has an academic background in Physics and worked in R&D, applications engineering and then product management. Mia Swain’s current focus is managing the commercial status and development lifecycle of Spirent’s commercial grade GNSS simulator and its software platform, ensuring that the products maximize their commercial value and next generation products meets the needs of the market.