July 24, 2023
Jeremy Bennington
Tags: GNSS Foresight, LEO, SimIQ, SimXona, Xona
Business is booming in Low Earth Orbit (LEO). ABI Research predicts that up to 2,400 new LEO satellites will be launched in 2023, joining the 4,500 already in orbit, and with the number approved for deployment reaching 30,000 by the end of the decade. Meanwhile, the number of subscribers using LEO satellite services is set to reach 2.4 million this year, as companies like SpaceX continue to roll out fast LEO-based broadband.
LEO is an attractive proposition for providers of satellite broadband (sometimes referred to as Non-Terrestrial Networks or NTN), positioning, navigation and timing (PNT-GPS augmentation or replacement), and remote sensing services. This is because the proximity to Earth enables lower latency, stronger and more robust signals, and relatively low launch costs.
But designing a satellite constellation for use in LEO is a complex business, and investors, partners, customers, and regulators all want assurances that the constellation will function as promised once in orbit. As early field testing is financially and logistically impractical, LEO constellation developers need to test and validate PNT functionality as efficiently and accurately as possible in the lab.
With over 35 years’ experience of supplying advanced simulation, test, and measurement solutions to the space industry, Spirent offers test solutions for LEO constellation planners and developers, each addressing three of their biggest challenges.
Many of the services being developed for LEO deployment are intended for use in urban locations. From fast satellite broadband to precise navigation services, signals broadcast by LEO satellites must be able to reach receivers in towns and cities effectively.
However, radio signals from satellites are easily blocked by impediments including terrain, buildings, and other structures, creating fluctuating patches of poor coverage in densely-populated areas where demand for services is likely to be high. In order to offer reliable and acceptable service levels, constellation planners need sophisticated tools to ensure the right number of satellites are launched and in the right orbits. With constellation deployment being a capital-intensive effort over many years, predicting service coverage as the constellation grows is critical to determining where services can be offered and at what cost.
Spirent’s cloud-based signal forecasting service, GNSS Foresight, accurately models and predicts patterns of signal coverage from deployed and planned LEO constellations in real-world locations. Using accurate orbit models and 3D maps of real cities worldwide, Foresight enables LEO designers and developers not only to understand the coverage of proposed satellites and constellations in critical areas, but also to demonstrate this to prospective partners, customers, investors, and regulators.
In doing so, Foresight de-risks investment for all parties and enables developers to deploy only as many satellites as are needed to achieve the desired coverage—thus minimizing deployment costs and enabling more sustainable growth for constellation operators. In terms of time-to-market and time-to-revenue, Foresight enables constellation planners to see when a minimum viable product is (or will be) operational. Cloud-based delivery also means lower costs, greater accessibility, and the scalability to grow a service from design to operation.
Satellites destined for LEO operation typically rely on Global Navigation Satellite Systems (GNSS) for PNT data. GNSS data guides mission-critical capabilities on the LEO satellite, including establishing itself in orbit, navigating while in orbit, and de-orbiting at end of life. It also provides time synchronization for operation and communications. If the LEO service is licensed to broadcast on different frequencies in different regions, GNSS data can also indicate when a satellite’s coverage is passing out of one region and into another, enabling compliance with legal frequency requirements.
The GNSS system built into every satellite must be positioned optimally on the satellite to ensure clear and uninterrupted signal reception. The receiver must also be capable of reliably receiving and processing GNSS signals in the unique conditions presented by LEO operation, including increased Doppler shift due to the high velocity of LEO satellites relative to the GNSS satellites they utilize.
Realistic lab testing is essential to characterizing the performance of the onboard GNSS receiver in both optimal and impaired signal conditions. This requires a simulator platform capable not only of generating realistic GNSS signals and signal impairments, but also of modeling the unique and challenging physics of satellite motion in LEO. Changes in atmospheric drag and gravity over different parts of the Earth while in orbit need to be accounted for in GNSS signal reception and operation of the LEO constellation and services.
For robust and rigorous testing of GNSS receivers at the design, selection, validation and integration stages of LEO satellite development, Spirent offers our powerful GSS7000 and GSS9000 GNSS simulators, with the SimORBIT enhanced orbit propagation tool for calculating high-accuracy orbits.
Successful deployment of LEO constellations requires not only the space segment to function as intended but also the user segment: the receivers and equipment that will use the LEO signals.
Similar to other satellite or wireless services, LEO applications need rigorous lab testing to ensure devices can receive and process signals from LEO constellations—including satellites and constellations that have not yet been deployed. Equipment and receiver developers therefore need an efficient and cost-effective way of realistically replicating current and future LEO signals in the test lab.
This is a challenge that Spirent addresses with the SimIQ software solution. It enables developers of L-band LEO signals to play those signals through a GSS7000 or GSS9000 simulator by uploading the relevant I/Q files. The Spirent simulator upconverts the I/Q files into high-fidelity RF signals, with any impairments, for replay to the chipset or receiver under test. This helps to control the cost of testing by removing the need to invest in separate simulators for GNSS and LEO signals. This capability is already helping trailblazers to test using Xona Space System’s PULSAR™ signals, long before the constellation is deployed.
With attractive market opportunities springing up in everything from remote sensing to non-terrestrial networks, there’s never been a more exciting time to be a LEO solutions developer.
But the path to successful deployment and adoption means overcoming a number of test hurdles, and Spirent is here to help.
Watch our webinar Test Considerations for LEO Constellations and LEO-Enabled Equipment to learn more.
