Satellite Time and Location (STL) Technology

What is STL or Satellite Time and Location Technology?

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- everything RF

Apr 10, 2023

Satellite Time and Location (STL) Technology or STL, is a global Positioning, Navigation, and Timing (PNT) service developed by Satelles Inc, a company that provides GPS-based PNT satellite services, in partnership with Orolia, a company that develops high-end crystal, rubidium, maser, and integrated GPS/GNSS clocks for space missions. The STL service utilizes the Iridium constellation of satellites in the Low Earth Orbit (LEO) to provide relatively superior geo-location services to customers compared to traditional GNSS/GPS infrastructure. Orolia has partnered with Satelles to integrate the STL technology into the SecureSync, a multi-constellation GNSS time and frequency platform, providing a secure and accurate PNT service, even in environments where traditional GPS signals cannot penetrate. The STL service has been developed to a point where it is available today for customers to experience an accurate and secure global coverage anytime and anywhere.

This service is unique in that the signals generated by the LEO satellites are relatively powerful, very secure, and available globally. These high power signals complement GPS systems and are therefore ideal for use in GPS-denied environments where GPS signals are obstructed or degraded, especially in indoor areas. Satellites utilizing STL technology also generate complex, unique type of signals that are combined with signal authentication schemes to deliver a highly secure time and location service. Thus, when STL is used in tandem with GPS and other GNSS signals, the resulting infrastructure provides a relatively powerful, resilient backup PNT solution for critical positioning and timing applications, compared to relying on GPS/GNSS signals alone.

Similar to GPS and other GNSS constellations, the STL uses several microwave frequency bands for communication between satellites and between satellites and ground terminals and gateways. These frequency bands include the L-band (from 1 to 2 GHz), K-band (from 18 to 26.5 GHz), and Ka-band (26.5 to 40 GHz). These satellite systems use the L-band frequencies to communicate directly with the ground terminals such as users (subscribers) or other satellite-enabled mobile devices. The K/Ka-band frequencies are utilized for inter-satellite links and also to communicate with gateways on Earth.

 STL Technology, Image Credit: Satelles Inc

Advantages of STL Technology over GPS and other GNSS Technologies

1. Relatively High Signal Strength from LEO Satellites: The proximity of LEO satellites is such that they are roughly 25 times closer to the Earth than other GNSS satellites. In addition to this, a high-power satellite signal is also generated from these satellites, which results in a signal (STL-based) that is roughly 1000 times or 30 dB higher in amplitude than GPS. This high-power signal allows STL signals to penetrate deeply into GPS-denied environments, providing PNT services even in challenging environments like indoors areas.

2. Wide Area Global Coverage: The Iridium satellite constellation consists of 66 polar-orbit LEO satellites that are linked to each other to form a mesh network. The LEO satellites are cross-linked to provide a continuous orbit and time information even at times when most are not in view of ground terminals. This forms an efficient and flexible global network in space to provide accurate time and location information anywhere – in urban and rural areas, air, sea, and in Polar Regions.

3. Highly Secure Transmission: The STL-based satellites generate special overlapping spot beams where each beam provides a unique location-specific key. A key is a random stream of binary bits that are used to encrypt and protect the data from adversaries. These keys are programmed to change every second, making it difficult for eavesdroppers to use earlier keys to decode the data. STL also combines this beam pattern technique with other signal authentication techniques to allow an even higher degree of security as needed in critical space missions.

User Equipments (UEs) that integrate STL technology are designed to detect PNT data manipulation. This is carried out by constantly comparing the PNT data from GPS/GNSS systems and STL to determine whether the values deviate beyond a pre-determined threshold. An STL-enabled receiver is capable of generating an alarm when the GNSS signal is intercepted by a third-party user delivering false or potentially dangerous PNT information. In such cases, the receiver will automatically switch to STL mode and will lock onto it as the authentic source of PNT data.

4. Accurate Timing Reference: STL uses precision timing reference devices such as temperature-compensated crystal oscillators (TCXO), oven-controlled crystal oscillators (OCXO), and atomic clocks, to generate high precision clock signals for receiver synchronization and other coordination purposes. It also provides a zero long-term drift in timing, which results in an accuracy in the order of sub-microseconds and sub-hundred nanoseconds.

In conclusion, STL offers an augmented and secure backup for GPS and other GNSS systems by harnessing encrypted information using Iridium LEO satellites. It ensures PNT information that is precise, highly secure, and accessible on a global scale, and impervious to cyberattacks, making it almost insusceptible to GNSS vulnerabilities such as signal manipulation. STL signals can easily reach into buildings and other hard-to-reach environments by GPS/GNSS systems due to their high-power signal. Therefore, with the ability to deliver such high precise PNT service, even in challenging environments, STL technology offers a critical resource for various mobile operators, power utility companies, government, satellite-enabled drones, government, scientific research, and other satellite communication networks.