Test Results from a LEO-Satellite-Based Assured Time and Location Solution

This paper describes a LEO-satellite-based solution for assured time and location that is highly resilient and physically secure. The system is able to augment or serve as a back-up to existing GNSS solutions by providing secure time and location measurements in the presence of high attenuation (e.g. deep indoors), active jamming, or malicious spoofing. Experimental time and location results are presented based on simplex broadcasts from the Iridium satellite constellation. Characteristics of the system that enhance security and resilience are also described and demonstrated. The Iridium constellation, illustrated in Figure 1, consists of 66 Low Earth Orbiting (LEO) satellites which are primarily used for global communications. The authors have worked in conjunction with Iridium to develop the Satelles Time and Location (STL) solution. STL employs the Iridium LEO satellite constellation to transmit specially structured time and location signals which, due to their high RF power and signal coding gain, are able to penetrate into difficult attenuation environments, including deep indoors. Similar to GNSS, these signals are specifically designed to enable precision time and frequency measurements by a receiver. In this paper, the authors describe the system, including the ground segment, space segment, and user equipment. The positioning performance of the system is measured experimentally in multiple operational configurations, including high attenuation environments. The results are presented, and the suitability of a resilient and secure positioning solution as an augmentation or back-up to GNSS is discussed.