GNSS Augmentation by FM Radio Symbiosis

Emerging applications, such as improved all-weather safety for self-driving vehicles, require public positioning precision and reliability beyond the capability of open global navigation satellite system (GNSS) services. To meet these requirements, next-generation public positioning, navigation, and time (PNT) services should: 1) deliver ubiquitously available differential corrections and assistance information for massive numbers of concurrent users with fixed delay, indoor penetration and stable bit rate signals and 2) have navigation signals that are extremely enriched against challenging scenarios. The dilemma is that the free-of-charge public PNT service makes it a formidable challenge to build a dedicated information infrastructure. In this context, a natural question arises: where should we seek next-generation public PNT services in the age of Internet of Things? In this paper, we propose GNSS augmentation by FM radio symbiosis. Specifically, we propose GNSS augmentation-optimized digital data broadcasting for which the signal symbiotically co-exists with the analog FM radio in band and in channel without sensibly affecting the existing FM service. With this symbiotic digital data broadcasting, we then propose a GNSS augmentation system that can: 1) broadcast real-time kinematics correction to massive numbers of concurrent GNSS receivers to achieve outdoor precision at the centimeter-level; 2) deliver fine time GNSS assistance for significantly improved receiver sensitivity; and 3) provide common-view timing to enable GNSS independent ground positioning beacon signals. A prime challenge therein is to separate the symbiotic digital signal from the much stronger, spectrum-overlapping co-channel FM signal; this challenge represents a non-orthogonal de-multiplexing problem that is solved by a novel modulation structure. A prototype was designed, and field tests by authorized third parties were conducted with excellent results.