Advances in Signal Processing for GNSSs [From the Guest Editors]

Where am I? What time is it? These are intimately related questions that have accompanied humanity for centuries. From past times when sailors were excitingly discovering recondite regions on Earth, to current outer space exploration, from the fascinating development of calendars by ancient civilizations all over the world—typically for agricultural purposes—to current developments of extremely accurate atomic clocks, reliable position and time measures have played an important role in human progress and will continue to do so. Today, knowledge about one’s own (or another’s) position is used in countless applications and represents an enabling piece of information. Mass-market location-based services, whose rise is tightly related to the advent of smartphones, call for it. Additionally, most critical infrastructures depend on accurate and secure access to position and timing references. Such infrastructures include ubiquitous road/rail/maritime/air transportation facilities but also for other applications of importance to everyday life, like the synchronization of distant base stations in cellular communications, time synchronization in the power grid, or high-frequency trading and other banking operations. In this context, it is fair to claim that use of global navigation satellite systems (GNSSs) is the technology of choice whenever it is available. GNSS is the general term used to identify those systems and technologies pioneered by the global positioning system (GPS), which enables positioning and timing based on a constellation of satellites and other augmentation systems. GNSS technology today is ubiquitous in many transversal infrastructures and has become the backbone of all applications where precise position, navigation, and timing (PNT) of user equipment is required. Moreover, GNSS is the pervasive PNT technology in outdoor environments, where its performance, coverage, and reliability exceeds that of other technical solutions.