GPS Modernization: Capabilities of the New Civil Signals

Currently, the Global Positioning System (GPS) is undergoing stunning changes that will enhance both military and civil capabilities. We say that GPS is being modernized. In fact, this modernization is a fabric of change that includes three elements. It includes integrity machines, which are monitors that provide error bounds to safety-critical users in real time. It also includes a family of techniques to protect GPS users from accidental and malevolent radio frequency interference (RFI). Most of these RFI hardening techniques are based on so-called navigation signals of opportunity, such as inertial measurements or terrestrial radio navigation. Finally, GPS modernization includes new satellite signals that will provide the benefits of frequency diversity. Over the next ten years, a second civil signal, at 1227.60 MHz, and a third civil signal, at 1176.45 MHz, will join the current civil signal at 1575.42 MHz. These new signals will improve the fundamental signal acquisition and tracking performance of the GPS receiving engine. They will also enable a new family of alternatives for mitigating the ionospheric errors that currently limit the accuracy of GPS. This paper will focus on the new civil signals and the capabilities they enable.