摘要：Until now, civilian global satellite navigation systems (GNSS) receivers have had essentially only one signal, the GPS L1 C/A-code, reliably available for navigation. However, in the coming years, many more operational GNSS signals, systems, and frequencies will become available to civilian users.
Some of these signals represent new navigation systems, while others are modernizations of existing GNSSes. Although we cannot predict how these signals will be used when they become more prevalent, the current GNSS environment allows us to take a glimpse into the potentials and challenges of that future.
