L2C

L2C is a civil signal in the Global Positioning System (GPS) modernization program. It is transmitted on the L2 frequency (1227.60 MHz) and provides civilian users with a second, independent signal to improve positioning accuracy and reliability. L2C operates alongside the legacy L1 C/A signal, enabling dual-frequency measurements that enhance ionospheric correction and overall precision. The L2C signal comprises two components: a data channel carrying the navigation message and a pilot channel that carries a replica of the data-bearing code to aid tracking, improving signal robustness in challenging environments.

Development and deployment of L2C began in the 1990s as part of GPS modernization. The first satellites broadcasting L2C were launched in the mid-2000s, and near-global coverage was achieved as more satellites carried the signal. Modern GPS receivers widely support L2C, often alongside L1 and L5 signals, enabling improved accuracy and reliability in a range of conditions, including urban canyons and environments with interference.

Impact and usage of L2C include enhanced dual-frequency positioning through better ionospheric correction, greater resilience to certain interference, and improved multipath mitigation. While L2C is now widely supported, some older receivers may not implement the signal, in which case reliance on L1 C/A remains common. L2C serves as a key element in GPS modernization, contributing to more robust and accurate civilian positioning.