GPS Modernization and the L2C Signal
L2C is the name given to one of the new signals to be broadcast from the satellites in the modernised GPS constellation. This new signal is intended for civilian use (hence the “C”), and will be broadcast on the L2 frequency at 1227.6MHz by all satellites from block IIR-M onwards.
The L2C signal is one of the key means by which the modernized GPS will offer improved accuracy and availability for civilian applications based on dual-frequency receivers. Not only is the signal intended to be easy to track, but it will also offer redundancy for the L1 signal in areas prone to interference.
In addition, having the L1 and L2C signals broadcast simultaneously on different frequencies will provide a relatively simple means for dual-frequency receivers to measure and mitigate the ionospheric delay error for each satellite.
The structure of the L2C will be different from the L1 signal (which will continue to be broadcast unchanged to assure backward compatibility with existing receivers), and will comprise two separate code chains, dubbed CM and CL, which are multiplexed to form a 1,023,000bit/s signal. The L2C signal characteristics will provide 2.7dB greater data recovery and 0.7dB greater carrier tracking than the existing L1 C/A.
The full nature of the L2C signal is defined in the IS-GPS-200 standards document, and the signals are not likely to be broadcast until at least 2013. However, designers working on dual-frequency receiver designs for use with the modernised GPS can test their ideas and prototypes today using Spirent's family of Multi-GNSS constellation simulators.
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