L5 adds a third civilian frequency for demanding applications

L5 was designed for applications that need more robustness than the original civilian GPS signal could provide, particularly aviation and other safety-of-life transportation. It uses a protected aeronautical radionavigation band, higher transmitted power and a modern signal design. Combined with L1 and L2C, the third frequency also gives advanced receivers additional ways to detect and correct propagation errors. GPS was becoming not simply more accurate, but more diverse: different civil signals could now be optimised for different classes of users.