> With 32 satellites in orbit, GPS pretty much serves as the global reference. The US doesn’t share military grade signals with countries but civilian signals, in L1 (1575.4 MHz) and L2 (1227.6 MHz) frequencies, is free for all. But as is true with all innovators, it’s believed the US practises ‘selective denial’. In times of war, and sometimes even otherwise, the signals can be corrupted. Isro Chairman K Radhakrishnan says, “During the Gulf War, signals from some satellites were interrupted.”
> Amid such uncertainties, when the default control and navigation systems in defence projects are equipped with GPS devices, a country’s security rides on these radio signals whose control lies elsewhere. For this reason, in its upgraded BrahMos missile, India has added Glonass receivers to the standard GPS receivers because Russia, unlike US, gives access to military signals.
http://forbesindia.com/article/real-issue/isros-very-own-gps...