GPS and other GNSS signals are now woven into the fabric of technologies we use across many industries. In fact, they play a key role in the operation of critical infrastructure such as communications networks, financial systems, power grids, and more. Despite the fact common GNSS systems do a good job providing solutions for diverse applications, they were never designed to be used in many of the ways applied today. There are distinct deficiencies which were never accounted for when it was first conceived years ago, and as critical applications push the envelope these manifest themselves more often.
First, GNSS signals are weak and easily interrupted accidentally or by intent. In fact, by the time they reach the ground, signals are weaker than the noise naturally generated by the earth itself. They also have limited ability to penetrate structures and work indoors. And with the increasing availability of software defined radios, the ability to spoof GNSS systems is easier than ever. For critical systems that rely upon these signals, these are serious problems.