GPS was known as a revolutionary positioning and navigation technique that could be used in all sorts of unexpected ways. This item has stood the test of time with new uses for GPS still being discovered.

But, GPS may not be a panacea for all of our positioning needs–that there are some situations in which GPS fails us. In particular, it was noted that GPS signals are “blocked” by buildings, making indoor use of GPS impossible.

But what was impossible 15 years ago is possible today. New designs have greatly improved the sensitivity of GPS receivers so they can make code-phase measurements even on the severely attenuated signals inside buildings. And if the signal is too weak for the receiver to extract the satellite navigation message itself, the necessary data can be sent to the receiver using a cellular telephone network, which also can supply timing information to help the GPS receiver acquire signals more quickly.