Why does GPS work when underground and under big buildings but radio signals, Wi-Fi, and cell phone signals struggle?
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I want to start off with everything people are saying about dead reckoning is true, modern phones especially use all sorts of signals to get more accurate positions in disadvantaged situations.
To explain how gps can work in a building or a short distance underground, you need to know of a property of the GPS signals. The term is autocorrelation, but what you need to know is if you do a correlation (think multiplication but for signals) with itself it will be boosted, but if you correlate with something else, like itself but shifted in time, it will just turn out to be noise. What this lets us do is take a signal that we shouldn’t be able to receive, like one that has less power than the noise around us, and boost it if we know the shape it should be.
With every generation of gps we have added faster (more accurate) and longer signals (more boosted), which require better clocks than what is on most consumer devices. Luckily you can use the older generation signals to make your local clock work better and lock on to the longer signals, which can be the difference between receiving the GPS and not.
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