How to build indoor GPS?

Radio signal from GPS/GLONASS/Galileo/Beidou satellites is too weak to penetrate through walls. Thus, we can’t have regular GPS indoor.

Therefore, one needs to build an Indoor “GPS” – a local indoor positioning system:

• RTLS – real-time locating system
• LPS – local positioning system
• IPS – indoor positioning system
• INS – indoor navigation system
• Indoor “GPS”

Effectively, all acronyms above is the same thing, but with different names and slightly different meanings:

• RTLS and LPS are not necessarily indoor. For example, GPS is also an RTLS. But, typically, by RTLS means non-global and non-satellite based systems
• IPS provides positioning, but not necessarily navigation, i.e. it is good for tracking something or somebody
• INS has to provide positioning in order to provide navigation. However, in practice INS and IPS are very often used interchangeably for defining all sorts of non-GNSS based systems

By the way, GNSS stands for Global Navigation. Satellite System. GPS, GLONASS, Galileo, Beidou are GNSS systems.