Indoor positioning systems are designed to localize or navigate mobile objects (vehicles, robots, AGVs, carts, people, assets) indoor when GPS (or other GNSS) system is not available or not viable. Thus, effectively, indoor positioning system is like GPS but indoor, i.e. Indoor “GPS” and they do not rely on satellites, because the satellites radio signals are not available indoor (or underground) – they can not go through the roof or ground.
Indoor positioning and navigation systems are crucially important for our daily lives and yet they are not yet as prolific as GPS, for example. Why so? What is hindering the progress? What are indoor positioning systems and how do they work? What is the difference between global positioning systems and local positioning system, for example indoor positioning systems?
There is no fundamental difference between indoor local positioning systems and outdoor local positioning systems. They use the same architectures and even very similar beacons. But there are important details that have to be taking into account.
Presumably, you are familiar with Global Navigation Satellite Systems (GNSS) such as GPS, Glonass, Galileo, Baidu and less global GNSS from Japan, India, etc.
They rely on several satellites used as anchors, ground stations and mobile receivers that receive modulated radio signal from the satellites equipped with atomic clock. By knowing precisely when your GNSS receiver received a signal from a particular satellite and by extracting the exact time that was inside the received message, the GNSS receiver can calculate a propagation delay between your location and each satellites.
By relying on the known propagation speed of radio waves, the GNSS receiver and by knowing the locations of the satellites, the receiver can calculate its location with a typical accuracy of a 2-10m using multilateration (trilateration).
It is relatively easy to get power supply for stationary beacons indoor: regular power grid + converters, unprotected batteries, PoE – many options.
It is more difficult outdoor:
– Sources maybe simply not available
– Bringing power can be expensive than beacons themselves particularly for explosive environment (oil/gas refineries)
Wind can affect ultrasound based systems in two ways, at least:
– Wind produces noise that can reduce signal to noise ratio and limit the distance or decrease accuracy
– Since wind is a moving air, the speed of air is not accounted in the system and the measured location can be distorted
Luckily, these factors are not severe unless the wind is strong.
Drops of rain produce noise similar to ultrasound pulses. Thus, it is important to protect ultrasound receiving beacons from the noise produced by the drops. All kind of special shields and umbrellas usually do the job well.
Typically, outdoor is an open space. It is possible to cover the same territory with a fraction of stationary beacons required indoor.
It is possible to do sensor fusion with GNSS systems, for example, GPS or RTK GPS for the best performance.