Indoor positioning in large environments: ultrasonic and UWB technologies

This work describes and compares two positioning systems, based respectively on ultrasonic (US) and on ultra-wide band radio (UWB) technologies, which can be used in large indoor areas, such as medium-sized warehouses. The ultrasonic positioning system involved is based on the measurement of times-of-arrival for the ultrasonic signals, emitted from a set of beacons at known positions to the mobile receiver. In this setup, time synchronization is provided by an infrared link, and spherical trilateration is used to estimate the mobile node ́s position. The UWB system is a commercial product by Decawave, and it is based on the measurement of round-trip times between emitters and receivers. Both positioning systems are evaluated in an uncluttered warehouse environment (24x14 m), where there is line-of-sight from emitters to receiver at most locations. Emitters are placed on the walls, covering most of the evaluation area with suitable geometric conditions. The performed evaluation shows that both systems achieve an accuracy even below decimeters, and, in a certain way, they can be considered complementary, since they are affected by different propagation phenomena and types of noise. Even though the UWB technology is becoming increasingly popular, the lower cost of ultrasonic systems, as well as the confinement of signals in rooms and the corresponding high level of security related to the positioning process, can also make it attractive.