Time of arrival

Time of arrival (TOA or ToA), sometimes called time of flight (ToF), is the travel time of a radio signal from a single transmitter to a remote single receiver.

Compared to the TDOA technique, time of arrival uses the absolute time of arrival at a certain base station rather than the measured time difference between departing from one and arriving at the other station. The distance can be directly calculated from the time of arrival as signals travel with a known velocity. Time of arrival data from two base stations will narrow a position to a position circle; data from a third base station is required to resolve the precise position to a single point. Many radiolocation systems, including GPS, use ToA.

As with TDOA, synchronization of the network base station with the locating reference stations is important. This synchronization can be done in different ways:

Two way ranging is a cooperative method for determining the range between two radio transceiver units. When synchronisation of the oscillators of the involved transmitters is not viable, hence the clocks differ, then applying the measurement as a two ways travel to the receiver and mirrored back to the transmitter compensates for some of the phase differences between the oscillators involved. This concept is applied with the Real-time locating system (RTLS) concept as defined in the international standard ISO/IEC FCD 24730-5.

An introductory description of the concept is given with. In contrast to some faulty explanations, the concept may be applied as well with IEEE 802.15.4aCSS as with IEEE 802.15.4aUWB modulation.

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