Three ways to track the location of an object
16 Jul 2011 - - 0 Comments
Wireless geo-location tracking refers to the various methods used to determine and record the location of an object using electromagnetic waves. Any characteristic of the wave that varies with the location can be used.
There are three most common methods for wireless geo-location tracking.
There are three most common methods for wireless geo-location tracking.
-Location using trilateration
Multilateration, also known as hyperbolic positioning, is a method for locating a radio transmitter by computing the Time Difference Of Arrival (TDOA) of a signal transmitted from it to three or more receivers. The TDOA indicates the distance between each receiver and the transmitter, from which the location of the transmitter can be deduced. The same method can be used to locate a receiver by measuring the TDOA of a signal transmitted from three or more synchronized transmitters. Another form of location using distances is trilateration, in which the distances are measured based on the time delay between transmitter and receiver. This is the method used in the GPS system, in which the time of travel for signals transmitted from four or more satellites to a GPS receiver is used to locate the receiver in three-dimensional space. Signal attenuation, as indicated by the Received Signal Strength (RSS) can also be used in place of TDOA or time of travel to determine the distance. In above three cases, it is assumed that signal propagation (the attenuation or time of travel) is a stable function of distance and can be predicted and modeled mathematically.
-Location using triangulationMultilateration, also known as hyperbolic positioning, is a method for locating a radio transmitter by computing the Time Difference Of Arrival (TDOA) of a signal transmitted from it to three or more receivers. The TDOA indicates the distance between each receiver and the transmitter, from which the location of the transmitter can be deduced. The same method can be used to locate a receiver by measuring the TDOA of a signal transmitted from three or more synchronized transmitters. Another form of location using distances is trilateration, in which the distances are measured based on the time delay between transmitter and receiver. This is the method used in the GPS system, in which the time of travel for signals transmitted from four or more satellites to a GPS receiver is used to locate the receiver in three-dimensional space. Signal attenuation, as indicated by the Received Signal Strength (RSS) can also be used in place of TDOA or time of travel to determine the distance. In above three cases, it is assumed that signal propagation (the attenuation or time of travel) is a stable function of distance and can be predicted and modeled mathematically.
Another wireless geo-location technique is called Angle of Arrival, or AoA, in which receivers use arrays of directional antennas to determine the Angle of Arrival of the incoming waves. With three or more receivers, the emitter can be located, although with limited accuracy (it is difficult to have very narrow beams). A current application of AoA is in the geo-location of cell phones used to place an emergency call (911 in North America, 112 in Europe). In this technique, the assumption is that the wave has travelled in a straight line from the transmitter to the receiver.
-Location by RF fingerprinting
When using a characteristic of the wave that cannot be modeled mathematically or when waves are reflected and do not travel in a straight line between transmitter and receiver, a technique called RF (Radio Frequency) fingerprinting can be used. In this technique, a chosen characteristic of the signal (spread spectrum, phase shift, signal strength...) is recorded with the receiver at each location during a calibration period. The characteristics of several signals from different transmitters effectively create a kind of fingerprint identifying the location. With a database of fingerprints and the corresponding locations, a positioning system can be built.
When using a characteristic of the wave that cannot be modeled mathematically or when waves are reflected and do not travel in a straight line between transmitter and receiver, a technique called RF (Radio Frequency) fingerprinting can be used. In this technique, a chosen characteristic of the signal (spread spectrum, phase shift, signal strength...) is recorded with the receiver at each location during a calibration period. The characteristics of several signals from different transmitters effectively create a kind of fingerprint identifying the location. With a database of fingerprints and the corresponding locations, a positioning system can be built.
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