RIPS
Document Actions
Traditional radio interferometry has many applications in physics, geodesy and astronomy. The method is based on two directional antennas measuring the radio signal from a single source and performing cross correlation. The resultant interference signal can be further analyzed to create radio images of distant celestial objects, determine the relative location of two receivers very precisely, or conversely, determine the location of a radio source when the location of the two receivers are known. A radio interferometer is an expensive device requiring tunable directional antennas, very high sampling rates and high-precision time synchronization. Hence, it is not directly applicable to WSNs.
The novel idea behind the proposed Radio Interferometric Positioning System (RIPS) is to utilize two transmitters to create the interference signal directly. If the frequencies of the two emitters are almost the same then the composite signal will have a low frequency envelope that can be measured by cheap and simple hardware readily available on a WSN node. Trying to use this signal to deduce information on the positions of the two transmitters and the receiver directly would require tight synchronization of the nodes involved mandating hardware support. Instead, we use the relative phase offset of the signal at two receivers which is a function of the relative positions of the four nodes involved and the carrier frequency. By making multiple measurements in an at least 8-node network, it is possible to reconstruct the relative location of the nodes in 3D.
The key attribute of this method is that the phase offset of a low frequency signal is measured, yet it corresponds to the wavelength of the high-frequency carrier signal. Hence, we can use low precision techniques that are feasible on the highly resource constrained nodes.
Recent results of a field experiment are very promising: the prototype achieved 4 cm average localization accuracy for a quasi random deployment of 16 COTS XSM nodes at ground level covering two football fields. The maximum range measured was 170 m which was four times the observed communication range.
GReAT 1.6.2 Released
