Wireless triangulation using RSSI signals
Most wireless receiver modules available today have a received signal strength indicator (RSSI) that gives the signal strength measured at the receiver and which is associated with each received signal source. This information is usually part of a packet stream that gives the source identification and RSSI level in power levels of dBm. The RSSI signal is usually a nice diagnostic tool that shows the margin of the received signal compared to the sensitivity of the receiver.
It does also give some indication of how close the source of the signal is, if one has an estimate of the source power. If one does not know the strength of the source, then one or even two RSSI signals is of little use in finding the location or distance to the source, although most triangulation methods such as those that use phased arrays can provide a bearing angle to the source.
However, four networked transceivers arranged in a triangular pattern and equipped with omnidirectional antennas can determine both the transmitter's power level and the Cartesian coordinates (x,y,z) of the transmitter relative to the receivers when they share their RSSI information. A simplified version of this method was first described in patent #7,283,127, issued October 16, 2007, which claims the methods for triangulation of static magnetic fields and briefly mentions the use of a similar algorithm for triangulation with alternating electromagnetic fields.