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Narrowband RF distance measurement using phase locked FM transceivers

Measuring distance in short-range radio devices greatly enhances the user experience. The distance information gives the user the opportunity to make intelligent decisions to which device in range he may want to connect. Previous efforts using radio signal strength or ultra-wideband technologies have not shown to be successful. In this paper, a narrowband RF technique is presented that is based on phase locking in phase modulated RF signals. The technique is compatible with existing technologies like Bluetooth and IEEE 802.15.4 systems. Simulations match well with theory. Experimental results with a prototype operating at 2.4 GHz show that accuracies below 0.5 m are well within reach.