Method of and apparatus for deriving a signal for enabling a radio wave source location to be derived

Abstract

The location of a cellular telephone handset relative to the sites of two pairs of fixed cellular transceivers is determined by responding to the phase difference of radio waves the handset emits, as coupled to the sites. The phase difference is detected by supplying replicas of the waves received at the first and second sites to first and second electro-acoustical transducers at opposite ends of a Bragg cell. One Bragg cell is thus associated with each pair of cellular transceivers. A laser beam incident on each Bragg cell is deflected by a moving optical grating resulting from the interaction of acoustic waves applied by the electro-acoustical transducers to the particular Bragg cell. The laser beam deflection angle for each Bragg cell determines the relative phase angle of the acoustic waves in that cell. Indications of the deflection angles, positions of the transceivers and propagation speeds of replicas of the radio waves propagating in communication links between the sites are combined to indicate the handset location.