Interferometric location sensing

Apparatus for location finding, comprising:

• a mobile transceiver comprising at least one receive antenna, which is configured to receive, at a given second location, radio signals transmitted from a plurality of fixed transceivers, each having multiple antennas, at different, respective first locations;
• and
• a processor, which is configured to process the received radio signals so as to detect a respective phase difference between the radio signals received from the multiple antennas of each of the fixed transceivers, to compute multiple loci corresponding respectively to respective angles of departure from each the fixed transceivers to the mobile transceiver based on the respective phase differences, and to find location coordinates of the mobile transceiver based on the angles of departure and the first locations of the fixed transceivers by identifying an intersection of the loci as the second location of the mobile transceiver,
• wherein the radio signals transmitted over the air between a given fixed transceiver and the mobile transceiver comprise at least first and second radio signals, which are associated respectively with first and second ones of the multiple antennas and are both modulated with a given sequence of symbols, and
• wherein the processor is configured to detect the respective phase difference by identifying a given symbol in the sequence in each of first and second radio signals received at the mobile transceiver, and measuring a delay in arrival at the mobile transceiver of the given symbol between the first and second radio signals.

A system for location finding, comprising:

• a plurality of fixed transceivers, each having multiple antennas, at different, respective first locations, wherein the fixed transceivers are configured to receive via the multiple antennas radio signals transmitted from a mobile transmitter at a given second location;
• and
• a processor, which is configured to process the received radio signals so as to detect a respective phase difference between the radio signals received by the multiple antennas of each of the fixed transceivers, to compute multiple loci corresponding respectively to respective angles of arrival from the mobile transceiver to each of the fixed transceivers based on the respective phase differences, and to find location coordinates of the mobile transceiver based on the angles of arrival and the first locations of the fixed transceivers by identifying an intersection of the loci as the second location of the mobile transceiver,
• wherein the radio signals transmitted over the air between a given fixed transceiver and the mobile transceiver comprise at least first and second radio signals, which are associated respectively with first and second ones of the multiple antennas and are both modulated with a given sequence of symbols, and
• wherein the processor is configured to detect the respective phase difference by identifying a given symbol in the sequence in each of first and second radio signals received at the mobile transceiver, and measuring a delay in arrival at the mobile transceiver of the given symbol between the first and second radio signals.

A computer software product for use in conjunction with radio signals transmitted and received between a plurality of fixed transceivers having multiple antennas at different, respective first locations and a mobile transceiver at a second location, the product comprising a tangible, non-transitory computer-readable medium in which program instructions are stored, which instructions, when read by a processor, cause the processor to receive from at least one of the transceivers a respective phase difference detected by the at least one of the transceivers between the received radio signals that are associated with each of the multiple antennas of each of the fixed transceivers,

• wherein the instructions cause the processor to compute multiple loci corresponding respectively to respective angles between each the fixed transceivers and the mobile transceiver based on the respective phase differences, and to find location coordinates of the mobile transceiver based on the angles and the first locations of the fixed transceivers by identifying an intersection of the loci as the second location of the mobile transceiver,
• wherein the radio signals transmitted over the air between a given fixed transceiver and the mobile transceiver comprise at least first and second radio signals, which are associated respectively with first and second ones of the multiple antennas and are both modulated with a given sequence of symbols, and
• wherein the processor is configured to detect the respective phase difference by identifying a given symbol in the sequence in each of first and second radio signals received at the mobile transceiver, and measuring a delay in arrival at the mobile transceiver of the given symbol between the first and second radio signals.