System and method for simultaneous location tracking of multiple wireless terminals
A location-tracking system that includes multiple detector units that are deployed in a region of interest. The detector units receive uplink signals from wireless terminals that are active in the region, and measure the strengths of the received uplink signals. The system computes the locations of the terminals based on the measured signal strengths and the known locations of the detector units. The location-tracking system receives and analyzes downlink signals from one or more of the base stations of the wireless network. The detector unit uses the downlink signal to recover and synchronize to the timing of the wireless network's air-interface. Based on the extracted uplink allocations, and having synchronized with the air-interface, the system is able to distinguish between the uplink signal components originating from each terminal, and thus compute the location of each terminal.
1. A method, comprising:
using multiple detector units, intercepting uplink signals from multiple wireless communication terminals that communicate simultaneously with one or more base stations of a wireless network;
intercepting a downlink signal that has been sent from at least one of the base stations and extracting from the downlink signal time-frequency uplink allocations assigned to the respective wireless terminals; and
computing respective locations of the wireless terminals based on the uplink signals received by the detector units and on the extracted time-frequency uplink allocations.
2. The method according to claim 1 , wherein extracting the time-frequency uplink allocations comprises receiving the downlink signal in at least one of the detector units.
3. The method according to claim 1 , wherein extracting the time-frequency uplink allocations comprises receiving the downlink signal in a given detector unit, synchronizing the time-frequency uplink signals received in the given detector unit with the downlink signal received in the given detector unit, and synchronizing the multiple detector units with one another.
4. The method according to claim 1 , wherein extracting the time-frequency uplink allocations comprises receiving the downlink signal in each detector unit, and synchronizing the uplink signals received in each detector unit with the downlink signal received in that detector unit.
5. The method according to claim 1 , wherein computing the locations comprises distinguishing, using the time-frequency uplink allocations, between at least first and second components of the received uplink signals that originate from respective first and second wireless terminals, and computing first and second locations of the first and second wireless terminals using the first and second components, respectively.
6. The method according to claim 5 , wherein the first and second components overlap in time.
7. The method according to claim 5 , wherein the first and second components overlap in frequency.
8. The method according to claim 1 , wherein computing the locations comprises measuring respective signal strengths with which a component of the uplink signal, originating from a given wireless terminal, received at the detector units, and computing a location of the given wireless terminal based on the signal strengths.
9. The method according to claim 1 , and comprising soliciting one or more of the wireless communication terminals to transmit the uplink signals, by transmitting one or more silent messages to the wireless communication terminals.
10. A system, comprising:
multiple detector units, which are configured to receive uplink signals from multiple wireless communication terminals that communicate simultaneously with one or more base stations of a wireless network and are configured to intercept a downlink signal that has been sent by at least one of the base stations; and
one or more processors, which are configured to extract from the downlink signal time-frequency uplink allocations assigned to the respective wireless terminals, and to compute respective locations of the wireless terminals based on the uplink signals received by the detector units and on the extracted uplink allocations.
11. The system according to claim 10 , wherein at least one of the detector units comprises a downlink receiver that is configured to receive the downlink signal, and wherein the processors are configured to extract the time-frequency uplink allocations from the received downlink signal.
12. The system according to claim 10 , wherein a given detector unit comprises a downlink receiver that is configured to receive the downlink signal, and wherein the processors are configured to synchronize the uplink signals received in the given detector unit with the downlink signal received in the given detector unit, and to synchronize the multiple detector units with one another.
13. The system according to claim 10 , wherein the multiple detector units comprise respective downlink receivers that are each configured to receive the downlink signal, and wherein the processors are configured to synchronize the uplink signals received in each detector unit with the downlink signal received in that detector unit.
14. The system according to claim 10 , wherein the processors are configured to distinguish, using the time-frequency uplink allocations, between at least first and second components of the received uplink signals that originate from respective first and second wireless terminals, and to compute first and second locations of the first and second wireless terminals using the first and second components, respectively.
15. The system according to claim 14 , wherein the first and second components overlap in time.
16. The system according to claim 14 , wherein the first and second components overlap in frequency.
17. The system according to claim 10 , wherein the processors or the detector units are configured to measure respective signal strengths with which a component of the uplink signal, originating from a given wireless terminal, is received at the detector units, and wherein the processors are configured to compute a location of the given wireless terminal based on the signal strengths.
18. The system according to claim 10 , and comprising a transmitter that is configured to solicit one or more of the wireless communication terminals to transmit the uplink signals, by transmitting one or more silent messages to the wireless communication terminals.