Radio frequency identification (rfid) system for determining location

Abstract

A system and bent-pipe transponder component for determining a location of an individual or object in three dimensional space. The system includes a transmitter configured to transmit a first wireless electromagnetic signal at a first frequency and at least one transponder that is configured to responsively emit a second wireless electromagnetic signal having a second frequency that is frequency-shifted from the first frequency. An included receiver detecting the first and second wireless electromagnetic signals is configured to provide an output of location information for the at least one transponder. A bent-pipe transponder component may include a receiving antenna, an emitting antenna, and a frequency shift stage comprising an oscillator and a first mixer, with the frequency stage mixing a received first wireless electromagnetic signal with the output of the oscillator via the first mixer to produce the emitted second wireless electromagnetic signal.

1 . A system for determining a location of an individual or object in three dimensional space, the system comprising:
 a transmitter for transmitting a first wireless electromagnetic signal having a first signal frequency;   at least one transponder, wherein the transponder is configured, in response to receiving the first wireless electromagnetic signal from the transmitter, to emit a second wireless electromagnetic signal having a second signal frequency that is frequency-shifted from the first signal frequency of the first electromagnetic signal; and   a receiver for detecting the first and second wireless electromagnetic signals, wherein the receiver is configured, based upon detection of the first and second wireless electromagnetic signals, to provide an output of location information for the at least one transponder.   
     
     
         2 . The system of  claim 1  wherein the first wireless electromagnetic signal comprises a frequency modulated continuous wave, and the second wireless electromagnetic signal comprises a frequency-shifted version of the frequency modulated continuous wave. 
     
     
         3 . The system of  claim 1  wherein the first wireless electromagnetic signal comprises an orthogonal frequency division multiplexed signal having a plurality of sub-carriers, and the second wireless electromagnetic signal comprises a frequency-shifted version of the orthogonal frequency division multiplexed signal. 
     
     
         4 . The system of  claim 1  wherein the transmitter is configured to transmit the first wireless electromagnetic signal with a first signal frequency of between 200 MHz and 1000 MHz. 
     
     
         5 . The system of  claim 4  wherein the transmitter is configured to transmit the first wireless electromagnetic signal with a first signal frequency of between 420 MHz and 450 MHz. 
     
     
         6 . The system of  claim 1  wherein the transponder includes a frequency shift stage comprising an oscillator and a first mixer, whereupon the frequency stage mixes the received first wireless electromagnetic signal with the output of the oscillator via the first mixer to produce the second wireless electromagnetic signal. 
     
     
         7 . The system of  claim 6  wherein the oscillator of each transponder of the at least one transponder has a different frequency relative to the oscillators of others of the transponders, such that each transponder emits the second wireless electromagnetic signal at a different signal frequency relative to that of the first wireless electromagnetic signal and that of second wireless electromagnetic signals emitted by others of the transponders. 
     
     
         8 . The system of  claim 7  wherein the oscillator comprises at least one oscillator adjustable to a plurality of different frequencies. 
     
     
         9 . The system of  claim 1  wherein the transponder is configured to emit the second wireless electromagnetic signal with a second signal frequency of between 200 MHz and 1000 MHz. 
     
     
         10 . The system of  claim 9  wherein the transponder is configured to transmit the second wireless electromagnetic signal with a first signal frequency of between 420 MHz and 450 MHz. 
     
     
         11 . The system of  claims 10  wherein the first signal frequency and the second signal frequency differ by at least 5 MHz. 
     
     
         12 . The system of  claim 1  wherein the receiver includes a plurality of antenna elements distributed across a three dimensional volume of space, and the receiver is configured to estimate a distance, a horizontal angle, and a vertical angle between the receiver and the at least one transponder based upon analysis of a phase delay between the first wireless electromagnetic signal and the second wireless electromagnetic signal as received by the plurality of antenna elements. 
     
     
         13 . The system of  claim 12  wherein receiver includes a phased array antenna comprised of the plurality of antenna elements. 
     
     
         14 . The system of  claim 12  wherein the receiver includes a non-phased array antenna comprised of the plurality of antenna elements, and the receiver is configured to separately analyze the phase delay for each of the plurality of antenna elements. 
     
     
         15 . The system of  claim 1  wherein the receiver includes a display screen, and the output is a representative output on the display screen showing the location of individual ones of the at least one transponder. 
     
     
         16 . A bent-pipe transponder for use in determining a location of an individual or object in three dimensional space, the transponder comprising:
 a receiving antenna;   an emitting antenna; and   a frequency shift stage comprising an oscillator and a first mixer, wherein the frequency stage mixes a first wireless electromagnetic signal received by the receiving antenna with the output of the oscillator via the first mixer to produce a second wireless electromagnetic signal that is emitted by the emitting antenna, such that the transponder receives the first wireless electromagnetic signal at a first signal frequency and responsively emits the second wireless electromagnetic signal with a second signal frequency that is frequency-shifted from the first signal frequency.   
     
     
         17 . The bent-pipe transponder of  claim 16  wherein the oscillator comprises a pluggable module or is adjustable to a plurality of different frequencies. 
     
     
         18 . The bent-pipe transponder of  claim 16  wherein the transponder further comprises a battery and a signal amplifier configured to amplify the second wireless electromagnetic signal prior to emission by the emitting antenna. 
     
     
         19 . The bent-pipe transponder of  claim 16  wherein the transponder further comprises a receive filter disposed between the receiving antenna and the first mixer, the receive filter comprising a surface acoustic wave or coaxial resonator filter passing the first signal frequency but not the second signal frequency. 
     
     
         20 . The bent-pipe transponder of  claim 19  wherein the transponder further comprises an emission filter disposed between the first mixer and the emitting antenna, the emission filter comprising a surface acoustic wave or coaxial resonator filter passing the second signal frequency but not the first signal frequency.