Methods and Apparatus for Wideband Localization

Abstract

A wideband, radio-frequency localization system may estimate the one-dimensional, two-dimensional or three-dimensional position and trajectory of a static or moving object. These estimates may have a high spatial accuracy and low latency. The localization may be determined based on phase or amplitude of a wideband signal in each frequency band in a set of multiple frequency bands. The localization may be based on a single shot of measurements across a wide band of radio frequencies, without frequency hopping. The measurements of the wideband signal may be taken over time and over space at multiple receivers. The localization may be based on measurements taken while a backscatter node remains in a first reflective state or in a second reflective state, rather than when the backscatter node is transitioning between reflective states. In some cases, the localization achieves sub-centimeter spatial resolution in each of three spatial dimensions.

What is claimed: 
     
         1 . A system comprising:
 (a) one or more radio frequency (RF) transmitters;   (b) one or more RF receivers; and   (c) one or more computers;   
       wherein
 (i) the one or more transmitters are configured to wirelessly transmit a largeband signal in such a way that the largeband signal travels from the one or more transmitters to a backscatter node, reflects from the backscatter node and travels to the one or more RF receivers, 
 (ii) the one or more RF receivers are each configured to take measurements of the largeband signal, 
 (iii) the one or more computers are programmed
 (A) to identify, based on the measurements, when the backscatter node is in a first reflective state and when the backscatter node is in a second reflective state, the first reflective state differing from the second reflective state in that a reflection response of the backscatter node is different in the first reflective state than in the second reflective state, which reflection response is phase or amplitude of RF reflection from the backscatter node as a function of RF radiation incident on the backscatter node, or 
 (B) to identify, based on the measurements, when the backscatter node is transitioning between the first and second reflective states, and 
 
 (iv) the one or more computers are further programmed to calculate estimates of phase or amplitude of the largeband signal for each frequency band in a set of multiple frequency bands of the largeband signal, which estimates are based on a portion of the measurements, which portion of the measurements is taken when the backscatter node is in the first reflective state or in the second reflective state and is not taken when the backscatter node is transitioning between the first and second reflective states. 
 
     
     
         2 . The system of  claim 1 , wherein the one or more computers are programmed to determine a one-dimensional, two-dimensional or three-dimensional position of the backscatter node, based on the estimates of phase or amplitude. 
     
     
         3 . The system of  claim 1 , wherein:
 (a) the system further includes an additional transmitter, which additional transmitter is configured to transmit an additional signal; and   (b) the system is configured to transmit the largeband signal in such a way that the largeband signal reflects from the backscatter node while the reflection response of the backscatter node is modulated by the backscatter node in response to the additional signal.   
     
     
         4 . The system of  claim 1 , wherein the one or more computers are programmed to decode data that is encoded, by orthogonal frequency-division multiplexing, in the largeband signal. 
     
     
         5 . The system of  claim 1 , wherein:
 (a) the system further comprises a radio frequency identification (RFID) reader; and   (b) the backscatter node is an RFID tag.   
     
     
         6 . A method comprising:
 (a) wirelessly transmitting, with one or more radio frequency (RF) transmitters, a largeband signal in such a way that the largeband signal travels from the one or more RF transmitters to a backscatter node, reflects from the backscatter node and travels to one or more RF receivers;   (b) taking measurements, with the one or more RF receivers, of the largeband signal;   (c) performing calculations
 (i) to identify, based on the measurements, when the backscatter node is in a first reflective state and when the backscatter node is in a second reflective state, the first reflective state differing from the second reflective state in that a reflection response of the backscatter node is different in the first reflective state than in the second reflective state, which reflection response is phase or amplitude of RF reflection from the backscatter node as a function of RF radiation incident on the backscatter node, or 
 (ii) to identify, based on the measurements, when the backscatter node is transitioning between the first and second reflective states; and 
   (d) calculating estimates of phase or amplitude of the largeband signal for each frequency band in a set of multiple frequency bands of the largeband signal, which estimates are based on a portion of the measurements, which portion of the measurements is taken when the backscatter node is in the first reflective state or in the second reflective state and is not taken when the backscatter node is transitioning between the first and second reflective states.   
     
     
         7 . The method of  claim 6 , wherein the method further comprises determining a one-dimensional, two-dimensional or three-dimensional position of the backscatter node, based on the estimates of phase or amplitude. 
     
     
         8 . The method of  claim 6 , wherein:
 (a) the method further comprises transmitting, with an additional transmitter, an additional signal; and   (b) the largeband signal reflects from the backscatter node while the reflection response of the backscatter node is modulated by the backscatter node in response to the additional signal.   
     
     
         9 . The method of  claim 6 , wherein the method further comprises decoding data that is encoded, by orthogonal frequency-division multiplexing, in the largeband signal. 
     
     
         10 . The method of  claim 6 , wherein the backscatter tag is a radio frequency identification tag.