Method and apparatus to determine time and distance between transceivers using phase measurements

Abstract

Systems, apparatuses and methods are disclosed for estimating a signal travel time, and thus distance between transceivers, in an orthogonal frequency division multiplexing (OFDM) system. The signal travel time is measured between a transmit time (t T ) and a receive window time (t window ) adjusted by the phase delay (T Φ ). The phase delay (T Φ ) is determined as a difference between a receive time (t R ) and the receive window time (t window ). The receive time (t R ) may be determined based on either an amplitude of the received signal at the receive window time (t window ) or when the received signal crosses a positive-negative axis. In synchronous systems, either a one-way time (OWT) or round-trip time (RTT) may be used for estimation. In asynchronous systems, an RTT is used for estimation.

What is claimed is: 
     
         1 . A method for estimating a one-way time (OWT) in an orthogonal frequency division multiplexing (OFDM) system, the method comprising:
 receiving an OFDM signal at a first transmit time (t T1 ) from a first transceiver sent to a second transceiver in a window B having a window B start time (t windowB ); and   determining a window B phase difference (T ΦB ) from a first difference of a receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   wherein the first transceiver and the second transceiver are synchronous.   
     
     
         2 . The method of  claim 1 , the method further comprising sending the receive time (t R1 ) from the second transceiver to the first transceiver for computing the OWT based on:
 the window B start time (t windowB ) of the window B;   the window B phase difference (T ΦB ); and   the transmit time (t T1 ).   
     
     
         3 . The method of  claim 1 , the method further comprising:
 receiving the receive time (t R1 ) at the second transceiver and from the first transceiver; and   computing the OWT based on:
 the window B start time (t windowB ) of the window B; 
 the window B phase difference (T ΦB ); and 
 the transmit time (t T1 ). 
   
     
     
         4 . The method of  claim 1 , wherein the OFDM signal comprises a plurality of OFDM sub-channels carrying a signal having a cyclic prefix. 
     
     
         5 . The method of  claim 1 , wherein determining the window B phase difference (T ΦB ) comprises:
 determining the first difference of the receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   determining a second difference of a second receive time of the OFDM signal and the window B start time (t windowB ) of the window B; and   combining the first difference and the second difference to form the window B phase difference (T ΦB ).   
     
     
         6 . The method of  claim 5 , wherein combining the first difference and the second difference comprises averaging the first difference and the second difference. 
     
     
         7 . An apparatus for estimating a one-way time (OWT) in an orthogonal frequency division multiplexing (OFDM) system, the apparatus comprising:
 means for receiving an OFDM signal at a first transmit time (t T1 ) from a first transceiver sent to the apparatus in a window B having a window B start time (t windowB ); and   means for determining a window B phase difference (T ΦB ) from a first difference of a receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   wherein the first transceiver and the second transceiver are synchronous.   
     
     
         8 . The apparatus of  claim 7 , further comprising means for sending the receive time (t R1 ) from the second transceiver to the first transceiver for computing the OWT based on:
 the window B start time (t windowB ) of the window B;   the window B phase difference (T ΦB ); and   the transmit time (t T1 ).   
     
     
         9 . The apparatus of  claim 7 , further comprising:
 means for receiving the receive time (t R1 ) at the apparatus and from the first transceiver; and   means for computing the OWT based on:
 the window B start time (t windowB ) of the window B; 
 the window B phase difference (T ΦB ); and 
 the transmit time (t T1 ). 
   
     
     
         10 . The apparatus of  claim 7 , wherein the means for determining the window B phase difference (T ΦB ) comprises:
 means for determining the first difference of the receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   means for determining a second difference of a second receive time of the OFDM signal and the window B start time (t windowB ) of the window B; and   means for combining the first difference and the second difference to form the window B phase difference (T ΦB ).   
     
     
         11 . An apparatus for estimating a one-way time (OWT) in an orthogonal frequency division multiplexing (OFDM) system, the apparatus comprising:
 a second transceiver configured to receive an OFDM signal at a first transmit time (t T1 ) from a first transceiver sent to the apparatus in a window B having a window B start time (t windowB ); and   a processor coupled to the second transceiver and configured to determine a window B phase difference (T ΦB ) from a first difference of a receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   wherein the first transceiver and the second transceiver are synchronous.   
     
     
         12 . The apparatus of  claim 11 , further comprising software instructions to send the receive time (t R1 ) from the second transceiver to the first transceiver for computing the OWT based on:
 the window B start time (t windowB ) of the window B;   the window B phase difference (T ΦB ); and   the transmit time (t T1 ).   
     
     
         13 . The apparatus of  claim 11 , further comprising software instructions to:
 receive the receive time (t R1 ) at the second transceiver and from the first transceiver; and   compute the OWT based on:
 the window B start time (t windowB ) of the window B; 
 the window B phase difference (T ΦB ); and 
 the transmit time (t T1 ). 
   
     
     
         14 . The apparatus of  claim 11 , wherein the software instructions to determine the window B phase difference (T ΦB ) comprises software instructions to:
 determine the first difference of the receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   determine a second difference of a second receive time of the OFDM signal and the window B start time (t windowB ) of the window B; and   combine the first difference and the second difference to form the window B phase difference (T ΦB ).   
     
     
         15 . A non-transitory computer-readable storage medium for estimating a one-way time (OWT) in an orthogonal frequency division multiplexing (OFDM) system, the non-transitory computer-readable storage medium including program code stored thereon, comprising program code to:
 receive an OFDM signal at a first transmit time (t T1 ) from a first transceiver sent to a second transceiver in a window B having a window B start time (t windowB ); and   determine a window B phase difference (T ΦB ) from a first difference of a receive time (t R1 ) of the OFDM signal and a window B start time (t windowB ) of the window B.   
     
     
         16 . The non-transitory computer-readable storage medium of  claim 15 , further comprising program code to:
 receive the receive time (t R1 ) at the second transceiver and from the first transceiver; and   compute the OWT based on:
 the window B start time (t windowB ) of the window B; 
 the window B phase difference (T ΦB ); and 
 the transmit time (t T1 ). 
   
     
     
         17 . The non-transitory computer-readable storage medium of  claim 15 , wherein the program code to determine the window B phase difference (T ΦB ) comprises program code to:
 determine the first difference of the receive time (t R1 ) of the OFDM signal and the window B start time (t windowB ) of the window B;   determine a second difference of a second receive time of the OFDM signal and the window B start time (t windowB ) of the window B; and   combine the first difference and the second difference to form the window B phase difference (T ΦB ).