Object tracking via radio reflections

Abstract

In one aspect, a reference transmit signal is distributed to each of one or more transmit antennas, and delayed by multiple different times before transmission from the transmit antennas. The reference transmit signal (or a delayed version of the reference signal) is also used at each of the receive antennas to determine propagation (time of flight) times reflecting from bodies from each of the transmit antennas to the receive antenna. In another aspect, locations of multiple objects are determined by iteratively (a) determining a location of a body based on determined propagation times between multiple transmitter-receiver pairs, and (b) having determined a location, effectively removing the effect of reflections from that location from the remaining signals.

1 . A method for object tracking in an environment, the method comprising:
 forming a first reference signal comprising a first component having a varying frequency with time;   forming a plurality of modified reference signals corresponding to the first reference signal, each modified reference signal comprising a modified component being a shift of the first component in at least one of frequency and time;   causing the plurality of modified reference signals to be transmitted from one or more transmitting antennas;   processing one or more received signals, each received signal corresponding to a different receiving antenna of one or more receiving antennas;   processing each of the one or more received signals according to the first reference signal to form corresponding one or more processed received signals;   determining a plurality of propagation delays, each propagation time delay corresponding to one receiving antenna of the one or more receiving antennas and one transmitting antenna of the one or more transmitting antennas, including determining from each processed received signal of the one or more processed received signals one or more of the plurality of propagation delays;   using the plurality of propagation delays to track one or more objects in the environment according to propagation delays of reflections of the transmitted modified reference signals from locations of the one or more objects.   
     
     
         2 . The method of  claim 1  wherein using the plurality of propagation delays to track the one or more objects include at least one of localizing said objects and monitoring motion of said objects. 
     
     
         3 . The method of  claim 1  wherein causing the modified reference signals to be transmitted includes causing concurrent transmission different modified reference signals from at least two different transmitting antennas. 
     
     
         4 . The method of  claim 2  wherein each of the different modified reference signals comprises a different time delay of the first reference signal. 
     
     
         5 . The method of  claim 1  wherein forming the first reference signal comprising a first component having a varying frequency with time includes forming said reference signal such that the first component comprises a frequency sweep from a first frequency to a second frequency from a first time to a second time. 
     
     
         6 . The method of  claim 5  wherein the frequency sweep comprises a linear sweep. 
     
     
         7 . The method of  claim 1  wherein forming the plurality of modified reference signals comprises, forming at least a first modified reference signal as a time delay of the first reference signal. 
     
     
         8 . The method of  claim 1  wherein forming the plurality of modified reference signals comprises forming at least a first modified reference signal as modulation of the first reference signal with a carrier signal. 
     
     
         9 . The method of  claim 1  wherein processing the one or more received signals comprises, forming at least a first processed received signal as a modulation of a received signal with the first reference signal. 
     
     
         10 . The method of  claim 9  wherein determining the plurality of propagation delays comprises performing a spectral analysis of the modulation of the received signal. 
     
     
         11 . The method of  claim 10  wherein determining the plurality of propagation delays comprises indentifying a plurality of spectral peaks in the spectral analysis, each spectral peak corresponding to a propagation delay. 
     
     
         12 . The method of  claim 1  applied to one or more of control of an appliance, input to a gaming or virtual reality system, elderly monitoring, fall detection, intrusion detection, and a security system. 
     
     
         13 . The method of  claim 1  wherein repeated to track motion of the one or more objects. 
     
     
         14 . The method of  claim 13  further comprising selecting the one or more transmitting antennas from a plurality of antennas for each repetition, the one or more transmitting antennas varying between at least some iterations. 
     
     
         15 . The method of  claim 14  wherein at least one antenna is a receiving antenna in one iteration and a transmitting antenna in another iteration. 
     
     
         16 . (canceled) 
     
     
         17 . (canceled) 
     
     
         18 . A method for multi-object localization in an environment, the method comprising:
 receiving signals representing radio frequency reflections of signals emitted from one or more transmitting antennas of a plurality of antennas and received at one or more receiving antennas of the plurality of antennas after reflection from a plurality of objects in the environment;   determining from the received signals, for each pair of a transmitting antenna of the plurality of transmitting antennas and a receiving antenna of the plurality of receiving antennas of a plurality of different pairs of transmitting antennas and receiving antennas, a time profile characterizing a degree of reflection for different propagation times from the transmitting antenna to the receiving antenna, thereby forming a plurality of time profiles, each time profile being associated with a corresponding transmitting antenna and a corresponding receiving antenna;   using the plurality of time profiles and locations in the environment of the transmitting and the receiving antennas corresponding to said time profiles to identify a first location of reflection of a plurality of locations in the environment;   performing one or more iterations of
 cancelling an effect of a reflection from a previously identified location of reflection in each of one or more of the time profiles, and 
 using the time profiles in which effects of reflections from one or more identified locations have been cancelled and locations of the transmitting and the receiving antennas corresponding to said time profiles to identify a further location of reflection of the plurality of reflections in the environment; and 
   providing the plurality of locations of reflection identified in the environment.   
     
     
         19 . The method of  claim 17  wherein the signals emitted from the transmitting antennas are concurrently emitted. 
     
     
         20 . The method of  claim 17  wherein the objects in the environment comprise moving objects. 
     
     
         21 . The method of  claim 17  further comprising:
 determining, for an identified location of refection, a plurality of time portions of the received signals corresponding to reflections from the identified location of reflection. 
 
     
     
         22 . The method of  claim 21  further comprising:
 processing the determined plurality of time portions of the received signals to determine motion characteristics of an object at the identified location. 
 
     
     
         23 . The method of  claim 17  further comprising causing concurrent emission of radio frequency signals from the one or more transmitting antennas of a plurality of antennas. 
     
     
         24 . The method of  claim 17  wherein determining a time profile for a pair of a transmitting antenna and a receiving antenna includes determining said time profile to characterize a distribution of reflected energy as a function of a propagation time from the transmitting antenna to the receiving antenna. 
     
     
         25 . The method of  claim 17  wherein using the time profiles to identify a location of reflection includes, for each time profile forming a spatial distribution of potential locations of reflections represented in said time profile, combining the spatial distributions for multiple time profiles to form a combined spatial distribution, and determining a location in the environment according to the combined spatial distribution. 
     
     
         26 . The method of  claim 25  wherein determining the location according to the combined spatial distribution includes determining a location of an extremum value in the combined distribution. 
     
     
         27 . The method of  claim 25  wherein the spatial distribution comprises a two-dimensional spatial distribution and the determined location corresponds to a two-dimensional coordinate in the environment. 
     
     
         28 . The method of  claim 27  wherein the locations of the transmitting and receiving antennas are non-coplanar. 
     
     
         29 . The method of  claim 25  wherein the spatial distribution comprises a three-dimensional spatial distribution and the determined location corresponds to a three-dimensional coordinate in the environment. 
     
     
         30 . The method of  claim 17  wherein cancelling an effect of a reflection from a previously identified location of reflection in a time profile includes attenuating a portion of the time profile corresponding to a propagation time from the location of the transmitting antenna via the identified location to the location of the receiving antenna. 
     
     
         31 . The method of  claim 30  wherein attenuating a portion of the time profile comprises zeroing the time profile in a portion of said profile corresponding to the propagation time. 
     
     
         32 . The method of  claim 30  wherein attenuating a portion of the time profile includes using an estimated mean and standard deviation of an estimate of the propagation time from the location of the transmitting antenna via the identified location to the location of the receiving antenna. 
     
     
         33 . The method of  claim 17  further comprising removing an effect a reflection from a static object in the plurality of time profiles. 
     
     
         34 . The method of  claim 33  further comprising removing an effect of multipath reflection from at least one location of the plurality of reflections also reflecting from a static object. 
     
     
         35 . (canceled) 
     
     
         36 . Software stored on a non-transitory machine-readable medium comprising instruction stored thereon, when executed on a processor of a localization system causes said system to
 receive signals representing radio frequency reflections of signals emitted from one or more transmitting antennas of a plurality of antennas and received at one or more receiving antennas of the plurality of antennas after reflection from a plurality of objects in the environment;   determine from the received signals, for each pair of a transmitting antenna of the plurality of transmitting antennas and a receiving antenna of the plurality of receiving antennas of a plurality of different pairs of transmitting antennas and receiving antennas, a time profile characterizing a degree of reflection for different propagation times from the transmitting antenna to the receiving antenna, thereby forming a plurality of time profiles, each time profile being associated with a corresponding transmitting antenna and a corresponding receiving antenna;   use the plurality of time profiles and locations of the transmitting and the receiving antennas corresponding to said time profiles to identify a first location of reflection of a plurality of locations in the environment;   perform one or more iterations of
 cancelling an effect of a reflection from a previously identified location of reflection in each of one or more of the time profiles, and 
 using the time profiles in which effects of reflections from one or more identified locations have been cancelled and locations of the transmitting and the receiving antennas corresponding to said time profiles to identify a further location of reflection of the plurality of reflections in the environment. 
   
     
     
         37 . A localization system comprising:
 a plurality of antennas;   one or more signal generators coupled to multiple of the antennas, the one or more signal generators configured to provide signals for concurrent transmission from the multiple antennas;   one or more receivers coupled to corresponding antennas configured to receive signals comprising reflections of the concurrently transmitted signals; and   a received signal processor configured to infer locations of multiple objects based on the received signals;   wherein the received signal processor is configured to
 determine from the received signals, for each pair of a transmitting antenna of the plurality of transmitting antennas and a receiving antenna of the plurality of receiving antennas of a plurality of different pairs of transmitting antennas and receiving antennas, a time profile characterizing a degree of reflection for different propagation times from the transmitting antenna to the receiving antenna, thereby forming a plurality of time profiles, each time profile being associated with a corresponding transmitting antenna and a corresponding receiving antenna; 
 use the plurality of time profiles and locations of the transmitting and the receiving antennas corresponding to said time profiles to identify a first location of reflection of a plurality of locations in the environment; 
 perform one or more iterations of
 cancelling an effect of a reflection from a previously identified location of reflection in each of one or more of the time profiles, and 
 using the time profiles in which effects of reflections from one or more identified locations have been cancelled and locations of the transmitting and the receiving antennas corresponding to said time profiles to identify a further location of reflection of the plurality of reflections in the environment.