Super resolution radio frequency location determination

Abstract

Using a phase interferometry method which utilizes both amplitude and phase allows the determination and estimation of multipath signals. To determine the location of an object, a signal that contains sufficient information to allow determination of both amplitude and phase, like a packet that includes a sinewave portion, is provided from a master device. A slave device measures the phase and amplitude of the received packet and returns this information to the master device. The slave device returns a packet to the master that contains a similar sinewave portion to allow the master device to determine the phase and amplitude of the received signals. Based on the two sets of amplitude and phase of the RF signals, the master device utilizes a fast Fourier transform or techniques like multiple signal classification to determine the indicated distance for each path and thus more accurately determines a location of the slave device.

1 . A method of determining object distance using radio frequency signals, the method comprising:
 using a first oscillator, transmitting a first measurement packet at a first frequency from a master device to a slave device whose distance is to be measured;   using a second oscillator, receiving the first measurement packet at the slave device;   determining, by the slave device, phase and amplitude of the first measurement packet;   using the second oscillator, transmitting from the slave device to the master device the determined phase and amplitude of the received first measurement packet;   using the first oscillator, receiving the determined phase and amplitude of the first measurement packet at the master device;   using the second oscillator, transmitting a second measurement packet at a second frequency different from the first frequency from the slave device to the master device;   using the first oscillator, receiving the second measurement packet at the master device;   determining, by the master device, the phase and amplitude of the received second measurement packet;   determining, by the master device, multipath signals using the phases and amplitudes of the first and second measurement packets;   determining the distance from the master device to the slave device, by the master device, using the determined multipath signal; and   maintaining respective phases of the first and second oscillators.   
     
     
         2 . The method of  claim 1 , wherein determining the multipath signals includes:
 performing a net channel estimate to determine the master to slave channel response across frequency; and   performing a fast Fourier transform (FFT) on the net channel estimate; and   wherein determining the distance includes:   performing an inverse fast Fourier transform (IFFT) on the principal multi-path component of the FFT result.   
     
     
         3 . The method of  claim 2 , wherein the FFT is performed directly on the net channel estimate when the phases of the measured frequencies are coherent. 
     
     
         4 . The method of  claim 2 , wherein determining the multipath signals further includes performing phase change correction of the determined phases of the first and second measurement packets prior to performing the FFT when the phases of the measured frequencies are incoherent. 
     
     
         5 . The method of  claim 2 , wherein determining the multipath signals includes determining the minimum phase roots of the determined phases of the first and second measurement packets prior to performing the FFT when the phases of the measured frequencies are incoherent. 
     
     
         6 . The method of  claim 2 , wherein determining the distance includes:
 utilizing a super resolution algorithm on the IFFT result.   
     
     
         7 . The method of claim i, wherein the first and second measurement packets each contain a sine wave portion for determining the phase and the amplitude of the first and second measurement packets. 
     
     
         8 . The method of  claim 1 , wherein the determined phase and amplitude of the first measurement packet is provided in the second measurement packet. 
     
     
         9 . A master device for determining object distance using radio frequency signals, the device comprising:
 a processor;   a radio frequency interface coupled to the processor and including an oscillator used for transmitting and receiving packets;   program storage coupled to the processor and containing programs to cause the processor to:
 using the oscillator, transmit a first measurement packet at a first frequency to a slave device whose distance is to be measured, the slave device including a slave device processor and a slave device radio frequency interface coupled to the processor and including a slave device oscillator used for transmitting and receiving packets; 
 using the oscillator, receive a determined phase and amplitude of the first measurement packet as received at the slave device; 
 using the oscillator, receive a second measurement packet at a second frequency different from the first frequency from the slave device; 
 determine the phase and amplitude of the received second measurement packet; 
 determine multipath signals using the phases and amplitudes of the first and second measurement packets; and 
 determine the distance from the master device to the slave device using the determined multipath signal, 
   wherein both the master device and the slave device maintain the phase of their oscillators used to transmit and receive the measurement packets over transmitting and receiving steps.   
     
     
         10 . The master device of  claim 9 , wherein determining the multipath signals includes:
 performing a net channel estimate to determine the master to slave channel response across frequency; and   performing a fast Fourier transform on the net channel estimate; and   wherein determining the distance includes:   performing an inverse fast Fourier transform (IFFT) on the principal multi-path component of the FFT result.   
     
     
         11 . The master device of  claim 10 , wherein the FFT is performed directly on the net channel estimate when the phases of the measured frequencies are coherent. 
     
     
         12 . The master device of  claim 10 , wherein determining the multipath signals further includes performing phase change correction of the determined phases of the first and second measurement packets prior to performing the FFT when the phases of the measured frequencies are incoherent. 
     
     
         13 . The master device of  claim 10 , wherein determining the multipath signals includes determining the minimum phase roots of the determined phases of the first and second measurement packets prior to performing the FFT when the phases of the measured frequencies are incoherent. 
     
     
         14 . The master device of  claim 10 , wherein determining the distance includes:
 utilizing a super resolution algorithm on the IFFT result.   
     
     
         15 . The master device of  claim 9 , wherein the first and second measurement packets each contain a sine wave portion for determining the phase and the amplitude of the first and second measurement packets. 
     
     
         16 . The master device of  claim 9 , wherein the determined phase and amplitude of the first measurement packet is provided in the second measurement packet. 
     
     
         17 . A slave device for determining object distance using radio frequency signals, the slave device comprising:
 a processor;   a radio frequency interface coupled to the processor and including an oscillator used for transmitting and receiving packets;   program storage coupled to the processor and containing programs to cause the processor to:
 using the oscillator, receive a first measurement packet at a first frequency from a master device, the master device including a master processor and a master radio frequency interface coupled to the processor and including a master oscillator used for transmitting and receiving packets; 
 determine phase and amplitude of the first measurement packet; 
 using the oscillator, transmit to the master device the determined phase and amplitude of the received first measurement packet; and 
 using the oscillator, transmit a second measurement packet at a second frequency different from the first frequency from the slave device to the master device, 
   wherein both the master device and the slave device maintain the phase of their oscillators used to transmit and receive the measurement packets over transmitting and receiving steps.   
     
     
         18 . The slave device of  claim 17 , wherein the first and second measurement packets each contain a sine wave portion for determining the phase and the amplitude of the first and second measurement packets. 
     
     
         19 . The slave device of  claim 17 , wherein the programs further cause the processor to:
 enter receiving mode upon receiving an indication that the distance measurement is starting.   
     
     
         20 . The slave device of  claim 17 , wherein the radio frequency signals are Bluetooth® signals.