Channel extrapolation from one frequency and time to another

Abstract

An improved channel estimation technique is provided herein that determines accurate scatterer parameters for the scattering objects in the wireless channel, and extrapolates the scatterer parameters in both time and frequency to characterize the scattering objects for a different time and a different frequency. In one embodiment, a wireless device determines scatterer parameters that characterizes the scattering objects of a reception channel, and extrapolates the scatterer parameters in both time and frequency to predict the scatterer parameters for a future time and frequency, e.g., a future transmission time and frequency.

1 . A method implemented by a wireless device of characterizing a wireless communication channel, the method comprising:
 determining a first set of scatterer parameters based on signal samples received by a wireless receiver via a first communication channel associated with a first frequency and a first time, wherein the first set of scatterer parameters comprises a set of scattering coefficients for each of a plurality of path delays, and wherein each scattering coefficient corresponds to a scattering object; and   determining a second set of scatterer parameters for a second communication channel associated with a second frequency and a second time by calculating extrapolated scattering coefficients for the second set of scatterer parameters based on the first set of scatterer parameters, the first and second frequencies, and the first and second times.   
   
   
       2 . The method of  claim 1  wherein the first communication channel corresponds to an uplink communication channel associated with an uplink frequency and an uplink time, and wherein the second communication channel corresponds to a downlink communication channel associated with a downlink frequency and a downlink time. 
   
   
       3 . The method of  claim 1  wherein the first communication channel corresponds to a reception communication channel associated with a reception frequency and a reception time, and wherein the second communication channel corresponds to a transmission communication channel associated with a transmission frequency and a transmission time. 
   
   
       4 . The method of  claim 1  further comprising determining extrapolated channel estimates for the second communication channel based on the second set of scatterer parameters. 
   
   
       5 . The method of  claim 4  further comprising using the extrapolated channel estimates to pre-process transmission signals to reduce interference at one receiver from transmitted signals intended for another receiver. 
   
   
       6 . The method of  claim 1  further comprising determining a matrix of complex delay coefficients based on the plurality of signal samples received via the first communication channel over an evaluation period, wherein different rows of said delay coefficient matrix correspond to different time intervals within the evaluation period and wherein different columns of said delay coefficient matrix correspond to different path delays, and wherein determining individual sets of scattering coefficients for individual path delays in the first set of scatterer parameters comprises applying a time-to-frequency transform to individual columns of the delay coefficient matrix. 
   
   
       7 . The method of  claim 6  wherein the signal samples comprise OFDM signal samples, wherein the evaluation period comprises a plurality of OFDM symbol periods, and wherein different rows of said delay coefficient matrix correspond to different OFDM symbol periods. 
   
   
       8 . The method of  claim 6  wherein applying the time-to-frequency transform to individual columns of the delay coefficient matrix comprises applying a Prony algorithm to individual columns of the delay coefficient matrix. 
   
   
       9 . The method of  claim 1  wherein calculating the extrapolated scattering coefficients for the second set of scatterer parameters comprises:
 rotating a phase of the scattering coefficients of the first set of scatterer parameters based on a frequency difference between the first and second frequencies to obtain rotated scattering coefficients; and   rotating a phase of the rotated scattering coefficients based on a time difference between the first and second times to obtain the extrapolated scattering coefficients for the second set of scatterer parameters.   
   
   
       10 . The method of  claim 9  wherein each scattering coefficient in the first set of scatterer parameters is associated with a Doppler frequency, the method further comprising scaling the Doppler frequencies in the first set of scatterer parameters based on a ratio between the first and second frequencies to obtain a Doppler frequency for each scattering coefficient in the second set of scatterer parameters. 
   
   
       11 . The method of  claim 1  wherein each scattering coefficient in the first set of scatterer parameters is associated with a rate of change of delay, and wherein calculating the extrapolated scattering coefficients comprises:
 calculating extrapolated path delays for the second set of scatterer parameters based on the path delays of the first set of scatterer parameters and the rate of change of delay; and   calculating the extrapolated scattering coefficients based on the extrapolated path delays and the second frequency.   
   
   
       12 . The method of  claim 11  wherein calculating the extrapolated scattering coefficients based on the extrapolated path delays and the second frequency comprises:
 determining reflection coefficients for the first set of scatterer parameters based on the path delays and scattering coefficients of the first set of scatterer parameters and the first frequency; and   rotating a phase of the reflection coefficients based on the extrapolated path delays and the second frequency to calculate the extrapolated scattering coefficients.   
   
   
       13 . The method of  claim 1  wherein the receiver comprises a plurality of antenna elements, the method further comprising calculating a phase progression across the antenna elements based on the first and second frequencies to determine different transmission signal directions corresponding to different scattering objects. 
   
   
       14 . A wireless device configured to characterize a wireless communication channel, the wireless device comprising:
 a first processing element configured to determine a first set of scatterer parameters based on signal samples received by a wireless receiver via a first communication channel associated with a first frequency and a first time, wherein the first set of scatterer parameters comprises a set of scattering coefficients for each of a plurality of path delays, and wherein each scattering coefficient corresponds to a scattering object; and   a second processing element configured to determine a second set of scatterer parameters for a second communication channel associated with a second frequency and a second time by calculating extrapolated scattering coefficients for the second set of scatterer parameters based on the first set of scatterer parameters, the first and second frequencies, and the first and second times.   
   
   
       15 . The wireless device of  claim 14  wherein the first communication channel corresponds to an uplink communication channel associated with an uplink frequency and an uplink time, and wherein the second communication channel corresponds to a downlink communication channel associated with a downlink frequency and a downlink time. 
   
   
       16 . The wireless device of  claim 14  wherein the first communication channel corresponds to a reception communication channel associated with a reception frequency and a reception time, and wherein the second communication channel corresponds to a transmission communication channel associated with a transmission frequency and a transmission time. 
   
   
       17 . The wireless device of  claim 14  wherein the second processing element is further configured to determine extrapolated channel estimates for the second communication channel based on the second set of scatterer parameters. 
   
   
       18 . The wireless device of  claim 17  wherein the second processing element is further configured to use the extrapolated channel estimates to pre-process transmission signals to reduce interference at one receiver from transmitted signals intended for another receiver. 
   
   
       19 . The wireless device of  claim 14  wherein the first processing element is further configured to determine a matrix of complex delay coefficients based on the plurality of signal samples received via the first communication channel over an evaluation period, wherein different rows of said delay coefficient matrix correspond to different time intervals within the evaluation period and wherein different columns of said delay coefficient matrix correspond to different path delays, and to determine individual sets of scattering coefficients for individual path delays in the first set of scatterer parameters by applying a time-to-frequency transform to individual columns of the delay coefficient matrix. 
   
   
       20 . The wireless device of  claim 19  wherein the signal samples comprise OFDM signal samples, wherein the evaluation period comprises a plurality of OFDM symbol periods, and wherein different rows of said delay coefficient matrix correspond to different OFDM symbol periods. 
   
   
       21 . The wireless device of  claim 19  wherein the first processing element is configured to apply the time-to-frequency transform to individual columns of the delay coefficient matrix by applying a Prony algorithm to individual columns of the delay coefficient matrix. 
   
   
       22 . The wireless device of  claim 14  wherein the second processing element is configured to calculate the extrapolated scattering coefficients for the second set of scatterer parameters by:
 rotate a phase of the scattering coefficients of the first set of scatterer parameters based on a frequency difference between the first and second frequencies to obtain rotated scattering coefficients; and   rotate a phase of the rotated scattering coefficients based on a time difference between the first and second times to obtain the extrapolated scattering coefficients for the second set of scatterer parameters.   
   
   
       23 . The wireless device of  claim 22  wherein each scattering coefficient in the first set of scatterer parameters is associated with a Doppler frequency, wherein the second processing element is further configured to scale the Doppler frequencies in the first set of scatterer parameters based on a ratio between the first and second frequencies to obtain a Doppler frequency for each scattering coefficient in the second set of scatterer parameters. 
   
   
       24 . The wireless device of  claim 14  wherein each scattering coefficient in the first set of scatterer parameters is associated with a rate of change of delay, and wherein the second processing element is configured to calculate the extrapolated scattering coefficients by:
 calculating extrapolated path delays for the second set of scatterer parameters based on the path delays of the first set of scatterer parameters and the rate of change of delay; and   calculating the extrapolated scattering coefficients based on the extrapolated path delays and the second frequency.   
   
   
       25 . The wireless device of  claim 24  wherein the second processing element is configured to calculate the extrapolated scattering coefficients based on the extrapolated path delays and the second frequency by:
 determining reflection coefficients for the first set of scatterer parameters based on the path delays and scattering coefficients of the first set of scatterer parameters and the first frequency; and   rotating a phase of the reflection coefficients based on the extrapolated path delays and the second frequency to calculate the extrapolated scattering coefficients.   
   
   
       26 . The wireless device of  claim 14  wherein the receiver comprises a plurality of antenna elements, wherein the second processing element is further configured to calculate a phase progression across the antenna elements based on the first and second frequencies to determine different transmission signal directions corresponding to different scattering objects.