Reciprocity based channel state information acquisition for frequency division duplex system

Abstract

Various embodiments disclosed herein provide for a reciprocity based channel state information acquisition scheme for frequency division duplex wireless communications systems. By converting channel state information from a traditional frequency-time domain to a Delay-Doppler domain, the channel state information feedback overhead can be reduced since the multi-path of radio propagation is reciprocal in terms of each ray and each cluster of antenna elements. Since the surrounding objects create the same multipath fading for both uplink and downlink transmissions, modeling the channel state information in the Delay-Doppler domain, and adjusting the sign of the Doppler value (negative/positive) can account for the multipath characteristics in both uplink and downlink.

What is claimed is: 
     
         1 . A method, comprising:
 determining, by network equipment comprising a processor, channel state information based on a reference signal received from a user equipment, wherein the reference signal and the channel state information are represented according to a frequency time domain; and   transforming, by the network equipment, the channel state information from being represented in the frequency time domain to being represented in a delay Doppler domain.   
     
     
         2 . The method of  claim 1 , wherein the transforming comprises applying a difference between an uplink frequency of an uplink channel and a downlink frequency of a downlink channel to a channel covariance matrix. 
     
     
         3 . The method of  claim 2 , wherein the applying of the difference comprises adjusting a mathematical sign of a Doppler value, resulting in a determination of a Doppler difference between a transmission and a reception of the uplink channel. 
     
     
         4 . The method of  claim 2 , wherein the applying of the difference comprises adjusting an array response based on the difference between the uplink frequency and the downlink frequency. 
     
     
         5 . The method of  claim 1 , wherein the transforming comprises:
 deriving a channel covariance matrix in the delay Doppler domain based on the reference signal.   
     
     
         6 . The method of  claim 1 , further comprising:
 facilitating, by the network equipment, a transmission of a channel covariance matrix to the user equipment, wherein the channel covariance matrix is derived from the reference signal.   
     
     
         7 . The method of  claim 6 , wherein the facilitating of the transmission comprises utilizing the channel covariance matrix to generate a transmission parameter. 
     
     
         8 . The method of  claim 1 , further comprising:
 generating, by the network equipment, short term channel state information acquisition based on a determined channel covariance matrix.   
     
     
         9 . The method of  claim 8 , further comprising:
 beamforming, by the network equipment, channel state information reference signal ports of the short term channel state information acquisition, wherein the beamforming comprises using a dominant eigen mode of the determined channel covariance matrix.   
     
     
         10 . The method of  claim 1 , wherein the transforming comprises employing a transformation function to perform the transforming, and wherein the transformation function is a Symplectic Finite Fourier transform. 
     
     
         11 . The method of  claim 1 , wherein the transforming comprises employing a transformation function to perform the transforming, and wherein the transformation function is a Discrete Symplectic Fourier Transform. 
     
     
         12 . A system, comprising:
 a processor; and   a memory that stores executable instructions that, when executed by the processor, facilitate performance of operations, comprising:
 based on a reference signal received from a user equipment in a frequency-time domain, determining channel state information; and 
 converting the channel state information from the frequency-time domain to delay Doppler domain channel state information. 
   
     
     
         13 . The system of  claim 12 , wherein the operations further comprise:
 based on the reference signal and the converting, deriving a channel covariance matrix in a delay Doppler domain; and   sending, to the user equipment, a transmission that comprises the channel covariance matrix.   
     
     
         14 . The system of  claim 13 , wherein the sending comprises utilizing the channel covariance matrix to generate a transmission parameter. 
     
     
         15 . The system of  claim 12 , wherein the converting comprises applying a difference between an uplink frequency of an uplink channel and a downlink frequency of a downlink channel to a channel covariance matrix. 
     
     
         16 . The system of  claim 15 , wherein the applying comprises adjusting a mathematical sign of a Doppler value, resulting in a determination of a Doppler difference between a transmission and a reception of the uplink channel. 
     
     
         17 . The system of  claim 15 , wherein the applying comprises adjusting an array response based on the difference between the uplink frequency and the downlink frequency. 
     
     
         18 . A non-transitory machine-readable medium, comprising executable instructions that, when executed by a processor, facilitate performance of operations, comprising:
 determining channel state information from a reference signal received via an uplink channel; and   based on the reference signal being received in a frequency-time domain, transforming the channel state information associated with the reference signal from the frequency-time domain to a delay Doppler domain.   
     
     
         19 . The non-transitory machine-readable medium of  claim 18 , wherein the transforming comprises:
 applying a difference between an uplink frequency of the uplink channel and a downlink frequency of a downlink channel to a channel covariance matrix; and   adjusting an array response associated with the channel covariance matrix based on the difference between the uplink frequency and the downlink frequency.   
     
     
         20 . The non-transitory machine-readable medium of  claim 19 , wherein the channel covariance matrix represents a quality of a transmission link between a first antenna element at a transmitter and a second antenna element at a receiver.