# US 2019/0245602 A1 · Reciprocity based channel state information acquisition for frequency division duplex system

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- Number: US 2019/0245602 A1
- Document ID: US20190245602A1
- Status: Published application
- Kind: A1
- Application number: 15/891,162
- Filed: 2018-02-07
- Published: 2019-08-08
- Earliest claimed: 2018-02-07
- Assignees: AT&T Intellectual Property I, L.P.
- Applicants: At&T Intellectual Property I, L.P.
- Inventors: Xiaoyi Wang; Arunabha Ghosh; Salam Akoum
- Web page: https://patentgrep.com/patent/US20190245602A1

## CPC

- H04L 25/0204: {of multiple channels}
- H04B 1/0475: {with means for limiting noise, interference or distortion (H04B1/0483 takes precedence)}
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04L 25/021: {Estimation of channel covariance}
- H04L 25/0224: {using sounding signals}
- H04L 25/03012: {operating in the time domain (H04L25/03165, H04L25/03178 take precedence)}
- H04L 27/2613: {Structure of the reference signals}
- H04L 27/2671: {Time domain}
- H04B 7/0617: {for beam forming}
- H04L 5/0053: {Allocation of signalling, i.e. of overhead other than pilot signals}
- H04L 5/14: Two-way operation using the same type of signal, i.e. duplex
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION

## 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

## Claims

### Claim 1

A base station device, comprising:
a processor; and
a memory that stores executable instructions that, when executed by the processor, facilitate performance of operations, comprising:
receiving a reference signal from a user equipment device;
generating, based on the reference signal, channel state information in a delay Doppler domain, wherein the channel state information comprises a channel response matrix; and
applying an uplink and downlink difference to the channel response matrix to reflect a Doppler difference in reception and transmission respectively.

### Claim 2 (depends on 1)

The base station device of claim 1, wherein the reference signal is represented according to a frequency time domain.

### Claim 3 (depends on 2)

The base station device of claim 2, wherein the operations further comprise:
converting frequency-time domain channel state information associated with the reference signal into delay Doppler domain channel state information.

### Claim 4 (depends on 1)

The base station device of claim 1, wherein the channel response matrix represents a quality of a transmission link between an antenna element at a transmitter and an antenna element at a receiver and wherein a channel covariance matrix is a covariance matrix of the channel response matrix.

### Claim 5 (depends on 1)

The base station device of claim 1, wherein the reference signal is represented according to the delay Doppler domain.

### Claim 6 (depends on 1)

The base station device of claim 1, wherein the operations further comprise:
adjusting an array response associated with the channel response matrix based on a frequency difference between an uplink frequency and a downlink frequency.

### Claim 7 (depends on 1)

The base station device of claim 1, wherein the operations further comprise:
generating a transmission parameter comprising at least one of a precoder matrix indicator or a rank indicator based on the channel response matrix.

### Claim 8 (depends on 7)

The base station device of claim 7, wherein the transmission parameter is represented according to a same domain as the channel response matrix.

### Claim 9 (depends on 1)

The base station device of claim 1, wherein the operations further comprise:
beamforming a channel state indicator reference signal based on an eigen mode of the channel response matrix.

### Claim 10

A method, comprising:
receiving, by a user equipment device comprising a processor, an uplink reference signal from a user equipment device;
based on the uplink reference signal, determining, by the user equipment device, delay Doppler domain channel state information, wherein the delay Doppler domain channel state information comprises a covariance matrix; and
based on whether an element is an uplink element, adjusting, by the user equipment device, a Doppler value of an element of the covariance matrix.

### Claim 11 (depends on 10)

The method of claim 10, further comprising:
converting, by the user equipment device, channel state information in a frequency-time domain into the delay Doppler domain channel state information.

### Claim 12 (depends on 11)

The method of claim 11, wherein the covariance matrix represents a quality of a transmission link between an antenna element at a transmitter and an antenna element at a receiver.

### Claim 13 (depends on 10)

The method of claim 10, further comprising:
based on a frequency difference between an uplink frequency of an uplink channel and a downlink frequency of a downlink channel, adjusting, by the user equipment device, an array response associated with the covariance matrix.

### Claim 14 (depends on 10)

The method of claim 10, further comprising:
based on the covariance matrix, generating, by the user equipment device, a transmission parameter comprising at least one of a precoder matrix indicator or a rank indicator.

### Claim 15 (depends on 14)

The method of claim 14 wherein the transmission parameter is in a same domain as the covariance matrix.

### Claim 16 (depends on 10)

The method of claim 10, further comprising:
beamforming, by the user equipment device, a channel state indicator reference signal based on an eigen mode of the covariance matrix.

### Claim 17

A machine-readable storage medium, comprising executable instructions that, when executed by a processor of a device, facilitate performance of operations, comprising:
receiving a reference signal from a user equipment device;
based on the reference signal, generating channel state information in a delay Doppler domain, wherein the channel state information comprises a channel response matrix, and wherein the channel response matrix represents a quality of a transmission link between an antenna element at a transmitter and an antenna element at a receiver; and
applying an uplink and downlink difference to the channel response matrix to reflect a Doppler difference in reception and transmission respectively.

### Claim 18 (depends on 17)

The machine-readable storage medium of claim 17, wherein the reference signal is in a frequency time domain.

### Claim 19 (depends on 18)

The machine-readable storage medium of claim 18, wherein the operations further comprise:
converting frequency-time domain channel state information associated with the reference signal into delay Doppler domain channel state information.

### Claim 20 (depends on 19)

The machine-readable storage medium of claim 19, wherein the operations further comprise:
converting the channel response matrix from the delay-Doppler domain to a frequency-time domain.