# US 11,115,097 B2 · Adaptive explicit CSI feedback and overhead reduction

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- Number: US 11,115,097 B2
- Document ID: US11115097B2
- Status: Granted
- Kind: B2
- Application number: 16/477,220
- Filed: 2017-12-28
- Published: 2019-11-28
- Granted: 2021-09-07
- Earliest claimed: 2017-02-02
- Assignees: Nokia Technologies Oy
- Applicants: Nokia Technologies Oy
- Inventors: Xiaomao Mao
- Web page: https://patentgrep.com/patent/US11115097B2

## CPC

- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04B 7/0417: Feedback systems
- H04B 7/0421: {utilizing implicit feedback, e.g. steered pilot signals}
- H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B 7/0478: {Special codebook structures directed to feedback optimisation}
- H04B 7/0634: {Antenna weights or vector/matrix coefficients}
- H04B 7/0639: {Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection}
- H04B: TRANSMISSION

## Abstract

A method including evaluating a number of constituent precoders to be used in providing a single precoder to include in an explicit channel state information (CSI) report, to be transmitted from a user terminal to at least one device in a network, and combining the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one. The method includes configuring to signal to transmit the explicit CSI report including the single precoder from the user terminal to the at least one device in the network.

## Claims

### Claim 1

A method, comprising:
evaluating, using circuitry of a user terminal, a number of constituent precoders to be used in providing a single precoder to include in an explicit channel state information report, to be transmitted from the user terminal to at least one device in a network;
wherein the evaluating of the number of constituent precoders to be used in providing the single precoder is at least partially based on a measurement using the user terminal comprising: a speed of the user terminal, and/or an angular spread associated with the at least one device in the network;
determining, using the circuitry of the user terminal, the number of constituent precoders based on the user terminal measurement;
wherein the constituent precoders comprise eigenvectors and the single precoder comprises at least one of a dominant eigenvector and a single vector combined of several eigenvectors;
wherein determining a number of eigenvectors to be used in providing the single vector comprises determining the angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix;
determining that the single precoder is the dominant eigenvector, in response to a determination that the number of constituent precoders to be used in providing the single precoder is equal to or less than one;
determining the angular spread based on: a power gain difference between respective eigenvalues of the eigenvectors and a dominant eigenvalue; and a steering direction difference between respective eigenvectors and the dominant eigenvector;
combining the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one; and
configuring a signal to transmit the explicit channel state information report including the single precoder from the user terminal to the at least one device in the network.

### Claim 2 (depends on 1)

The method of claim 1, wherein determining the angular spread further comprises:
determining whether λ0−λi<ρ and s(U0)−s(Ui)<ξ,
where threshold ρ denotes the power gain difference between eigen values λ0 and λi and threshold ξ denotes the steering direction difference between eigenvectors; and
selecting eigenvector Ui to be included in the number of eigenvectors in response to a determination that λ0−λ1<ρ and s(U0)−s(Ui)<ξ,
where s(*) represents a function abstracting a steering direction of an eigenvector, and i represents an eigenvector index.

### Claim 3 (depends on 2)

The method of claim 2, further comprising:
determining whether i=0; and
reporting only the dominant eigenvector in response to a determination that i=0.

### Claim 4 (depends on 2)

The method of claim 2, further comprising:
determining whether i≥1; and
combining eigenvectors U0, . . . Ui into one vector and reporting the one vector in response to a determination that i≥1.

### Claim 5 (depends on 1)

The method of claim 1, wherein determining the number of eigenvectors to be used in providing the single vector further comprises:
accessing a user terminal speed threshold, where the user terminal speed threshold is denoted as τ;
determining the user terminal speed, ν, of the user terminal; and
enabling the combined vector feedback if the user terminal speed ν≥τ.

### Claim 6 (depends on 1)

The method of claim 1, wherein determining the number of eigenvectors to be used in providing the single vector to include in the explicit channel state information report further comprises:
applying eigen-decomposition to R, where U denotes an eigenvector, Λ denotes an eigenvalue, U0 denotes the dominant eigenvector and λ0 denotes the dominant eigenvalue, H denotes a Hermitian operator, and
R=UΛU{circumflex over ( )}H,
Λ=(λ0,λ1, . . . ,λN), and
U=(U0,U1, . . . ,UN).

### Claim 7 (depends on 1)

The method of claim 1, wherein signaling to transmit the explicit channel state information report further comprises:
reporting the user terminal speed from the user terminal to the at least one device in the network, where the at least one device in the network is configured to determine whether to combine the eigenvectors based on the user terminal speed;
configuring to receive instructions from the at least one device in the network to combine the eigenvectors;
combining the eigenvectors; and
configuring to send the explicit channel state information report to the at least one device in the network including the combined eigenvectors.

### Claim 8

An apparatus, comprising:
at least one processor; and
at least one non-transitory memory including computer program code,
the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to at least:
evaluate, using circuitry of a user terminal, a number of constituent precoders to be used in providing a single vector to include in an explicit channel state information report, to be transmitted from the user terminal to at least one device in a network;
wherein the evaluating of the number of constituent precoders to be used in providing the single precoder is at least partially based on a measurement using the user terminal comprising: a speed of the user terminal, and/or an angular spread associated with the at least one device in the network;
determine, using the circuitry of the user terminal, the number of constituent precoders based on the user terminal measurement;
wherein the constituent precoders comprise eigenvectors and the single precoder comprises at least one of a dominant eigenvector and a single vector combined of several eigenvectors;
wherein determining a number of eigenvectors to be used in providing the single vector comprises determining the angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix;
determine that the single precoder is the dominant eigenvector, in response to a determination that the number of constituent precoders to be used in providing the single precoder is equal to or less than one;
determine the angular spread based on: a power gain difference between respective eigenvalues of the eigenvectors and a dominant eigenvalue; and a steering direction difference between respective eigenvectors and the dominant eigenvector;
combine the constituent precoders to form the single vector in response to a determination that the number of constituent precoders to be used is greater than one; and
configure a signal to transmit the explicit channel state information report including the single precoder from the user terminal to the at least one device in the network.

### Claim 9 (depends on 8)

The apparatus of claim 8, where, when determining the angular spread, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:
determining whether λ0−λi<ρ and s(U0)−s(Ui)<ξ,
where threshold ρ denotes the power gain difference between eigen values λ0 and λi and threshold ξ denotes the steering direction difference between eigenvectors; and
select eigenvector Ui to be included in the number of eigenvectors in response to a determination that λ0−λi<ρ and s(U0)−s(Ui)<ξ,
where s(*) represents a function abstracting a steering direction of an eigenvector, and i represents an eigenvector index.

### Claim 10 (depends on 9)

The apparatus of claim 9, where the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
determine whether i=0; and
report only the dominant eigenvector in response to a determination that i=0.

### Claim 11 (depends on 9)

The apparatus of claim 9, where the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
determine whether i≥1; and
combine eigenvectors U0, . . . Ui into one vector and report the one vector in response to a determination that i≥1.

### Claim 12 (depends on 8)

The apparatus of claim 8, where, when determining the number of eigenvectors to be used in providing the single vector, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:
access a user terminal speed threshold, where the user terminal speed threshold is denoted as τ;
determine the user terminal speed, ν, of the user terminal; and
enable the combined vector feedback if the user terminal speed ν≥τ.

### Claim 13 (depends on 12)

The apparatus of claim 12, where, when determining the user terminal speed of the user terminal, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:
determine the user terminal speed based on a Doppler offset, where
Δ
⁢
⁢
f
=
v
c
⁢
f
0
,
where, Δf is the Doppler offset, f0 is a carrier frequency and c is a speed of light.

### Claim 14 (depends on 8)

The apparatus of claim 8, where, when combining the eigenvectors to form the single vector, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:
apply maximum ratio combining to combine the eigenvectors with eigenvalues as the combining coefficients.

### Claim 15

A non-transitory computer readable medium encoded with instructions that, when executed by a computer, cause performance of:
evaluating, using circuitry of a user terminal, a number of constituent precoders to be used in providing a single precoder to include in an explicit channel state information report, to be transmitted from the user terminal to at least one device in a network;
wherein the evaluating of the number of constituent precoders to be used in providing the single precoder is at least partially based on a measurement using the user terminal comprising: a speed of the user terminal, and/or an angular spread associated with the at least one device in the network;
determining, using the circuitry of the user terminal, the number of constituent precoders based on the user terminal measurement;
wherein the constituent precoders comprise eigenvectors and the single precoder comprises at least one of a dominant eigenvector and a single vector combined of several eigenvectors;
wherein determining a number of eigenvectors to be used in providing the single vector comprises determining the angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix;
determining that the single precoder is the dominant eigenvector, in response to a determination that the number of constituent precoders to be used in providing the single precoder is equal to or less than one;
determining the angular spread based on: a power gain difference between respective eigenvalues of the eigenvectors and a dominant eigenvalue; and a steering direction difference between respective eigenvectors and the dominant eigenvector;
combining the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one; and
configuring a signal to transmit the explicit channel state information report including the single precoder from the user terminal to the at least one device in the network.