Device and method for compressing and/or decompressing channel state information

1. A computation device for compressing channel state information (CSI), the CSI representing a channel transfer function H having a spatial dimension (n) and a frequency dimension (f), the computation device comprising:

a processor configured to:

perform a spatial transformation and a frequency-to-time transformation on the channel transfer function H in any order to obtain a transformed channel transfer function HT;

select values h τ,k of the transformed channel transfer function HT; and

generate compressed channel state information (CCSI) based on the values h τ,k of the transformed channel transfer function HT, wherein k represents spatial components and τ represents time taps,

wherein the channel transfer function H relates to a number N of antennas and a number F of frequency ranges, and is given in the form of a matrix:

HTR

=

(

H

0

H

1

⋮

H

f

⋮

H

F

-

1

)

=

(

h

0

,

0

h

0

,

1

…

h

0

,

n

…

h

0

,

N

-

1

h

1

,

0

h

1

,

1

⋯

h

1

,

n

⋯

h

1

,

N

-

1

⋮

⋮

⋱

⋮

⋱

⋮

h

f

,

0

h

f

,

1

⋯

h

f

,

n

⋯

h

f

,

N

-

1

⋮

⋮



⋮



⋮

h

F

-

1

,

0

h

F

-

1

,

1

…

h

F

-

1

,

n

…

h

F

-

1

,

N

-

1

)

,

and wherein the processor is configured to perform the spatial transformation before the frequency-to-time transformation by performing the spatial transformation for each row of the matrix H and performing the frequency-to-time transformation for each column of a matrix resulting from the spatial transformation, or

wherein the processor is configured to perform the frequency-to-time transformation before the spatial transformation by performing the frequency-to-time transformation for each column of the matrix H and performing the spatial transformation for each row of a matrix resulting from the frequency-to-time transformation.

2. The computation device according to claim 1 , wherein, to generate the compressed channel state information (CCSI), the processor is configured to:

select, from the transformed channel transfer function HT, a predetermined number L of values h τ,k of the transformed channel transfer function HT having the greatest amplitudes or all values h τ,k of the transformed channel transfer function HT exceeding a predetermined amplitude; and

generate a channel state report based on the selected values of the transformed channel transfer function HT.

3. The computation device according to claim 1 , wherein the processor is further configured to:

generate the channel state report such that the channel state report comprises, for each selected value of the transformed channel transfer function HT, the position τ, k of the selected value in the transformed channel transfer function HT; and/or

generate a channel state report such that the channel state report comprises, for each selected value of the transformed channel transfer function HT, a triplet including the amplitude and phase of the selected value and an index indicating the position τ, k of the selected value in the transformed channel transfer function HT; and/or

perform a normalization of the amplitude of the selected values with respect to the selected value having a maximum amplitude; and/or

perform a quantization of the amplitude and/or a phase of the selected values.

4. The computation device according to claim 1 , wherein the channel transfer function H is a function of one row of antennas having a number N of antennas and one polarization direction of the antennas, and the processor is configured to perform the spatial transformation as a one-dimensional spatial transformation, or

wherein the channel transfer function H is a function of more than one row of antennas and/or more than one polarization direction of the antennas, each row and polarization direction having a number of antennas, and the processor is configured to perform the following steps for each frequency dimension (f);

re-shape a linear array comprising all the elements (h f,n ) of the channel transfer function H related to the respective frequency dimension (f) into a multi-dimensional array according to the number of rows and polarization directions;

perform the spatial transformation as a multi-dimensional spatial transformation; and

re-arrange the results of the spatial transformation to a linear array.

5. The computation device according to claim 1 , wherein the spatial transformation comprises a Discrete Fourier Transformation (DFT), a Fast Fourier Transformation (FFT), or a Principal Component Analysis (PCA) transformation, and/or the frequency-to-time transformation comprises an Inverse Discrete Fourier Transformation or an Inverse Fast Fourier Transformation.

6. A restoring device for restoring channel state information (CSI) from compressed channel state information (CCSI), the CSI representing a channel transfer function H having a spatial dimension (n) and a frequency dimension (f), the restoring device comprising:

a processor configured to:

de-compress the CCSI to obtain a restored transformed channel transfer function HTR; and

re-transform the restored transformed channel transfer function HTR by performing a time-to-frequency transformation and an inverse spatial transformation on the restored transformed channel transfer function HTR in any order to obtain a restored transfer function HR,

wherein the restored transformed channel transfer function HTR relates to a number T of time taps and a number K of spatial components, and is given in the form of a matrix:

HTR

=

(

H

0

H

1

⋮

H

τ

⋮

H

T

-

1

)

=

(

h

0

,

0

h

0

,

1

…

h

0

,

k

…

h

0

,

K

-

1

h

1

,

0

h

1

,

1

⋯

h

1

,

k

⋯

h

1

,

K

-

1

⋮

⋮

⋱

⋮

⋱

⋮

h

τ

,

0

h

τ

,

1

⋯

h

τ

,

k

⋯

h

τ

,

K

-

1

⋮

⋮



⋮



⋮

h

T

-

1

,

0

h

T

-

1

,

1

…

h

T

-

1

,

k

…

h

T

-

1

,

K

-

1

)

,

and wherein the processor is configured to perform the time-to-frequency transformation before the inverse spatial transformation by performing the time-to-frequency transformation for each column of the matrix HTR and performing the inverse spatial transformation for each row of a matrix resulting from the time-to-frequency transformation, or

wherein the processor is configured to perform the inverse spatial transformation before the time-to-frequency transformation by performing the inverse spatial transformation for each row of the matrix HTR and performing the time-to-frequency transformation for each column of a matrix resulting from the inverse spatial transformation.

7. The restoring device according to claim 6 , wherein, to de-compress the CCSI, the processor is configured to:

re-arrange values included in the CCSI, according to position information τ, k included in the CCSI, in a two-dimensional matrix; and/or

perform a de-quantization of an amplitude and/or a phase of the values; and/or

re-normalize the amplitude of the values,

wherein k represents a spatial component position and τ represents a time tap position of the CCSI.

8. The restoring device according to claim 7 , wherein the restored channel transfer function HR is a function of one row of antennas having a number N of antennas and one polarization direction of the antennas, and the processor is configured to perform the inverse spatial transformation as a one-dimensional inverse spatial transformation, or

wherein the restored channel transfer function HR is a function of more than one row of antennas and/or more than one polarization direction of the antennas, each row and/or polarization direction having a number of antennas, and the processor is configured to perform the following steps for each time tap τ;

re-shape a linear array comprising all the elements h τ,k of the restored transformed channel transfer function HTR related to the respective time tap τ into a multi-dimensional array according to the number of rows and polarization directions;

perform the inverse spatial transformation as a multi-dimensional inverse spatial transformation; and

re-arrange the results of the inverse spatial transformation into a linear array.

9. The restoring device according to claim 6 , wherein the time-to-frequency transformation comprises a Discrete Fourier Transformation or a Fast Fourier Transformation, and/or the inverse spatial transformation comprises an Inverse Discrete Fourier Transformation (IDFT), an Inverse Fast Fourier Transformation (IFFT), or an Inverse Principal Component Analysis (PCA) transformation.

10. A computation method for compressing channel state information (CSI), the CSI representing a channel transfer function H having a spatial dimension (n) and a frequency dimension (f), the computation method comprising:

performing, by a processor, a spatial transformation and a frequency-to-time transformation on the channel transfer function H in any order to obtain a transformed channel transfer function HT;

selecting values h τ,k of the transformed channel transfer function HT; and

generating compressed channel state information (CCSI) based on the values h τ,k of the transformed channel transfer function HT, wherein k represents spatial components and τ represents time taps,

wherein the channel transfer function H relates to a number N of antennas and a number F of frequency ranges, and is given in the form of a matrix:

HTR

=

(

H

0

H

1

⋮

H

f

⋮

H

F

-

1

)

=

(

h

0

,

0

h

0

,

1

…

h

0

,

n

…

h

0

,

N

-

1

h

1

,

0

h

1

,

1

⋯

h

1

,

n

⋯

h

1

,

N

-

1

⋮

⋮

⋱

⋮

⋱

⋮

h

f

,

0

h

f

,

1

⋯

h

f

,

n

⋯

h

f

,

N

-

1

⋮

⋮



⋮



⋮

h

F

-

1

,

0

h

F

-

1

,

1

…

h

F

-

1

,

n

…

h

F

-

1

,

N

-

1

)

,

and wherein the spatial transformation is performed before the frequency-to-time transformation by performing the spatial transformation for each row of the matrix H and performing the frequency-to-time transformation for each column of a matrix resulting from the spatial transformation, or

wherein the frequency-to-time transformation is performed before the spatial transformation by performing the frequency-to-time transformation for each column of the matrix H and performing the spatial transformation for each row of a matrix resulting from the frequency-to-time transformation.

11. A method for restoring channel state information (CSI) from compressed channel state information (CCSI), the CSI representing a channel transfer function H having a spatial dimension (n) and a frequency dimension (f), the method comprising:

de-compress, by a processor, the CCSI to obtain a restored transformed channel transfer function HTR; and

re-transform, by the processor, the restored transformed channel transfer function HTR by performing a time-to-frequency transformation and an inverse spatial transformation on the restored transformed channel transfer function HTR in any order to obtain a restored transfer function HR,

wherein the restored transformed channel transfer function HTR relates to a number T of time taps and a number K of spatial components, and is given in the form of a matrix:

HTR

=

(

H

0

H

1

⋮

H

f

⋮

H

F

-

1

)

=

(

h

0

,

0

h

0

,

1

…

h

0

,

n

…

h

0

,

N

-

1

h

1

,

0

h

1

,

1

⋯

h

1

,

n

⋯

h

1

,

N

-

1

⋮

⋮

⋱

⋮

⋱

⋮

h

f

,

0

h

f

,

1

⋯

h

f

,

n

⋯

h

f

,

N

-

1

⋮

⋮



⋮



⋮

h

F

-

1

,

0

h

F

-

1

,

1

…

h

F

-

1

,

n

…

h

F

-

1

,

N

-

1

)

,

and wherein the processor is configured to perform the time-to-frequency transformation before the inverse spatial transformation by performing the time-to-frequency transformation for each column of the matrix HTR and performing the inverse spatial transformation for each row of a matrix resulting from the time-to-frequency transformation, or

wherein the processor is configured to perform the inverse spatial transformation before the time-to-frequency transformation by performing the inverse spatial transformation for each row of the matrix HTR and performing the time-to-frequency transformation for each column of a matrix resulting from the inverse spatial transformation.

12. A non-transitory computer-readable medium, having computer program instructions stored thereon, which when executed by a processor, cause the processor to execute the method of claim 10 .