Apparatus and method for decoding a received signal

1. An apparatus for filtering a received signal to obtain a filtered signal, wherein the received signal has been transmitted by conducting a transmission, wherein the apparatus comprises:

a detector configured to detect whether the transmission is either a single-user Multiple Input Multiple Output transmission or a multi-user Multiple Input Multiple Output transmission, and

a filter application unit, wherein the filter application unit is configured to apply a first receive filter with a first filter characteristic on the received signal to obtain the filtered signal when the transmission is the single-user Multiple Input Multiple Output transmission, and wherein the filter application unit is configured to apply a second receive filter with a second, different filter characteristic on the received signal to obtain the filtered signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein the detector is configured to determine whether a ratio of a maximum of main-diagonal coefficients of an interference-plus-noise covariance matrix and an average noise power is greater than one to determine whether the transmission is the multi-user Multiple Input Multiple Output transmission or the single-user Multiple Input Multiple Output transmission,

wherein the filter application unit is configured to apply a Minimum-Mean-Square-Error receive filter as the second receive filter on the received signal when the transmission is the multi-user Multiple Input Multiple Output transmission, the Minimum-Mean-Square-Error receive filter being defined according to

m

_

MMSE

H

=

g

_

1

H

⁢

R

_

ηη

_

-

1

g

_

1

H

⁢

R

_

ηη

-

1

⁢

g

_

1

as the second receive filter on the received signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein g 1 denotes a matrix-vector product H 1 p i , wherein H 1 denotes the channel from an eNodeB to a user equipment, wherein p i denotes a precoding vector recommended by the user equipment, wherein g 1 H denotes a Hermitian of the matrix-vector product g 1 , and wherein R ηη −1 denotes an inverse matrix of a covariance matrix R ηη .

2. An apparatus according to claim 1 ,

wherein the detector is configured to detect that the transmission is the single-user Multiple Input Multiple Output transmission when the received signal does not comprise signal components for a co-scheduled user equipment, and

wherein the detector is configured to detect that the transmission is the multi-user Multiple Input Multiple Output transmission when the received signal does comprise signal components for at least one co-scheduled user equipment.

3. An apparatus according to claim 1 , wherein the filter application unit is configured to apply a Maximum-Ratio-Combiner receive filter as the first receive filter on the received signal when the transmission is the single-user Multiple Input Multiple Output transmission.

4. An apparatus according to claim 3 , wherein the filter application unit is configured to apply the Maximum-Ratio-Combiner receive filter being defined according to

m

_

MRC

H

=

g

_

1

H

g

_

1

H

⁢

g

_

1

,

as the first receive filter on the received signal when the transmission is the single-user Multiple Input Multiple Output transmission.

5. An apparatus according to claim 1 , wherein the detector is configured to detect that the transmission is the multi-user Multiple Input Multiple Output transmission when the received signal comprises interference signal components.

6. An apparatus according to claim 5 , wherein the detector is configured to detect that the transmission is the single-user Multiple Input Multiple Output transmission when the received signal comprises no interference signal components.

7. An apparatus for filtering a received signal to obtain a filtered signal, wherein the received signal has been transmitted by conducting a transmission, wherein the apparatus comprises:

a detector configured to detect whether the transmission is either a single-user Multiple Input Multiple Output transmission or a multi-user Multiple Input Multiple Output transmission, and

a filter application unit, wherein the filter application unit is configured to apply a first receive filter with a first filter characteristic on the received signal to obtain the filtered signal when the transmission is the single-user Multiple Input Multiple Output transmission, and wherein the filter application unit is configured to apply a second receive filter with a second, different filter characteristic on the received signal to obtain the filtered signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein the detector is configured to detect that the transmission is the multi-user Multiple Input Multiple Output transmission when a maximum of main-diagonal coefficients of an interference-plus-noise covariance matrix is greater than an average noise power, and

wherein the detector is configured to detect that the transmission is the single-user Multiple Input Multiple Output transmission when the maximum of the main-diagonal coefficients of the interference-plus-noise covariance matrix is not greater than the average noise power,

wherein the detector is configured to determine the interference-plus-noise covariance matrix by conducting a singular value decomposition of a residual matrix {tilde over (R)} ηη being defined as

R

_

~

ηη

=

1

K

⁢

∑

i

=

1

K

⁢

y

_

1

,

i

⁢

y

_

1

,

i

H

-

σ

d

2

⁢

g

_

1

⁢

g

_

1

H

wherein y 1,i is an i-th component of the received signal, wherein y 1,i H is an i-th component of a Hermitian signal of the received signal.

8. An apparatus according to claim 7 , wherein the detector is configured to determine the interference-plus-noise covariance matrix {tilde over (Σ)} ηη by conducting the singular value decomposition of the residual matrix {tilde over (R)} ηη according to:

Ũ ηη {tilde over (Σ)} ηη {tilde over (V)} ηη H ={tilde over (R)} ηη .

9. An apparatus according to claim 8 , wherein the detector is configured to detect that the transmission is the multi-user Multiple Input Multiple Output transmission when the maximum of the main-diagonal coefficients of the interference-plus-noise covariance matrix is greater than the average noise power,

wherein the maximum of the main-diagonal coefficients is defined as:

max{[{tilde over (Σ)} ηη ] ii },

wherein the average noise power is defined as:

σ

_

n

2

=

1

N

r

-

1

⁢

∑

k

=

1

N

r

-

1

⁢

σ

~

n

,

k

2

,

and

wherein the detector is configured to detect that the transmission is the single-user Multiple Input Multiple Output transmission when the maximum of the main-diagonal coefficients of the interference-plus-noise covariance matrix is not greater than an average noise power.

10. An apparatus according to claim 1 , wherein the detector is configured to determine that the transmission is the multi-user Multiple Input Multiple Output transmission when a ratio of a maximum of main-diagonal coefficients of an interference-plus-noise covariance matrix and an average noise power is greater than one.

11. An apparatus according to claim 10 , wherein the detector is configured to determine that the transmission is the single-user Multiple Input Multiple Output transmission when a ratio of a maximum of main-diagonal coefficients of an interference-plus-noise covariance matrix and an average noise power is not greater than one.

12. An apparatus according to claim 11 , wherein the maximum of the main-diagonal coefficients is defined by:

max{[{tilde over (Σ)} ηη ] ii },

wherein the average noise power is defined by:

σ

_

n

2

=

1

N

r

-

1

⁢

∑

k

=

1

N

r

-

1

⁢

σ

~

n

,

k

2

,

and wherein the ratio is defined by:

μ

~

th

=

max

⁢

{

[

Σ

~

_

ηη

]

ii

}

σ

_

n

2

.

13. An apparatus for filtering a received signal to obtain a filtered signal, wherein the received signal has been transmitted by conducting a transmission, wherein the apparatus comprises:

a detector configured to detect whether the transmission is either a single-user Multiple Input Multiple Output transmission or a multi-user Multiple Input Multiple Output transmission, and

a filter application unit, wherein the filter application unit is configured to apply a first receive filter with a first filter characteristic on the received signal to obtain the filtered signal when the transmission is the single-user Multiple Input Multiple Output transmission, and wherein the filter application unit is configured to apply a second receive filter with a second, different filter characteristic on the received signal to obtain the filtered signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein the filter application unit is configured to apply a Maximum-Ratio-Combiner receive filter as the first receive filter on the received signal when the transmission is the single-user Multiple Input Multiple Output transmission, and wherein the filter application unit is configured to apply a Minimum-Mean-Square-Error receive filter as the second receive filter on the received signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein the filter application unit is configured to apply the Maximum-Ratio-Combiner receive filter being defined according to

m

_

MRC

H

=

g

_

1

H

g

_

1

H

⁢

g

_

1

,

as the first receive filter on the received signal when the transmission is the single-user Multiple Input Multiple Output transmission, and

wherein the filter application unit is configured to apply the Minimum-Mean-Square-Error receive filter being defined according to

m

_

MMSE

H

=

g

_

1

H

⁢

R

_

ηη

_

-

1

g

_

1

H

⁢

R

_

ηη

-

1

⁢

g

_

1

as the second receive filter on the received signal when the transmission is the multi-user Multiple Input Multiple Output transmission,

wherein g 1 denotes the matrix-vector product H 1 p i , wherein H 1 denotes the channel from an eNodeB to a user equipment, wherein p i denotes a precoding vector recommended by the user equipment, wherein g 1 H denotes a Hermitian of the matrix-vector product g 1 , and wherein R ηη −1 denotes an inverse matrix of a covariance matrix R ηη .