# US 8,787,493 B2 · Precoding technique

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- Number: US 8,787,493 B2
- Document ID: US8787493B2
- Status: Granted
- Kind: B2
- Application number: 13/817,604
- Filed: 2011-08-12
- Published: 2013-07-25
- Granted: 2014-07-22
- Earliest claimed: 2010-08-12
- Assignees: Telefonaktiebolaget L M Ericsson (publ)
- Applicants: Eckhard Ohlmer; Udo Wachsmann
- Inventors: Eckhard Ohlmer; Udo Wachsmann
- Web page: https://patentgrep.com/patent/US8787493B2

## CPC

- H04L 1/0042: {Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape (H04L1/0067 takes precedence)}
- H04B 7/0417: Feedback systems
- H04B 7/063: {Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection}
- H04B 7/0634: {Antenna weights or vector/matrix coefficients}
- H04B 7/0465: {taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION

## Abstract

A technique for precoding a signal to be transmitted over a physical channel from a sender to a receiver is provided. A method includes receiving precoding information and applying precoding matrix at the sender based on the precoding information. The precoding information is received via a feedback mechanism from the receiver. The application of the precoding matrix results in a precoded signal for transmission over the physical channel. The precoding matrix enhances mutual information at the receiver.

## Claims

### Claim 1

A method of precoding a signal to be transmitted over a physical channel from a sender to a receiver, the method comprising:
receiving precoding information by a feedback mechanism from the receiver;
applying a precoding matrix (W) at the sender based on the precoding information to generate a precoded signal for transmission over the physical channel, the precoding matrix configured for a detection based on an estimation error and enhancing mutual information (I) at the receiver, wherein a covariance (E) of the estimation error is related to a gradient of the mutual information with respect to the precoding matrix by a relation,
wherein the relation is employed for computing the precoding matrix.

### Claim 2 (depends on 1)

The method of claim 1, wherein the precoding information comprises at least one of: system information and the mutual information.

### Claim 3 (depends on 2)

The method of claim 2, wherein the system information comprises at least one of: a state (H) of the physical channel, statistics of the signal, and statistics of noise.

### Claim 4 (depends on 2)

The method of claim 2:
wherein the signal comprises a plurality of symbols out of a symbol alphabet transmitted in a data block;
wherein the system information comprises a probability distribution for the data block.

### Claim 5 (depends on 2)

The method of claim 2, wherein the system information comprises statistical information about at least one of additive noise caused by interference with another radio signal and additive receiver noise.

### Claim 6 (depends on 1)

The method of claim 1, wherein the precoding matrix is determined at the sender based on the precoding information.

### Claim 7 (depends on 1)

The method of claim 1:
wherein the physical channel comprises a plurality of sending antennas;
wherein the signal comprises a plurality of payload signals;
wherein the application of the precoding matrix includes mapping the plurality of payload signals to the sending antennas by means of the precoding matrix.

### Claim 8 (depends on 1)

The method of claim 1, wherein the precoding matrix is computed in accordance with a maximum likelihood estimator.

### Claim 9 (depends on 1)

The method of claim 1, wherein the physical channel comprises a plurality of spatial layers that are successively detectable by removing interference of a detected layer from a transmitted signal.

### Claim 10 (depends on 1)

The method of claim 1:
wherein the physical channel comprises a plurality of spatial layers;
wherein the precoding matrix is computed in accordance with a suboptimal detection metric that decomposes in accordance with the plurality of spatial layers.

### Claim 11 (depends on 10)

The method of claim 10, wherein at least one of the suboptimal detection metric and the mutual information is representable by a product or a sum over the plurality of spatial layers.

### Claim 12 (depends on 10)

The method of claim 10, further comprising computing at least one of the mutual information per spatial layer and a gradient thereof with respect to the precoding matrix.

### Claim 13 (depends on 12)

The method of claim 12, further comprising determining the precoding matrix based on a relationship between the gradient of the mutual information and at least one of a Minimum Mean Square Error estimator and a Mean Square Error matrix.

### Claim 14 (depends on 13)

The method of claim 13, wherein the determining the precoding matrix comprises determining a Mean Square Error matrix (El) that is independent of the l-th physical layer.

### Claim 15 (depends on 14)

The method of claim 14, wherein the gradient of the mutual information is computed in accordance with:
∇
W
⁢
I
⁡
(
y
;
x
)
PLD
=
1
σ
v
2
⁢
⁢
H
H
⁢
HW
⁡
(
∑
l
=
1
N
t
⁢
E
-
E
l
)
where:
x denotes a transmitted signal;
y denotes a received signal;
PLD denotes Parallel Layer Detection;
σv2 denotes noise variance;
H denotes channel state
Nt denotes a number of transmit antennas.

### Claim 16 (depends on 10)

The method of claim 10, wherein the precoding matrix allows for parallel decoding of the precoded signal at the receiver.

### Claim 17 (depends on 10)

The method of claim 10:
wherein the signal comprises a payload signal on each of the spatial layers;
wherein the precoding matrix allows for independently decoding the plurality of payload signals.

### Claim 18 (depends on 1)

The method of claim 1, wherein the physical channel comprises at least one of a plurality of sending antennas at the sender and a plurality of receiving antennas at the receiver.

### Claim 19 (depends on 18)

The method of claim 18, wherein the precoding matrix represents a beamforming matrix.

### Claim 20 (depends on 1)

The method of claim 1:
wherein the transmission includes a plurality of physical channels, each exhibiting a channel state;
wherein for each channel state a dedicated precoding matrix is determined and applied for the transmission.

### Claim 21 (depends on 20)

The method of claim 20:
wherein the physical channel includes an OFDM channel;
wherein the plurality of channel states is associated to a plurality of sub-carriers of the OFDM channel.

### Claim 22 (depends on 1)

The method of claim 1:
wherein the signal comprises a plurality of symbols out of a symbol alphabet;
wherein the precoding information relates to the symbol alphabet.

### Claim 23 (depends on 1)

The method of claim 1, wherein the precoding matrix is selected from an arbitrary codebook or predefined codebook.

### Claim 24 (depends on 23)

The method of claim 23, wherein the codebook is a set of different precoding matrices.

### Claim 25 (depends on 23)

The method of claim 23, wherein mutual information is maximized within the codebook.

### Claim 26 (depends on 23)

The method of claim 23, wherein the precoding matrix is selected from the codebook by comparison with an optimal precoding matrix.

### Claim 27 (depends on 23)

The method of claim 23:
wherein a channel state (H) of the physical channel is decomposed using a unitary matrix;
wherein the precoding matrix depends on the unitary matrix.

### Claim 28 (depends on 27)

The method of claim 27, wherein the codebook is a structured codebook optimized for the selection.

### Claim 29 (depends on 23)

The method of claim 23, wherein the precoding matrix is quantized and the precoding information includes the quantized precoding matrix.

### Claim 30

A method of precoding a signal to be transmitted over a physical channel from a sender to a receiver, the method comprising:
providing precoding information via a feedback mechanism to the sender, wherein a precoding matrix (W) is computed at the receiver and configured for a detection based on an estimation error and enhancing mutual information (I) at the receiver, wherein a covariance (E) of the estimation error is related to a gradient of the mutual information with respect to the precoding matrix by a relation, the relation being employed for computing the precoding matrix,
wherein the precoding information comprises the precoding matrix;
receiving, from the sender and over the physical channel, a signal precoded by the precoding matrix based on the precoding information.

### Claim 31 (depends on 30)

The method of claim 30 wherein the precoding information comprises at least one of: system information and the mutual information.

### Claim 32 (depends on 30)

The method of claim 30:
wherein the physical channel comprises a plurality of spatial layers;
wherein the precoding matrix is computed in accordance with a suboptimal detection metric that decomposes in accordance with the plurality of spatial layers.

### Claim 33

A computer program product stored in a non-transitory computer readable medium for precoding a signal to be transmitted over a physical channel from a sender to a receiver, the computer program product comprising software instructions which, when run on one or more computing devices, causes the one or more computing devices to:
receive precoding information by a feedback mechanism from the receiver;
apply a precoding matrix at the sender based on the precoding information to generate a precoded signal for transmission over the physical channel, the precoding matrix configured for a detection based on an estimation error and enhancing mutual information at the receiver, wherein a covariance of the estimation error is related to a gradient of the mutual information with respect to the precoding matrix by a relation,
wherein the relation is employed for computing the precoding matrix.

### Claim 34

A device for precoding a signal to be transmitted over a physical channel from a sender to a receiver, the device comprising:
a receiver unit configured to receive precoding information by a feedback mechanism from the receiver;
an application unit configured to apply a precoding matrix at the sender based on the precoding information resulting in a precoded signal for transmission over the physical channel, the precoding matrix being configured for a detection based on an estimation error and enhancing mutual information at the receiver, wherein a covariance of the estimation error is related to a gradient of the mutual information with respect to the precoding matrix, wherein the relation is employed for computing the precoding matrix.

### Claim 35 (depends on 34)

The device of claim 34, wherein the device comprises a portion of a user equipment of a radio network.

### Claim 36 (depends on 34)

The device of claim 34, wherein the device comprises a portion of a radio access network device of a radio network.

### Claim 37

A device for precoding a signal to be transmitted over a physical channel from a sender to a receiver, the device comprising:
a feedback unit configured to provide precoding information via a feedback mechanism to the sender, wherein a precoding matrix is computed at the receiver and configured for a detection based on an estimation error and enhancing mutual information at the receiver, wherein a covariance of the estimation error is related to a gradient of the mutual information with respect to the precoding matrix by a relation, wherein the relation is employed for computing the precoding matrix, wherein the precoding information comprises the precoding matrix;
a receiver unit configured to receive, from the sender and over the physical channel, a signal precoded by the precoding matrix based on the precoding information.

### Claim 38 (depends on 37)

The device of claim 37, wherein the device comprises a portion of a user equipment of a radio network.

### Claim 39 (depends on 37)

The device of claim 37, wherein the device comprises a portion of a radio access network device of a radio network.