Linear transformation of symbols to at least partially compensate for correlation between antennas in space time block coded systems

• US 20040185909A1
• Filed: 03/20/2003
• Published: 09/23/2004
• Est. Priority Date: 03/20/2003
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Alexiou, Angeliki, Qaddi, Mohammed
• Granted Patent: US 7,197,082 B2
• Time in Patent Office: Days
• US Class Current: 455/562.1
• CPC Class Codes: H04L 1/0618 Space-time coding

Abstract

A method is provided of transmitting signals from two or more antennas in a wireless telecommunications network, in which at least one data sequence is space-time block encoded. Before transmitting the data sequence, a linear transformation is applied to the data sequence, the linear transformation being adapted to use knowledge of correlation among the antennas to at least partially compensate the transmitted signals for said correlation. The linear transformation depends on the eigenvalues of an antenna correlation matrix. The linear transformation further depends on a ratio of symbol energy (E_s) to noise variance (σ²). The method includes transmitting the encoded and transformed data sequence.

Claims

1. A method of transmitting signals from two or more antennas in a wireless telecommunications network, comprising:

space-time block encoding at least one data sequence;

before transmitting the data sequence, applying to the data sequence a linear transformation adapted to use knowledge of correlation among the antennas to at least partially compensate the transmitted signals for said correlation, wherein the linear transformation depends on the eigenvalues of an antenna correlation matrix, and wherein the linear transformation further depends on a ratio of symbol energy (E_s) to noise variance (σ

²); and

transmitting the encoded and transformed data sequence.

2. The method of claim 1, wherein the linear transformation is applied prior to block encoding the data sequence.

3. The method of claim 1, wherein the linear transformation is applied after block encoding the data sequence.

4. The method of claim 1, wherein the linear transformation further depends on an eigenvector of the antenna correlation matrix.

5. The method of claim 4, wherein:

the channel correlation matrix has two eigenvalues, denominated λ

_r,1, λ

_r,2;

the method further comprises calculating a value of a parameter β

related to the quantity

$\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_s}{{\mathrm{\sigma <br><br>}}^2}\right);<br><br>$

and

the linear transformation is determined from β and

from the eigenvector of the antenna correlation matrix.

6. A method of linear transformation of symbols from or to a space-time block encoder so as to at least partially compensate for correlation between antennas of a transmitter comprising two antennas, the method comprising the steps of:

determining an antenna correlation matrix (R),

determining the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determining the ratio of symbol energy (E_s) to noise variance (σ

²),

calculating a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_s}{{\mathrm{\sigma <br><br>}}^2}\right),$

determining the eigenvector (w₁, w₂) of the antenna correlation matrix (R), and

determining a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).

7. A method according to claim 6, in which the linear transformation matrix is determined as

8. A method according to claim 7, in which when antenna correlation is zero, β

is zero so the linear transformation matrix becomes

9. A method according to claim 7 in which when antenna correlation is one, one eigenvalue of antenna correlation matrix R is zero so the linear transformation matrix becomes

10. A method of space-time block encoding comprising linear transformation of symbols so as to at least partially compensate for correlation between antennas of a transmitter comprising two antennas, the method comprising the steps of:

determining a antenna correlation matrix (R),

determining the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determining the ratio of symbol energy (E_s) to noise variance (σ

²),

calculating a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

determining the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

determining a linear transformation matrix (L) from the value of β and

the eigenvector (w₁, w₂),

space-time block encoding the symbols, and

applying the linear transformation matrix (L) to the symbols space-time block encoded or to be space-time block encoded.

11. A method according to claim 10, in which the space-time block encoding is such that at a first transmission time instant (t₁) a first symbol (x₁) is transmitted from a first of the two antennas and a second symbol (x₂) is transmitted from the second of the two antennas, then at the next transmission instant (t₂) a negative complex conjugate of the first symbol (−

x₂*) is transmitted from the first antenna and a complex conjugate (x₁*) of the second symbol is transmitted from the second antenna.

12. A method according to claim 10, in which the space-time block encoding is Alamouti space-time block encoding.

13. A method of transmitting signals in a mobile telecommunications network, comprising space-time block encoding comprising linear transformation of symbols so as to at least partially compensate for correlation between antennas of a transmitter comprising multiple antennas, comprising the steps of:

determining a antenna correlation matrix (R),

determining the eigenvalues (λ

_r,1,λ

_r,2)of the antenna correlation matrix (R),

determining the ratio of symbol energy (E_s) to noise variance (σ

²),

calculating a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

determining the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

determining a linear transformation matrix (L) from the value of β and

the eigenvector (w₁, w₂),

space-time block encoding the signals, and

applying the linear transformation matrix (L) to symbols space-time block encoded or to be space-time block encoded.

14. A linear transformation apparatus operative to transform symbols from or to a space-time block encoder so as to at least partially compensate for correlation between antennas of a transmitter comprising two antennas, comprising:

a processor operative to determine a antenna correlation matrix (R), and a processor operative to;

determine the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determine the ratio of symbol energy (E_s) to noise variance (σ

²),

calculate a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

 

determine the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

 

determine a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).

15. A transmitter for mobile telecommunications comprising a space time block encoder, and a linear transformation apparatus operative to transform symbols from or to a space-time block encoder so as to at least partially compensate for correlation between antennas, the transmitter comprising two antennas, the linear transformation apparatus comprising:

a processor operative to determine a antenna correlation matrix (R), and a processor operative to;

determine the eigenvalues (λ

_r,1,λ

₂ )of the antenna correlation matrix (R)

determine the ratio of symbol energy (E_s) to noise variance (σ

₂),

calculate a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

 

determine the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

 

determine a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).

16. A transmitter according to claim 15, in which the space-time block encoder operates such that at a first transmission time instant (t₁) a first symbol (x₁) is transmitted from a first of the two antennas and a second symbol (x₂) is transmitted from the second of the two antennas, then at the next transmission instant (t₂) a negative complex conjugate of the first symbol (−

x₂*) is transmitted from the first antenna and a complex conjugate (x₁*) of the second symbol is transmitted from the second antenna.

17. A transmitter according to claim 15, in which the space-time block encoder is an Alamouti space-time block encoder.

18. A transmitter according to claim 15, which is a base station operating according to a code division multiple access (CDMA) or wideband code division multiple access (W-CDMA) transmission scheme.

19. A transmitter according to claim 18, in which the base station operates in accordance with the Universal Mobile Telecommunications System (UMTS) standard.

20. A transmitter according to claim 15, in which the processor operative to determine the antenna correlation matrix (R) makes the determination from channel estimates.

21. A space-time block decoder comprising a processor operative to determine a antenna correlation matrix (R), and a processor operative to:

determine the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determine the ratio of symbol energy (E_s) to noise variance (σ

₂),

calculate a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

determine the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

determine a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).

22. A space-time block decoder according to claim 21, in which an effective channel (H_eq) used in decoding is taken to be HL where H is the channel matrix and L is the linear transformation matrix.

23. A space-time block decoder according to claim 22, in which the transmitted symbols (x₁, x₂) are estimated as

{circumflex over (x)}₁=(h_eq.1)*y₁−

h_eq.2(y₂)* {circumflex over (x)}₂=(h_eq.2)*y₂+h_eq.1(y₂)*

where the received signal Y=[y₁y₂].

24. A receiver for mobile telecommunications comprising a space-time block decoder and a channel estimator, the antenna correlation matrix (R) being determined from the received channel estimates provided by the channel estimator, the space-time block encoder comprising a processor operative to determine a antenna correlation matrix (R),and a processor operative to:

determine the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determine the ratio of symbol energy (E_s) to noise variance (σ

²),

calculate a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

determine the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

determine a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).

25. A receiver according to claim 24, which is a mobile user terminal operating in accordance with UMTS or another wideband-code division multiple access (W-CDMA) or code division multiple access (CDMA) standard.

26. A network for mobile telecommunications comprising a transmitter and a receiver,

the transmitter comprising a space-time block encoder and a linear transformation apparatus operative to transform symbols from or to the space-time block encoder by applying a linear transformation (L) so as to at least partially compensate for correlation between antennas, the transmitter comprising two antennas,

the coefficients of the linear transformation matrix (L) being sent from the receiver to the transmitter,

the receiver comprising a space-time block decoder and a channel estimator, the antenna correlation matrix (R) being determined from the received channel estimates provided by the channel estimator, the space-time block encoder comprising a processor operative to determine a antenna correlation matrix (R),and a processor operative to:

determine the eigenvalues (λ

_r,1,λ

_r,2) of the antenna correlation matrix (R),

determine the ratio of symbol energy (E_s) to noise variance (σ

²),

calculate a value of a parameter β

where

$\mathrm{\beta <br><br>}=\left(\frac{1}{{\mathrm{\lambda <br><br>}}_{r,2}^2}-\frac{1}{{\mathrm{\lambda <br><br>}}_{r,1}^2}\right)/\left(\frac{E_S}{{\mathrm{\sigma <br><br>}}^2}\right),$

 

determine the eigenvector (w₁, w₂) of the antenna correlation matrix (R),

 

determine a linear transformation matrix (L) to be applied to the symbols from the value of β and

the eigenvector (w₁, w₂).