Receiver and method for decoding a coded signal with the aid of a space-time coding matrix

• US 20070140370A1
• Filed: 03/05/2004
• Published: 06/21/2007
• Est. Priority Date: 09/01/2003
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Helard, Maryline, Bouvet, Pierre-Jean, Le Nir, Vincent, Le Gouable, Rodolphe
• Granted Patent: US 7,729,436 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04L 1/0618 Space-time coding

Abstract

The disclosure relates to a method for decoding a received signal comprising symbols which are distributed in space and time with the aid of a space-time coding matrix, comprising a space-time decoding stage and at least two iterations, each of which comprising the following sub-stages: diversity pre-decoding, the opposite of diversity pre-decoding carried out when the signal is emitted, providing precoded data; estimation of symbols forming said signal on the basis of said pre-decoded data, providing estimated symbols; diversity preceding identical to diversity preceding carried out during emission, applied to the estimated symbols in order to provide an estimated signal.

Claims

1. A method for the decoding of a received signal comprising symbols distributed in space, time and/or frequency by a space-time or space-frequency encoding matrix, wherein the method implements a space-time decoding step and at least one iteration, each iteration comprising the following sub-steps:

diversity pre-decoding, which is the inverse of a diversity pre-encoding carried out when said signal is emitted, delivering pre-decoded data;

estimation of the symbols forming said signal, from said pre-decoded data, delivering estimated symbols; and

diversity pre-encoding identical to said diversity pre-encoding implemented at emission, applied to said estimated symbols, to give an estimated signal, except for the last iteration.

2. The method according to claim 1 comprising:

the space-time decoding, which is the inverse of the space-time encoding implemented at emission, delivering a decoded signal;

equalization of said decoded signal, delivering an equalized signal;

conversion of a matrix of the equalized signals into a diagonal matrix, obtained from a total encoding/channel/decoding matrix taking account of at least said encoding matrix, and of a decoding matrix that is the conjugate transpose of said encoding matrix;

the diversity pre-decoding, which is the inverse of the diversity pre-encoding implemented at emission of said signal, delivering the pre-decoded data;

the estimation of the symbols forming said signal, from said pre-decoded data, delivering the estimated symbols;

the diversity pre-encoding, identical to said diversity pre-encoding implemented at emission, applied to said estimated symbols, to give the estimated signal; and

at least one iteration of an interference cancellation step implementing the following sub-steps;

subtraction, from said equalized signal, of said estimated signal multiplied by an interference matrix, delivering an optimized signal;

diversity pre-decoding of said optimized signal, that is the inverse of the diversity pre-encoding implemented at emission of said signal, delivering improved pre-decoded data;

estimation of the symbols forming said optimized signal, from the improved pre-decoded data, delivering new estimated symbols; and

diversity pre-encoding identical to said diversity pre-encoding implemented at emission, applied to said new estimated symbols to give a new estimated signal, except for the last iteration.

3. The method according to claim 2, wherein said space-time decoding and equalization steps and/or said equalization and conversion steps are done jointly.

4. The method according to claim 1, wherein said encoded symbols are emitted by means of at least two antennas, which produce different corresponding transmission channels and wherein the method of decoding takes the different corresponding transmission channels comprehensively into account.

5. The method according to claim 2, wherein said equalization step implements an equalization according to one of the techniques belonging to the group comprising:

MMSE type equalization;

EGC type equalization;

ZF type equalization; and

equalization taking account of a piece of information representing a signal-to-noise ratio between the received signal and a reception noise.

6. The method according to claim 2, wherein said steps of symbol estimation implement a soft decision, associating a piece of confidence information with the soft decision and said subtraction step or steps take account of said pieces of confidence information.

7. The method according to claim 2, wherein said received signal comprises a multicarrier signal.

8. The method according to claim 1, wherein said pre-encoding is obtained by one of the following methods:

a spread-spectrum technique; and

linear pre-encoding.

9. The method according to claim 1, wherein the method implements an automatic gain control step before or after said equalization step and/or during at least one of said iterations.

10. The method according to claim 1 and further comprising a channel-decoding step, symmetrical with a channel-encoding step implemented at emission.

11. The method according to claim 10, wherein said channel-decoding step implements a turbo-decoding operation.

12. The method according to claim 1 and further comprising at least one de-interlacing step and at least one re-interlacing step, corresponding to an interlacing implemented at emission.

13. The method according to claim 1 and further comprising a step of improvement of a channel estimation, taking account of the estimated symbols during at least one of said iterations.

14. The method according to claim 2 and further comprising transmitting by four antennas the signal to be received, referred to as the received signal, through at least one transmission channel, wherein said total encoding/channel/decoding matrix is equal to:

$G=\mathrm{\gamma <br><br>}<br><br>\left[\begin{array}{cccc}A& 0& 0& J\\ 0& A& -J& 0\\ 0& -J& A& 0\\ J& 0& 0& A\end{array}\right]$

with;

A=|h₁|²+|h₂|²+|h₃|²+|h₄|²
J=2Re{h₁h*₄−

h₂h*₃},

representing the interference, and

$\mathrm{\gamma <br><br>}=\frac{1}{{<br><br>h_1<br><br>}^2+{<br><br>h_2<br><br>}^2+{<br><br>h_3<br><br>}^2+{<br><br>h_4<br><br>}^2+\frac{1}{\mathrm{SNR}}}$ $\mathrm{where}<br><br>\text{;<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>H=\left[\begin{array}{cccc}{h}_1& h_2& h_3& h_4\\ -h_2^{*}& h_1^{*}& -h_4^{*}& h_3^{*}\\ -h_3^{*}& -h_4^{*}& h_1^{*}& h_2^{*}\\ h_4& -h_3& -h_2& h_1\end{array}\right]$

is a matrix grouping the space-time encoding and the transmission channel,

and SNR represents the signal-to-noise ratio.

15. The method according to claim 2 and further comprising transmitting by eight antennas the signal to be received, referred to as the received signal, through at least one transmission channel, wherein said total encoding/channel/decoding matrix is equal to:

$\begin{array}{c}G=<br><br>\mathrm{\gamma <br><br>}·<br><br>H^H·<br><br>H\\ =<br><br>\mathrm{\gamma <br><br>}<br><br>\left[\begin{array}{cccccccc}A& 0& 0& 0& J& 0& 0& 0\\ 0& A& 0& 0& 0& J& 0& 0\\ 0& 0& A& 0& 0& 0& J& 0\\ 0& 0& 0& A& 0& 0& 0& J\\ J& 0& 0& 0& A& 0& 0& 0\\ 0& J& 0& 0& 0& A& 0& 0\\ 0& 0& J& 0& 0& 0& A& 0\\ 0& 0& 0& J& 0& 0& 0& A\end{array}\right]\\ \mathrm{with}<br><br>\text{\hspace{1em}<br><br>}<br><br>A=<br><br>{<br><br>h_1<br><br>}^2+{<br><br>h_2<br><br>}^2+{<br><br>h_3<br><br>}^2+{<br><br>h_4<br><br>}^2+{<br><br>h_5<br><br>}^2+{<br><br>h_6<br><br>}^2+{<br><br>h_7<br><br>}^2+{<br><br>h_8<br><br>}^2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}\\ J=<br><br>2<br><br>\mathrm{Im}<br><br>\left\{h_1<br><br>h_5^{*}+h_2<br><br>h_6^{*}+h_3<br><br>h_7^{*}+h_4<br><br>h_8^{*}\right\}\\ \mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\gamma <br><br>}=<br><br>\frac{1}{{<br><br>h_1<br><br>}^2+{<br><br>h_2<br><br>}^2+{<br><br>h_3<br><br>}^2+{<br><br>h_4<br><br>}^2+{<br><br>h_5<br><br>}^2+{<br><br>h_6<br><br>}^2+{<br><br>h_7<br><br>}^2+{<br><br>h_8<br><br>}^2+\frac{1}{\mathrm{SNR}}}\\ \mathrm{where}<br><br>\text{\hspace{1em}<br><br>}<br><br>\text{;<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>H=<br><br>\left[\begin{array}{cccccccc}{h}_1& h_2& h_3& h_4& h_5& h_6& h_7& h_8\\ h_2& -h_1& h_4& -h_3& h_6& -h_5& h_8& -h_7\\ h_3& -h_4& -h_1& h_2& h_7& -h_8& -h_5& h_6\\ h_4& h_3& -h_2& -h_1& h_8& h_7& -h_6& -h_5\\ h_1^{*}& h_2^{*}& h_3^{*}& h_4^{*}& h_5^{*}& h_6^{*}& h_7^{*}& h_8^{*}\\ h_2^{*}& -h_1^{*}& h_4^{*}& -h_3^{*}& h_6^{*}& -h_5^{*}& h_8^{*}& -h_7^{*}\\ h_3^{*}& -h_4^{*}& -h_1^{*}& h_2^{*}& h_7^{*}& -h_8^{*}& -h_5^{*}& h_6^{*}\\ h_4^{*}& h_3^{*}& -h_2^{*}& -h_1^{*}& h_8^{*}& h_7^{*}& -h_6^{*}& -h_5^{*}\\ h_5& h_6& h_7& h_8& h_1& h_2& h_3& h_4\\ h_6& -h_5& h_8& -h_7& h_2& -h_1& h_4& -h_3\\ h_7& -h_8& -h_5& h_6& h_3& -h_4& -h_1& h_2\\ h_8& h_7& -h_6& -h_5& h_4& h_3& -h_2& -h_1\\ h_5^{*}& h_6^{*}& h_7^{*}& h_8^{*}& h_1^{*}& h_2^{*}& h_3^{*}& h_4^{*}\\ h_6^{*}& -h_5^{*}& h_8^{*}& -h_7^{*}& h_2^{*}& -h_1^{*}& h_4^{*}& -h_3^{*}\\ h_7^{*}& -h_8^{*}& -h_5^{*}& h_6^{*}& h_3^{*}& -h_4^{*}& -h_1^{*}& h_2^{*}\\ h_8^{*}& h_7^{*}& -h_6^{*}& -h_5^{*}& h_4^{*}& h_3^{*}& -h_2^{*}& -h_1^{*}\end{array}\right],\end{array}$

is a matrix grouping the space-time encoding and the transmission channel

and SNR represents the signal-to-noise ratio.

16. The method of claim 14 and further comprising, prior to the step of transmitting, encoding said signal to be received, wherein the encoding implements a space-time encoding such that:

$H=\left[\begin{array}{cccccccc}{h}_1& h_2& h_3& h_4& h_5& h_6& h_7& h_8\\ h_2& -h_1& h_4& -h_3& h_6& -h_5& h_8& -h_7\\ h_3& -h_4& -h_1& h_2& h_7& -h_8& -h_5& h_6\\ h_4& h_3& -h_2& -h_1& h_8& h_7& -h_6& -h_5\\ h_1^{*}& h_2^{*}& h_3^{*}& h_4^{*}& h_5^{*}& h_6^{*}& h_7^{*}& h_8^{*}\\ h_2^{*}& -h_1^{*}& h_4^{*}& -h_3^{*}& h_6^{*}& -h_5^{*}& h_8^{*}& -h_7^{*}\\ h_3^{*}& -h_4^{*}& -h_1^{*}& h_2^{*}& h_7^{*}& -h_8^{*}& -h_5^{*}& h_6^{*}\\ h_4^{*}& h_3^{*}& -h_2^{*}& -h_1^{*}& h_8^{*}& h_7^{*}& -h_6^{*}& -h_5^{*}\\ h_5& h_6& h_7& h_8& h_1& h_2& h_3& h_4\\ h_6& -h_5& h_8& -h_7& h_2& -h_1& h_4& -h_3\\ h_7& -h_8& -h_5& h_6& h_3& -h_4& -h_1& h_2\\ h_8& h_7& -h_6& -h_5& h_4& h_3& -h_2& -h_1\\ h_5^{*}& h_6^{*}& h_7^{*}& h_8^{*}& h_1^{*}& h_2^{*}& h_3^{*}& h_4^{*}\\ h_6^{*}& -h_5^{*}& h_8^{*}& -h_7^{*}& h_2^{*}& -h_1^{*}& h_4^{*}& -h_3^{*}\\ h_7^{*}& -h_8^{*}& -h_5^{*}& h_6^{*}& h_3^{*}& -h_4^{*}& -h_1^{*}& h_2^{*}\\ h_8^{*}& h_7^{*}& -h_6^{*}& -h_5^{*}& h_4^{*}& h_3^{*}& -h_2^{*}& -h_1^{*}\end{array}\right],$

17. A receiver for receiving a received signal, comprising symbols distributed in space and time and/or frequency by means of a space-time encoding matrix, wherein the receiver comprises means of space-time decoding that is the inverse of the space-time encoding implemented at emission, and:

means of diversity pre-decoding, performing a pre-decoding which is the inverse of a diversity pre-encoding carried out at emission of said signal, delivering pre-decoded data;

means of estimation of the symbols forming said signal, from the pre-decoded data, delivering new estimated symbols;

means of diversity pre-encoding, performing a pre-encoding identical to said diversity pre-encoding implemented at emission, applied to said new estimated symbols, to give a new estimated signal, said means of diversity pre-decoding, estimation, and diversity pre-encoding being implemented at least once for each symbol.

18. A method for the decoding of a received signal comprising symbols distributed in space, time and/or frequency by means of a space-time or space-frequency encoding matrix, wherein the method comprises:

diagonalization, obtained from a total encoding/channel/decoding matrix taking account of at least said encoding matrix, of a decoding matrix, corresponding to the matrix that is the conjugate transpose of said encoding matrix;

demodulation, symmetrical with a modulation implemented at emission;

de-interlacing symmetrical with an interlacing implemented at emission;

channel decoding symmetrical with a channel encoding implemented at emission;

re-interlacing, identical with the interlacing implemented at emission;

re-modulation identical with the modulation implemented at emission, delivering an estimated signal; and

at least one iteration of an interference cancellation step comprising a subtraction from an equalized signal of said estimated signal multiplied by an interference matrix, delivering an optimized signal.