TRANSMISSION/RECEPTION METHODS AND MODULES FOR A MULTIPLE-CARRIER MULTIPLE-ANTENNA SYSTEM USING TRAINING SEQUENCES

• US 20090304104A1
• Filed: 11/19/2007
• Published: 12/10/2009
• Est. Priority Date: 11/24/2006
• Status: Active Grant

• Current Assignee: 3G Licensing S.A. (Fineur International S.A.)
• Original Assignee: Orange S.A.
• Inventors: Le Saux, Benoit, Helard, Maryline, Boher, Laurent
• Granted Patent: US 8,290,081 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0434 using multiple eigenmodes
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/068 using space frequency diversity space-frequency coding H04L1/0606
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0244 with inversion
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2627 Modulators
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

The present invention relates to a transmission method and device suitable for a system using Nt transmit antennas TX_i and Nr receive antennas RX_j. The symbols transmitted are inserted in a time-frequency frame that contains a training sequence. Each training sequence is constructed from replicas of a basic training sequence. At least one of the training sequences includes at least two replicas at least one of which is phase offset.

Claims

1. A transmission method suitable for a system with Nt transmit antennas and Nr receive antennas, where Nt and Nr are at least 1, a transmit antenna being separated from a receive antenna by a transmission sub-channel, implemented by Nt multiple-carrier transmitters each including a multiplexing and modulation module using N_FFT orthogonal functions (MX₁ to MX_Nt) forming orthogonal symbols intended to be transmitted by the Nt transmit antennas TX₁ to TX_Nt, the method including:

a step of determining a basic training sequence ({tilde over (c)}(p)) from the position of Np pilot symbols in a time-frequency frame;

a step of determining

$\mathrm{Kn}=\left(\underset{i=1}{\overset{\mathrm{Nt}}{\sum <br><br>}}<br><br>K_i\right)$

replicas of the basic training sequence ({tilde over (c)}(p)) such that at least one replica is time offset from the basic sequence, with K_i≧

1 and at least one K_i≧

2, subject to the constraints that the extreme time offset between replicas must be less than the number Np of pilot carriers and that the minimum time offset between replicas of two training sequences is greater than or equal to the maximum spread of the delays of the sub-channels; and

a step of determining a training sequence for each transmit antenna TX_i as the sum of the K_i replicas.

2. A symbol transmission method according to claim 1, wherein a guard interval is added before transmitting an orthogonal symbol and the constraint on the minimum value of the time offset is complied with by choosing a minimum time offset equal to the value of the guard interval.

3. A symbol transmission method according to claim 1, wherein each training sequence consists of K replicas of the basic training sequence ({tilde over (c)}(p)).

4. A symbol transmission method according to claim 1, wherein the replicas are determined in the frequency domain and the time offset is determined by a phase offset value.

5. A symbol transmission method according to claim 4, wherein the phase offset values are chosen in a particular order.

6. A symbol transmission method according to claim 5, wherein the order is known to at least one receiver associated with a receive antenna of the system.

7. A symbol transmission method according to claim 4, wherein the phase offset is a function of a carrier index.

8. A symbol transmission method according to claim 1, wherein the basic training sequence is spread over a plurality of orthogonal symbols.

17. A computer program on an information medium, said program including program instructions adapted to execute a transmission method according claim 1 when said program is loaded in and executed in a transmitter.

18. An information medium including program instructions adapted to execute a transmission method according to claim 1 when said method is loaded in and executed in a transmitter.

9. A method for estimating transmission sub-channels in a multiple-antenna system using Nt transmit antennas (TX₁ to TX_Nt), where Nt is at least 1, at least one receive antenna (RX₁ to RX_Nt), and a time-frequency frame for each transmit antenna including Np pilot symbols (sp) forming a training sequence and data symbols of a payload signal, each of the Nt training sequences being the sum of K_i replicas of a basic training sequence ({tilde over (c)}(p)), either time offset or not, such that the values K_i are greater than or equal to 1 and at least one value K_i is greater than or equal to 2, being known to the receiver, and enabling the receiver to estimate an impulse response corresponding to the transmission channel separating a transmit antenna (TX₁ to TX_Nt) from a receive antenna RX_j concerned, the data symbols and the pilot symbols being frequency-modulated by a multiplexing and modulation module using N_FFT orthogonal functions (MX₁ to MX_Nt) to form orthogonal symbols that are transmitted by the transmit antennas in the form of a multiple-carrier signal using N_FFT carriers, the method including:

a step of computing a matrix A constructed in the form of blocks from the training sequences and from the Fourier matrix of dimensions N_FFT×

N_FFT, the number of blocks of which is equal to the product of the number of orthogonal symbols of the basic training sequence by the sum of the values K_i, a block being determined by the product of a diagonal matrix formed of the pilot symbols contained in an orthogonal symbol of the training sequence associated with the block multiplied by the Fourier matrix and including, for a receive antenna (RX_j) concerned;

a step of computing K_i estimates of at least one of the Nt impulse responses in the time domain by multiplying by the pseudo-inverse matrix of the matrix A Np pilot symbols extracted from a frequency-domain signal (R_j(n)) obtained after demodulation of a time-domain signal received by the receive antenna (RX_j) concerned by means of a Fourier transform of size N_FFT;

a step of computing an average over the K_i estimates of the impulse response concerned.

10. A transmission channel estimation method according to claim 9, wherein the computation of the Nt impulse responses is extended by means of interpolation to the carriers modulated by data.

11. A transmission channel estimation method according to claim 9, wherein the step of computing the Nt impulse responses is repeated for each receive antenna concerned of the multiple-antenna system.

19. A computer program on an information medium, said program including program instructions adapted to execute a channel estimation method according to claim 9 when said program is loaded in and executed in a receiver.

20. An information medium including program instructions adapted to execute a channel estimation method according to claim 9 when said program is loaded in and executed in a receiver.

12. A transmission module including a multiplexing and modulation module using N_FFT orthogonal functions (MX₁ to MX_Nt), suitable for a multiple-antenna system using Nt transmit antennas (TX₁ to TX_Nt), Nr receive antennas, where Nt and Nr are at least 1, and a time-frequency frame for each transmit antenna including pilot symbols and data symbols of a payload signal, the data symbols and the pilot symbols being frequency-modulated by the multiplexing and modulation module (MX₁ to MX_Nt) to form orthogonal symbols that are transmitted by a transmit antenna in the form of a multiple-carrier signal using N_FFT carriers and using Np pilot carriers, the module including:

a module for determining a basic training sequence ({tilde over (c)}(p)) from the position of Np pilot symbols in the time-frequency frame associated with a particular transmit antenna (TX₁);

a module for determining Kn, where

$\mathrm{Kn}=\left(\underset{i=1}{\overset{\mathrm{Nt}}{\sum <br><br>}}<br><br>K_i\right),$

replicas of the basic training sequence ({tilde over (c)}(p)) such that at least one replica is time offset from the basic sequence, with K_i≧

1 and at least one K_i≧

2, subject to the constraints that the extreme time difference between replicas is less than the number Np of pilot carriers and that the minimum time offset between replicas of two training sequences is greater than or equal to the maximum spread of the delays of the sub-channels connecting a transmit antenna to a receive antenna; and

a module for determining a training sequence for each transmit antenna TX_i as the sum of K_i replicas.

13. A transmitter for a multiple-antenna system which includes at least one transmission module according to claim 12.

14. A module for estimating transmission channels in a multiple-antenna system using Nt transmit antennas (TX₁ to TX_Nt), where Nt is at least 1, at least one receive antenna (RX₁ to RX_Nt), and a time-frequency frame for each transmit antenna including pilot symbols (sp) forming a training sequence and data symbols of a payload signal, the Nt training sequences being known to the receiver and enabling the receiver to estimate Nt impulse responses corresponding to the Nt transmission channels respectively separating one of the transmit antennas (TX₁ to TX_Nt) from the receive antenna RX_j concerned, the data symbols and the pilot symbols being frequency-modulated by a multiplexing and modulation module using N_FFT orthogonal functions (MX₁ to MX_Nt) to form orthogonal symbols that are transmitted by the transmit antennas in the form of a multiple-carrier signal using N_FFT carriers with Np pilot carriers, characterized in that it includes means for computing a matrix A constructed in the form of blocks from the training sequences and from the Fourier matrix of dimensions N_FFT×

N_FFT, the number of blocks of which is equal to the product of the number of orthogonal symbols of the basic training sequence by the sum of the values K_i, a block being determined by the product of a diagonal matrix formed of the pilot symbols contained in an orthogonal symbol of the training sequence associated with the block multiplied by the Fourier matrix, and, for a receive antenna (RX_j) concerned;

means for computing K_i estimates of at least one of the Nt impulse responses in the time domain by multiplying Np pilot symbols extracted from a frequency-domain signal (R_j(n)) obtained after demodulation of a time-domain signal received by the receive antenna (RX_j) concerned by means of an FFT of size N_FFT by the pseudo-inverse matrix of the matrix A; and

means for computing the average of the K_i estimates of the impulse response concerned.

15. A receiver for a multiple-antenna system which includes at least one module according to claim 14 for estimating transmission channels.

16. A multiple-antenna system which includes at least one receiver according to claim 15.