Space-time coding digital transmission systems and methods

• US 20040042560A1
• Filed: 12/24/2002
• Published: 03/04/2004
• Est. Priority Date: 07/04/2000
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Balp, Hugues, Ferreol, Anne
• Granted Patent: US 7,477,696 B2
• Time in Patent Office: Days
• US Class Current: 375/308
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04L 1/0618 Space-time coding

Abstract

The invention concerns digital signal transmission. In particular, it concerns high speed transmission using layered space-time encoding architecture adapted to all types of propagation channels.

The invention therefore proposes a digital signal transmission system comprising:

a space-time encoder (1) receiving a flow of data to be transmitted d[i], formatting this data d[i] as symbol vectors v[k] of dimension P (P>1) and generating said symbol vectors v[k], and

modulator-transmitters {2^p}_(1≦p≦P), each receiving one component of the symbol vector m[k] output from the space-time encoder (1), applying the constellation of a predetermined modulation to said symbol m_p[k], and converting the symbol obtained a_p[k] into a signal s_p(t) presenting time diversity transmitted on said antenna (24^p) connected to said transmitter (2^p).

To demodulate in parallel the Q signals of the space-time observation $\underset{\_}{y}\left[k\right]=\sum _{j=0}^{J-1}H_y\left(\mathrm{jTs}\right)·\underset{\_}{a}\left[k-j\right]+{\underset{\_}{b}}_y\left[k\right]$

where a[k] is the symbol vector transmitted at instant t=kTs+i, H_y(t) the transfer function taking into account at least the transmission-reception, modulation, channel filters and the transmission-reception antenna gains and b_y(t) the noise, the invention proposes a two dimensional suitable estimator-demodulator.

Claims

1. Digital signal transmission system comprising:

a space-time encoder (1) receiving a flow of data to be transmitted d[i], encoding this data d[i] as symbol vectors m[k] of dimension P (P>

1) and generating said symbol vectors m[k], and

P modulator-transmitters {2^p}<sub>(1≦

p≦

P)</sub>, each receiving one component of the symbol vector m[k] output from the space-time encoder (1), applying the constellation of a predetermined modulation to said symbol m_p[k], and converting the symbol obtained a_p[k] into a signal s_p(t) transmitted on said antenna (24^p) connected to said transmitter (2^p)

wherein the transmitters are adapted to transmit signals s(t) with time diversity.

2. Transmission system according to claim 1, wherein these P modulator-transmitters {2^p}:

each produce a symbol a_p[k] in parallel at instant k,

each form a filter of function h_p(t), such that the function h_p(t) of the transmitter (2^p) is different from those of the other transmitters {2^q}<sub>(q≠

p)</sub>;

;

h₁(t)≠

h₂(t)≠

. . . ≠

h_P[(t),

each generate at their respective transmission antennas (24^p) the signal s_p[k] corresponding at least to the filtering by the function h_p(t) of the symbols a_p[k].

3. Transmission system according to the previous claim, wherein the function h_p(t) has one or more of the following features:

any wave form h identical or not to that of the function h_q(t) of the transmitter (2^q, q≠

p) and a delay τ

_p delaying the transmission of the received symbol a_p[k] by said duration τ

_p, such that the function h_p(t)=h(t−

τ

_p) with τ

₁≠

=τ

₂≠

. . . τ

_p for all values of p (1≦

p≦

P),

any wave form h identical or not to that of the function h_q(t) of the transmitter (2^q) (q≠

p) and a frequency shift f_p such that the function of the filter h_p(t)=h·

exp(j2π

f_pt) with f₁≠

f₂ ≠

. . . f_p for all values of p (1≦

p≦

P),

a wave form h_p with h₁≠

h₂≠

. . . h_p for all values of p (1≦

p≦

P), (form of type NRZ, Nyquist with roll-off α

or α

_p, etc.)

4. Transmission system according to one of the previous claims:

wherein said space-time encoder (1) comprises at least a demultiplexer with P channels (11) generating a symbol vector m[k] and/or at least one or more of the following devices;

an encoder (12^p) generating a symbol vector c[k],

a device (13) used to add at least an apprenticeship sequence app known by the receiver to the useful symbol vectors m[k] or encoded symbol vectors c[k] in order to create the symbol vectors v[k],

and/or wherein each modulator-transmifter (2^p) comprises one or more of the following devices;

a linear or linearizable modulator,

a modulator with or without time memory,

a BPSK or GMSK modulator,

a device applying the constellation of said predetermined modulation (21^p) to the received symbols v_{e,uns p}[k] generating the symbols a_p[k],

a device used to add at least the p^th component of an apprenticeship sequence app known by the receiver to the symbols a_p[k],

a filter (22^p) filtering the constellated symbols a_p[k],

a filter (22^p) filtering the vector of oversampled symbols

$\begin{array}{cc}{\underset{\_}{u}}_p^K<br><br>\left(t=\mathrm{kTs}+i\right)=\left[\begin{array}{c}{u}_p<br><br>\left(t\right)\\ \mathrm{⋮<br><br>}\\ u_p<br><br>\left(t-K+1\right)\end{array}\right]=\left[\begin{array}{c}{\underset{\_}{0}}_i\\ a_p<br><br>\left[k\right]\\ {\underset{\_}{0}}_{\mathrm{Ts}-1}\\ a_p<br><br>\left[k-1\right]\\ \mathrm{⋮<br><br>}\end{array}\right]& \mathrm{for}<br><br>\text{\hspace{1em}<br><br>}<br><br>0\le <br><br>i<<br><br>\mathrm{Ts}\end{array}$$\mathrm{with}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\underset{\_}{0}}_i={\left[\begin{array}{ccc}0& \mathrm{\cdots <br><br>}& 0\end{array}\right]}^T<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>\dim <br><br>\left({\underset{\_}{0}}_i\right)=i\times <br><br>1$

an element (23^p) to modulate the signal to be transmitted on the carrier frequency f₀.

9. Estimator-demodulator receiving in parallel N signals e,uns y(t) formed from L samples resulting from the transmission of digital signals by a transmission system according to one of claims 1 to 4, wherein these signals y(t) represent a space-time observation since each of the N spatial components comprises L samples.

19. Digital signal transmission system comprising at least a transmission system according to one of claims 1 to 4, and a reception system either comprising an estimator-demodulator according to one of claims 8 to 13, or according to claim 14, wherein it comprises, in addition, at least a transmission channel such that a signal s_p(t) transmitted by said transmission system takes M separate paths (M≧

1) in said transmission channel before reaching said reception system.

20. Transmission system according to the previous claim, wherein the number of transmission antennas P of said transmission system is greater than or equal to the number of paths M (P≧

M).

21. Transmission system according to the previous claim, wherein the number of transmission antennas P of said transmission system is less than or equal to the number of paths M (P≦

M).

22. Use of the transmission system according to one of claims 1 to 4 and of the reception system either comprising an estimator-demodulator according to one of claims 8 to 13, or according to claim 14 to the transmission of digital signals on a transmission channel such that a signal s_p(t) transmitted by said transmission system takes M separate paths (M≧

1) in said transmission channel before reaching said reception system and such that the number of transmission antennas P of said transmission system is greater than or equal to the number of paths M (P≧

M).

23. Use of the transmission system according to one of claims 1 to 4 and of the reception system either comprising an estimator-demodulator according to one of claims 8 to 13, or according to claim 14 to the transmission of digital signals on a transmission channel such that a signal s_p(t) transmitted by said transmission system takes M separate paths (M≧

1) in said transmission channel before reaching said reception system and such that the number of transmission antennas P of said transmission system is greater than or equal to the number of paths M (P≦

M).

5. Digital signal transmission method comprising:

a space-time encoding step comprising at least the encoding of the flow of data to be transmitted d[i] as symbol vectors m[k] of dimension P (P>

1), and

a modulation-transmission step comprising at least;

application in parallel of the constellation of a predetermined modulation to the P symbols m[k],

transmission in parallel of the P signals s(t) obtained from the constellated symbols a[k] from P spatially separate points,

wherein the modulation-transmission step is adapted to transmit the signals s(t) with time diversity.

6. Transmission method according to the previous claim, wherein the modulation-transmission step comprises, in addition, at least, on each channel p (1≦

p≦

P), filtering of symbols a_p[k] generating a signal s_p(t) such that the filtering of channel p is different from that carried out on the other P-1 parallel channels.

7. Transmission method according to the previous claim, wherein said filtering carried out on channel p has one or more of the following features:

any wave form h identical or not to that of the channel q, for all values of p and q (1≦

q≠

p≦

P) and a delay of duration τ

_p different from that of channel q,

any wave form h identical or not to that of the channel q, for all values of p and q (1≦

q≠

p≦

P) and a frequency shift f_p different from that of channel q,

a form h_p different from that of channel q, for all values of p and q (1≦

q≠

p≦

P).

16. Estimation and demodulation method comprising a step of reception in parallel of N signals y(t) resulting from the transmission according to the transmission method of one of claims 5 to 7, wherein the observation y(t) is space-time since each of the N spatial components comprises L samples.

8. Estimator-demodulator receiving in parallel N signals y(t) formed from L samples, wherein these signals y(t) represent a space-time observation since each of the N spatial components comprises L samples.

10. Estimator-demodulator of signals transmitted by a transmitter according to claim 8 or 9, wherein it comprises at least the following devices:

a two dimensional Wiener filter estimator (334),

said estimated two dimensional filter (331) Ŵ

_Q receiving the observations y(t) and the estimation of the coefficients of said filter Ŵ

_Q,

a detector (332) of the modulation states of the estimated symbols â

[k]=Ŵ

_Q y(t) generating the symbols detected {overscore (a)}[k], then

a demodulator (333) generating the symbols ^Λ

v[k],

11. Estimator-demodulator of the signals transmitted by a transmitter according to claim 8 or 9, wherein it comprises at least the following devices:

a first recursive two dimensional filter (331B) Ĥ

_y^Q receiving said estimation of its coefficients and the symbols already detected {overscore (a)}(k−

Q) . . . {overscore (a)}(k−

J+1),

an adder used to remove the vector which is the result of the first filter applied to the received observations y(t) and obtain v_q(t),

a second transverse two dimensional filter (331T) Ŵ

_Q receiving y_Q(t) and said estimation of its coefficients and generating the estimated received symbols â

_Q[k],

a detector (332) of the modulation states of the estimated symbols â

[k]=Ŵ

_q y(t) generating the detected symbols ã

[k], then

a demodulator (333) generating the symbols ^Λ

v[k],

an estimator (334) of the coefficients Ŵ

_Q of the transverse filter (331T) and Ĥ

_y^Q of the recursive filter (331B).

12. Estimator-demodulator of the signals transmitted by a transmitter according to claim 8 or 9, wherein it comprises at least a two dimensional estimator-demodulator of the symbols {a[k] . . . a[k−

J+1]} using a Viterbi algorithm.

13. Estimator-demodulator according to one of claims 10 to 12, wherein it has one or more of the following features:

the filter estimator (334) is an estimator either in the sense of maximum resemblance, the sense of least squares, or using a Viterbi algorithm, the demodulator (333) corresponds to a modulation of one or more of the following types;

linear, linearizable, with time memory, without time memory, BPSK, GMSK,

at least some of the received signals v(t) represent an apprenticeship sequences app known by said estimator-demodulator allowing one or more of the following operations;

estimation of said filter (331),

estimation in the sense of the least squares of said recursive filter (331B) such that its coefficients Ĥ

_y^Q are the first Q columns of the matrix

${\hat{H}}_y^Q=R_{y·<br><br>{\underset{\_}{\mathrm{app}}}_y}<br><br>R_{{\underset{\_}{\mathrm{app}}}_y·<br><br>{\underset{\_}{\mathrm{app}}}_y}^{-1},$

estimation with the zero-forcing method of said transverse filter (331T) such that its coefficients are

${\hat{W}}_Q=R_{{\underset{\_}{\mathrm{app}}}_y·<br><br>y}<br><br>R_{y·<br><br>y}^{-1},$

estimation using the Wiener method in the sense of maximum resemblance of said filter (331T) such that its coefficients are

${\hat{W}}_Q=R_{{\underset{\_}{\mathrm{app}}}_y·<br><br>y}<br><br>R_{y·<br><br>y}^{-1},$

initialization of the estimation of said filter(s) (331 or 331T and 331B),

initialization of said filtering (331B),

initialization of the Viterbi algorithm of the estimator-demodulator (33).

14. Digital signal reception system comprising:

a receiver (3) comprising at least a network of N reception antennas and an estimator-demodulator (33) according to one of claims 8 to 13, and

a space-time decoder (4)

wherein

said receiver (3) comprises at least;

N reception devices {31ⁿ}<sub>(1≦

n≦

N)</sub>, comprising at least an element used to put the received signal in the baseband, generating an observation vector x(t) of dimension N,

a windower (32) producing from observations x(t) the discrete observations x[kTs+i] with t=kts+i and 0≦

i ≦

Ts given that the observations x[kTs+i] depend on the transmitted signal vectors a[k] to a[k−

J+1] and generating a space-time observation

$\underset{\_}{y}<br><br>\left(t\right)=\left[\begin{array}{c}\underset{\_}{x}<br><br>\left(t\right)\\ \underset{\_}{x}<br><br>\left(t-1\right)\\ \mathrm{⋮<br><br>}\\ \underset{\_}{x}<br><br>\left(t+L-1\right)\end{array}\right]$

from N observations x(t),

and/or wherein the space-time decoder (4) comprises at least one or more of the following devices;

an element (41) capable of removing the apprenticeship sequences app,

a decoder (42) with P channels in input/output,

a multiplexer (43) with P channels in input.

15. Estimation and demodulation method comprising a step of reception in parallel of N signals y(t), wherein the observation y(t) is space-time since each of the N spatial components comprises L samples.

17. Estimation and demodulation method according to claim 15 or 16, wherein it uses one of the following two dimensional algorithms:

a direct estimation algorithm of the a[k] in the sense of the least squares from the observation y(t),

a decision feed-back algorithm, i.e. using demodulated symbol vectors for estimation in the sense of the least squares,

a Viterbi algorithm.

18. Estimation and demodulation method according to claim 17, wherein:

the demodulation carried out on the estimated symbols corresponds to a linear or linearizable modulation with or without time memory or BPSK or GMSK,

and/or wherein at least some of the received signals represent an apprenticeship sequence used by said algorithms.