Estimating a transmission channel with pilot symbols distributed in lattice structure

• US 20040246886A1
• Filed: 06/02/2004
• Published: 12/09/2004
• Est. Priority Date: 10/23/2001
• Status: Active Grant

• Current Assignee: Cassidian SAS (Airbus SE)
• Original Assignee: EADS Secure Networks
• Inventors: Mege, Philippe, Brutel, Christophe
• Granted Patent: US 7,310,378 B2
• Time in Patent Office: Days
• US Class Current: 370/203
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 25/025 using least-mean-square [LMS] method
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/2698 double density OFDM/OQAM system, e.g. OFDM/OQAM-IOTA system

Abstract

A method for estimating a transmission channel from a multicarrier signal transmitted through said transmission channel, comprising real pilot symbols and so-called pure imaginary pilot symbols, consists in selecting one or several values z_k of the received signal corresponding respectively to one or several real pilot symbols, and one or several values z_l of the received signal corresponding respectively to one or several pure imaginary pilot symbols. The pilot symbols are sufficiently close both in frequency and in time such that it can be assumed that the fading of the signal through the transmission channel has a complex value α substantially identical for the symbols. An estimated value {circumflex over (α)} of α for the pilot symbols concerned is then determined by minimizing a least square equation involving the values z_k and the values z_l.

Claims

1. A method of estimating a transmission channel on the basis of a signal received after transmission through said transmission channel, said signal being a multicarrier signal constructed on a time/frequency lattice defined by a frequency axis and a time axis, and comprising frames having M×

N symbols distributed over M subcarriers each of which is divided into N determined symbol times, each frame comprising P pilot symbols distributed timewise and frequencywise in such a way as to cover the frame according to a lattice structure, where the numbers M, N and P are nonzero integers, the pilot symbols comprising on the one hand symbols known as real pilot symbols, transmitted as symbols having a real value, and on the other hand symbols known as pure imaginary pilot symbols, transmitted as symbols having a pure imaginary value, the method comprising the steps of;

a) selecting one or more values z_k of the signal received corresponding to one or more real pilot symbols of respective values c_k on the one hand, and one or more values z_l of the signal received corresponding respectively to one or more pure imaginary pilot symbols of respective values c_l on the other hand, these pilot symbols being sufficiently close together both along the frequency axis and along the time axis for it to be possible to consider that the fading of the signal through the transmission channel has had a substantially identical (in modulus and in phase) complex value α

for these pilot symbols;

b) determining complex numbers u and v and a real number λ

by minimizing the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_1^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>u\right)-\mathrm{\lambda <br><br>}·<br><br>c_k<br><br>}^2+\underset{l}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_l·<br><br>v\right)-\mathrm{\lambda <br><br>}·<br><br>c_l<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x or the modulus of the complex variable x,

where λ

is a real number,

where u and v are orthogonal (that is to say Re(u*.v)=0, where Re(w) denotes the real part operator for the complex number w, and where w* denotes the complex conjugate of the complex number w), such that ∥

u∥

=∥

v∥

,

c) determining an estimated value {circumflex over (α

)} of the value α

of the fading of the signal through the transmission channel for the pilot symbols concerned, by calculating;

{circumflex over (α

)}=λ

/u.

2. The method of estimating a transmission channel of claim 1, wherein λ

is equal to unity, u is equal to β

, and v is equal to −

i·

β

, where β

denotes the inverse of α

,

wherein step b) consists in determining real numbers Re(β

) and Im(β

) by minimizing the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_2^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>\mathrm{\beta <br><br>}\right)-c_k<br><br>}^2+\underset{l}{\sum <br><br>}<br><br>{<br><br>\mathrm{Im}<br><br>\left(z_l·<br><br>\mathrm{\beta <br><br>}\right)-c_l<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x

where Re(x) denotes the real part operator for the complex variable x, and

where Im(x) denotes the imaginary part operator for the complex variable x,

and wherein step c) consists in determining the estimated value {circumflex over (α

)} of the value α

of the fading of the signal through the transmission channel for the pilot symbols concerned, by inverting the complex number Re(β

)+i·

Im(β

).

3. The method of claim 2, wherein step b) comprises the solving of the following system of two equations in two unknowns:

4. The method of claim 2, wherein step a) comprises the selection of the value z₁ of the signal received corresponding to one and only one real pilot symbol of value c₁ on the one hand, and of the value z₂ of the signal received corresponding to one and only one pure imaginary pilot symbol of value c₂ on the other hand,

and wherein step b) comprises the solving of the following system of equations in two unknowns:

$\{\begin{array}{c}\mathrm{Re}<br><br>\left(z_1·<br><br>\mathrm{\beta <br><br>}\right)-c_1=0\\ \mathrm{Im}<br><br>\left(z_2·<br><br>\mathrm{\beta <br><br>}\right)-c_2=0\end{array}.$

5. The method of claim 1, wherein λ

is equal to ρ

, u is equal to e<sup>−

i·

φ</sup>

, and v is equal to −

i·

e<sup>−

i·

φ</sup>

, where ρ and

φ

are real numbers that respectively denote the modulus and the phase of {circumflex over (α

)} ({circumflex over (α

)}=ρ

·

e<sup>i·

φ</sup>

),

wherein step b) and step c) are carried out jointly and consist in determining an estimated value {circumflex over (α

)} of the fading of the signal through the transmission channel for the pilot symbols concerned, which value is defined by {circumflex over (α

)}=ρ

·

e<sup>i·

φ</sup>

where ρ and

φ

minimize the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_3^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>{\mathrm{<br><br>}}^{-i·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_k<br><br>}^2+\underset{l}{\sum <br><br>}<br><br>{<br><br>\mathrm{Im}<br><br>\left(z_l·<br><br>{\mathrm{<br><br>}}^{-i·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_l<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x,

where Re(x) denotes the real part operator for the complex variable x, and

where Im(x) denotes the pure imaginary part operator for the complex variable x.

6. The method of claim 5, wherein step b) comprises the solving of the following system of two equations in two unknowns:

7. The method of claim 5, wherein step a) comprises the selection of the value z₁ of the signal received corresponding to one and only one real pilot symbol of value c₁ on the one hand, and of the value Z₂ of the signal received corresponding to one and only one pure imaginary pilot symbol of value c₂ on the other hand,

and wherein step b) comprises the solving of the following system of equations in two unknowns:

$\{\begin{array}{c}\mathrm{Re}<br><br>\left(z_1·<br><br>{\mathrm{<br><br>}}^{-i·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_1=0\\ \mathrm{Im}<br><br>\left(z_2·<br><br>{\mathrm{<br><br>}}^{-i·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_2=0\end{array}$

8. The method of claim 1, wherein the symbols selected in step a) belong to one and the same single frame.

9. The method of claim 1, wherein the symbols selected in step a) belong to two frames transmitted consecutively through the transmission channel.

10. The method of claim 1, wherein the symbols selected in step a) belong to a group of pilot symbols that are pairwise adjacent in the frame, in the direction of the frequency axis and/or in the direction of the time axis.

11. A device for estimating a transmission channel on the basis of a signal received after transmission through said transmission channel, said signal being a multicarrier signal constructed on a time/frequency lattice defined by a frequency axis and a time axis, and comprising frames having M×

N symbols distributed over M subcarriers each of which is divided into N determined symbol times, each frame comprising P pilot symbols distributed timewise and frequencywise in such a way as to cover the frame according to a lattice structure, where the numbers M, N and P are nonzero integers, the pilot symbols comprising on the one hand symbols known as real pilot symbols, transmitted as symbols having a real value, and on the other hand symbols known as pure imaginary pilot symbols, transmitted as symbols having a pure imaginary value, comprising;

means for selecting one or more values z_k of the signal received corresponding to one or more real pilot symbols of respective values c_k on the one hand, and one or more values z_l of the signal received corresponding respectively to one or more pure imaginary pilot symbols of respective values c_l on the other hand, these pilot symbols being sufficiently close together both along the frequency axis and along the time axis for it to be possible to consider that the fading of the signal through the transmission channel has had a substantially identical complex value α

for these pilot symbols;

means for determining complex numbers u and v and a real number λ

minimizing the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_1^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>u\right)-\mathrm{\lambda <br><br>}·<br><br>c_k<br><br>}^2+\underset{l}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_l·<br><br>v\right)-\mathrm{\lambda <br><br>}·<br><br>c_l<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x or the modulus of the complex variable x,

where λ

is a real number,

where u and v are orthogonal (that is to say Re(u*.v)=0, where Re(w) denotes the real part operator for the complex number w, and where w* denotes the complex conjugate of the complex number w), such that ∥

u∥

=∥

v∥

,

means for determining an estimated value {circumflex over (α

)} of the value α

of the fading of the signal through the transmission channel for the pilot symbols concerned, by calculating;

{circumflex over (α

)}=λ

/u.

12. A device for estimating a transmission channel on the basis of a signal received after transmission through said transmission channel, said signal being a multicarrier signal constructed on a time/frequency lattice defined by a frequency axis and a time axis, and comprising frames having M×

N symbols distributed over M subcarriers each of which is divided into N determined symbol times, each frame comprising P pilot symbols distributed timewise and frequencywise in such a way as to cover the frame according to a lattice structure, where the numbers M, N and P are nonzero integers, the pilot symbols comprising on the one hand symbols known as real pilot symbols, transmitted as symbols having a real value, and on the other hand symbols known as pure imaginary pilot symbols, transmitted as symbols having a pure imaginary value, comprising;

means for selecting one or more values z_k of the signal received corresponding to one or more real pilot symbols of respective values c_k on the one hand, and one or more values z_l of the signal received corresponding respectively to one or more pure imaginary pilot symbols of respective values c_l on the other hand, these pilot symbols being sufficiently close together both along the frequency axis and along the time axis for it to be possible to consider that the fading of the signal through the transmission channel has had a substantially identical complex value cc for these pilot symbols;

means for determining real numbers Re(β

) and Im(β

) minimizing the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_2^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>\mathrm{\beta <br><br>}\right)-c_k<br><br>}^2+\underset{l}{\sum <br><br>}<br><br>{<br><br>\mathrm{Im}<br><br>\left(z_l·<br><br>\mathrm{\beta <br><br>}\right)-c_l<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x

where Re(x) denotes the real part operator for the complex variable x,

where Im(x) denotes the pure imaginary part operator for the complex variable x, and

where β

denotes the inverse of α

; and

,

means for determining an estimated value {circumflex over (α

)} of the fading of the signal through the transmission channel for the pilot symbols concerned, by inverting the complex number Re(β

)+i·

Im(β

).

13. A device for estimating a transmission channel on the basis of a signal received after transmission through said transmission channel, said signal being a multicarrier signal constructed on a time/frequency lattice defined by a frequency axis and a time axis, and comprising frames having M×

N symbols distributed over M subcarriers each of which is divided into N determined symbol times, each frame comprising P pilot symbols distributed timewise and frequencywise in such a way as to cover the frame according to a lattice structure, where the numbers M, N and P are nonzero integers, the pilot symbols comprising on the one hand symbols known as real pilot symbols, transmitted as symbols having a real value, and on the other hand symbols known as pure imaginary pilot symbols, transmitted as symbols having a pure imaginary value, comprising;

means for selecting one or more values z_k of the signal received corresponding to one or more real pilot symbols of respective values c_k on the one hand, and one or more values z_l of the signal received corresponding respectively to one or more pure imaginary pilot symbols of respective values c_l on the other hand, these pilot symbols being sufficiently close together both along the frequency axis and along the time axis for it to be possible to consider that the fading of the signal through the transmission channel has had a substantially identical complex value α

for these pilot symbols; and

means for determining an estimated value {circumflex over (α

)} of the fading of the signal through the transmission channel for the pilot symbols concerned, which value is defined by {circumflex over (α

)}=ρ

·

e<sup>i·

φ</sup>

where ρ and

φ

are real numbers which minimize the following least squares expression;

${\mathrm{\varepsilon <br><br>}}_3^2=\underset{k}{\sum <br><br>}<br><br>{<br><br>\mathrm{Re}<br><br>\left(z_k·<br><br>{\mathrm{<br><br>}}^{-\mathrm{<br><br>}·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_k<br><br>}^2+\underset{1}{\sum <br><br>}<br><br>{<br><br>\mathrm{Im}<br><br>\left(z_1·<br><br>{\mathrm{<br><br>}}^{-\mathrm{<br><br>}·<br><br>\mathrm{\varphi <br><br>}}\right)-\mathrm{\rho <br><br>}·<br><br>c_1<br><br>}^2$

where the sign Σ

denotes the summation operator,

where ∥

x∥

denotes the absolute value operator for the real variable x

where Re(x) denotes the real part operator for the complex variable x, and

where Im(x) denotes the pure imaginary part operator for the complex variable x.