Method and system for adapting an effective spreading sequence in a communication system using direct sequence spreading

• US 20060285524A1
• Filed: 06/21/2005
• Published: 12/21/2006
• Est. Priority Date: 06/21/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Schotten, Hans Dieter
• Granted Patent: US 7,693,037 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04J 13/18 Allocation of orthogonal codes

Abstract

A method and system for adapting an effective spreading sequence in a wire-line or a wireless communication system using direct sequence spreading system is described. A station of the communication system determines a state of a communication channel, represented by, e.g., an impulse response, a step response, or any other characteristic known to one skilled in the art. The station determines the channel state by measurements of a received signal or by receiving a feedback signal comprising an information enabling the station to determine the plurality of linearly related phases The station then determines a plurality of linearly related phases in accordance with the state of the communication channel, and then applies at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence.

Claims

1. A method for adapting an effective spreading sequence in a communication system, comprising:

determining a state of a communication channel;

determining a plurality of linearly related phases in accordance with the state of the communication channel; and

applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence.

2. The method as claimed in claim 1, wherein said determining a state of the communication channel comprises:

determining an impulse response of the communication channel.

3. The method as claimed in claim 1, wherein said determining a state of the communication channel comprises:

determining an operating environment of the communication system;

selecting a pre-determined model for the state of the communication channel in accordance with said determined operating environment;

determining parameters of the pre-determined model in accordance with the state of the communication channel; and

determining the state of the communication channel from the parameters and the pre-determined model.

4. The method as claimed in claim 1, wherein said determining a plurality of linearly related phases comprises:

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left(\underset{m}{\sum <br><br>}<br><br>{\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m\right)<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

m is an index;

M is number of phases;

* identifies a complex conjugate;

C_ss(m) is a value of an aperiodic autocorrelation of the effective spreading sequence; and

C_hh(m) is a value of an aperiodic autocorrelation of an impulse response of the communication channel; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

5. The method as claimed in claim 1, wherein said determining a plurality of linearly related phases comprises:

calculating for each of a plurality of indexes m a corresponding value of an aperiodic autocorrelation of an impulse response of the communication channel C_hh(m);

determining an index m_max>

0 for which a magnitude of the value C_hh(m) attains maximum;

determining a value of an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max)

6. The method as claimed in claim 5, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

7. The method as claimed in claim 5, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprises:

determining a phase of C_hh(m_max);

determining a phase of C_ss(m_max);

and

determining the plurality of linearly related phases in accordance with the phases of C_hh(M_max) and the C_ss(m_max).

8. The method as claimed in claim 7, wherein said determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that minimizes the expression;

$\left({\hspace{0.17em}<br><br>}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)\right)$

wherein;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

9. The method as claimed in claim 1, wherein said determining a plurality of linearly related phases comprises:

determining indexes m₁ and m₂ for the largest and the second largest magnitudes of an impulse response of the communication channel h(m);

calculating an aperiodic autocorrelation of the impulse response of the communication channel C_hh(m_max), wherein m_max=m₁−

m_2;

calculating an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max).

10. The method as claimed in claim 9, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss (m_max) comprises:

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left(e^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

11. The method as claimed in claim 1, wherein said determining a plurality of linearly related phases comprises:

determining indexes m₁ and m₂ for the largest and the second largest magnitudes of an impulse response of the communication channel h(m);

determining a phase of C_hh(m_max) , wherein m_max=m₁−

m_2;

determining a phase of C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

12. The method as claimed in claim 11, wherein said determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that minimizes the expression;

$({\hspace{0.17em}<br><br>}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

where;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

13. The method as claimed in claim 11, wherein said determining the phase of C_hh(m_max) comprises:

determining the phase difference between h(m₁) and h(m_2).

14. The method as claimed in claim 1, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

s′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is number of phases.

15. The method as claimed in claim 1, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is the number of phases.

16. The method as claimed in claim 1 further comprising:

transmitting a feedback signal comprising information enabling determination of a plurality of linearly related phases.

17. The method as claimed in claim 3 further comprising:

transmitting a feedback signal comprising said selected pre-determined model; and

transmitting a feedback signal comprising said determined parameters.

18. An apparatus for adapting an effective spreading sequence in a communication system, comprising:

means for determining a state of a communication channel;

means for determining a plurality of linearly related phases in accordance with the state of the communication channel; and

means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence.

19. The apparatus as claimed in claim 18, wherein said means for determining a state of the communication channel comprise:

means for determining an impulse response of the communication channel.

20. The apparatus as claimed in claim 18, wherein said means for determining a state of the communication channel comprise:

means for determining an operating environment of the communication system;

means for selecting a pre-determined model for the state of the communication channel in accordance with said determined operating environment;

means for determining parameters of the pre-determined model in accordance with the state of the communication channel; and

means for determining the state of the communication channel from the parameters and the pre-determined model.

21. The apparatus as claimed in claim 18, wherein said means for determining a plurality of linearly related phases comprise:

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left(\underset{m}{\sum <br><br>}<br><br>{\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m\right)<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

m is an index;

M is number of phases;

* identifies a complex conjugate;

C_ss(m) is a value of an aperiodic autocorrelation of the effective spreading sequence; and

C_hh(m) is a value of an aperiodic autocorrelation of an impulse response of the communication channel; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

22. The apparatus as claimed in claim 18, wherein said means for determining a plurality of linearly related phases comprise:

means for calculating for each of a plurality of indexes m a corresponding value of an aperiodic autocorrelation of an impulse response of the communication channel C_hh(m);

means for determining an index m_max>

0 for which a magnitude of the value C_hh(m) attains maximum;

means for determining a value of an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) .

23. The apparatus as claimed in claim 22, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

24. The apparatus as claimed in claim 22, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a phase of C_hh(m_max);

means for determining a phase of C_ss(m_max) ;

and

means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

25. The apparatus as claimed in claim 24, wherein said means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right))$

wherein;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

26. The apparatus as claimed in claim 18, wherein said means for determining a plurality of linearly related phases comprise:

means for determining indexes m₁ and m₂ for the largest and the second largest magnitudes of an impulse response of the communication channel h(m);

means for calculating an aperiodic autocorrelation of the impulse response of the communication channel C_hh(m_max), wherein m_max=m₁−

m_2;

means for calculating an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) .

27. The apparatus as claimed in claim 26, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{{\text{\hspace{1em}<br><br>}}^{\mathrm{hh}}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

28. The apparatus as claimed in claim 18, wherein said means for determining a plurality of linearly related phases comprise:

means for determining indexes m₁ and m₂ for the largest and the second largest magnitudes of an impulse response of the communication channel h(m);

means for determining a phase of C_hh(m_max), wherein m_max=m₁ −

m_2;

means for determining a phase of C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

29. The apparatus as claimed in claim 28, wherein said means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

where;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

30. The apparatus as claimed in claim 28, wherein said means for determining the phase of C_hh(m_max) comprise:

means for determining the phase difference between h(m₁) and h(m₂₎

31. The apparatus as claimed in claim 18, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is number of phases.

32. The apparatus as claimed in claim 18, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is the number of phases.

33. The apparatus as claimed in claim 18 further comprising:

means for transmitting a feedback signal comprising information enabling determination of a plurality of linearly related phases.

34. The apparatus as claimed in claim 20 further comprising:

means for transmitting a feedback signal comprising said selected pre-determined model; and

means for transmitting a feedback signal comprising said determined parameters.

35. A method for adapting an effective spreading sequence in a communication system, comprising:

receiving a feedback signal comprising information enabling determination of a plurality of linearly related phases;

determining the plurality of linearly related phases in accordance with the feedback; and

applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence.

36. The method as claimed in claim 35, wherein said receiving a feedback signal comprising information enabling determination of a plurality of linearly related phases comprises:

receiving a feedback signal comprising a phase factor α

.

37. The method as claimed in claim 36, wherein said determining the plurality of linearly related phases in accordance with the feedback comprises:

evaluating for each index m an equation;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M};<br><br>$

wherein;

M is number of phases.

38. The method as claimed in claim 37, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence; and

j is an imaginary unit.

39. The method as claimed in claim 37, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit.

40. The method as claimed in claim 35, wherein said receiving a feedback signal comprising information enabling determination of a plurality of linearly related phases comprises:

receiving a feedback signal comprising a pre-determined model characterizing the communication channel; and

receiving a feedback signal comprising at least one parameter of the pre-determined model.

41. The method as claimed in claim 40, wherein said determining the plurality of linearly related phases comprises:

determining an aperiodic autocorrelation of an impulse response C_hh(m) of the communication channel in accordance with the pre-determined model and the parameters;

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left(\underset{m}{\sum <br><br>}<br><br>{\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m\right)<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

m is an index;

M is number of phases;

* identifies a complex conjugate;

C_ss(m) is a value of an aperiodic autocorrelation of the effective spreading sequence; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

42. The method as claimed in claim 40, wherein said determining the plurality of linearly related phases comprises:

calculating for each of a plurality of indexes m a corresponding value of an aperiodic autocorrelation of an impulse response C_hh(m) of the communication channel in accordance with the pre-determined model and the parameters;

determining an index m_max>

0 for which a magnitude of the value C_hh(m) attains maximum;

determining a value of an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max).

43. The method as claimed in claim 42, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left(\underset{m}{\sum <br><br>}<br><br>{\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

44. The method as claimed in claim 42, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprises:

determining a phase of C_hh(m_maxx);

determining a phase of C_ss(m_max) ;

and

determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

45. The method as claimed in claim 44, wherein said determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right))$

wherein;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

46. The method as claimed in claim 40, wherein said determining the plurality of linearly related phases comprises:

determining an impulse response of the communication channel h(m) in accordance with the pre-determined model and the parameters;

determining indexes M₁ and m₂ for the largest and the second largest magnitudes of the impulse response of the communication channel h(m);

calculating an aperiodic autocorrelation of the impulse response of the communication channel C_hh(m_max), wherein m_max=m₁−

m₂;

calculating an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max).

47. The method as claimed in claim 46, wherein said determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

48. The method as claimed in claim 35, wherein said determining a plurality of linearly related phases comprises:

determining an impulse response of the communication channel h(m) in accordance with the pre-determined model and the parameters;

determining indexes m₁ and m₂ for the largest and the second largest magnitudes of the impulse response of the communication channel h(m);

determining a phase of C_hh(m_max), wherein m_max=m₁−

m₂;

determining a phase of C_ss(m_max); and

determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) .

49. The method as claimed in claim 48, wherein said determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprises:

determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right))$

where;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

determining the plurality of linearly related phases in accordance with the phase shift factor α

.

50. The method as claimed in claim 48, wherein said determining the phase of C_hh(m_max) comprises:

determining the phase difference between h(m) and h(m_2).

51. The method as claimed in claim 35, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is number of phases.

52. The method as claimed in claim 35, wherein said applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprises:

evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is the number of phases.

53. An apparatus for adapting an effective spreading sequence in a communication system, comprising:

means for receiving a feedback signal comprising information enabling determination of a plurality of linearly related phases;

means for determining the plurality of linearly related phases in accordance with the feedback; and

means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence.

54. The apparatus as claimed in claim 53, wherein the feedback signal comprises a phase factor α

.

55. The apparatus as claimed in claim 54, wherein said means for determining the plurality of linearly related phases in accordance with the feedback comprise:

means for evaluating for each index m an equation;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M};<br><br>$

wherein;

M is number of phases.

56. The apparatus as claimed in claim 55, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence; and

j is an imaginary unit.

57. The apparatus as claimed in claim 55, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit.

58. The apparatus as claimed in claim 53, wherein the feedback signal comprises a pre-determined model characterizing the communication channel;

and at least one parameter of the pre-determined model.

59. The apparatus as claimed in claim 58, wherein said means for determining the plurality of linearly related phases comprise:

means for determining an aperiodic autocorrelation of an impulse response C_hh(m) of the communication channel in accordance with the pre-determined model and the parameters;

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left(\underset{m}{\sum <br><br>}<br><br>{\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m\right)<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

m is an index;

M is number of phases;

* identifies a complex conjugate;

C_ss(m) is a value of an aperiodic autocorrelation of the effective spreading sequence; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

60. The apparatus as claimed in claim 58, wherein said means for determining the plurality of linearly related phases comprise:

means for calculating for each of a plurality of indexes m a corresponding value of an aperiodic autocorrelation of an impulse response C_hh(m) of the communication channel in accordance with the pre-determined model and the parameters;

means for determining an index m_max>

0 for which a magnitude of the value C_hh(m) attains maximum;

means for determining a value of an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) .

61. The apparatus as claimed in claim 60, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

62. The apparatus as claimed in claim 60, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a phase of C_hh(m_max);

means for determining a phase of C_ss(m_max) ;

and

means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

63. The apparatus as claimed in claim 62, wherein said means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right))$

wherein;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

64. The apparatus as claimed in claim 58, wherein said means for determining the plurality of linearly related phases comprise:

means for determining an impulse response of the communication channel h(m) in accordance with the pre-determined model and the parameters;

means for determining indexes m₁ and m₂ for the largest and the second largest magnitudes of the impulse response of the communication channel h(m);

means for calculating an aperiodic autocorrelation of the impulse response of the communication channel C_hh(m_max), wherein m_max=m₁−

m₂;

means for calculating an aperiodic autocorrelation of an effective spreading sequence C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max).

65. The apparatus as claimed in claim 64, wherein said means for determining the plurality of linearly related phases in accordance with the C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that maximizes the expression;

$\mathrm{Re}<br><br>\left({\mathrm{e<br><br>}}^{\frac{\mathrm{j2\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)·<br><br>C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

wherein;

Re identifies real part;

j is an imaginary unit;

M is number of phases;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

66. The apparatus as claimed in claim 53, wherein said means for determining a plurality of linearly related phases comprise:

means for determining an impulse response of the communication channel h(m) in accordance with the pre-determined model and the parameters;

means for determining indexes m₁ and m₂ for the largest and the second largest magnitudes of the impulse response of the communication channel h(m);

means for determining a phase of C_hh(m_max) wherein M_max=m₁−

m₂;

means for determining a phase of C_ss(m_max); and

means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max).

67. The apparatus as claimed in claim 66, wherein said means for determining the plurality of linearly related phases in accordance with the phases of C_hh(m_max) and the C_ss(m_max) comprise:

means for determining a value of a phase shift factor α

that minimizes the expression;

${(}^{\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m_{\max }}{M}}<br><br>+\mathrm{arc}<br><br>\left(C_{\mathrm{ss}}<br><br>\left(m_{\max }\right)\right)+\mathrm{arc}<br><br>\left(C_{\mathrm{hh}}^{*}<br><br>\left(m_{\max }\right)\right)$

where;

M is number of phases;

arc() is a phase of the argument;

* identifies a complex conjugate; and

means for determining the plurality of linearly related phases in accordance with the phase shift factor α

.

68. The apparatus as claimed in claim 66, wherein said means for determining the phase of C_hh(m_max) comprise:

means for determining the phase difference between h(m₁) and h(m₂).

69. The apparatus as claimed in claim 53, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is number of phases.

70. The apparatus as claimed in claim 53, wherein said means for applying at least one of the plurality of linearly related phases to at least one sample of the effective spreading sequence comprise:

means for evaluating for each index m an equation;

s′

(m)=e<sup>−

jθ

(m)</sup>·

s(m)

wherein;

S′

(m) is the adapted spreading sequence;

s(m) is the effective spreading sequence;

j is an imaginary unit;

$\mathrm{\theta <br><br>}<br><br>\left(m\right)=\frac{2<br><br>\mathrm{\pi <br><br>\alpha <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>m}{M}$

is the m-th phase;

α

is a phase factor; and

M is the number of phases.