DSP-based variable aperture code generation technique

• US 20030156660A1
• Filed: 05/08/2002
• Published: 08/21/2003
• Est. Priority Date: 02/20/2002
• Status: Active Grant

• Current Assignee: Thomson Licensing (Vantiva SA)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Mohan, Chandra, Zhang, Zhiming, Zoltowski, Michael David, Tomezak, Gregory John, Krogmeier, James Vincent
• Granted Patent: US 7,042,959 B2
• Time in Patent Office: Days
• US Class Current: 375/301
• CPC Class Codes: H04B 1/68 for wholly or partially suppressing the carrier or one side band
• CPC Class Codes: H04L 27/04 Modulator circuits; Transmitter circuits

Abstract

Variable Aperture Coded (VAC) signals for VAC modulation are advantageously generated by a digital signal processor (12) that yields a VAC signal having a single narrow in the positive frequency region. A Discrete-Time Hilbert transformer (12) isolates the only the positive spectral peaks, thus yielding a VAC signal that affords greater control over zero crossings.

Claims

1. Apparatus for generating a single side band (SSB) variable aperture coded (VAC) signal, comprising:

a digital signal processor (12) for generating a discrete time VAC signal which has a sinusoidal shape and a spectral peak in appositive frequency range; and

means (14) for isolating the positive spectral peak and a portion of surrounding spectrum in the VAC signal generated by the digital signal processor.

2. The apparatus according to claim 1 wherein the isolating means comprises a Discrete-Time Hilbert transformer.

3. The apparatus according to claim 1 wherein the digital signal processor generates the discrete time VAC signal in accordance with the relationship:

4. The apparatus according to claim 3 wherein the time shift T_k is a random variable that is generated in accordance with the relationship:

T_k=T_k+1+(M+I_kΔ

)T_c

with T₀=0 and Δ

=1.

5. The apparatus according to claim 3 wherein sinusoidal waveforms ρ

<sub>−

1</sub>, ρ

₀(t), and ρ

₊₁(t) are obtained in accordance with the relationship;

6. The apparatus in accordance with claim 5 wherein the basis function ρ

_basis(t) is a sinc function given by the relationship;

7. The apparatus according to claim 5 wherein the basis function ρ

_basis(t) comprises a raised cosine function that satisfies the relationship

ρ

_basis(nτ

c)=δ

[n].

8. The apparatus according to claim 5 wherein the coefficients α

_lk^(m) are given by the relationship

9. A method for generating a single side band (SSB) variable aperture coded (VAC) signal, comprising the steps of:

digitally generating a discrete time VAC signal which has a sinusoidal shape and a spectral peak in appositive frequency range; and

isolating the positive spectral peak and a portion of surrounding spectrum in the digitally generated VAC signal.

10. The method according to claim 9 wherein the digitally generated VAC signal is synthesized in accordance with the relationship:

11. The method according to claim 10 wherein the time shift T_k, is a random variable that is generated in accordance with the relationship:

T_k=T_k+1+(M+I_kΔ

)T_c

with T₀=0 and Δ

=1.

12. The method according to claim 10 wherein sinusoidal waveforms ρ

<sub>−

1</sub>, ρ

₀(t), and ρ

₊₁(t) are obtained in accordance with the relationship;

13. The method in accordance with claim 12 wherein the basis function ρ

_basis(t) is a sinc function given by the relationship;

14. The method according to claim 12 wherein the basis function ρ

_basis(t) comprises a raised cosine function that satisfies the relationship

ρ

_basis(nτ

c)=δ

[n].

15. The method according to claim 12 wherein the coefficients α

_Ik^(m) are given by the relationship

16. The method according to claim 9 wherein the VAC signal is generated by first generating a digitally generating a square wave signal and then applying a windowing function that rounds the square wave signal.

17. The method according to claim 16 further including the step of filtering the rounded square wave signal by a Finite Impulse Response filter.

18. The method according to claim 9 including wherein the digital generation of the sinusoidal function is done at base band.

19. The method according to claim 9 wherein an intermediate sinusoidal signal is digitally generated at base band and is converted to a single sideband signal at an intermediate frequency.

20. The method according to claim 19 wherein the single sideband signal is up converted to a higher RF frequency.