Computational circuits and methods for processing modulated signals having non-constant envelopes

• US 20030031268A1
• Filed: 07/26/2002
• Published: 02/13/2003
• Est. Priority Date: 03/23/2001
• Status: Active Grant

• Current Assignee: Zarbana Digital Fund LLC (Intellectual Ventures LLC)
• Original Assignee: Zarbana Digital Fund LLC (Intellectual Ventures LLC)
• Inventors: Wight, James Stuart
• Granted Patent: US 7,127,005 B2
• Time in Patent Office: Days
• US Class Current: 375/295
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes
• CPC Class Codes: H04B 1/68 for wholly or partially suppressing the carrier or one side band
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2215/067 by modulation dispersion
• CPC Class Codes: H04L 27/2614 Peak power aspects

Abstract

Circuits and methods are provided for use in a wireline or wireless transmitter to complement the digital generation of non-constant envelope modulation signals therein. A digital signal processor is configured for deconstructing a predetermined signal having an undesirable property into one or more fragment signals which do not have the undesirable property. In a preferred embodiment the predetermined signal is preconditioned by applying a preconditioning deconstruction process to another signal from which the predetermined signal is derived, whereby that other signal is deconstructed into one or more preconditioned fragment signals having an improved property over the other signal. For OFDM modulation schemes this undesirable property may be a relatively high peak-to-average power ratio. Signals formed from the fragment signals are subject to conversion to analog signals and processing by power efficient, dynamic-range limited analog circuits i.e. S Class power amplifiers (and, for wireless applications, low compression-point up-converters), before being recombined for transmission.

Claims

1. A signal deconstruction circuit for use in transmitter circuitry and configured for complementing modulation circuitry of said transmitter for digitally generating a non-constant envelope modulation signal, said deconstruction circuit comprising a digital signal processor configured for deconstructing a predetermined signal having an undesirable property into one or more fragment signals which do not have said undesirable property, whereby signals derived from said fragment signals are subject to conversion to analog signals, processing by power efficient, dynamic-range limited analog circuits and recombination.

2. A circuit according to claim 1 wherein said undesirable property is a relatively high peak-to-average power ratio.

3. A circuit according to claim 2 wherein said modulation circuitry comprises an Inverse Fourier transform processor and said deconstruction circuit is operative on said predetermined signal after said Inverse Fourier transform processor.

4. A circuit according to claim 2 wherein said modulation circuitry comprises an Inverse Fourier transform processor and said deconstruction circuit is operative on said predetermined signal before said Inverse Fourier transform processor, said circuit comprising a carrier-sorting engine and said modulation being OFDM.

5. A circuit according to claim 4 wherein said carrier-sorting engine is configured to sort carriers of said predetermined signal into a plurality of groups, each said group forming one said fragment signal whereby said modulation circuitry comprises a plurality of Inverse Fourier transform processors for transforming said fragment signals, each said Inverse Fourier transform processor being smaller than would be required to transform said predetermined signal itself.

6. A circuit according to claim 5 wherein said carriers are simultaneously sorted in more than one way for each said group to produce a plurality of alternative fragment signals therefor, whereby said fragment signals are selected on the basis of their peak-to-average power ratio.

7. A circuit according to claim 3 comprising a phasor fragmentation engine.

8. A circuit according to claim 7 wherein said predetermined signal is preconditioned by a second deconstruction circuit.

9. A circuit according to claim 7 wherein said phasor fragmentation engine is configured to deconstruct said predetermined signal into a plurality of equal, varying amplitude fragment signals the phasors of which combine to form a phasor corresponding to said predetermined signal, wherein said amplitude of said fragment signals is a predetermined proportion of the variation of the amplitude of said predetermined signal about the mean amplitude thereof.

10. A circuit according to claim 7 wherein said phasor fragmentation engine deconstructs said predetermined signal into a plurality of equal and constant amplitude fragment signals.

11. A circuit according to claim 8 wherein said second deconstruction circuit comprises a carrier sorting engine.

12. A circuit according to claim 8 wherein said second deconstruction circuit comprises a preconditioning phasor fragmentation engine.

13. A circuit according to claim 10 wherein said phasor fragmentation engine is configured for converting sequences of complex time samples output from said Inverse Fourier transform processor into parallel sequences of two equal magnitude phasors, equal to Vmax/2, at two phases, whereby said phases of said two equal magnitude phasors are calculated to be θ

−

φ and

θ

+φ

, respectively, whereby φ

=cos<sup>−

1</sup> (V/Vmax) wherein V is the amplitude of the current complex time sample of said predetermined signal and θ

is the phase thereof, and Vmax is the maximum amplitude of said predetermined signal over the period of said sequence.

14. A circuit according to claim 10 wherein said phasor fragmentation engine is configured for converting sequences of complex time samples output from said Inverse Fourier transform processor into parallel sequences of three equal magnitude phasors, equal to Vmax/3, at three phases, whereby said phases of two said equal magnitude phasors are calculated to be θ

−

φ and

θ

+φ

, respectively, and said third phase is equal to θ

being the phase of said predetermined signal, whereby φ

=cos<sup>−

1</sup>[(1.5 V/V_MAX)−

0.5], V is the amplitude of the current complex time sample of said predetermined signal and Vmax is the maximum amplitude of said predetermined signal over the period of said sequence.

15. A circuit according to claim 3 comprising a virtual range-hopped engine configured for shifting a peak signal output from said Inverse Fourier transform processor to time samples targeted for attenuation by a preselected windowing function.

16. A circuit according to claim 8 wherein said second deconstruction circuit comprises a light windowing engine.

17. A signal deconstruction method for complementing the generation of a digitally generated non-constant envelope modulation signal in transmitter circuitry, said method comprising deconstructing a predetermined signal having an undesirable property into a plurality of fragment signals which do not have said undesirable property whereby signals derived from said fragment signals are subject to conversion to analog signals, processing by power efficient, dynamic-range limited analog circuits and recombination.

18. A method according to claim 17 whereby said undesirable property is a relatively high peak-to-average power ratio.

19. A method according to claim 18 whereby said modulation signal is generated using an Inverse Fourier transform processor and said deconstructing is performed prior to modulation by said Inverse Fourier transform processor.

20. A method according to claim 18 whereby said modulation signal is generated using an Inverse Fourier transform processor and said deconstructing is performed subsequent to modulation by said Inverse Fourier transform processor.

21. A method according to claim 19 whereby said deconstructing comprises sorting carriers of said predetermined signal into a plurality of groups, each said group forming one said fragment signal, whereby said modulation is performed by a plurality of Inverse Fourier transform processors for transforming said fragment signals, each said Inverse Fourier transform processor being smaller than would be required to transform said predetermined signal itself.

22. A method according to claim 21 whereby said carriers are simultaneously sorted in more than one way for each said group to produce a plurality of alternative fragment signals for each said group and selecting said fragment signals on the basis of peak-to-average power ratio.

23. A method according to claim 20 whereby said predetermined signal is deconstructed into a plurality of equal, varying amplitude fragment signals the phasors of which combine to form a phasor corresponding to said predetermined signal, wherein said amplitude of said fragment signals is a predetermined proportion of the variation of the amplitude of said predetermined signal about the mean amplitude thereof.

24. A method according to claim 20 wherein said predetermined signal is deconstructed into a plurality of equal and constant amplitude fragment signals.

25. A method according to claim 24 comprising converting sequences of complex time samples output from said Inverse Fourier transform processor into parallel sequences of three equal magnitude phasors, equal to Vmax/3, at three phases, whereby said phases of two said equal magnitude phasors are calculated to be θ

−

φ and

θ

+φ

, respectively, and said third phase is equal to θ

being the phase of said predetermined signal, whereby φ

=cos<sup>−

1</sup>[(1.5 V/V_MAX)−

0.5], V is the amplitude of the current complex time sample of said predetermined signal and Vmax is the maximum amplitude of said predetermined signal over the period of said sequence.

26. A method according to claim 20 comprising shifting a peak signal output from said Inverse Fourier transform processor to time samples targeted for attenuation by a preselected windowing function.