Constrained-envelope digital communications transmitter and method therefor

• US 6,999,522 B2
• Filed: 09/28/2001
• Issued: 02/14/2006
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Shearer, lll, Daniel Davidson MacFarlane
• Primary Examiner(s): Vanderpuye, Kenneth
• Assistant Examiner(s): Nguyen, Dung X.
• Application Number:
  US09/967,408
• Publication Number:
  US 20030063682A1
• Time in Patent Office: 1,600 Days
• Field of Search: 375/295, 375/135, 375/140, 375/141, 375/146, 375/296
• US Class Current: 375/295
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 27/2614 Peak power aspects
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set

Abstract

A constrained-envelope digital communications transmitter (10) places constraints on the envelope of a spectrally constrained, digitally modulated communication signal (42) to lower peak-to-average power ratio without allowing significant spectral regrowth. A communication signal (14,42) is applied to a plurality of cascade-coupled constrained-envelope generators (50). Each constrained-envelope generator (50) detects overpeak events (52) and configures corrective impulses (54) for the overpeak events (52). The corrective impulses (54) are filtered into shaped pulses (88) that exhibit a constrained spectrum and combine with the communication signal (14, 42) to reduce an unwanted signal peak. Trailing portions (92) of the shaped pulses (88) are fed-back and combined with the communication signal (14,42) so that future overpeak events (52) are identified after compensation is made for the influence of the trailing portions (92) of any recently past shaped pulses (88) on the communication signal (14,42).

Claims

1. A method of operating a digital communications transmitter to constrain envelope and spectral regrowth while processing a communication signal, said method comprising:

monitoring an overpeak-capable signal stream to identify occurrences of overpeak events by determining when a threshold is exceeded;

generating, when one of said overpeak events is identified, a corrective impulse configured to compensate for an amount by which said overpeak-capable signal stream is in excess of said threshold;

filtering said corrective impulse to generate a shaped pulse having a leading portion and a trailing portion;

feeding-back said trailing portion of said shaped pulse so that, after said one of said overpeak events, said overpeak-capable signal stream is responsive to said trailing portion of said shaped pulse and said communication signal; and

producing a constrained-envelope signal stream in response to said communication signal and said corrective impulse.

2. A method as claimed in claim 1 wherein:

said communication signal is a first communication signal;

said constrained-envelope signal stream is both a first constrained-envelope signal stream and a second communication signal; and

said method additionally comprises repeating said monitoring, generating, filtering, feeding-back, and producing activities with respect to said second communication signal to produce a second constrained-envelope signal stream.

3. A method as claimed in claim 2 wherein, when said monitoring and generating activities are used to produce said first constrained envelope signal stream, said threshold is greater than when said monitoring and generating activities are repeated to produce said second constrained-envelope signal stream.

4. A method as claimed in claim 1 wherein said monitoring, generating, filtering, feeding-back, and producing activities are performed in a first constrained-envelope generator and said method additionally comprises coupling a second constrained-envelope generator in cascade with said first constrained-envelope generator.

5. A method as claimed in claim 1 wherein said shaped pulse is configured to have a predetermined duration, and said method additionally comprises:

delaying said communication signal by more than one-half of said predetermined duration to produce a delayed communication signal; and

combining said delayed communication signal with a signal responsive to said corrective impulse.

6. A method as claimed in claim 5 wherein:

said communication signal is a spectrally-unconstrained signal stream;

said combining activity combines said corrective impulse with said delayed communication signal to produce a combined signal stream; and

said filtering activity filters said combined signal stream in a pulse-shaping filter.

7. A method as claimed in claim 5 wherein:

said communication signal is a spectrally-constrained signal stream generated by a first pulse-shaping filter;

said filtering activity filters said corrective impulse in a second pulse-shaping filter; and

said combining activity combines said leading portion of said shaped pulse generated by said filtering activity with said delayed communication signal.

8. A method as claimed in claim 1 wherein said filtering activity generates said leading portion of said shaped pulse in a first filter and generates said trailing portion of said shaped pulse in a second filter, said leading and trailing portions being generated concurrently.

9. A method as claimed in claim 8 wherein said shaped pulse is substantially symmetrical in time, building from a near zero value to a peak in said leading portion then diminishing from said peak to a near zero value in said trailing portion, and said first and second filters are configured so that said leading portion includes said peak and said trailing portion does not include said peak.

10. A method as claimed in claim 8 wherein:

said communication signal is a spectrally-unconstrained signal stream;

said first filter is a pulse-shaping filter that filters said spectrally-unconstrained signal stream combined with said corrective impulse so that said entire shaped pulse is generated while concurrently pulse-shaping said spectrally-unconstrained signal stream; and

said second filter is a pulse-shaping filter that filters said spectrally-unconstrained signal stream combined with said corrective impulse so that said trailing portion of said shaped pulse is generated while concurrently pulse-shaping said spectrally-unconstrained signal stream.

11. A method as claimed in claim 8 wherein:

said communication signal is a spectrally-unconstrained signal stream; and

said first filter generates said entire shaped pulse so that said trailing portion of said shaped pulse is twice-generated, once in each of said first and second filters.

12. A method as claimed in claim 8 wherein said communication signal is a spectrally-constrained signal stream generated by a pulse-shaping filter, and said method additionally comprises:

adding said trailing portion of said shaped pulse to said communication signal to produce said overpeak-capable signal stream;

delaying said overpeak-capable signal stream to produce a delayed-overpeak-capable signal stream; and

adding said leading portion of said shaped pulse to said delayed-overpeak-capable signal stream.

13. A digital communications transmitter with constrained-envelope and constrained spectral regrowth, said transmitter comprising:

a digital modulator configured to generate a spectrally-unconstrained digital communication signal;

a first constrained-envelope generator configured to filter said digital communication signal and produce a first constrained-envelope, constrained-spectrum signal stream, and said first constrained-envelope generator including a first monitoring circuit configured to identify occurrences of overpeak events in said spectrally-unconstrained digital communication signal by determining when a first threshold is exceeded; and

a second constrained-envelope generator configured to filter said first constrained-envelope, constrained-spectrum signal stream and produce a second constrained-envelope, constrained-spectrum signal stream, and said second constrained-envelope generator including a second monitoring circuit configured to identify occurrences of overpeak events in said first constrained-envelope, constrained-spectrum signal stream by determining when a second threshold is exceeded, wherein said first threshold is greater than said second threshold.

14. A digital communications transmitter with constrained-envelope and constrained spectral regrowth, said transmitter comprising:

a digital modulator configured to generate a spectrally-unconstrained digital communication signal;

a first constrained-envelope generator configured to filter said digital communication signal and produce a first constrained-envelope, constrained-spectrum signal stream, said first constrained-envelope generator comprising;

a monitoring circuit configured to identify occurrences of overpeak events in an overpeak-capable signal stream by determining when a threshold is exceeded, said overpeak-capable signal stream being responsive to said communication signal and to a trailing portion of a shaped pulse;

an impulse generator coupled to said monitoring circuit and configured to generate a corrective impulse configured to compensate for an amount by which said overpeak-capable signal stream is in excess of said threshold; and

a filtering circuit coupled to said impulse generator and configured to generate a leading portion of said shaped pulse and said trailing portion of said shaped pulse; and

a second constrained-envelope generator configured to filter said first constrained-envelope, constrained-spectrum signal stream and produce a second constrained-envelope, constrained spectrum signal stream.

15. A digital communications transmitter as claimed in claim 14 wherein said shaped pulse is configured to have a predetermined duration, and said first constrained-envelope generator additionally comprises:

a delay circuit for delaying said communication signal by more than one-half of said predetermined duration to produce a delayed communication signal; and

a combining circuit for combining said delayed communication signal with a signal responsive to said corrective impulse.

16. A digital communications transmitter as claimed in claim 14 wherein said filtering circuit generates said leading portion of said shaped pulse in a first filter and generates said trailing portion of said shaped pulse in a second filter, said leading and trailing portions being generated concurrently.

17. A digital communications transmitter as claimed in claim 16 wherein said shaped pulse is substantially symmetrical in time, building from a near zero value to a peak in said leading portion then diminishing from said peak to a near zero value in said trailing portion, and said first and second filters are configured so that said leading portion includes said peak and said trailing portion does not include said peak.

18. A digital communications transmitter with constrained envelope and constrained spectral regrowth, said transmitter comprising:

a digital modulator configured to generate a spectrally-unconstrained digital communication signal;

a monitoring circuit coupled to said digital modulator and configured to identify occurrences of overpeak events in an overpeak-capable signal stream by determining when a threshold is exceeded, said overpeak-capable signal stream being responsive to said digital communication signal and to a trailing portion of a shaped pulse;

an impulse generator coupled to said monitoring circuit and configured to generate a corrective impulse configured to compensate for an amount by which said overpeak-capable signal stream is in excess of said threshold; and

a filtering circuit coupled to said impulse generator and configured to generate a leading portion and said trailing portion of said shaped pulse.

19. A digital communications transmitter as claimed in claim 18 wherein said shaped pulse is configured to have a predetermined duration, and said digital communications transmitter additionally comprises:

a delay circuit for delaying said spectrally unconstrained digital communication signal by more than one-half of said predetermined duration to produce a delayed communication signal; and

a combining circuit for combining said delayed communication signal with a signal responsive to said corrective impulse.

20. A digital communications transmitter as claimed in claim 19 wherein:

said combining circuit combines said corrective impulse with said delayed communication signal to produce a combined signal stream; and

said filtering circuit filters said combined signal stream in a pulse-shaping filter.

21. A digital communications transmitter as claimed in claim 18 wherein said filtering circuit generates said leading portion of said shaped pulse in a first filter and generates said trailing portion of said shaped pulse in a second filter, said leading and trailing portions being generated concurrently.

22. A digital communications transmitter as claimed in claim 21 wherein:

said first filter of said filtering circuit is a pulse-shaping filter that filters said spectrally unconstrained digital communication signal in combination with said corrective impulse so that said entire shaped pulse is generated while concurrently pulse-shaping said spectrally unconstrained digital communication signal; and

said second filter of said filtering circuit is a pulse-shaping filter that filters said spectrally unconstrained digital communication signal in combination with said corrective impulse so that said trailing portion of said shaped pulse is generated while concurrently pulse-shaping said spectrally unconstrained digital communication signal.

23. A digital communications transmitter as claimed in claim 21 wherein said first filter of said filtering circuit generates said entire shaped pulse so that said trailing portion of said shaped pulse is twice-generated, once in each of said first and second filters of said filtering circuit.

24. A digital communications transmitter with constrained-envelope and constrained spectral regrowth, said transmitter comprising:

a pulse-shaping filter configured to produce a spectrally-constrained communication signal;

a monitoring circuit coupled to said pulse spreading-filter and configured to identify occurrences of overpeak events in an overpeak-capable signal stream by determining when a threshold is exceeded, said overpeak-capable signal stream being responsive to said spectrally-constrained communication signal and to a trailing portion of a shaped pulse;

an impulse generator coupled to said monitoring circuit and configured to generate a corrective impulse configured to compensate for an amount by which said overpeak-capable signal stream is in excess of said threshold;

a filtering circuit coupled to said impulse generator and configured to filter said corrective impulse and generate said shaped pulse to exhibit a predetermined duration, with a leading portion and said trailing portion;

a delay circuit for delaying said spectrally-constrained communication signal by more than one-half of said predetermined duration to produce a delayed communication signal;

a first combining circuit coupled to said filtering circuit, to said pulse-shaping filter, and to said monitoring circuit for combining said spectrally-constrained communication signal and said trailing portion of said shaped pulse to produce said overpeak-capable signal stream; and

a second combining circuit coupled to said filtering circuit and to said delay circuit for combining said delayed communication signal with said leading portion of said shaped pulse.