Methods and Apparatus for Reducing Average-to-Minimum Power Ratio in Communications Signals

• US 20100316164A1
• Filed: 06/11/2009
• Published: 12/16/2010
• Est. Priority Date: 06/11/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Wang, Hua, Liang, Paul Cheng-Po, Mori, Kenichi
• Granted Patent: US 8,385,464 B2
• Time in Patent Office: Days
• US Class Current: 375/298
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04L 27/361 Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation
• CPC Class Codes: H04L 27/363 using non - square modulating pulses, modulators specifically designed for this transmission of non - square QAM H04L27/3494

Abstract

A baseband circuit for a communications transmitter includes a baseband modulator, a pulse-shaping filter, and an AMPR reduction circuit. The baseband modulator is configured to generate a sequence of symbols formatted in accordance with a non-constant envelope modulation scheme. The pulse-shaping filter is configured to band-limit the sequence of samples to provide a sequence of samples. The AMPR reduction circuit is configured to analyze and modify one or more samples in the sequence of samples, if a sample in the sequence of samples that has been previously analyzed by the AMPR reduction circuit is determined to have a magnitude less than a predetermined low-magnitude threshold.

Claims

1. A baseband circuit for a communications transmitter, comprising:

a baseband modulator configured to generate a sequence of symbols formatted in accordance with a non-constant envelope modulation scheme;

a pulse-shaping filter configured to band-limit said sequence of samples and provide a sequence of samples; and

an average-to-minimum power ratio (AMPR) reduction circuit configured to analyze and modify one or more samples in said sequence of samples if a sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than a low-magnitude threshold.

2. The baseband circuit of claim 1 wherein said AMPR reduction circuit comprises a pulse generator configured to generate and combine an AMPR-reducing pulse with samples in said sequence of samples if the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than a low-magnitude threshold.

3. The baseband circuit of claim 2 wherein said sequence of samples is processed in terms of its in-phase (I) and quadrature-phase (Q) components and said pulse generator is configured to generate an AMPR-reducing pulse having I and Q components.

4. The baseband circuit of claim 2 wherein said AMPR reduction circuit comprises a plurality of registers configured to receive and store said sequence of samples.

5. The baseband circuit of claim 4 wherein said plurality of registers and said pulse generator are formed as in-phase channel (I-channel) and quadrature-phase channel (Q-channel) tapped delay lines.

6. The baseband circuit of claim 4 wherein said AMPR reduction circuit includes a feedback path from said plurality of registers to said pulse generator.

7. The baseband circuit of claim 6 wherein said feedback path includes a threshold comparator configured to compare the magnitude of the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit to said low-magnitude threshold.

8. The baseband circuit of claim 6 wherein said feedback path includes an insertion vector generator configured to generate an insertion vector for scaling the AMPR-reducing pulse generated by said pulse generator.

9. The baseband circuit of claim 8 wherein said insertion vector generator is configured to generate a complex insertion vector and said pulse generator is configured to generate a complex pulse that alters both the magnitude and phase of said one or more samples in said sequence of samples.

10. A method of reducing the average-to-minimum power ratio (AMPR) in a communications signal, comprising:

determining whether the magnitude of a first sample in a sequence of samples of a communications signal is less than a low-magnitude threshold;

if the magnitude of said first sample is determined to be less than said low magnitude threshold, modifying said first sample and a second sample in the sequence of samples that follows said first sample;

determining whether the magnitude of the previously modified second sample is less than said low-magnitude threshold; and

if the magnitude of said previously modified second sample is determined to be less than said low-magnitude threshold, further modifying said previously modified second sample.

11. The method of claim 10 wherein modifying said first sample comprises increasing the magnitude of said first sample to or above said low-magnitude threshold, modifying said second sample comprises increasing the magnitude of said second sample, and further modifying said previously modified second sample comprises increasing the magnitude of said previously modified second sample to or above said low-magnitude threshold.

12. The method of claim 11 wherein further modifying said previously modified second sample comprises altering the phase of said previously modified second sample in a direction perpendicular to a signal trajectory between said first sample and said previously modified second sample.

13. The method of claim 10 wherein further modifying said previously modified second sample comprises:

calculating an insertion vector having an insertion angle and insertion phase;

generating an AMPR-reducing pulse having a magnitude and phase determined by the insertion angle and insertion phase of said insertion vector; and

inserting said AMPR-reducing pulse in the temporal vicinity of said previously modified second sample to reduce the AMPR of said communications signal.

14. A communications transmitter, comprising:

a baseband processor configured to generate a sequence samples of a baseband signal, each sample of said sequence of samples having an in-phase (I) coordinate and a quadrature (Q) phase coordinate, said baseband processor including an average-to-minimum power ratio (AMPR) reduction circuit configured to produce a modified sequence of samples by modifying the I and Q coordinates of one or more samples in said sequence of samples if a sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than a low-magnitude threshold;

an upconverter coupled to said baseband processor; and

a power amplifier coupled to said upconverter.

15. The communications transmitter of claim 14 wherein said AMPR reduction circuit comprises a pulse generator configured to generate an AMPR-reducing pulse having I and Q coordinates that are combined with I and Q coordinates of said one or more samples in said sequence of samples if the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than said low-magnitude threshold.

16. The communications transmitter of claim 15 wherein said pulse generator comprises I-channel and Q-channel tapped delay lines.

17. The communications transmitter of claim 15 wherein said AMPR reduction circuit includes a feedback path having a threshold comparator configured to compare the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit to said low-magnitude threshold.

18. The communications transmitter of claim 17 wherein said feedback path further includes an insertion vector generator configured to generate an insertion vector for scaling the AMPR-reducing pulse generated by said pulse generator if said threshold comparator determines that the magnitude of the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is less than said low-magnitude threshold.

19. A polar transmitter, comprising:

a baseband processor configured to generate a sequence samples of a baseband signal, each sample of said sequence of samples having an in-phase (I) coordinate and a quadrature (Q) phase coordinate, said baseband processor including an average-to-minimum power ratio (AMPR) reduction circuit configured to produce a modified sequence of samples by modifying the I and Q coordinates of one or more samples in said sequence of samples if a sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than a low-magnitude threshold;

a rectangular-to-polar converter configured to convert said modified sequence of samples to polar-coordinate amplitude and angle component signals;

an amplitude modulator configured to generate an amplitude-modulated power supply signal from amplitude information in said polar-coordinate amplitude component signal;

an angle modulator configured to generate an angle-modulated signal from angle information in said polar-coordinate angle component signal; and

a power amplifier configured to generate an angle- and amplitude-modulated carrier signal from said amplitude-modulated power supply signal and said polar-coordinate angle-modulated signal.

20. The polar transmitter of claim 19 wherein said AMPR reduction circuit comprises a pulse generator configured to generate an AMPR-reducing pulse having I and Q coordinates that are combined with I and Q coordinates of said one or more samples in said sequence of samples if the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is determined to have a magnitude less than said low-magnitude threshold.

21. The polar transmitter of claim 20 wherein said pulse generator comprises I-channel and Q-channel tapped delay lines.

22. The polar transmitter of claim 20 wherein said AMPR reduction circuit includes a feedback path having a threshold comparator configured to compare the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit to said low-magnitude threshold.

23. The polar transmitter of claim 22 wherein said feedback path further includes an insertion vector generator configured to generate an insertion vector for scaling the AMPR-reducing pulse generated by said pulse generator if said threshold comparator determines that the magnitude of the sample in said sequence of samples that has been previously analyzed by said AMPR reduction circuit is less than said low-magnitude threshold.