OPTIMIZED CLIPPING FOR PEAK-TO-AVERAGE POWER RATIO REDUCTION

• US 20080101502A1
• Filed: 09/24/2007
• Published: 05/01/2008
• Est. Priority Date: 10/30/2006
• Status: Active Grant

• Current Assignee: Maxlinear Incorporated
• Original Assignee: Quantenna Communications, Inc. (ON Semiconductor Corporation)
• Inventors: Navidpour, Seyed M., Farrokhi, Farrokh, Goldsmith, Andrea
• Granted Patent: US 8,073,073 B2
• Time in Patent Office: Days
• US Class Current: 375/296
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 27/2623 Reduction thereof by clipping

Abstract

A technique for PAR reduction involves producing an optimized clipping pulse. The optimized clipping pulse may be designed to meet certain requirements, such as a spectral mask target or an EVM target, when applied to a signal.

Claims

1. A method comprising:

providing a signal;

repeating for a plurality of iterations;

finding one or more peaks in the time domain associated with the signal;

clipping the one or more peaks using an optimized clipping pulse;

updating the signal.

2. The method of claim 1, wherein the iterations may be referred to as iterative cancellation, further comprising:

providing an error vector magnitude (EVM) target;

using a peak clipping pulse with iterative cancellation to meet the EVM target while minimizing peak-to-average ratio (PAR).

3. The method of claim 1, wherein the iterations may be referred to as iterative cancellation, further comprising:

providing spectral mask specifications;

using a peak clipping pulse with iterative cancellation to meet the spectral mask specifications while minimizing peak-to-average ratio (PAR).

4. The method of claim 1, wherein the iterations may be referred to as iterative cancellation, further comprising:

providing an error vector magnitude (EVM) target;

providing spectral mask specifications;

using a peak clipping pulse with iterative cancellation to meet the EVM target and spectral mask specifications.

5. The method of claim 1, wherein finding the one or more peaks includes finding an amplitude and location in time of at least one of the one or more peaks.

6. The method of claim 1, wherein reducing the one or more peaks includes shifting and scaling a peak canceller pulse.

7. The method of claim 1, wherein updating the signal includes subtracting a peak canceller pulse from the signal.

8. The method of claim 1, further comprising designing the peak clipping pulse to be roughly flat across a band of interest so as not to introduce in-band distortion.

9. The method of claim 1, further comprising:

limiting a spectral mask in the frequency domain;

optimizing the clipping pulse in the frequency domain without specific tone or frequency band constraints.

10. The method of claim 1, further comprising:

limiting a spectral mask in the frequency domain;

optimizing the clipping pulse in the time domain without specific tone or frequency band constraints.

11. A system comprising:

a peak clipping pulse generator;

a plurality of peak-to-average ratio (PAR) reduction stages coupled to the peak clipping pulse generator,

wherein, in operation,

a first of the PAR reduction (PARR) stages receives a signal,

the peak clipping pulse generator provides a first peak clipping pulse to the first of the PARR stages,

the first of the PARR stages applies the first peak clipping pulse to the signal to generate a first stage PARR signal;

the first of the PARR stages provides the first stage PARR signal to one or more later stages of the plurality of PARR stages,

a last of the one or more later PARR stages outputs a PARR signal.

12. The system of claim 11, further comprising an OFDM modulator, wherein, in operation, the OFDM modulator provides the signal to the first of the PARR stages.

13. A system comprising:

a peak detector coupled to a signal input;

a pulse generator;

a shifter coupled to the peak detector and the pulse generator;

an adder coupled to the signal input and the shifter;

a signal updater coupled to the adder and a signal output;

wherein, in operation,

a first signal is received at the signal input,

the peak detector detects peak time and amplitude of the first signal,

the pulse generator generates an optimized peak clipping pulse,

the shifter receives at least the peak time and amplitude of the first signal from the peak detector and the optimized peak clipping pulse from the pulse generator and produces a shifted clipping pulse,

the adder receives the first signal and the shifted clipping pulse and scales the first signal with the shifted clipping pulse,

the signal updater receives the scaled and shifted clipping pulse and subtracts the scaled and shifted clipping pulse from the first signal to produce a second signal.

14. The system of claim 13, wherein, in operation, the second signal is output on the signal output.

15. The system of claim 13, wherein the optimized peak clipping pulse is a first optimized peak clipping pulse, the shifted clipping pulse is a first shifted clipping pulse, the scaled and shifted clipping pulse is a first scaled and shifted clipping pulse, and wherein, in operation,

the peak detector detects peak time and amplitude of the second signal,

the pulse generator generates a second optimized peak clipping pulse,

the shifter receives at least the peak time and amplitude of the second signal from the peak detector and the second optimized peak clipping pulse from the pulse generator and produces a second shifted clipping pulse,

the adder receives the second signal and the second shifted clipping pulse and scales the second signal with the second shifted clipping pulse,

the signal updater receives the second scaled and shifted clipping pulse and subtracts the second scaled and shifted clipping pulse from the second signal to produce a third signal.

16. The system of claim 13, further comprising a second stage peak-to-amplitude ratio (PAR) reducer, wherein, in operation,

the second signal is provided to the second stage PAR reducer,

the second stage PAR reducer PAR reduces the second signal,

the second stage PAR reducer outputs the PAR reduced signal.

17. The system of claim 13, wherein the first signal includes an orthogonal frequency-division multiplexing (OFDM) signal.

18. The system of claim 13, wherein:

the peak clipping pulse is roughly flat across a band of interest so as not to introduce in-band distortion,

the peak clipping pulse complies with spectral mask and error vector magnitude (EVM) requirements.

19. The system of claim 13, wherein the peak detector, the pulse generator, the shifter, the adder, and the signal updater comprise a first PAR reducer, further comprising:

a modulator coupled to the first PAR reducer;

one or more additional PAR reducers;

one or more additional modulators respectively coupled to the one or more additional PAR reducers;

a multiple-input multiple-output (MIMO) spatial mapper coupled to the modulator and the one or more additional modulators;

wherein, in operation, the spatial mapper maps a plurality of MIMO signals onto respective ones of the modulator and one or more additional modulators and the modulator and one or more additional modulators provide the plurality of MIMO signals to respective ones of the first PAR reducer and one or more additional PAR reducers.

20. The system of claim 13, wherein the peak detector, the pulse generator, the shifter, the adder, and the signal updater comprise a first PAR reducer, further comprising:

a plurality of PAR reducers, including the first PAR reducer;

a stream parser;

a modulator/mapper block, coupled to the stream parser, having a plurality of modulator/mappers;

a multiple-input multiple-output (MIMO) space-time encoder coupled to the modulator/mapper block;

a MIMO spatial mapper coupled to the MIMO space-time encoder;

an OFDM modulator block, coupled to the MIMO spatial mapper and the plurality of PAR reduction stages, having a plurality of OFDM modulators;

wherein, in operation,

the stream parser receives a raw signal,

the stream parser breaks the signal into a plurality of separate signals,

the modulator/mappers each receive and process the separate signals;

the modulator/mappers each provide the separate signals to the MIMO space-time encoder,

the MIMO space-time encoder provides the separate signals to the MIMO spatial mapper,

the MIMO spatial mapper provides the separate signals to respective ones of the OFDM modulators,

the OFDM modulators provide the separate signals to respective ones of the PAR reducers, wherein one of the separate signals is the first signal.

21. A method comprising:

generating an initial clipping pulse;

evaluating a peak-to-average ratio reduction (PARR) algorithm with the initial clipping pulse on one or more OFDM signals;

until performance is acceptable,

adjusting pulse properties, yielding an adjusted clipping pulse;

evaluating the PARR algorithm with the adjusted clipping pulse on one or more OFDM signals;

providing the adjusted clipping pulse as an optimized clipping pulse.

22. The method of claim 21 wherein the pulse properties include one or more of the properties selected from the group consisting of:

peak pulse width, shape of rolloff, and off-peak pulse width.

23. The method of claim 21, further comprising:

providing an error vector magnitude (EVM) target;

providing spectral mask specifications;

designing a peak clipping pulse to meet the EVM target and spectral mask specifications, without restrictions in the frequency domain, when applied to a signal.