Block-Based Crest Factor Reduction

• US 20140044215A1
• Filed: 08/07/2012
• Published: 02/13/2014
• Est. Priority Date: 08/07/2012
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Mundarath, Jayakrishnan C., Dehner, Leo G., Kotecha, Jayesh H., Rashev, Peter Z.
• Granted Patent: US 9,100,253 B2
• Time in Patent Office: Days
• US Class Current: 375/297
• CPC Class Codes: H04L 27/2624 by soft clipping

Abstract

A method and apparatus for a radio base station (200) generates a multicarrier communication signal having a reduced crest factor by processing a block of samples (231) with a peak search window (271) to identify and suppress signal peaks exceeding a power threshold value.

Claims

1. An apparatus for generating a multicarrier communication signal having a reduced crest factor, comprising:

a sampling block unit for storing a block of input samples from a multicarrier communication signal; and

a crest factor reduction unit coupled to the sampling block memory for performing block-based processing to detect one or more signal peaks in the block of input samples stored in the sampling block memory which exceed a specified power threshold, and to cancel at least a first selected signal peak selected from the one or more signal peaks by applying a first cancellation pulse to the block of input samples stored in the sampling block memory which is phase-aligned with the selected signal peak.

2. The apparatus of claim 1, where the apparatus comprises an integrated circuit for a wireless communication device comprising at least a first radio frequency (RF) signal path connected between the integrated circuit and at least a first antenna, the integrated circuit comprising at least a first vector signal processor for implementing the crest factor reduction unit, and a first internal buffer memory for implementing the sampling block unit.

3. The apparatus of claim 1, where the sampling block unit stores a block length of samples collected from the multicarrier communication signal, where each stored sample has a corresponding sample index for locating said sample in the sampling block unit.

4. The apparatus of claim 1, where the crest factor reduction unit is configured to perform non-sequential, block-based processing on the block of input samples stored in the sampling block memory.

5. The apparatus of claim 1, where the crest factor reduction unit is configured to perform block-based processing in a plurality of iterative passes on the block of input samples stored in the sampling block memory and in a way that real-time transmission continuity of the multicarrier communication signals is not impacted.

6. The apparatus of claim 1, where the crest factor reduction unit is configured to detect one or more signal peaks in the block of input samples by calculating a differential signal envelope from the block of input samples stored in the sampling block memory which exceed the specified power threshold.

7. The apparatus of claim 1, where the crest factor reduction unit is configured to use a peak search window when searching the block of input samples stored in the sampling block memory to detect one or more signal peaks.

8. The apparatus of claim 1, where the crest factor reduction unit is configured to use one or more predetermined cancellation criteria when cancelling at least the first selected largest signal peak to implement a minimum separation requirement between adjacent cancelled peaks by sequentially repeating application of the one or more predetermined cancellation criteria to select a plurality of cancelled peaks within the block of input signals.

9. The apparatus of claim 8, where a first predetermined cancellation criterion is that a minimum separate distance exists between any cancelled signal peaks and where the canceled peaks are associated with the largest peak power levels within the processed block of input signals after further processing such as rate interpolation and/or digital to analog conversion.

10. The apparatus of claim 1, where the crest factor reduction unit is configured to simultaneously cancel a plurality of selected signal peaks selected from the one or more signal peaks by applying a corresponding plurality of cancellation pulses to the block of input samples stored in the sampling block memory which are phase-aligned with the plurality of selected signal peaks.

11. The apparatus of claim 1, further comprising a memory device for storing cross-over samples and differential values from adjacent blocks of input samples to ensure continuity of processing between the blocks of input samples.

12. The apparatus of claim 1, where the crest factor reduction unit is configured to perform block-based processing by using a peak search window to select a first low rate signal peak that exceeds the specified power threshold in the block of input samples, up-sampling a plurality of low rate input samples in a defined neighborhood around the first low rate signal peak to generate a plurality of up-sampled values, and identifying a true signal peak from the plurality of up-sampled values, where the true signal peak has a specified phase and amplitude.

13. The apparatus of claim 12, where the crest factor reduction unit is configured to cancel at least the first selected signal peak by using the specified phase of the true signal peak to adjust the phase of the first cancellation pulse.

14. The apparatus of claim 1, where the crest factor reduction unit comprises:

a global peak search unit coupled to the sampling block memory for identifying K signal areas of the multicarrier communication signal where one or more true signal peaks in the block of input samples stored in the sampling block memory can be found at an intermediate signal sampling rate L;

a true peak search unit coupled to the global peak search unit for identifying selected parameters of the one or more true signal peaks in the K signal areas by searching a peak vicinity area of signal area samples at higher signal sampling rate M, where L<

M; and

a cancellation waveform generator unit for generating the cancellation pulse for each of the one or more true signal peaks by scaling and time-aligning a cancellation waveform based on the selected parameters of the corresponding true signal peak.

15. The apparatus of claim 14, where the global peak search unit comprises:

an L-phase interpolation filter for generating K signal phases from the block of input samples stored in the sampling block memory;

a peak estimation unit for analyzing the K signal phases at low signal sampling rate S<

L to determine one or more power parameters; and

a true peak area selection unit for selecting one or more of the K signal phases for output to the true peak search unit based on the one or more power parameters for each signal phase.

16. A method for generating a multicarrier communication signal having a reduced crest factor, comprising:

generating a first multicarrier communication signal from a plurality of baseband transmission signals;

storing a block of input samples from the first multicarrier communication signal in a sampling block memory;

performing non-sequential, block-based processing on the block of input samples stored in the sampling block memory to suppress one or more signal peaks in the block of input samples by generating one or more cancellation pulse waveforms; and

applying the one or more cancellation pulse waveforms to the block of input samples stored in the sampling block memory to generate a second multicarrier communication signal having a reduced crest factor.

17. The method of claim 16, where performing non-sequential, block-based processing on the block of input samples comprises:

detecting one or more signal peaks in the block of input samples which exceed a specified power threshold, and

suppressing at least a first selected signal peak selected from the one or more signal peaks by applying a first cancellation pulse to the block of input samples stored in the sampling block memory which is phase-aligned with the first selected signal peak.

18. The method of claim 16, where performing non-sequential, block-based processing on the block of input samples comprises:

using a peak search window to select a first low rate signal peak from the block of input samples that exceeds a specified power threshold;

up-sampling a plurality of low rate input samples in a defined neighborhood around the first low rate signal peak to generate a plurality of up-sampled values; and

identifying a true signal peak from the plurality of up-sampled values, where the true signal peak has a specified phase and amplitude.

19. The method of claim 16, where performing non-sequential, block-based processing on the block of input samples comprises:

identifying K signal areas from the block of input samples stored in the sampling block memory where one or more true signal peaks can be found at an intermediate signal sampling rate L;

identifying selected parameters of the one or more true signal peaks in the K signal areas by searching a peak vicinity area of signal area samples at higher signal sampling rate M, where L<

M; and

generating a cancellation pulse waveform for each of the one or more true signal peaks by scaling and time-aligning a cancellation waveform based on the selected parameters of the corresponding true signal peak.

20. The method of claim 16, where the steps of performing non-sequential, block-based processing and applying the one or more cancellation pulse waveforms are iteratively applied with a plurality of passes to the block of input samples stored in the sampling block memory.