MULTI-BAND CREST FACTOR REDUCTION

• US 20130163512A1
• Filed: 12/21/2011
• Published: 06/27/2013
• Est. Priority Date: 12/21/2011
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: REXBERG, Leonard, MALMQVIST, Hkan
• Granted Patent: US 9,215,120 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04B 1/0046 Decimation, i.e. data rate reduction techniques
• CPC Class Codes: H04B 1/005 adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04L 27/2624 by soft clipping
• CPC Class Codes: H04L 5/001 the frequencies being arranged in component carriers

Abstract

Clipping a widely-separated, multi-carrier signal is effectively performed without having to use a high sampling speed. Clipping is performed in a first stage at a combined signal level, but with a predetermined carrier separation of at least twice the channel bandwidth (2CBW), followed by repositioning the carriers at baseband zero frequency. After clipping, carriers are placed at their respective center frequencies with full carrier separation reintroduced in a second stage. Iterative clipping stages smooth out signal reshaping and re-settled amplitudes for combined carriers.

Claims

1. A method for crest factor reduction (CFR) of a multi-carrier signal, each carrier of the multi-carrier signal having a respective center frequency and a channel bandwidth (CBW), the method comprising:

positioning a baseband version of each of the carriers to a frequency separation between adjacent carriers of at least 2 CBW,

thereafter, combining the positioned carriers into a composite signal,

clipping the composite signal,

repositioning each carrier of the clipped composite signal back into a baseband version centered at zero frequency, and

positioning each carrier at their respective center frequency.

2. The method according to claim 1, wherein said clipping adds clipping distortion signal components to each carrier of the clipped composite signal.

3. The method according to claim 1, further comprising, after repositioning each carrier of the clipped composite signal back into a baseband version centered at zero frequency, filtering clipping distortion outside each carrier'"'"'s channel bandwidth.

4. The method according to claim 1, further comprising after clipping the composite signal:

separating out clipping distortion, and

after repositioning clipping distortion of each carrier of the clipped composite signal back into a baseband version centered at zero frequency;

filtering clipping distortion outside each carrier'"'"'s channel bandwidth, and

adding the filtered clipping distortion to the respective base band version of each carrier centered at zero frequency.

5. The method according to claim 1, further comprising iteratively applying the method.

6. The method according to claim 1, further comprising grouping the center frequencies of the carriers of the crest factor reduced multi-carrier signal into a plurality of frequency bands, each frequency band comprising a single carrier or a plurality of carriers, the edges of the frequency bands being separated in frequency by 0 Hz to several GHz.

7. The method according to claim 1, wherein positioning each carrier at their respective center frequency, includes analog RF up-conversion, digital complex frequency tuning, or a combination of both.

8. The method according to claim 1, wherein the multi-carrier signal comprises three or more carriers.

9. An apparatus for crest factor reduction (CFR) of a multi-carrier signal, each carrier of the multi-carrier signal having a respective center frequency and a channel bandwidth (CBW), the apparatus comprising processing circuitry configured to:

position a baseband version of each of the carriers to a frequency separation between adjacent carriers of at least 2 CBW,

thereafter, combine the positioned carriers into a composite signal,

clip the composite signal,

reposition each carrier of the clipped composite signal back into a baseband version centered at zero frequency, and

position each carrier of the crest factor reduced multi-carrier signal at their respective center frequency.

10. The apparatus of claim 9, wherein the processing circuitry configured to clip the composite signal is configured to add clipping distortion signal components to each carrier of the clipped composite signal.

11. The apparatus of claim 10, wherein the processing circuitry is further configured to, after repositioning each carrier of the clipped composite signal back into a baseband version centered at zero frequency, filter clip distortion outside each carrier'"'"'s channel bandwidth.

12. The apparatus of claim 11, wherein the processing circuitry configured to clip the composite signal is further configured to, after clipping the composite signal:

separate out clipping distortion, and

after repositioning clipping distortion of each carrier of the clipped composite signal back into a baseband version centered at zero frequency;

filter clipping distortion outside each carrier'"'"'s channel bandwidth, and

add the filtered clipping distortion to the respective base band version of each carrier centered at zero frequency.

13. The apparatus of claim 9, wherein the processing circuitry is further configured as a plurality of sequential replicated stages.

14. The apparatus of claim 9, wherein the processing circuitry is further configured to group the center frequencies of the carriers of the crest factor reduced multi-carrier signal into a plurality of frequency bands, each frequency band comprising a single carrier or a plurality of carriers, the edges of the frequency bands being separated in frequency by 0 Hz to several GHz.

15. The apparatus of claim 9, wherein the multi-carrier signal comprises three or more carriers.

16. The apparatus of claim 9, wherein the processing circuitry configured to reposition each carrier is further configured to reposition each carrier of the crest factor reduced multi-carrier signal at their respective center frequencies by analog RF up-conversion, digital complex frequency tuning, or a combination of both.

17. An apparatus for crest factor reduction (CFR) of a multi-carrier signal, each carrier of the multi-carrier signal having a respective center frequency and a channel bandwidth (CBW), the apparatus comprising:

first baseband carrier positioning circuitry to position a baseband version of each of the carriers to a frequency separation between adjacent carriers of at least 2 CBW,

a carrier combiner to combine the positioned carriers into a composite signal,

clipping circuitry to clip the composite signal,

second baseband carrier positioning circuitry to reposition each carrier of the clipped composite signal back into a baseband version centered at zero frequency, and

filter circuitry to filter clipping distortion outside each carrier'"'"'s channel bandwidth, and

a tuner to reposition each carrier of the clipped composite signal to their respective center frequencies.

18. The apparatus of claim 17, further comprising separator circuitry for separating out clipping distortion, and adding circuitry to add the filtered clipping distortion to the respective base band version of each carrier centered at zero frequency.