Spectral shaping in multiband OFDM transmitter with clipping

• US 7,505,522 B1
• Filed: 10/06/2004
• Issued: 03/17/2009
• Est. Priority Date: 10/06/2003
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Staccato Communications Incorporated
• Inventors: Larsson, Torbjorn A.
• Primary Examiner(s): Fan, Chieh M
• Assistant Examiner(s): Lee, Siu M
• Application Number:
  US10/960,430
• Time in Patent Office: 1,623 Days
• Field of Search: 375260-267
• US Class Current: 375/260
• CPC Class Codes: H04L 25/03828 Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties partial response systems H04L25/497
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2623 Reduction thereof by clipping

Abstract

A method of shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum is disclosed. The method comprises receiving an input signal that has a frequency spectrum that includes a frequency peak, and limiting the amplitude of the frequency peak to a predetermined clip level. An orthogonal frequency division multiplexing (OFDM) transmitter is disclosed. The OFDM transmitter comprises an input interface configured to receive an input signal that includes a frequency spectrum that includes a frequency peak, and a processor coupled to the input interface, configured to limit the amplitude of the frequency peak to a predetermined clip level.

Claims

1. A method of shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum, comprising:

receiving an input signal at an interface; and

inserting a modified synchronization sequence in the input signal by a processor to generate an amplitude limited signal that has a substantially even frequency spectrum;

wherein;

the modified synchronization sequence includes one or more reduced spectral peaks in a preamble waveform; and

the modified synchronization sequence was previously derived, including by;

applying a Fourier transform to a synchronization sequence to obtain a plurality of spectral components;

selecting a spectral component from the plurality of spectral components;

determining the clip level relative to the amplitude of the selected spectral component; and

clipping the plurality of spectral components to the clip level.

2. A method as recited in claim 1, wherein the modified synchronization sequence corresponds to a preamble.

3. A method as recited in claim 1, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a maximum amplitude.

4. A method as recited in claim 1,

wherein the clip level is selected to be approximately 3 dB below the amplitude of the selected spectral component.

5. A method as recited in claim 1, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a minimum amplitude.

6. A method as recited in claim 1, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a minimum amplitude and the clip level is determined to be less than or equal to the minimum amplitude.

7. A method as recited in claim 1, the modified synchronization sequence is selected from a plurality of pre-computed, modified synchronization sequences that correspond to a plurality of preamble sequences.

8. An orthogonal frequency division multiplexing (OFDM) transmitter comprising:

an input interface configured to receive an input signal; and

a processor coupled to the input interface, configured to insert in the input signal a modified synchronization sequence to generate a clipped signal that has a substantially flat frequency spectrum, wherein;

the modified synchronization sequence includes one or more reduced spectral peaks in a preamble waveform; and

the modified synchronization sequence was previously computed, including by;

applying a Fourier transform to the input signal to obtain a plurality of spectral components;

selecting a spectral component from the plurality of spectral components;

determining the clip level relative to the amplitude of the selected spectral component; and

clipping the plurality of spectral components to the clip level.

9. An OFDM transmitter as recited in claim 8, wherein the modified synchronization sequence corresponds to a preamble.

10. An OFDM transmitter as recited in claim 8, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a maximum amplitude.

11. An OFDM transmitter as recited in claim 8,

wherein the clip level is selected to be approximately 3 dB below the amplitude of the selected spectral component.

12. An OFDM transmitter as recited in claim 8, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a minimum amplitude.

13. An OFDM transmitter as recited in claim 8, wherein selecting a spectral component from the plurality of spectral components includes selecting a spectral component with a minimum amplitude and the clip level is determined to be less than or equal to the minimum amplitude.

14. An OFDM transmitter as recited in claim 8, wherein the modified synchronization sequence is selected from a plurality of pre-computed, modified synchronization sequences that correspond to a plurality of preamble sequences.