Modified OFDM subcarrier profile

• US 20050117670A1
• Filed: 08/27/2004
• Published: 06/02/2005
• Est. Priority Date: 08/27/2003
• Status: Active Grant

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Webster, Mark A., Seals, Michael J., Halford, Steven D., Garrett, Albert L.
• Granted Patent: US 7,272,109 B2
• Time in Patent Office: Days
• US Class Current: 375/330
• CPC Class Codes: H04L 27/2602 Signal structure

Abstract

A 10 MHz channelized orthogonal frequency division multiplexing (OFDM) transmitter is provided that communicates using a modified OFDM packet structure with a half-rate oscillator having standard accuracy. The transmitter has an inverse fast fourier transform (IFFT) data processor that appends an outer pair of data subcarriers on either end of an OFDM subcarrier profile. An IFFT long sync processor appends an outer pair of binary phase shift key (BPSK) subcarriers on either end of an OFDM long sync subcarrier profile. By copying or appending the information of the data subcarriers closest to zero Hz. to more robust locations, 10 MHz channelized OFDM can be achieved with half-rate clocks and 20 PPM oscillators.

Claims

1. A 10 MHz channelized OFDM transmitter that communicates using a modified OFDM packet structure with a half-rate oscillator having standard accuracy, comprising:

an IFFT data processor that appends an outer pair of data subcarriers on either end of an OFDM subcarrier profile; and

an IFFT long sync processor that appends an outer pair of BPSK subcarriers on either end of an OFDM long sync subcarrier profile.

2. The 10 MHz channelized OFDM transmitter of claim 1, wherein said IFFT data processor shifts positive-frequency OFDM subcarriers up by one IFFT bin position and that shifts negative-frequency OFDM subcarriers down by one IFFT bin position.

3. The 10 MHz channelized OFDM transmitter of claim 2, wherein said IFFT data processor shifts each OFDM pilot tone and data subcarrier by one position.

4. The 10 MHz channelized OFDM transmitter of claim 2, wherein said IFFT data processor maintains frequency positions of OFDM pilot tones and shifts data subcarriers around said OFDM pilot tones.

5. The 10 MHz channelized OFDM transmitter of claim 1, wherein said IFFT data processor duplicates a pair of inner-most data subcarriers to said appended outer pair of data subcarriers.

6. The 10 MHz channelized OFDM transmitter of claim 5, wherein said IFFT data processor copies a pair of complex coefficients corresponding with said inner-most data subcarriers to bins of an IFFT block associated with said appended outer pair of data subcarriers for inverse Fourier processing.

7. The 10 MHz channelized OFDM transmitter of claim 5, further comprising:

said IFFT data processor copying a pair of complex coefficients corresponding with said inner-most data subcarriers to first and second outer complex coefficients, respectively;

an IFFT block that generates original time domain samples using said OFDM subcarrier profile;

a tone generator device that provides time domain samples corresponding to first and second outer data subcarrier tones;

a first multiplier that multiplies said first complex coefficient by said time domain samples corresponding to said first outer data subcarrier tone for generating first data subcarrier time domain samples;

a second multiplier that multiplies said second complex coefficient by said time domain samples corresponding to said second outer data subcarrier tone for generating second data subcarrier time domain samples; and

an adder that adds said original time domain samples to said first data subcarrier time domain samples and to said second data subcarrier time domain samples.

8. The 10 MHz channelized OFDM transmitter of claim 7, wherein said tone generator comprises:

a memory device that stores time domain samples of said first outer data subcarrier tone; and

a conjugate block that receives and converts said time domain samples of first outer data subcarrier tone into time domain samples of said second outer data subcarrier tone.

9. The 10 MHz channelized OFDM transmitter of claim 1, wherein said IFFT long sync processor comprises a first IFFT long sync processor that loads standard OFDM long sync subcarriers and a second IFFT long sync processor that appends said outer pair of BPSK subcarriers.

10. A 10 MHz channelized OFDM receiver that communicates using a modified OFDM packet structure with a half-rate oscillator having standard accuracy, comprising:

an IFFT data processor that reads an outer pair of data subcarriers on either end of an OFDM subcarrier profile; and

an IFFT long sync processor that reads an outer pair of BPSK subcarriers on either end of an OFDM long sync subcarrier profile.

11. The 10 MHz channelized OFDM receiver of claim 10, wherein said FFT data processor reads positive-frequency OFDM subcarriers shifted up by one IFFT bin position and that reads negative-frequency OFDM subcarriers shifted down by one FFT bin position.

12. The 10 MHz channelized OFDM receiver of claim 11, wherein said FFT data processor reads each OFDM pilot tone and data subcarrier shifted by one position.

13. The 10 MHz channelized OFDM receiver of claim 11, wherein said FFT data processor reads OFDM pilot tones at standard locations and reads data subcarriers shifted around said OFDM pilot tones.

14. The 10 MHz channelized OFDM receiver of claim 10, wherein said FFT data processor reads a pair of duplicated data subcarriers at said appended outer pair of data subcarriers.

15. The 10 MHz channelized OFDM receiver of claim 14, wherein said FFT data processor selected from among original data subcarriers and said duplicated data subcarriers.

16. The 10 MHz channelized OFDM receiver of claim 14, wherein said FFT data processor coherently combines original data subcarriers with said duplicated data subcarriers.

17. The 10 MHz channelized OFDM receiver of claim 10, further comprising:

said IFFT long sync processor comprising a first FFT long sync processor that reads standard OFDM long sync subcarriers and that computes a first FEQ output;

said IFFT long sync processor comprising a second IFFT long sync processor that reads said outer pair of BPSK subcarriers and that computes a second FEQ output; and

select logic that discards an inner-most pair of long sync subcarriers.