Symbol boundary detector method and device for OFDM systems

• US 7,203,245 B1
• Filed: 03/31/2003
• Issued: 04/10/2007
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Murphy, Timothy F.
• Primary Examiner(s): Tran; Khai
• Application Number:
  US10/403,552
• Time in Patent Office: 1,471 Days
• Field of Search: 375/260, 375/232, 375/229, 370/206, 370/386, 455/403, 455/452
• US Class Current: 375/260
• CPC Class Codes: H04L 1/0047 Decoding adapted to other signal detection operation in conjunction with sequence estimation or equalization H04L25/03286
• CPC Class Codes: H04L 1/0052 Realisations of complexity reduction techniques, e.g. pipelining or use of look-up tables
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

The present invention relates to the field of data communication electronics and to a wired or wireless signal transmitter or receiver and methods providing improved signal-to-noise ratio (SNR) performance for the reception of data packets transmitted in the form of symbols modulated onto a signal. More particularly, methods and methods are disclosed for detecting the preamble and symbol boundaries of received data packets encoded with OFDM and other multi-carrier symbol transmission systems. Also disclosed are combinations of sensitive preamble detection and data payload and/or signal field encoding methods to spread data redundantly, to improve reception under a low SNR condition. This invention may be applied to a variety of standards utilizing OFDM and similar technologies, including IEEE 802.11a, Hiperlan/2 and MMAC. Particular aspects of the present invention are disclosed in the claims, specification and drawings.

Claims

1. A method of aligning input signal stream processing to a boundary between instances of a repeated symbol, wherein the input signal stream includes complex samples, the complex samples represent a signal band that includes a plurality of subcarriers, and at least some of the subcarriers are modulated with the repeated symbol, the method including:

calculating complex FFT values for a set of the complex samples, wherein the set spans an actual boundary between two repeated symbols;

determining an average phase angle difference between the actual boundary and the set of the complex samples, utilizing the calculated complex FFT values and expected FFT values for the pairs of subcarriers; and

aligning successive sets of the complex samples relative to the boundary.

2. The method of claim 1, further including determining from the average phase angle difference an offset between the set of complex samples and the boundary between the two repeated symbols.

3. The method of claim 1, wherein the average phase angle difference corresponds to a function of

4. The method of claim 3, wherein L has a value of 0, 1, or −

1.

5. The method of claim 1, wherein the signal and the two repeated symbols comply with an IEEE 802.11 standard, and the average phase angle difference corresponds to a function of

6. The method of claim 5, wherein L, has a value of 1+0j or −

1+0j.

7. A device that aligns processing of an input signal stream to a boundary between instances of a repeated symbol, wherein the input signal stream includes complex samples, the complex samples represent a signal band that includes a plurality of subcarriers, and at least some of the subcarriers are modulated with the repeated symbol, the device including logic to:

calculate complex FFT values for a set of the complex samples, wherein the set spans an actual boundary between two repeated symbols;

determine an average phase angle difference between the actual boundary and the set of the complex samples, utilizing the calculated complex FFT values and expected FFT values for the pairs of subcarriers; and

align successive sets of the complex samples relative to the boundary.

8. The device of claim 7, further including logic to determine from the average phase angle difference an offset between the set of complex samples and the boundary between the two repeated symbols.

9. The device of claim 7, implemented in an FPGA.

10. The device of claim 7, implemented in a gate array.

11. The device of claim 7, implemented on an integrated circuit.

12. The device of claim 7, implemented on an integrated circuit and further including an onboard analog to digital converter that produces the complex samples.

13. The device of claim 7, wherein the average phase angle difference corresponds to a function of

14. The device of claim 13, wherein L has a value of 0, 1, or −

1.

15. The device of claim 7, wherein the signal and the two repeated symbols comply with an IEEE 802.11 standard, and the average phase angle difference corresponds to a function of

16. The device of claim 15, wherein L has a value of 1+0j or −

1+0j.