Method and apparatus for decoding orthogonal codes

• US 7,200,192 B2
• Filed: 12/26/2002
• Issued: 04/03/2007
• Est. Priority Date: 12/26/2002
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: ZyDAS Technology Corp. (Qualcomm, Inc.)
• Inventors: Wei, Lee-Fang, Jauh, Yuh-Ren, Wang, Bor-Chin, Hwang, Wen-Yih
• Primary Examiner(s): Bocure; Tesfaldet
• Assistant Examiner(s): PANWALKAR, VINEETA S
• Application Number:
  US10/329,864
• Publication Number:
  US 20040125884A1
• Time in Patent Office: 1,559 Days
• Field of Search: 375/130, 375/150, 375140-142, 375/147, 375/148, 375/229, 375/232, 375/233, 375/265, 375259-261, 375/285, 375/316, 375/340, 375/341, 375/346, 375/350, 714/792, 714/794, 714/796, 714/780, 714/786, 714/746, 714/699, 714/752
• US Class Current: 375/341
• CPC Class Codes: H04L 23/02 adapted for orthogonal signalling
• CPC Class Codes: H04L 25/03203 Trellis search techniques
• CPC Class Codes: H04L 25/03267 with decision feedback equalisers
• CPC Class Codes: H04L 25/03337 Arrangements involving per-survivor processing

Abstract

An approach for decoding a substantially orthogonal code, such as a CCK code, based on its trellis diagram is provided. Compared to the conventional decoder based on codeword correlation, the unconventional decoder here has the advantage that it can work together with a decision feedback equalizer without suffering from the error propagation effect of the equalizer. In other words, the unconventional decoder makes joint decision feedback equalizer and decoder workable, which in turn enables reliable transmission of a signal encoded by a substantially orthogonal code over a multi-path channel.

Claims

1. A method for receiving signal and recovering data from a communication channel, comprising the steps of:

(a) receiving channel-impaired symbols of a sequence of codewords from said communication channel, said sequence of codewords being generated by applying a substantially orthogonal channel code to said data, each codeword being a sequence of symbols, each symbol being selected from a signal constellation;

(b) decoding said channel-impaired symbols to recover said data using a decoding process that is based on a trellis diagram;

said decoding utilizing a plurality of feedback equalizers to respectively process for each of said channel-impaired symbols a plurality of tentative decisions.

2. The method of claim 1, wherein said substantially orthogonal channel code is a CCK code used in a wireless local area network.

3. The method of claim 1, wherein said trellis diagram has at least two stages of state transitions that start from a beginning state and go through at least one stage of intermediate states before reaching an ending state, each of said state transitions being associated with a symbol of said signal constellation.

4. The method of claim 3, wherein said decoding process further comprises the steps of:

maintaining a plurality of surviving paths before processing a current received channel-impaired symbol, each surviving path comprising a sequence of tentative decisions on a plurality of past received channel-impaired symbols; and

updating said plurality of surviving paths in accordance with a stage of state transitions corresponding to said current received channel-impaired symbol.

5. The method of claim 1, wherein said communication channel is a multi-path channel.

6. The method of claim 5, wherein said step (b) further includes using a decision on a past received channel-impaired symbol to remove interference on a current received channel-impaired symbol.

7. A method for receiving signal and recovering data from a multi-path channel, comprising the steps of:

(a) receiving channel-impaired symbols of a sequence of codewords from said multi-path channel, said sequence of codewords being generated by applying a substantially orthogonal channel code to said data, each codeword being a sequence of symbols, each symbol being selected from a signal constellation;

(b) using a decision on a past received channel-impaired symbol to remove interference on a current received channel-impaired symbol, said current and past channel-impaired symbols belonging to a same said codeword; and

(c) decoding said channel-impaired symbols to recover said data using a decoding process;

wherein said decoding process in said step (c) provides said decision in step (b), and utilizes a plurality of feedback equalizers to respectively process for each of said channel-impaired symbols a plurality of tentative decisions.

8. The method of claim 7, wherein said substantially orthogonal channel code is a CCK code used in a wireless local area network.

9. The method of claim 7, wherein said decoding process maintains a plurality of surviving paths before processing a current received channel-impaired symbol, each surviving path comprising a sequence of tentative decisions on a plurality of past received channel-impaired symbols, a tentative decision of a surviving path being used as said decision in step (b).

10. The method of claim 9, wherein said decoding process is based on a trellis diagram, said trellis diagram having at least two stages of state transitions that start from a beginning state and go through at least one stage of intermediate states before reaching an ending state, each of said state transitions being associated with a symbol of said signal constellation.

11. The method of claim 10, wherein said decoding process updates said plurality of surviving paths in accordance with a stage of state transitions corresponding to said current received channel-impaired symbol.

12. An apparatus for receiving signal and recovering data from a communication channel, comprising:

a receiving unit for receiving channel-impaired symbols of a sequence of codewords from said communication channel, said sequence of codewords being generated by encoding said data in a substantially orthogonal channel encoder, each codeword being a sequence of symbols, each symbol being selected from a signal constellation; and

a decoder for decoding said channel-impaired symbols to recover said data, said decoder being based on a trellis diagram, and utilizing a plurality of feedback equalizers to respectively process for each of said channel-impaired symbols a plurality of tentative decisions.

13. The apparatus of claim 12, wherein said encoder is a CCK encoder used in a wireless local area network.

14. The apparatus of claim 12, wherein said trellis diagram has at least two stages of state transitions that start from a beginning state and go through at least one stage of intermediate states before reaching an ending state, each of said state transitions being associated with a symbol of said signal constellation.

15. The apparatus of claim 14, wherein said decoder maintains a plurality of surviving paths before processing a current received channel-impaired symbol, each surviving path comprising a sequence of tentative decisions on a plurality of past received channel-impaired symbols;

and updates said plurality of surviving paths in accordance with a stage of state transitions corresponding to said current received channel-impaired symbol.

16. The apparatus of claim 12, wherein said communication channel is a multi-path channel.

17. The apparatus of claim 16, wherein said decoder further includes at least one decision feedback equalizer that uses a decision on a past received channel-impaired symbol to remove interference on a current received channel-impaired symbol.

18. An apparatus for receiving signal and recovering data from a multi-path channel, comprising:

a receiving unit for receiving channel-impaired symbols of a sequence of codewords from said multi-path channel, said sequence of codewords being generated by encoding said data in a substantially orthogonal channel encoder, each codeword being a sequence of symbols, each symbol being selected from a signal constellation;

plurality of decision feedback equalizers for removing interference on a current received channel-impaired symbol using a decision on a past received channel-impaired symbol, said current and past channel-impaired symbols belonging to a same one of said codewords, said decision feedback equalizers respectively processing for each of said channel-impaired symbols a plurality of tentative decisions; and

a decoder portion for decoding said channel-impaired symbols to recover said data;

wherein said decoder portion provides said decision used by an associated decision feedback equalizer.

19. The apparatus of claim 18, wherein said encoder is a CCK encoder used in a wireless local area network.

20. The apparatus of claim 18, wherein said decoder maintains a plurality of surviving paths before processing a current received channel-impaired symbol, each surviving path comprising a sequence of tentative decisions on a plurality of past received channel-impaired symbols, a tentative decision of a surviving path being used as a decision in an associated equalizer.

21. The apparatus of claim 20, wherein said decoder is based on a trellis diagram, said trellis diagram having at least two stages of state transitions that start from a beginning state and go through at least one stage of intermediate states before reaching an ending state, each of said state transitions being associated with a symbol of said signal constellation.

22. The apparatus of claim 21, wherein said decoder updates said plurality of surviving paths in accordance with a stage of state transitions corresponding to said current received channel-impaired symbol.