Frame control encoder/decoder for robust OFDM frame transmissions

• US 6,289,000 B1
• Filed: 05/19/2000
• Issued: 09/11/2001
• Est. Priority Date: 05/19/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Intellon Corporation (Qualcomm, Inc.)
• Inventors: Yonge, Lawrence W. III
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Tran, Maikhanh
• Application Number:
  US09/574,959
• Time in Patent Office: 480 Days
• Field of Search: 370/203-208, 370/209, 370/210, 375/135, 375/136, 375/150, 375/261, 375/262, 375/265, 375/146-147, 375/295, 375/316, 375/346-347
• US Class Current: 370/203
• CPC Class Codes: H03M 13/2909 Product codes
• CPC Class Codes: H03M 13/2948 Iterative decoding H03M13/2957 takes precedence
• CPC Class Codes: H03M 13/3784 for soft-output decoding of block codes
• CPC Class Codes: H03M 13/3944 for block codes, especially trellis or lattice decoding thereof
• CPC Class Codes: H03M 13/45 Soft decoding, i.e. using symbol reliability information H03M13/41 takes precedence
• CPC Class Codes: H03M 13/658 Scaling by multiplication or division
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0052 Realisations of complexity reduction techniques, e.g. pipelining or use of look-up tables
• CPC Class Codes: H04L 1/0055 MAP-decoding
• CPC Class Codes: H04L 1/0065 Serial concatenated codes
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/04 using frequency diversity
• CPC Class Codes: H04L 27/2602 Signal structure

Abstract

An encoder/decoder scheme for robust transmission of PHY layer frame control information (to support medium access) in OFDM frames (or packets). The PHY layer frame control information to be modulated onto carriers in OFDM symbols is encoded using a product coding to form a product code block or matrix. The product coding is based on a shortened hamming code codeword set having properties of symmetry. Elements of the product code matrix are interleaved so that the elements are modulated onto the carriers of the symbols in diagonal groupings (across time and frequency) and with some degree of redundancy. The modulated elements are demodulated to produce soft decision values, which are de-interleaved to combine copies of the soft values for elements and re-order the soft values in the order of the elements prior to interleaving. The soft values for each row and each column are provided to a turbo product decoder, which performs a number of iterations of row/column decoding, each iteration applying a weighting to the results to enhance the reliability of the results of each next successive iteration. Upon completion of the final iteration, the decoder applies a hard decision to the soft values to produce a set of hard values for each of the soft values that corresponds to the frame control information. Given the symmetry of the code set, the row/column decoding generates a complete set of correlation values from only a subset of the complete set of correlation values and uses a reduced number of MAP decoding operations to select the best correlation values for each of the soft values.

Claims

1. A method of encoding frame data for an OFDM frame transmission, comprising:

producing a code block of elements from frame data to be modulated onto carriers of OFDM symbols in an OFDM frame; and

interleaving elements of the code block so that the elements are modulated onto the carriers of the OFDM symbols in groupings along diagonals were the elements to be organized as a matrix.

2. The method of claim 1, wherein the frame data comprises PHY layer frame control information to support a medium access control protocol.

3. The method of claim 2, wherein the OFDM frame includes at least one delimiter and the PHY layer frame control information is located in the at least one delimiter.

4. The method of claim 3, wherein the OFDM frame includes a body and the at least one delimiter comprises a start delimiter that precedes the body.

5. The method of claim 3, wherein the at least one delimiter further comprises an end delimiter that follows the body.

6. The method of claim 3, wherein the at least one delimiter comprises a response.

7. The method of claim 3, wherein the at least one delimiter is of a Request-to-Send type.

8. The method of claim 3, wherein the medium access control protocol is of a Carrier Sense Multiple Access type.

9. The method of claim 3, wherein the medium access control protocol is a Time Division Multiple Access protocol and the at least one delimiter includes beacon information used by the Time Division Multiple Access protocol.

10. The method of claim 3, wherein the medium access control protocol is of a token passing type.

11. The method of claim 1, wherein the code block comprises a product code block.

12. The method of claim 1, wherein interleaving comprises:

selecting from the elements along the diagonals to produce diagonal sequences.

13. The method of claim 12, wherein the sequences collectively form a vector of vector elements.

14. The method of claim 13, wherein interleaving further comprises:

selecting consecutive vector elements from the vector for modulation on carriers in a succession of symbols so that the elements along the diagonals appear on adjacent carriers and across adjacent symbols in the succession of symbols to produce the groupings along diagonals.

15. The method of claim 13, wherein the number of OFDM symbols is three, and wherein selecting comprises:

selecting a first element in a main one of the diagonals and then every third element from among consecutive elements in the diagonals; and

placing the selected first element and every third element in the vector in the order of selection.

16. The method of claim 15, wherein interleaving further comprises:

selecting consecutive vector elements from the vector for modulation on carriers in a succession of symbols so that the consecutive elements along the diagonals appear on adjacent carriers across adjacent symbols in the succession of symbols.

17. The method of claim 16, wherein selecting the consecutive vector elements from the vector for modulation on carriers in the successive symbols results in a level of redundancy.

18. The method of claim 13, wherein the number of OFDM symbols is four and the vector is arranged as an array of four columns of rows, and wherein selecting comprises:

selecting consecutive elements along each of the diagonals; and

placing the selected consecutive elements in the vector in groups of adjacent ones of the rows.

19. The method of claim 14, wherein selecting the vector elements from the vector for modulation on carriers in the successive symbols results in a level of redundancy.

20. The method of claim 1, wherein the code block is a product code block and wherein producing comprises:

deriving the product code block from a shortened extended hamming code codeword set.

21. The method of claim 1, wherein producing further comprises:

selecting a generator matrix to achieve symmetric properties of the codeword set.

22. The method of claim 1, wherein the OFDM frame includes a body and the frame data comprises frame control information that precedes the body.

23. The method of claim 1, wherein the OFDM frame is an acknowledgement frame and the frame data comprises frame control information carried in the acknowledgement packet.

24. An apparatus for encoding data for an OFDM frame transmission, comprising:

an encoder for producing a code block of elements from frame data to be modulated onto carriers of OFDM symbols in an OFDM packet; and

an interleaver coupled to the encoder for interleaving the elements so that the elements are modulated onto each carrier in groupings along diagonals were the elements to be organized as a matrix.

25. The apparatus of claim 24, wherein the frame data comprises PHY layer frame control information to support a medium access control protocol.

26. A computer program residing on a computer-readable medium for encoding data for an OFDM transmission, the computer program comprising instructions to cause a computer to:

produce a product code block of elements from data to be modulated onto carriers of OFDM symbols in an OFDM packet; and

interleave elements of the product code block so that the elements are modulated onto each carrier in groupings along diagonals were the elements organized as a matrix.

27. A method of processing encoded frame control information comprising:

producing soft decision values from frame control information encoded in code words having information bits, and modulated in an interleaved order onto carriers in OFDM symbols, the code words belonging to a set of code words having properties of symmetry;

de-interleaving the soft decision values to produce sets of soft decision values, each set associated with one of the code words; and

performing on each set of soft decision values a decoding procedure according to the properties of symmetry to reduce the complexity of the decoding procedure.

28. The method of claim 27, wherein the decoding procedure is a turbo decoding procedure, and wherein performing the turbo decoding procedure includes performing each of i iterations, and wherein performing each of i iterations comprises:

determining a new set of soft decision values from the set of soft decision values;

determining difference values for a difference between the set of soft decision values and the new set of soft decision values;

weighting the difference values; and

updating the set of soft decision values with the sum of the set of soft decision values and the weighted difference values.

29. The method of claim 28, wherein determining a new set of soft decision values comprises:

generating from the set of soft decision values correlation values corresponding to a subset of the set of code words; and

generating from correlation values corresponding to the subset correlation values corresponding to a remainder of the set of code words based on the properties of symmetry of the codeword set.

30. The method of claim 28, wherein determining a new set of soft decision values further comprises:

using the properties of symmetry of the code word set to select a best correlation value for each of the soft decision values.

31. The method of claim 27, wherein performing further comprises:

producing a hard decision value from each set of soft decision values for each of the information bits in the one of the code words with which the set of soft decision values is associated.

32. The method of claim 27, wherein the code words are produced by a product code and the turbo decoding procedure is a turbo product decoding procedure.

33. The method of claim 27, wherein the code words are in the form of a product code block of elements and the interleaved order includes copies of at least some of the elements, further comprising:

combining the copies.

34. The method of claim 33, wherein combining comprises:

producing carrier-to-noise ratio estimate values for the copies;

weighting the copies according to the carrier-to-noise ratio estimate values; and

summing the weighted copies.

35. An apparatus comprising:

a demodulator for producing soft decision values from delimiter information encoded in code words having information bits, and modulated in an interleaved order onto carriers in OFDM symbols, the code words belonging to a set of code words having properties of symmetry;

a de-interleaving coupled to the demodulator for de-interleaving the soft decision values to produce sets of soft decision values, each set associated with one of the code words; and

a decoder coupled to and for receiving the sets of soft decision values from the de-interleaver and for performing on each set of soft decision values a decoding procedure according to the properties of symmetry to reduce the complexity of the decoding procedure.

36. The apparatus of claim 35, wherein the decoder is a turbo decoder and further comprises:

means for generating from the set of soft values correlation values corresponding to a subset of the plurality of code words; and

means for generating from correlation values corresponding to the subset correlation values corresponding to the remainder of the plurality of code words based on the symmetry of the codeword set.

37. The apparatus of claim 36, wherein the turbo decoder further comprises:

means for using the properties of symmetry of the codeword set to select a best correlation value for each of the soft values.

38. The apparatus of claim 36, wherein the code words are produced by a product code and wherein the turbo decoder is a turbo product decoder.