Iterative detection and decoding for a MIMO-OFDM system

• US 7,154,936 B2
• Filed: 12/03/2001
• Issued: 12/26/2006
• Est. Priority Date: 12/03/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Ketchum, John W., Walton, Jay R., Bjerke, Bjorn A.
• Primary Examiner(s): Ghayour, Mohammed
• Assistant Examiner(s): GHULAMALI, QUTBUDDIN
• Application Number:
  US10/005,104
• Publication Number:
  US 20030103584A1
• Time in Patent Office: 1,849 Days
• Field of Search: 375/340, 375/341, 375/259, 375/260, 375/261, 375/262, 375/342, 375/264, 375/330, 375/136, 375/148, 375/149, 375/150, 370/337, 370/347, 370/349, 370/428, 714/750, 714/746, 714/786, 714/755, 714/758
• US Class Current: 375/148
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection
• CPC Class Codes: H04L 25/03305 Joint sequence estimation and interference removal joint detection of several desired signals H04L25/03331
• CPC Class Codes: H04L 25/03891 Spatial equalizers MIMO diversity systems H04B7/0413
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0023 Time-frequency-space

Abstract

Techniques to iteratively detect and decode data transmitted in a wireless (e.g., MIMO-OFDM) communication system. The iterative detection and decoding is performed by iteratively passing soft (multi-bit) “a priori” information between a detector and a decoder. The detector receives modulation symbols, performs a detection function that is complementary to the symbol mapping performed at the transmitter, and provides soft-decision symbols for transmitted coded bits. “Extrinsic information” in the soft-decision symbols is then decoded by the decoder to provide its extrinsic information, which comprises the a priori information used by the detector in the detection process. The detection and decoding may be iterated a number of times. The soft-decision symbols and the a priori information may be represented using log-likelihood ratios (LLRs). Techniques are provided to reduce the computational complexity associated with deriving the LLRs, including interference nulling to isolate each transmitted signal and “dual-maxima” approximation.

Claims

1. A method for recovering data transmitted in a wireless communication system, wherein the wireless communication system comprises a plurality of receive antennas, comprising:

receiving at least one data stream, wherein each data stream comprises a plurality of modulation symbols for a plurality of transmitted coded bits;

wherein the plurality of modulation symbols for each receive antenna is a respective modulation or coding scheme;

determining for each data stream a plurality of soft decision symbols based on the received plurality of modulation symbols and a first a priori information for the transmitted coded bits;

determining a second a priori information based on the plurality of soft decision symbols and the first a priori information for the transmitted coded bits;

determining the first a priori information for the transmitted coded bits based in part on the second a priori information;

repeating the determining the plurality of soft decision symbols and the determining the first a priori information and a plurality of times;

determining decoded bits for the transmitted coded bits based on the second a priori information.

2. The method of claim 1, further comprising:

deriving the first a priori information for the transmitted coded bits based on a first extrinsic information, deriving the first extrinsic information based on the second a priori information and a a posteriori information, deriving the second a priori information based on a second extrinsic information for the transmitted coded bits, and deriving the second extrinsic information based on the plurality of soft decision symbols and the first a priori information for the transmitted coded bits.

3. The method of claim 1, wherein the soft-decision symbols are represented as log-likelihood ratios (LLRs).

4. The method of claim 3, wherein a dual-maxima approximation is used to derive the LLRs for the coded bits.

5. The method of claim 1, wherein the soft-decision symbols comprise channel information.

6. The method of claim 1, wherein the soft-decision symbols comprise information for one or more spatial subchannels and one or more frequency subchannels used to transmit the plurality of modulation symbols.

7. The method of claim 2, further comprising:

deinterleaving the the second extrinsic information, wherein the deinterleaved second extrinsic information is decoded; and

interleaving the first extrinsic information, wherein the interleaved first extrinsic information is used to derive the soft decision symbols.

8. The method of claim 1, wherein the wireless communication system is a multiple-input multiple-output (MIMO) system.

9. The meted of claim 8, wherein the MIMO system implements orthogonal frequency division multiplexing (OFDM).

10. The method of claim 1, further comprising:

recovering a first subset of the modulation symbols for a first transmit antenna by nulling a other subsets of the modulation symbols for a other transmit antennas.

11. The method of claim 10, wherein the recovering the first subset of the modulation symbols for the first transmit antenna includes

pre-multiplying the received modulation symbols with a plurality of nulling matrices to derive the first subset of the recovered modulation symbols for a plurality of frequency subchannels of the first transmit antenna.

12. The method of claim 1, further comprising:

recovering a first subset of the modulation symbols for a first transmit antenna by nulling the modulation symbols for a other transmit antennas from the received modulation symbols, and

canceling interference due to the recovered modulation symbols from the received modulation symbols, thereby producing interference-cancelled modulation symbols, and

recovering a other subsets of the modulation symbols from the interference-cancelled modulation symbols.

13. The method of claim 1, further comprising:

deriving pre-decoding interference estimates based on the soft-decision symbols; and

canceling the pre-decoding interference estimates from input modulation symbols, and

wherein the input modulation symbols for a first transmit antenna are the received modulation symbols and the input modulation symbols for each subsequent transmit antenna are the interference-cancelled modulation symbols from the current transmit antenna.

14. The method of claim 1, wherein the soft-decision symbol for each coded bit comprises extrinsic information extracted from other coded bits.

15. The method of claim 1, wherein the decoding is based on a parallel concatenated convolutional decoding scheme.

16. The method of claim 1, wherein the decoding is based on a serial concatenated convolutional decoding scheme.

17. The method of claim 1, wherein the decoding is based on a convolutional decoding scheme.

18. The method of claim 1, wherein the decoding is based on a block decoding scheme.

19. The method of claim 1, wherein the decoding is based on a concatenated convolutional decoding scheme, and wherein a dual-maxima approximation is used for evaluating log-likelihood ratios (LLRs) for the decoding.

20. The method of claim 1, wherein the decoding for each transmit antenna is based on a respective decoding scheme.

21. The method of claim 1, wherein the plurality of modulation symbols are derived based on a non-Gray modulation scheme.

22. The method of claim 1, wherein the modulation symbols for each transmit antenna are derived based on a respective modulation scheme.

23. A receiver unit in a wireless communication system, wherein the wireless communication system comprises a plurality of receive antennas, comprising:

a detector operative to receive at least one data stream, wherein each data stream comprises a plurality of modulatian symbols for a plurality of transmitted coded bits, derive soft-decision symbols for the coded bits based on the received modulation symbols and a first a priori information for the coded bits derive the first a priori information for the coded bits based on a a posteriori information, and derive a second a priori information for the coded bits based on the soft-decision symbols and the first a priori information;

wherein the detector operative to receive the plurality of modulation and symbols from each receive antenna with a respective modulation or coding schemes;

a decoder operative to decode the second a priori information to derive the a posteriori information and to determine decoded bits of the transmitted coded bits; and

wherein the second a priori information is derived by the detector and decoded by the decoder a plurality of times prior to determining the decoded bits.

24. The receiver unit of claim 23, further comprising:

a deinterleaver operative to deinterleave a second extrinsic information based on the soft-decision symbols and the first a priori information for the transmitted coded bits, wherein the deinterleaved second extrinsic information is decoded by the decoder; and

an interleaver operative to interleave a first extrinsic information based on the second a priori information and the a posteriori information for the transmitted coded bits,

wherein the interleaved first extrinsic information is used by the detector to derive the soft-decision symbols.

25. The receiver unit of claim 23, wherein the soft-decision symbols represent log-likelihood ratios (LLRs) for the coded bits.

26. The receiver unit of claim 25, wherein the detector is operative to use a dual-maxima approximation to derive the LLRs for the coded bits.

27. The receiver unit of claim 23, wherein the detector is further operative to recover the modulation symbols for each transmit antenna by nulling the modulation symbols for other transmit antennas, and to derive the soft-decision symbols for the coded bits transmitted from each transmit antenna based on the recovered modulation symbols for the transmit antenna and the first a priori information.

28. The receiver unit of claim 27, wherein the detector is further operative to pre-multiply the received modulation symbols with a plurality of nulling matrices to derive the recovered modulation symbols for the plurality of frequency subchannels of each transmit antenna.

29. The receiver unit of claim 27, wherein the detector is further operative to cancel interference due to the recovered modulation symbols for each transmit antenna, and to recover the modulation symbols for each subsequent transmit antenna, except the last transmit antenna, based on the interference-cancelled modulation symbols.

30. The receiver unit of claim 23, wherein one decoder is provided for each independently coded data stream to be decoded by the receiver.

31. The receiver unit of claim 23, wherein at least one decoder is operative to perform concatenated convolutional decoding on the second a priori information.

32. The receiver unit of claim 23, wherein at least one decoder implements a maximum a posteriori (MAP) decoding algorithm.

33. The receiver unit of claim 23, further comprising:

a channel estimator operative to estimate one or more characteristics of a communication channel via which the plurality of modulation symbols are received; and

a transmitter unit operative to process and transmit channel state information indicative of the estimated channel characteristics.

34. The receiver unit of claim 33, wherein the channel state information is indicative of a particular coding and modulation scheme to be used for each transmit antenna.

35. The receiver unit of claim 33, wherein the channel state information is indicative of a particular coding and modulation scheme to be used for all transmit antennas.

36. The receiver unit of claim 23, wherein the wireless communication system is a multiple-input multiple-output (MIMO) system that implements orthogonal frequency division multiplexing (OFDM).

37. A terminal comprising the receiver unit of claim 23.

38. A base station comprising the receiver unit of claim 23.

39. An access point comprising the receiver unit of claim 23.

40. A receiver apparatus in a wireless communication system, wherein the wireless communication system comprises a plurality of receive antennas, comprising:

means for receiving at least one data stream, wherein each data stream comprises a plurality of modulation symbols for a plurality of coded bits transmitted via a plurality of frequency subchannels of the plurality of transmit antennas, wherein the plurality of modulation symbols for each receive antenna is a respective modulation or coding scheme;

means for deriving soft-decision symbols for the coded bits based on the received modulation symbols and a first a priori information for the coded bits;

means for deriving a second a priori information for the coded bits based on the soft-decision symbols and the first a priori information;

first means for decoding the second a priori information to derive the first a priori information, wherein the second a priori information is derived and decoded a plurality of times; and

first means for determining decoded bits of the transmitted coded bits based in part on the first a priori information.

41. The receiver apparatus of claim 40, further comprising:

means for recovering the modulation symbols for each transmit antenna by nulling the modulation symbols for other transmit antennas, and

wherein the soft-decision symbols for the coded bits transmitted from each transmit antenna are derived based on the recovered modulation symbols for the transmit antenna and the first a priori information for the transmit antenna.

42. The receiver apparatus of claim 40, further comprising:

means for deinterleaving a second extrinsic information based on the soft-decision symbols and the first a priori information for the transmitted coded bits, wherein the deinterleaved second extrinsic information is decoded; and

means for interleaving a first extrinsic information based on the second a priori information and a a posteriori information for the transmitted coded bits, wherein the interleaved first extrinsic information is used to derive the soft-decision symbols.