Methods and systems for extracting a joint probability from a map decision device and processing a signal using the joint probability information

• US 6,798,852 B2
• Filed: 12/20/2000
• Issued: 09/28/2004
• Est. Priority Date: 06/06/2000
• Status: Expired due to Fees

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Khayrallah, Ali S., Bottomley, Gregory E.
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/742,173
• Publication Number:
  US 20020003846A1
• Time in Patent Office: 1,378 Days
• Field of Search: 375/262, 375/265, 375/340, 375/341, 718/780, 718/792, 718/794, 718/795, 718/796
• US Class Current: 375/341
• CPC Class Codes: H03M 13/2707 Simple row-column interleaver, i.e. pure block interleaving
• CPC Class Codes: H03M 13/2721 the interleaver involves a diagonal direction, e.g. by using an interleaving matrix with read-out in a diagonal direction
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3905 Maximum a posteriori probability [MAP] decoding or approximations thereof based on trellis or lattice decoding, e.g. forward-backward algorithm, log-MAP decoding, max-log-MAP decoding
• CPC Class Codes: H03M 13/6325 Error control coding in combination with demodulation
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0055 MAP-decoding
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection
• CPC Class Codes: H04L 25/03318 Provision of soft decisions
• CPC Class Codes: H04L 25/03337 Arrangements involving per-survivor processing
• 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 27/22 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

Methods and devices for extracting a joint probability from a MAP decision device are provided. Probability information associated with a first symbol and a second symbol is obtained from the MAP decision device. A joint probability of the first symbol and the second symbol is determined from the probability information associated with the first symbol and the second symbol. Methods and devices for processing a signal containing information associated with a plurality of transmitted bits using the generated joint probability information are also provided. The MAP decision device in various embodiments is a demodulator or a decoder.

Claims

1. A method for extracting a joint probability from a MAP decision device comprising:

obtaining probability information associated with a first symbol and a second symbol from the MAP decision device; and

determining a joint probability of at least the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol.

2. The method of claim 1 wherein the probability information associated with the first symbol and the second symbol comprises at least one of a branch probability, a forward state probability and a backward state probability.

3. The method of claim 1 wherein the MAP decision device operates on a trellis and wherein determining a joint probability of the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol comprises determining a joint probability of the first symbol at a (k−

n)-th stage of the trellis, where n is at least one, and the second symbol at a k-th stage of the trellis from the probability information associated with the first symbol and the second symbol.

4. The method of claim 3 wherein obtaining probability information associated with a first symbol and a second symbol from the MAP decision device comprises:

calculating at least one forward state probability through the (k−

n)-th stage of the trellis;

calculating at least one backward state probability through the k-th stage of the trellis; and

calculating at least one branch probability between a state at the (k−

n)-th stage of the trellis and a state at the k-th stage of the trellis; and

wherein determining a joint probability of the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol comprises;

selecting an i-th information symbol at the (k−

n)-th stage of the trellis as the first symbol and a j-th information symbol at the k-th stage of the trellis as the second symbol; and

determining a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol.

5. The method of claim 4 wherein n equals one.

6. The method of claim 4 wherein determining a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol comprises:

selecting branch paths having an i-th symbol label of a branch from the (k−

n)-th stage corresponding to the selected i-th information symbol and a j-th symbol label of a branch into the k-th stage corresponding to the selected j-th information symbol;

generating a product of an associated forward state probability, backward state probability and branch probability for each of the selected branch paths; and

summing the generated products to provide the joint probability of the first symbol and the second.

7. The method of claim 6 wherein calculating at least one branch probability between a state at the (k−

n)-th stage of the trellis and a state at the k-th stage of the trellis further comprises calculating a channel information based probability and prior information about a branch based probability and combining the channel information based probability and prior information about a branch based probability to provide a branch probability for a branch.

8. The method of claim 7 wherein n equals one.

9. The method of claim 6 wherein n equals one.

10. The method of claim 6 wherein the MAP decision device is at least one of an equalizer and a decoder.

11. The method of claim 6 wherein a symbol comprises a bit.

12. The method of claim 1 wherein the MAP decision device is at least one of an equalizer and a decoder.

13. The method of claim 1 wherein a symbol comprises a bit.

14. The method of claim 1 wherein obtaining probability information associated with a first symbol and a second symbol from the MAP decision device further comprises obtaining probability information associated with a third symbol from the MAP decision device;

and

wherein determining a joint probability of at least the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol comprises determining a joint probability of at least the first symbol, the second symbol and the third symbol from the probability information associated with the first symbol, the second symbol and the third symbol.

15. A method for processing a signal containing information associated with a plurality of transmitted bits, the signal being received over a channel from a transmitter comprising:

demodulating the signal to provide demodulated received symbols;

decoding the demodulated received symbols to provide estimates of the transmitted bits;

wherein at least one of demodulating the received symbols and decoding the demodulated received symbols further comprises generating joint probability information from a MAP decision device, the joint probability information being used during at least one of demodulating and decoding to provide the estimates of the transmitted bits; and

wherein generating the joint probability information from a MAP decision device further comprises;

selecting a first one of the received symbols and a second one of the received symbols, the first symbol and the second symbol being expected to have a joint probability different from the product of their respective symbol probabilities;

obtaining probability information associated with the first symbol and the second symbol from the MAP decision device; and

determining a joint probability of at least the first symbol and the second symbol from the obtained probability information associated with the first symbol and the second symbol.

16. The method of claim 15 wherein the MAP decision device operates on a trellis and wherein determining a joint probability of the first symbol and the second symbol from the obtained probability information associated with the first symbol and the second symbol comprises determining a joint probability of the first symbol at a (k−

n)-th stage of the trellis, where n is at least one, and the second symbol at a k-th stage of the trellis from the probability information associated with the first symbol and the second symbol.

17. The method of claim 16 wherein obtaining probability information associated with the first symbol and the second symbol from the MAP decision device comprises:

calculating at least one forward state probability through the (k−

n)-th stage of the trellis;

calculating at least one backward state probability through the k-th stage of the trellis; and

calculating at least one branch probability between a state at the (k−

n)-th stage of the trellis and a state at the k-th stage of the trellis; and

wherein determining a joint probability of the first symbol and the second symbol from the obtained probability information associated with the first symbol and the second symbol comprises;

selecting an i-th information symbol at the (k−

n)-th stage of the trellis as the first symbol and a j-th information symbol at the k-th stage of the trellis as the second symbol; and

determining a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol.

18. The method of claim 17 wherein n equals one.

19. The method of claim 17 wherein determining a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol comprises:

selecting branch paths having an i-th symbol label of a branch from the (k−

n)-th stage corresponding to the selected i-th information symbol and a j-th symbol label of a branch into the k-th stage corresponding to the selected j-th information symbol;

generating a product of an associated forward state probability, backward state probability and branch probability for each of the selected branch paths; and

summing the generated products to provide the joint probability of the first symbol and the second.

20. The method of claim 15 wherein demodulating the received symbols further comprises generating joint probability information associated with the first and the second symbol from a MAP demodulator and wherein decoding the demodulated received symbols further comprises fixed-lag decoding the received symbols to provide adjusted probability information associated with one of the first and the second symbol based on probability information about the other of the first and the second symbol generated during decoding and the joint probability information associated with the first and the second symbol from demodulating.

21. The method of claim 20 wherein a plurality of the transmitted bits, including ones associated with the first symbol and the second symbol, are coded, interleaved and modulated for transmission as the signal.

22. The method of claim 15 wherein decoding the demodulated received symbols further comprises generating joint probability information associated with the first and the second symbol from a MAP decoder and wherein decoding the demodulated received symbols is followed by re-demodulating the received symbols to provide adjusted demodulated received symbols based on the joint probability information associated with the first and the second symbol from decoding.

23. The method of claim 22 wherein a plurality of the transmitted bits, including ones associated with the first symbol and the second symbol, are coded, interleaved and modulated for transmission as the signal.

24. The method of claim 15 wherein decoding the demodulated received symbols further comprises turbo decoding the demodulated received symbols, the turbo decoding including a first decoding separated by an interleaver from a second decoding and wherein turbo decoding the demodulated received symbols further comprises generating joint probability information associated with the first and the second symbol from the first decoding for use in the second decoding and from the second decoding for use in the first decoding.

25. The method of claim 24 wherein a plurality of the transmitted bits, including ones associated with the first symbol and the second symbol, are coded, interleaved and modulated for transmission as the signal.

26. The method of claim 15 wherein a plurality of the transmitted bits, including ones associated with the first symbol and the second symbol, are transmitted with inner modulation and an outer code.

27. The method of claim 26 wherein the inner modulation displays a correlation and wherein the outer code is selected to correspond to a correlated modulation block of the inner modulation.

28. The method of claim 27 wherein the inner modulation is 8-PSK having two consecutive correlated symbols and wherein the outer code has an alphabet including 64 letters and wherein generating joint probabilities information comprises generating 64 joint probabilities for consecutive symbol pairs and using the generated joint probabilities as letter probabilities for decoding the outer code.

29. The method of claim 27 wherein the transmitted bits are interleaved for transmission and wherein code letters of the outer code are scrambled without breaking the code letters up.

30. The method of claim 15 wherein obtaining probability information associated with the first symbol and the second symbol from the MAP decision device further comprises obtaining probability information associated with a third symbol from the MAP decision device;

and

wherein determining a joint probability of at least the first symbol and the second symbol from the obtained probability information associated with the first symbol and the second symbol comprises determining a joint probability of at least the first symbol, the second symbol and the third symbol from the obtained probability information associated with the first symbol, the second symbol and the third symbol.

31. A MAP decision device providing joint probability information comprising:

an intermediate value output circuit that generates probability information associated with a first symbol and a second symbol being processed by the MAP decision device; and

a joint probability calculation circuit that generates a joint probability of at least the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol.

32. The device of claim 31 wherein the MAP decision device is an equalizer or a decoder that provides soft information about processed symbols.

33. The device of claim 32 wherein the intermediate value output circuit generates at least one of branch probabilities, forward state probabilities and reverse state probabilities.

34. The device of claim 33 wherein a symbol is a bit.

35. The device of claim 33 wherein the MAP decision devices operates on a trellis and wherein the joint probability calculation circuit determines a joint probability of the first symbol at a (k−

n)-th stage of the trellis, where n is at least one, and the second symbol at a k-th stage of the trellis from the probability information associated with the first symbol and the second symbol.

36. The device of claim 35 wherein the intermediate value output circuit calculates forward state probabilities through the (k−

n)-th stage of the trellis, backward state probabilities through the k-th stage of the trellis and branch probabilities between a state at the (k−

n)-th stage of the trellis and a state at the k-th stage of the trellis, and wherein the joint probability determination circuit selects an i-th information symbol at the (k−

n)-th stage of the trellis as the first symbol and a j-th information symbol at the k-th stage of the trellis as the second symbol and determines a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol.

37. The device of claim 36 wherein n equals one.

38. The device of claim 36 wherein the joint probability determination circuit selects branch paths having an i-th symbol label of a branch from the (k−

n)-th stage corresponding to the selected i-th information symbol and a j-th symbol label of a branch into the k-th stage corresponding to the selected j-th information symbol, generates a product of an associated forward state probability, backward state probability and branch probability for each of the selected branch paths, and sums the generated products to provide the joint probability of the first symbol and the second.

39. The device of claim 31 wherein the intermediate value output circuit generates probability information associated with a third symbol being processed by the MAP decision device;

and

wherein the joint probability calculation circuit generates a joint probability of at least the first symbol, the second symbol and the third symbol from the probability information associated with the first symbol, the second symbol and the third symbol.

40. A receiver device for processing a signal containing information associated with a plurality of transmitted bits, the signal being received over a channel from a transmitter, the receiver device comprising:

a signal processor circuit that receives the signal;

a demodulator that demodulates the received signal to provide demodulated received symbols; and

a decoder that decodes the demodulated received symbols to provide estimates of the transmitted bits; and

wherein at least one of the demodulator and the decoder comprises a MAP decision device providing joint probability information, the MAP detection device comprising;

an intermediate value output circuit that generates probability information associated with a first symbol and a second symbol being processed by the MAP decision device; and

a joint probability calculation circuit that generates a joint probability of at least the first symbol and the second symbol from the probability information associated with the first symbol and the second symbol; and

wherein the generated joint probability is used by at least one of the demodulator and the decoder to provide the estimates of the transmitted bits.

41. The receiver device of claim 40 wherein the receiver device is one of a wireless terminal, a base station or a mobile switching center receiving the transmitted signal.

42. The receiver device of claim 41 wherein the first symbol and the second symbol have a joint probability different from a product of their respective symbol probabilities.

43. The receiver device of claim 42 wherein the first symbol and the second symbol have a coupling introduced by at least one of the transmitter and the channel.

44. The receiver device of claim 43 wherein the intermediate value output circuit generates at least one of branch probabilities, forward state probabilities and reverse state probabilities.

45. The device of claim 44 wherein a symbol is a bit.

46. The device of claim 44 wherein the MAP decision devices operates on a trellis and wherein the joint probability calculation circuit determines a joint probability of the first symbol at a (k−

n)-th stage of the trellis, where n is at least one, and the second symbol at a k-th stage of the trellis from the probability information associated with the first symbol and the second symbol.

47. The device of claim 46 wherein the intermediate value output circuit calculates forward state probabilities through the (k−

n)-th stage of the trellis, backward state probabilities through the k-th stage of the trellis and branch probabilities between a state at the (k−

n)-th stage of the trellis and a state at the k-th stage of the trellis, and wherein the joint probability determination circuit selects an i-th information symbol at the (k−

n)-th stage of the trellis as the first symbol and a j-th information symbol at the k-th stage of the trellis as the second symbol and determines a joint probability of the first symbol and the second symbol from the calculated forward state probabilities, reverse state probabilities and branch probabilities based on the selected i-th information symbol and j-th information symbol.

48. The device of claim 47 wherein n equals one.

49. The device of claim 47 wherein the joint probability determination circuit selects branch paths having an i-th symbol label of a branch from the (k−

n)-th stage corresponding to the selected i-th information symbol and a j-th symbol label of a branch into the k-th stage corresponding to the selected j-th information symbol, generates a product of an associated forward state probability, backward state probability and branch probability for each of the selected branch paths, and sums the generated products to provide the joint probability of the first symbol and the second.

50. The device of claim 40 wherein the intermediate value output circuit generates probability information associated with a third symbol being processed by the MAP decision device;

and

wherein the joint probability calculation circuit generates the joint probability of at least the first symbol, the second symbol and the third symbol from the probability information associated with the first symbol, the second symbol and the third symbol.