Adaptive modulation method

• US 6,359,934 B1
• Filed: 03/19/1999
• Issued: 03/19/2002
• Est. Priority Date: 03/19/1998
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Yoshida, Makoto
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Nguyen, Dung X.
• Application Number:
  US09/272,910
• Time in Patent Office: 1,096 Days
• Field of Search: 375/262, 375/341, 375/232, 375/295, 375/264, 375/298, 370/342, 370/230, 370/232, 370/233, 370/234, 370/235, 370/207, 370/278, 332/103
• US Class Current: 375/262
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0032 Without explicit signalling
• CPC Class Codes: H04L 1/0038 Blind format detection for detection of modulation format H04L27/0012
• 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 1/0059 Convolutional codes
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation

Abstract

Each modulation level estimating unit calculates mean or variance of a carrier wave power for received signals to which no modulation level information is added when being transmitted, and calculates the difference between the calculated mean or variance and a mean or variance at each modulation level, as one of likelihood function values Λ_ML#1 through Λ_ML#X of each modulation level. A maximum likelihood function value selector selects the modulation level corresponding to the likelihood function value having the maximum likelihood value from among the likelihood function values, and makes a data selector select as a demodulation signal the output of a modulation level demodulating unit, which corresponds to the selected modulation level.

Claims

1. A radio transmission method for adaptively changing a modulation level according to a channel condition comprising the steps of:

calculating mean of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

calculating as a likelihood value of each modulation level a difference between the calculated mean of the carrier wave power of the received signal, and a mean of the carrier wave power, which is prescribed for each modulation level; and

estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

2. The radio transmission method according to claim 1, further comprising the step of:

reducing an absolute value of the likelihood value by performing a likelihood value calculation for each received symbol.

3. The radio transmission method according to claim 1, further comprising the step of:

setting an estimation block length of a signal transmitted at a same modulation level according to an estimation error rate allowed by a system.

4. The radio transmission method according to claim 1, further comprising the steps of:

obtaining a received signal level; and

restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

5. The radio transmission method according to claim 1, further comprising the step of:

restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on a modulation level which is most recently estimated.

6. The radio transmission method according to claim 1, further comprising the step of:

suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

7. The radio transmission method according to claim 1, further comprising the step of:

implementing a non-adaptive modulation method by fixedly setting a modulation level when being transmitted.

8. A radio transmission method for adaptively changing a modulation level according to a channel condition, comprising the steps of:

calculating a variance of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

calculating as a likelihood value of each modulation level a difference between the calculated variance of the carrier wave power of the received signal, and a variance of the carrier wave power, which is prescribed for each modulation level; and

estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

9. The radio transmission method according to claim 8, further comprising the step of:

setting an estimation block length of a signal transmitted at a same modulation level according to an estimation error rate allowed by a system.

10. The radio transmission method according to claim 8, further comprising the steps of:

obtaining a received signal level; and

restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

11. The radio transmission method according to claim 8, further comprising the step of:

restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on a modulation level which is most recently estimated.

12. The radio transmission method according to claim 8, further comprising the step of:

suspending a subsequent estimation operation of the likelihood value at a corresponding modulation level if a distance between signal points exceeds a certain threshold.

13. The radio transmission method according to claim 8, further comprising the step of:

implementing a non-adaptive modulation method by fixedly setting a modulation level when being transmitted.

14. A radio transmission method for adaptively changing a modulation level according to a channel condition, comprising the steps of:

calculating a sample variance of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

calculating as a likelihood value of each modulation level a difference between the calculated sample variance of the carrier wave power of the received signal, and a sample variance of the carrier wave power, which is prescribed for each modulation level; and

estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

15. The radio transmission method according to claim 14, further comprising the step of:

setting an estimation block length of a signal transmitted at a same modulation level according to an estimation error rate allowed by a system.

16. The radio transmission method according to claim 14, further comprising the steps of:

obtaining a received signal level; and

restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

17. The radio transmission method according to claim 14, further comprising the step of:

restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on a modulation level which is most recently estimated.

18. The radio transmission method according to claim 14, further comprising the step of:

suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

19. The radio transmission method according to claim 14, further comprising the step of:

implementing a non-adaptive modulation method by fixedly setting a modulation level when being transmitted.

20. A radio transmission method for adaptively changing a modulation level according to a channel condition, comprising the steps of:

calculating a variance of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

calculating as a likelihood value of each modulation level a difference between the calculated variance of the carrier wave power of the received signals, and a sample variance of the carrier wave power, which is prescribed for each modulation level; and

estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

21. The radio transmission method according to claim 20, further comprising the step of:

setting an estimation block length of a signal transmitted at a same modulation level according to an estimation error rate allowed by a system.

22. The radio transmission method according to claim 20, further comprising the steps of:

obtaining a received signal level; and

restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

23. The radio transmission method according to claim 20, further comprising the step of:

restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on a modulation level which is most recently estimated.

24. The radio transmission method according to claim 20, further comprising the step of:

suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

25. The radio transmission method according to claim 20, further comprising the step of:

implementing a non-adaptive modulation method by fixedly setting a modulation level when being transmitted.

26. A radio transmission apparatus for adaptively changing a modulation level according to a channel condition, comprising:

a circuit for calculating a mean value of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

a circuit for calculating as a likelihood value of each modulation level a difference between the calculated mean value of the carrier wave power of the received signal, and a mean value of the carrier wave power, which is prescribed for each modulation level; and

a circuit for estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

27. The radio transmission apparatus according to claim 26, further comprising for each modulation level:

a circuit for calculating a square value of each received symbol;

a circuit for subtracting the mean value of the carrier wave power, which is prescribed for a corresponding modulation level, from the square value;

a circuit for accumulating a subtraction result by a predetermined number of symbols; and

a circuit for calculating an absolute value of an accumulation result, and for outputting a calculation result as a likelihood value of the corresponding modulation level.

28. The radio transmission apparatus according to claim 26, wherein

an estimation block length of a signal transmitted at a same modulation level is set according to an estimation error rate allowed by a system.

29. The radio transmission apparatus according to claim 26, further comprising:

a circuit for obtaining a received signal level; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated, based on the received signal level.

30. The radio transmission apparatus according to claim 26, further comprising:

a circuit for storing a modulation level which is most recently estimated; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on the stored modulation level which is most recently estimated.

31. The radio transmission apparatus according to claim 26, further comprising:

a circuit for suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

32. A radio transmission apparatus for adaptively changing a modulation level according to a channel condition, comprising:

a circuit for calculating a variance value of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

a circuit for calculating as a likelihood value of each modulation level a difference between the calculated variance value of the carrier wave power of the received signal, and a variance value of the carrier wave power, which is prescribed for each modulation level; and

a circuit for estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

33. The radio transmission apparatus according to claim 32, wherein

an estimation block length of a signal transmitted at a same modulation level is set according to an estimation error rate allowed by a system.

34. The radio transmission apparatus according to claim 32, further comprising:

a circuit for obtaining a received signal level;

and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

35. The radio transmission apparatus according to claim 32, further comprising:

a circuit for storing a modulation level which is most recently estimated; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on the stored modulation level which is most recently estimated.

36. The radio transmission apparatus according to claim 32, further comprising:

a circuit for suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

37. A radio transmission apparatus for adaptively changing a modulation level according to a channel condition, comprising:

a circuit for calculating a sample variance value of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

a circuit for calculating as a likelihood value of each modulation level a difference between the calculated sample variance value of the carrier wave power of the received signal, and a sample variance value of the carrier wave power, which is prescribed for each modulation level; and

a circuit for estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

38. The radio transmission apparatus according to claim 37, wherein

an estimation block length of a signal transmitted at a same modulation level is set according to an estimation error rate allowed by a system.

39. The radio transmission apparatus according to claim 37, further comprising:

a circuit for obtaining a received signal level; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

40. The radio transmission apparatus according to claim 37, further comprising:

a circuit for storing a modulation level which is most recently estimated; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on the stored modulation level which is most recently estimated.

41. The radio transmission apparatus according to claim 37, further comprising:

a circuit for suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.

42. A radio transmission apparatus for adaptively changing a modulation level according to a channel condition, comprising:

a circuit for calculating a variance value of a carrier wave power for received signals to which no modulation level information is added when being transmitted;

a circuit for calculating as a likelihood value of each modulation level a difference between the calculated variance value of the carrier wave power of the received signal, and a sample variance value of the carrier wave power, which is prescribed for each modulation level; and

a circuit for estimating as a modulation level of the received signal a modulation level corresponding to a maximum likelihood value among likelihood values of respective modulation levels.

43. The radio transmission apparatus according to claim 42, wherein

an estimation block length of a signal transmitted at a same modulation level is set according to an estimation error rate allowed by a system.

44. The radio transmission apparatus according to claim 42, further comprising:

a circuit for obtaining a received signal level; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated based on the received signal level.

45. The radio transmission apparatus according to claim 42, further comprising:

a circuit for storing a modulation level which is most recently estimated; and

a circuit for restricting a range of a modulation level for which the likelihood value is calculated when a current estimation is made, based on the stored modulation level which is most recently estimated.

46. The radio transmission apparatus according to claim 42, further comprising:

a circuit for suspending a subsequent estimation operation of the likelihood value for a corresponding modulation level if a distance between signal points exceeds a certain threshold.