Method and apparatus for discrete multitone communication bit allocation

• US 6,516,027 B1
• Filed: 02/18/1999
• Issued: 02/04/2003
• Est. Priority Date: 02/18/1999
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC USA Inc (NEC Corporation)
• Inventors: Choudhary, Prashant, Kapoor, Samir
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US09/252,418
• Time in Patent Office: 1,447 Days
• Field of Search: 375/227, 375/222, 375/225, 375/228, 375/219, 375/278, 375/296, 375/295, 375/224, 370/252, 370/484, 370/487, 379/93.26, 379/93.28, 455/59, 455/57.3
• US Class Current: 375/227
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04L 5/1438 Negotiation of transmission parameters prior to communication modified according to link quality H04L1/0001

Abstract

A method and apparatus for allocating bits to subchannels in a discrete multitone environment. The method employs the use of precalculated and prestored look-up tables which take into account a desired bit error rate, signal-to-noise ratio gap for a particular coding scheme, and gain scaling factor. This eliminates the need for the communication device to conduct complex and time consuming calculations. During the training sequence portion of data communication channel establishment, the measured signal-to-noise ratio for each subchannel is compared with values in the precalculated look-up tables to determine the bit allocation for that subchannel. The bit allocation value is stored in a data structure in the communication device. A gain scaling factor for each subchannel is then determined and stored as a data structure. The bit allocation and gain scaling data can then be transmitted to a partner communication device in order to instruct the transmitter how to load each subchannel.

Claims

1. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

storing at least one bits to signal-to-noise ratio table in a memory;

determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table.

2. A method according to claim 1, wherein said stored table is comprised of a plurality of minimum signal-to-noise ratio values and a corresponding plurality of respective bit values, said minimum signal-to-noise ratio values being determined in accordance with a maximum allowable gain scaling factor, wherein said signal-to-noise ratio values also correspond to said plurality of respective bit values.

3. A method according to claim 1, wherein said table is stored in a non-volatile storage device.

4. A method according to claim 1, wherein said table is stored in a random access memory.

9. A method according to claim 1, wherein said stored table is comprised of a plurality of signal-to-noise ratio values and a corresponding plurality of respective bit values, and

wherein said plurality of signal-to-noise ratio values are on a linear scale.

10. A method according to claim 1, wherein said bit allocation value is a non-integer.

11. A method according to claim 2, wherein said table is stored in a non-volatile storage device.

12. A method according to claim 2, wherein said table is stored in a random access memory.

13. A method according to claim 2, wherein one of said bit allocation values determined for one of said plurality of subchannels differs from said bit allocation value determined for at least one of said remaining subchannels.

14. A method according to claim 2, wherein said bit allocation value determined for at least one of said plurality of subchannels is determined in accordance with one of said stored tables, and said bit allocation value for at least one other of said plurality of subchannels is determined in accordance with another of said stored tables.

15. A method according to claim 2, wherein said bit allocation values are determined in batches, each batch being comprised of a predetermined quantity of said plurality of subchannels.

16. A method according to claim 2, wherein said bit allocation values are determined simultaneously for all of said plurality of subchannels.

17. A method according to claim 2, wherein said plurality of minimum signal-to-noise ratio values are on a linear scale.

18. A method according to claim 2, wherein said bit allocation value is a non-integer.

19. A method according to claim 2, wherein each said stored table comprises two separate tables and is stored as a first table and a second table, said first table is comprised of said plurality of minimum signal-to-noise ratio values and said corresponding plurality of respective bit values, and said second table is comprised of said signal-to-noise ratio values and said corresponding plurality of respective bit values.

5. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

storing at least one bits to signal-to-noise ratio table in a memory;

determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein one of said bit allocation value determined for one of said plurality of subchannels differs from said bit allocation value determined for at least one of said remaining subchannels.

6. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

storing at least one bits to signal-to-noise ratio table in a memory;

determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation value determined for at least one of said plurality of subchannels is determined in accordance with one of said stored tables, and said bit allocation value for at least one other of said plurality of subchannels is determined in accordance with another of said stored tables.

7. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

storing at least one bits to signal-to-noise ratio table in a memory;

determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation values are determined in batches, each said batch being comprised of a predetermined quantity of said plurality of subchannels.

8. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

storing at least one bits to signal-to-noise ratio table in a memory;

determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation values are determined simultaneously for all of said plurality of subchannels.

20. A method of allocating bits to a plurality of transmission subchannels in a communication system, the method comprising the steps of:

measuring a signal-to-noise ratio for each of said plurality of transmission subchannels;

adjusting said measured signal-to-noise ratio in accordance with an SNR-margin and a coding gain;

generating a plurality of signal-to-noise ratio difference values;

selecting a bit allocation value for each of said plurality of transmission subchannels, said bit allocation value corresponding to one of said plurality of signal-to-noise ratio difference values;

determining a gain scaling factor for each of said plurality of transmission subchannels; and

storing each of said bit allocation values and said gain scaling factors in one or more data structures.

21. A method according to claim 20, wherein each of said plurality of signal-to-noise ratio difference values is a difference between said adjusted measured signal-to-noise ratio for one of said plurality of transmission subchannels and a respective member of a first plurality of predetermined signal-to-noise ratio values.

22. A method according to claim 21, wherein said first plurality of corresponding predetermined signal-to-noise ratio values is determined by multiplying each respective member of a second plurality of predetermined signal-to-noise ratio values by a maximum allowable gain scaling factor.

23. A method according to claim 20, wherein said bit allocation selection step comprises the steps of:

searching said plurality of signal-to-noise ratio difference values to determine which of said values corresponds to a negative signal-to-noise ratio difference value having a smallest magnitude among said plurality of signal-to-noise ratio difference values; and

establishing said bit allocation value as an index value corresponding to said determined value.

24. A method according to claim 20, further comprising the step of transmitting said data structures to a partner communication device.

25. A method according to claim 20, wherein said plurality of signal-to-noise ratio difference values are on a linear scale.

26. A method according to claim 20, further comprising the step of determining a fixed data rate.

27. A method according to claim 26, wherein said fixed data rate is determined by decreasing a number of allocated bits for one or more of the plurality of subchannels until a bit rate corresponding to said fixed data rate is achieved.

28. A method according to claim 27, wherein said one or more subchannels are determined by selecting a one of said plurality of subchannels with the highest bits allocated, and in the case where more than one of said plurality of subchannels has the highest bits allocated selecting said one of said plurality of subchannels with the highest bits allocated and a largest gain scaling factor.

29. A method according to claim 20, wherein said bit allocation value is a non-integer.

30. A method according to claim 21, wherein said gain scaling factor is determined by dividing a signal-to-noise ratio corresponding said selected bit allocation value by said adjusted measured signal-to-noise ratio value.

31. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory for storing at least one bits to signal-to-noise ratio table;

a processing unit for determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table.

32. A data communication apparatus according to claim 31, wherein said bits to signal-to-noise ratio table is further comprised of a plurality of minimum signal-to-noise ratio values and a corresponding plurality of respective bit values, said minimum signal-to-noise ratio values being determined in accordance with a maximum allowable gain scaling factor, wherein said signal-to-noise ratio values also correspond to said plurality of respective bit values.

33. A data communication apparatus according to claim 31, wherein said memory is a non-volatile storage device.

34. A data communication apparatus according to claim 31, wherein said memory is a random access memory.

39. A data communication apparatus according to claim 31, wherein said stored table is comprised of a plurality of signal-to-noise ratio values and a corresponding plurality of respective bit values, and

wherein said plurality of signal-to-noise ratio values are on a linear scale.

40. A data communication apparatus according to claim 31, wherein said bit allocation value is a non-integer.

41. A data communication apparatus according to claim 32, wherein said memory is a non-volatile storage device.

42. A data communication apparatus according to claim 32, wherein said memory is a random access memory.

43. A data communication apparatus according to claim 32, wherein one of said bit allocation values determined for one of said plurality of subchannels differs from said bit allocation value determined for at least one of said remaining subchannels.

44. A data communication apparatus according to claim 32, wherein said bit allocation value determined for at least one of said plurality of subchannels is determined in accordance with one of said stored tables, and said bit allocation value for at least one other of said plurality of subchannels is determined in accordance with another of said stored tables.

45. A data communication apparatus according to claim 32, wherein said bit allocation values are determined in batches, each said batch being comprised of a predetermined quantity of said plurality of subchannels.

46. A data communication apparatus according to claim 32, wherein said bit allocation values are determined simultaneously for all of said plurality of subchannels.

47. A data communication apparatus according to claim 32, wherein said plurality of minimum signal-to-noise ratio values are on a linear scale.

48. A data communication apparatus according to claim 32, wherein said bit allocation value is a non-integer.

49. A data communication apparatus according to claim 32, wherein said bits to signal-to-noise ratio table comprises two separate tables and is stored as a first table and a second table, said first table is comprised of said plurality of minimum signal-to-noise ratio values and said corresponding plurality of respective bit values, and said second table is comprised of said signal-to-noise ratio values and said corresponding plurality of respective bit values.

35. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory for storing at least one bits to signal-to-noise ratio table;

a processing unit for determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein one of said bit allocation values determined for one of said plurality of subchannels differs from said bit allocation value determined for at least one of said remaining subchannels.

36. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory for storing at least one bits to signal-to-noise ratio table;

a processing unit for determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation value determined for at least one of said plurality of subchannels is determined in accordance with one of said stored tables, and said bit allocation value for at least one other of said plurality of subchannels is determined in accordance with another of said stored tables.

37. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory for storing at least one bits to signal-to-noise ratio table;

a processing unit for determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation values are determined in batches, each batch being comprised of a predetermined quantity of said plurality of subchannels.

38. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory for storing at least one bits to signal-to-noise ratio table;

a processing unit for determining a bit allocation value and a gain scaling factor for each of said plurality of transmission subchannels in accordance with said at least one stored bits to signal-to-noise ratio table;

wherein said bit allocation values are determined simultaneously for all of said plurality of subchannels.

50. A data communication apparatus for allocating bits to a plurality of transmission subchannels in a communication system, the data communication apparatus comprising:

a memory; and

a processing unit, the processing unit controlling functions for;

measuring a signal-to-noise ratio for each of the plurality of transmission subchannels;

adjusting said measured signal-to-noise ratio in accordance with an SNR-margin and a coding gain;

generating a plurality of signal-to-noise ratio difference values;

selecting a bit allocation value for each of the plurality of transmission subchannels, said bit allocation value corresponding to one of said plurality of signal-to-noise ratio difference values;

determining a gain scaling factor for each of said plurality of transmission subchannels; and

storing each of said bit allocation values and said gain scaling factors as one or more data structures in said memory.

51. A data communication apparatus according to claim 50, wherein each of said plurality of signal-to-noise ratio difference values is a difference between said adjusted measured signal-to-noise ratio for one of said plurality of transmission subchannels and a respective member of a first plurality of predetermined signal-to-noise ratio values.

52. A data communication apparatus according to claim 51, wherein said first plurality of corresponding predetermined signal-to-noise ratio values is determined by multiplying each respective member of a second plurality of predetermined signal-to-noise ratio values by a maximum allowable gain scaling factor.

53. A data communication apparatus according to claim 50, wherein said bit allocation selection step comprises the steps of:

searching said plurality of signal-to-noise ratio difference values to determine which of said values corresponds to a negative signal-to-noise ratio difference value having a smallest magnitude among said plurality of signal-to-noise ratio difference values; and

establishing said bit allocation value as an index value corresponding to said determined value.

54. A data communication apparatus according to claim 50, further comprising the step of transmitting said data structures to a partner communication device.

55. A data communication apparatus according to claim 50, wherein said plurality of signal-to-noise ratio difference values are on a linear scale.

56. A data communication apparatus according to claim 50, further comprising the step of determining a fixed data rate.

57. A data communication apparatus according to claim 56, wherein said fixed data rate is determined by decreasing a number of allocated bits for one or more of the plurality of subchannels until a bit rate corresponding to said fixed data rate is achieved.

58. A data communication apparatus according to claim 57, wherein said subchannels are determined by selecting a one of said plurality of subchannels with the highest bits allocated, and in the case where more than one of said plurality of subchannels has the highest bits allocated selecting said one of said plurality of subchannels with the highest bits allocated and a largest gain scaling factor.

59. A data communication apparatus according to claim 50, wherein said bit allocation value is a non-integer.

60. A data communication apparatus according to claim 51, wherein said gain scaling factor is determined by dividing a signal-to-noise ratio corresponding said selected bit allocation value by said adjusted measured signal-to-noise ratio value.