Receiver based adaptive modulation scheme

• US 6,701,129 B1
• Filed: 09/27/2000
• Issued: 03/02/2004
• Est. Priority Date: 09/27/2000
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Steer, David G., Hashem, Bassam M., Periyalwar, Shalini S.
• Primary Examiner(s): Nguyen, Duc M.
• Application Number:
  US09/670,342
• Time in Patent Office: 1,252 Days
• Field of Search: 455/422.1, 455/423, 455/67.11, 455/63.1, 455/69, 455/72, 455/73, 455/466, 455/522, 375/225, 375/242, 375/222, 375/377, 370/468, 370/347, 370/442, 370/914
• US Class Current: 455/67.11
• 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 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0029 Reduction of the amount of signalling, e.g. retention of useful signalling or differential signalling power control H04W52/04
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters

Abstract

A method is provided for adapting modulation schemes to changing channel quality with reduced overhead signalling. A remote unit measures the channel quality of a radio channel along which a signal from a base station reached the remote unit. Based on the channel quality, the remote unit determines a desired set of transmission parameters from a list of sets of transmission parameters. The remote unit determines a difference in position within the list between the current set of transmission parameters and the desired set of transmission parameters. The remote unit transmits the difference to the base station, which selects a new set of transmission parameters using the current set of transmission parameters and the difference. The method requires little signalling between the remote unit and the base station, and is particularly beneficial in communication systems employing many sub-carriers, such as OFDM systems.

Claims

1. A method of adapting a current Link Mode (LM) in a radio communication system, a LM being a set of at least one transmission parameter, the communication system including a base station which transmits a signal to a remote unit using the current LM, the method comprising the steps of:

storing a sequence of allowed LMs at the base station and at the remote unit, each LM having a sequential position within the sequence;

at the remote unit, determining a channel quality of the signal;

at the remote unit, determining a desired LM from amongst the sequence of allowed LMs based on the channel quality;

at the remote unit, determining a sequential difference defined as a difference between the sequential position of the current LM and the sequential position of the desired LM;

transmitting the sequential difference from the remote unit to the base station;

at the remote unit, setting a new current LM to be the desired LM; and

at the base station, setting the new current LM using the sequential difference.

2. The method of claim 1 further comprising the step of transmitting the desired LM from the remote unit to the base station if a predefined condition is met.

3. The method of claim 1 wherein the channel quality is a signal to interference ratio.

4. The method of claim 1 wherein the channel quality is determined from the transmission error rate.

5. The method of claim 1 wherein the at least one transmission parameter includes a modulation scheme.

6. The method of claim 1 wherein the at least one transmission parameter includes a coding rate.

7. The method of claim 6 wherein the at least one transmission parameter includes a modulation scheme.

8. The method of claim 1 wherein the at least one transmission parameter includes antenna directional coefficients.

9. The method of claim 1 wherein the at least one transmission parameter includes space-time coding coefficients for multiple antenna systems.

10. The method of claim 1 wherein the signal is transmitted over a plurality of sub-carriers, each sub-carrier belonging to one of a plurality of groups of sub-carriers, each group of sub-carriers having a current LM, and wherein:

the step of determining a channel quality determines a channel quality for each sub-carrier the step of determining a desired LM determines a desired LM for at least one group of sub-carriers;

the step of determining a sequential difference determines a sequential difference for at least one group of sub-carriers;

the step of transmitting the sequential difference transmits a sequential difference for at least one group of sub-carriers;

the step of setting a new current LM at the remote unit sets a new current LM for at least one group of sub-carriers; and

the step of setting a new current LM at the base station sets a new current LM for at last one group of sub-carriers.

11. The method of claim 10 further comprising the step of transmitting the desired LM for at least one group of sub-carriers from the remote unit to the base station if a predefined condition is met.

12. The method of claim 10 wherein the channel quality of each sub-carrier is a signal to interference ratio.

13. The method of claim 12 wherein the base station transmits a pilot signal over at least one pilot sub-carrier such that the pilot signal is either on or off, the pilot sub-carrier having a signal strength when it is received by the remote unit and a carrier frequency, and the step of determining the signal to interference ratio of a sub-carrier having a carrier frequency closer to the carrier frequency of the pilot sub-carrier than to a carrier frequency of any other pilot sub-carrier calculates a ratio of the signal strength when the pilot signal is on to the signal strength when the pilot signal is off.

14. The method of claim 13 wherein the communication system employs Orthogonal Frequency Division Multiplexing.

15. The method of claim 10 wherein each group of sub-carriers contains sub-carriers having contiguous sub-band numbers.

16. The method of claim 10 wherein each group of sub-carriers contains a single sub-carrier.

17. The method of claim 10 wherein the at least one transmission parameter includes a modulation scheme.

18. The method of claim 10 wherein the at least one transmission parameter includes a coding rate.

19. The method of claim 18 wherein the at least one transmission parameter includes a modulation scheme.

20. The method of claim 10 wherein the communication system employs Orthogonal Frequency Division Multiplexing.

21. The method of claim 1 comprising the further steps of:

at the remote unit, selecting a packet number of a packet which will arrive at the remote unit after propagation of a return signal to the base station and propagation of a signal to the remote unit; and

transmitting the selected packet number from the remote unit to the base station; and

wherein the step of setting a new current LM at the remote unit sets a new current LM once the remote unit receives a packet identified by the selected packet number, and wherein the step of setting a new current LM at the base station sets a new current LM once the base station transmits a packet identified by the selected packet number.

22. A remote unit for a radio communication system, the remote unit including a decoder which decodes a signal received from a base station using a current Link Mode (LM), a LM being a set of at least one transmission parameter, and the remote unit comprising:

means for storing a sequence of allowed LMs, each LM having a sequential position within the sequence;

means for determining a channel quality of the signal;

means for determining a desired LM from amongst the sequence of allowed LMs based on the channel quality;

means for determining a sequential difference defined as a difference between the sequential position of the current LM and the sequential position of the desired LM;

means for transmitting the sequential difference to the base station; and

means for setting a new current LM to be the desired LM.

23. The remote unit of claim 22 further comprising means for transmitting the desired LM to the base station in the event that a predefined condition is met.

24. The remote unit of claim 22 wherein the channel quality is a signal to interference ratio.

25. The remote unit of claim 22 wherein the at least one transmission parameter includes a modulation scheme.

26. The remote unit of claim 22 wherein the at least one transmission parameter includes a coding rate.

27. The remote unit of claim 26 wherein the at least one transmission parameter includes a modulation scheme.

28. The remote unit of claim 22 wherein the signal is received over a plurality of sub-carriers, each sub-carrier belonging to one of a plurality of groups of sub-carriers, each group of sub-carriers having a current LM, and wherein:

the means for determining a channel quality comprise means for determining a channel quality for each sub-carrier;

the means for determining a desired LM comprise means for determining a desired LM for at least one group of sub-carriers

the means for determining a sequential difference comprise means for determining a sequential difference for at least one group of sub-carriers;

the means for transmitting the sequential difference comprise means for transmitting a sequential difference for at least one group of sub-carriers; and

the means for setting a new current LM comprise means for setting a new current LM for at least one group of sub-carriers.

29. The remote unit of claim 28 further comprising means for transmitting the desired LM for at least one group of sub-carriers in the event that a predefined condition is met.

30. The remote unit of claim 28 wherein the channel quality of each sub-carrier is a signal to interference ratio.

31. The remote unit of claim 30 wherein at least one sub-carrier is a pilot sub-carrier which carries a pilot signal, the pilot signal being either on or off, the pilot sub-carrier having a signal strength when it is received by the remote unit and a carrier frequency, and the means for determining a signal to interference ratio of a sub-carrier having a carrier frequency closer to the carrier frequency of the pilot sub-carrier than to a carrier frequency of any other pilot sub-carrier comprise means for calculating a ratio of the signal strength when the pilot signal is on to the signal strength when the pilot signal is off.

32. The remote unit of claim 31 wherein the communication system employs Orthogonal Frequency Division Multiplexing.

33. The remote unit of claim 28 wherein each group of sub-carriers contains sub-carriers having contiguous sub-band numbers.

34. The remote unit of claim 28 wherein each group of sub-carriers contains a single sub-carrier.

35. The remote unit of claim 28 wherein the at least one transmission parameter includes a modulation scheme.

36. The remote unit of claim 28 herein the at least one transmission parameter includes a coding rate.

37. The remote unit of claim 36 wherein the at least one transmission parameter includes a modulation scheme.

38. The remote unit of claim 28 wherein the communication system employs Orthogonal Frequency Division Multiplexing.

39. A base station for a radio communication system, the base station transmitting a signal to a remote unit using a current Link Mode (LM), a LM being a set of at least one transmission parameter, the base station comprising:

means for maintaining a sequence of allowed LMs, each LM having a sequential position within the sequence;

means for receiving from the remote unit a sequential difference defined as a difference between the sequential position of the current LM and the sequential position of a desired LM, the desired LM belonging to the sequence of allowed LMs; and

means for setting a new current LM using the sequential difference.

40. The base station of claim 39 further comprising means for setting a new current LM to be equal to the desired LM in the event that the base station receives the desired LM from the remote unit.

41. The base station of claim 39 wherein the at least one transmission parameter includes a modulation scheme.

42. The base station of claim 39 wherein the at least one transmission parameter includes a coding rate.

43. The base station of claim 42 wherein the at least one transmission parameter includes a modulation scheme.

44. The base station of claim 39 wherein the signal is transmitted over a plurality of sub-carriers, each sub-carrier belonging to one of a plurality of groups of sub-carriers, each group of sub-carriers having a current LM, and wherein:

the means for receiving a sequential difference comprise means for receiving a sequential difference for at least one group of sub-carriers; and

the means for setting a new current LM comprise means for setting a new current LM for at least one group of sub-carriers using the sequential difference for that group of sub-carriers.

45. The base station of claim 44 wherein each group of sub-carriers contains sub-carriers having contiguous sub-band numbers.

46. The base station of claim 44 wherein each group of sub-carriers contains a single sub-carrier.

47. The base station of claim 44 wherein the base station transmits a pilot signal over at least one sub-carrier such that the pilot signal is either on or off.

48. The base station of claim 47 wherein the communication system employs Orthogonal Frequency Division Multiplexing.

49. The base station of claim 44 further comprising:

means for setting a new current LM for at least one group of sub-carriers to be equal to a desired LM for that group of sub-carriers in the event that the base station receives the desired LM for that group of sub-carriers.

50. The base station of claim 44 wherein the at least one transmission parameter includes a modulation scheme.

51. The base station of claim 44 wherein the at least one transmission parameter includes a coding rate.

52. The base station of claim 51 wherein the at least one transmission parameter includes a modulation scheme.

53. The base station of claim 44 wherein the communication system employs Orthogonal Frequency Division Multiplexing.