Power control for a wireless communication system utilizing orthogonal multiplexing

• US 20060019694A1
• Filed: 07/22/2004
• Published: 01/26/2006
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sutivong, Arak, Julian, David Jonathan, Agrawal, Awneesh
• Granted Patent: US 8,452,316 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/04 Error control
• CPC Class Codes: H04W 52/125 cascaded outer loop power control
• CPC Class Codes: H04W 52/146 Uplink power control
• CPC Class Codes: H04W 52/16 Deriving transmission power values from another channel
• CPC Class Codes: H04W 52/20 using error rate
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/241 taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• CPC Class Codes: H04W 52/242 taking into account path loss
• CPC Class Codes: H04W 52/243 taking into account interferences
• CPC Class Codes: H04W 52/247 where the output power of a terminal is based on a path parameter sent by another terminal
• CPC Class Codes: H04W 52/283 Power depending on the position of the mobile
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets
• CPC Class Codes: H04W 52/362 Aspects of the step size
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 52/54 Signalisation aspects of the TPC commands, e.g. frame structure
• CPC Class Codes: H04W 52/60 : using different transmission rates for TPC commands
• CPC Class Codes: H04W 88/08 : Access point devices

Abstract

Techniques for adjusting transmit power to mitigate both intra-sector interference to a serving base station and inter-sector interference to neighbor base stations are described. The amount of inter-sector interference that a terminal may cause may be roughly estimated based on the total interference observed by each neighbor base station, channel gains for the serving and neighbor base stations, and the current transmit power level. The transmit power may be decreased if high interference is observed by a neighbor base station and increased otherwise. The transmit power may be adjusted by a larger amount and/or more frequently if the terminal is located closer to the neighbor base station observing high interference and/or if the current transmit power level is higher, and vice versa. The intra-sector interference is maintained within an acceptable level by limiting a received SNR for the terminal to be within a range of allowable SNRs.

Claims

1. A method of performing power control for a wireless terminal in a wireless communication system, comprising:

obtaining, for each of at least one base station, an indication of interference observed by the base station, each of the at least one base station being a neighbor base station not designated to receive a data transmission sent by the wireless terminal or a serving base station designated to receive the data transmission sent by the wireless terminal; and

adjusting transmit power for the data transmission based on at least one indication obtained for the at least one base station.

2. The method of claim 1, further comprising:

limiting the transmit power for the data transmission to be within a range determined based on a measurement obtained for the data transmission.

3. The method of claim 1, further comprising:

estimating a received signal quality (SNR) for the data transmission at the serving base station; and

limiting the transmit power for the data transmission based on the estimated received SNR for the data transmission.

4. The method of claim 1, wherein the indication for each of the at least one base station comprises a first bit that indicates whether the interference observed by the base station is above or below a first interference threshold.

5. The method of claim 4, wherein the indication for each of the at least one base station further comprises a second bit that indicate whether the interference observed by the base station exceeds a second interference threshold that is higher than the first interference threshold.

6. The method of claim 1, wherein a plurality of indications are obtained for a plurality of neighbor base stations, and wherein the transmit power for the data transmission is adjusted based on an indication obtained for a single neighbor base station that is selected from among the plurality of neighbor base stations.

7. The method of claim 6, wherein the single neighbor base station is a neighbor base station with a smallest path loss to the wireless terminal among the plurality of neighbor base stations.

8. The method of claim 1, wherein only indications of interference for base stations in a designated set of base stations are considered for adjustment of the transmit power for the data transmission.

9. The method of claim 1, wherein the adjusting transmit power for the data transmission comprises

for each base station to be considered in adjusting the transmit power, adjusting the transmit power for the data transmission based on the indication of interference obtained for the base station, a channel gain for the base station, a current transmit power level for the data transmission, a range of allowable transmit power deltas, a maximum transmit power for the terminal, a peak-to-average backoff factor, or a combination thereof.

10. The method of claim 1, wherein the adjusting transmit power for the data transmission comprises

for each base station to be considered in adjusting the transmit power,

decreasing the transmit power if the interference observed by the base station is above a first interference threshold, and

increasing the transmit power if the interference observed by the base station is below the first interference threshold.

11. The method of claim 10, wherein the adjusting transmit power for the data transmission further comprises

for each base station to be considered in adjusting the transmit power,

setting the transmit power to a predetermined low power level if the interference observed by the base station is above a second interference threshold that is higher than the first interference threshold.

12. The method of claim 1, further comprising:

estimating a channel gain for the serving base station; and

for each neighbor base station to be considered in adjusting the transmit power,

estimating a channel gain for the neighbor base station, and

adjusting the transmit power for the data transmission based on an indication obtained for the neighbor base station and the estimated channel gains for the neighbor and serving base stations.

13. The method of claim 12, wherein the channel gains for the neighbor and serving base stations are estimated based on pilots received from the neighbor and serving base stations, respectively.

14. The method of claim 12, further comprising:

for each neighbor base station to be considered in adjusting the transmit power,

determining a probability for adjusting the transmit power upward or downward based on the channel gains for the neighbor and serving base stations, and

adjusting the transmit power for the data transmission based on the indication obtained for the neighbor base station and the probability determined for the neighbor base station.

15. The method of claim 14, wherein the probability is determined further based on a current level of the transmit power for the data transmission.

16. The method of claim 14, wherein the transmit power is adjusted in a fixed-size step and in accordance with the determined probability.

17. The method of claim 12, further comprising:

for each neighbor base station to be considered in adjusting the transmit power,

determining a step size for adjusting the transmit power based on the estimated channel gains for the neighbor and serving base stations, and

adjusting the transmit power for the data transmission based on the indication obtained for the neighbor base station and the step size determined for the neighbor base station.

18. The method of claim 17, wherein the step size is determined further based on a current level of the transmit power for the data transmission.

19. The method of claim 3, wherein the transmit power for the data transmission is determined by a reference power level and a transmit power delta, and wherein the transmit power delta is adjusted based on the at least one indication obtained for the at least one base station.

20. The method of claim 19, further comprising:

adjusting the reference power level such that a received SNR for a second transmission sent by the wireless terminal to the serving base station is maintained at a target SNR, and wherein the received SNR for the data transmission is estimated based on the target SNR for the second transmission.

21. The method of claim 20, wherein the second transmission is for a control channel sent by the terminal to the serving base station.

22. The method of claim 3, wherein the transmit power for the data transmission is limited such that the received SNR for the data transmission is within a range of received SNRs allowable for the data transmission.

23. The method of claim 3, further comprising:

limiting the transmit power for the data transmission to be at or below a maximum power level allowable for the wireless terminal.

24. The method of claim 1, wherein the obtaining the at least one indication of interference observed by the at least one base station and the adjusting the transmit power for the data transmission are performed by the wireless terminal.

25. The method of claim 1, wherein the obtaining the at least one indication of interference observed by the at least one base station and the adjusting the transmit power for the data transmission are performed by the serving base station.

26. The method of claim 25, wherein the at least one indication are obtained via signaling exchanged among the at least one base station.

27. The method of claim 25, further comprising:

obtaining an estimate of a channel gain between the wireless terminal and the serving base station;

for each neighbor base station to be considered in adjusting the transmit power,

obtaining an estimate of a channel gain between the wireless terminal and the neighbor base station, and

adjusting the transmit power for the data transmission based on the indication obtained for the neighbor base station and the estimated channel gains for the neighbor and serving base stations.

28. The method of claim 1, wherein the data transmission is sent using hybrid automatic retransmission (H-ARQ) that allows for early termination of a transmission of a packet decoded correctly by a base station designated to receive the data transmission.

29. The method of claim 1, wherein the wireless communication system is an orthogonal frequency division multiple access (OFDMA) system.

30. The method of claim 1, wherein the wireless communication system is a Time Division Multiple Access (TDMA) system.

31. The method of claim 1, wherein the wireless communication system is a Frequency Division Multiple Access (FDMA) system.

32. An apparatus operable to perform power control for a wireless terminal in a wireless communication system, comprising:

a processor operative to obtain, for each of at least one base station, an indication of interference observed by the base station, each of the at least one base station being a neighbor base station not designated to receive a data transmission sent from the wireless terminal or a serving base station designated to receive the data transmission sent from the wireless terminal; and

an adjustment unit operative to adjust transmit power for the data transmission based on at least one indication obtained for the at least one base station.

33. The apparatus of claim 32, further comprising:

a computation unit operative to estimate a received signal quality (SNR) for the data transmission at the serving base station and to limit the transmit power for the data transmission based on the estimated received SNR for the data transmission.

34. The apparatus of claim 32, wherein the adjustment unit is operative to, for each base station to be considered in adjusting the transmit power,

adjust the transmit power for the data transmission based on an indication obtained for the base station, a channel gain for the base station a current level of the transmit power for the data transmission, or a combination thereof.

35. An apparatus operable to perform power control for a wireless terminal in a wireless communication system, comprising:

means for obtaining, for each of at least one base station, an indication of interference observed by the base station, each of the at least one base station being a neighbor base station not designated to receive a data transmission sent by the wireless terminal or a serving base station designated to receive the data transmission sent by the wireless terminal; and

means for adjusting transmit power for the data transmission based on at least one indication obtained for the at least one base station.

36. The apparatus of claim 35, further comprising:

means for estimating a received signal quality (SNR) for the data transmission at a serving base station designated to receive the data transmission; and

means for limiting the transmit power for the data transmission based on the estimated received SNR for the data transmission.

37. The apparatus of claim 35, wherein for each base station to be considered in adjusting the transmit power, the transmit power for the data transmission is adjusted based on an indication obtained for the base station, a channel gain for the base station, a channel gain for the serving base station designated to receive the data transmission, a current level of the transmit power, or a combination thereof.

38. A method of performing power control in a wireless communication system, comprising:

ascertaining interference observed by a first base station not designated to receive a data transmission sent by a wireless terminal to a second base station;

adjusting transmit power for the data transmission based on the interference observed by the first base station; and

limiting the transmit power for the data transmission to maintain interference due to the data transmission at the second base station below a predetermined level.

39. The method of claim 38, wherein the interference observed by the first base station is ascertained based on a measurement report sent by the first base station, a current level of the transmit power used for the data transmission, an estimated distance to the first base station, or a combination thereof.

40. The method of claim 38, wherein the limiting the transmit power for the data transmission comprises

estimating a received signal quality (SNR) for the data transmission at the second base station, and

limiting the transmit power for the data transmission such that the received SNR for the data transmission is within a range of received SNRs allowable for the data transmission.

41. The method of claim 38, wherein the first base station is a base station with a strongest received signal at the wireless terminal among at least one base station received by the wireless terminal and not designated to receive the data transmission.

42. A method of performing power control for a wireless terminal in a wireless communication system, comprising:

adjusting transmit power for a first transmission sent on a first set of at least one frequency subband by the terminal to a serving base station designated to receive the first transmission, wherein the transmit power for the first transmission is adjusted to achieve a target received signal quality (SNR) for the first transmission at the serving base station; and

adjusting transmit power for a second transmission sent on a second set of at least one frequency subband by the terminal to the serving base station, wherein the transmit power for the second transmission is adjusted based on the transmit power for the first transmission and a transmit power delta.

43. The method of claim 42, wherein the first and second sets include different frequency subbands.

44. The method of claim 43, wherein the first set of at least one frequency subband is equal to the second set of at least one frequency subband.

45. The method of claim 42, further comprising:

obtaining, for each of at least one base station, an indication of interference observed by the base station, and wherein the transmit power for the second transmission is adjusted based on at least one indication obtained for the at least one base station.

46. The method of claim 45, wherein the transmit power for the second transmission is further adjusted based on a channel gain for each of the at least one base station, a current transmit power level for the first transmission, a range of allowable transmit power deltas, a maximum transmit power for the terminal, a peak-to-average backoff factor, or a combination thereof.

47. The method of claim 42, wherein the first transmission is for signaling sent on a control channel, and wherein the second transmission is for data sent on a data channel.

48. The method of claim 42, wherein the transmit power for the first transmission and the transmit power for the second transmission are adjusted at different rates.

49. A method of performing power control for a wireless terminal in a wireless communication system, comprising:

obtaining a reference power level corresponding to a target received signal quality (SNR) for a first transmission at a serving base station designated to received the first transmission from the terminal;

setting transmit power for a second transmission from the terminal to the serving base station based on the reference power level and a transmit power delta; and

adjusting the transmit power delta based on at least one parameter.

50. The method of claim 49, wherein the at least one parameter includes an indication of interference observed by each of at least one base station, a channel gain for each of the at least one base station, a current transmit power level for the first transmission, a range of allowable transmit power deltas, a maximum transmit power for the terminal, a peak-to-average backoff factor, or a combination thereof.

51. A method of reporting interference in a wireless communication system, comprising:

estimating interference observed at a base station;

forming an interference report for the estimated interference; and

broadcasting the interference report via a wireless channel.

52. The method of claim 51, wherein the interference does excludes signal power received for terminals transmitting to the base station.

53. The method of claim 51, further comprising:

comparing the estimated interference against a first interference threshold; and

setting a first bit based on whether the estimated interference is above or below the first interference threshold, and wherein the interference report comprises the first bit.

54. The method of claim 53, further comprising:

comparing the estimated interference against a second interference threshold that is higher than the first interference threshold; and

setting a second bit based on whether the estimated interference is above or below the second interference threshold, and wherein the interference report further comprises the second bit.

55. The method of claim 51, wherein the estimating interference observed at a base station comprises

obtaining an interference estimate for each of a plurality of subbands at the base station, and

deriving the estimated interference based on a plurality of interference estimates for the plurality of subbands.

56. The method of claim 55, wherein the estimated interference is an arithmetic average of the plurality of interference estimates for the plurality of subbands.

57. The method of claim 55, wherein the estimated interference is a geometric average of the plurality of interference estimates for the plurality of subbands.

58. The method of claim 55, wherein the estimated interference is obtained based on a capacity-based averaging of the plurality of interference estimates for the plurality of subbands.

59. An apparatus in a wireless communication system, comprising:

an interference estimator operative to estimate interference observed at a base station;

a controller operative to form an interference report for the estimated interference; and

a data processor operative to process the interference report for broadcast via a wireless channel.

60. The apparatus of claim 59, wherein the controller is operative to compare the estimated interference against an interference threshold and to set a bit based on whether the estimated interference is above or below the interference threshold, and wherein the interference report comprises the bit.

61. An apparatus in a wireless communication system, comprising:

means for estimating interference observed at a base station;

means for forming an interference report for the estimated interference; and

means for broadcasting the interference report via a wireless channel.

62. The apparatus of claim 61, further comprising:

means for comparing the estimated interference against an interference threshold; and

means for setting a bit based on whether the estimated interference is above or below the interference threshold, and wherein the interference report comprises the bit.

63. A method of scheduling data transmission in a wireless communication system, comprising:

obtaining, at a base station, a transmit power level supported by a wireless terminal for a data transmission to the base station, wherein the transmit power level is determined based on an indication of interference observed by each of at least one neighbor base station not designated to receive the data transmission; and

scheduling the wireless terminal for a data transmission based on the transmit power level supported by the wireless terminal.

64. The method of claim 63, further comprising:

adjusting a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission sent from the wireless terminal to the base station, and wherein the transmit power level is determined further based on the reference power level.

65. The method of claim 63, further comprising:

obtaining, at the base station, a particular number of subbands supported by the wireless terminal at the transmit power level, and wherein the wireless terminal is scheduled for the data transmission further based on the particular number of subbands supported at the transmit power level.

66. An apparatus in a wireless communication system, comprising:

a processor operative to obtain a transmit power level supported by a wireless terminal for a data transmission to a base station, wherein the transmit power level is determined based on an indication of interference observed by each of at least one neighbor base station not designated to receive the data transmission; and

a scheduler operative to schedule the wireless terminal for the data transmission based on the transmit power level supported by the wireless terminal.

67. The apparatus of claim 66, further comprising:

a controller operative to adjust a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission sent from the wireless terminal to the base station, and wherein the transmit power level is determined further based on the reference power level.

68. An apparatus in a wireless communication system, comprising:

means for obtaining a transmit power level supported by a wireless terminal for a data transmission to a base station, wherein the transmit power level is determined based on an indication of interference observed by each of at least one neighbor base station not designated to receive the data transmission; and

means for scheduling the wireless terminal for the data transmission based on the transmit power level supported by the wireless terminal.

69. The apparatus of claim 68, further comprising:

means for adjusting a reference power level for the wireless terminal to achieve a target signal quality (SNR) for a second transmission sent from the wireless terminal to the base station, and wherein the transmit power level is determined further based on the reference power level.