ENHANCED SRS TRANSMISSION FOR MIMO OPERATION IN LTE-A

• US 20140112168A1
• Filed: 02/21/2013
• Published: 04/24/2014
• Est. Priority Date: 10/24/2012
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Chen, Wanshi, Gaal, Peter, Xu, Hao, Wei, Yongbin, Geirhofer, Stefan
• Granted Patent: US 9,596,065 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 7/0404 the mobile station comprising multiple antennas, e.g. to provide uplink diversity
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0456 Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• CPC Class Codes: H04B 7/046 taking physical layer constraints into account
• CPC Class Codes: H04B 7/0602 using antenna switching H04B7/0686 takes precedence; antenna beam directivity switching H01Q3/24
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0619 using feedback from receiving side feedback signaling for adaptive modulation/coding H04L1/0001
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04B 7/0802 using antenna selection H04B7/0868 takes precedence; antenna beam directivity switching H01Q3/24
• CPC Class Codes: H04J 11/005 of intercell interference
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/0051 of dedicated pilots, i.e. pilots destined for a single user or terminal
• CPC Class Codes: H04L 5/0073 Allocation arrangements that take into account other cell interferences for intercell interference mitigation or co-ordination in orthogonal multiplex systems H04J11/005
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal

Abstract

Enhanced sounding reference signal (SRS) transmissions for multiple input, multiple output (MIMO) operation are disclosed in which a user equipment (UE) detects an observed interference level for each receiver chain of the UE. In response to an imbalance, the UE precodes a SRS targeting downlink operation to indicate the imbalance. The UE then transmits the precoded SRS. In alternative aspects, the precoded SRS vector may be determined by an evolved nodeB (eNB). In such aspects, the eNB determines the precoded SRS vector targeting downlink operations for the served UEs, wherein the determined precoded SRS vector includes determining the precoded SRS vector on a per UE basis, enabling the precoded SRS vector for either one or both of frequency division duplex (FDD) systems and time division duplex (TDD) systems, or enabling the precoded SRS vector for aperiodic SRS only. The eNB then transmits the determined precoded SRS vector to the UE.

Claims

1. A method of wireless communication, comprising:

detecting, at a mobile device, an observed interference level for each one of a plurality of receiver chains of the mobile device;

in response to detecting an imbalance in the observed interference level for the plurality of receiver chains, precoding a sounding reference signal (SRS) to indicate the imbalance; and

transmitting the precoded SRS.

2. The method of claim 1, wherein the precoding the SRS targets downlink operations.

3. The method of claim 1, wherein the precoding further includes an indication to compensate a transmit power for one or more imbalanced receiver chains of the plurality of receiver chains, wherein the indication is based on the detected imbalance.

4. The method of claim 1, wherein the precoded SRS is processed using a first virtual antenna port while an SRS targeting uplink operations is processed using a second virtual antenna port, wherein the first and second virtual antenna ports are separate.

5. The method of claim 4, further including:

using a first symbol on the first virtual antenna port for the precoded SRS; and

using a second symbol on the second virtual antenna port for the SRS targeting uplink operations, wherein the first and second symbols are different.

6. The method of claim 1, wherein the precoding is also applied to a physical uplink shared channel when the precoded SRS and an SRS targeting uplink operations are processed using a same virtual antenna port.

7. The method of claim 1, further including:

detecting, at the mobile device, transmit power within a threshold level of maximum power; and

in response to the detecting, disabling the precoding at the mobile device.

8. The method of claim 2, further including:

receiving, by the mobile device, a control signal indicating a power compensation to apply to the one or more imbalanced receiver chains in response to the indication;

detecting, at the mobile device, a transmit power of the mobile device; and

applying a percentage of the power compensation to the one or more imbalanced receiver chains, wherein the percentage is determined based on how close the transmit power is to the maximum transmit power of the mobile device.

9. The method of claim 1, wherein the precoding is based, at least in part, on a covariance matrix of the imbalance.

10. The method of claim 9, wherein the mobile device is an antenna selection capable mobile device without multiple input multiple output (MIMO) capabilities, wherein the precoding is based, at least in part, on a diagonal matrix corresponding to the covariance matrix.

11. The method of claim 2, wherein the mobile device is an antenna selection capable mobile device without multiple input multiple output (MIMO) capabilities;

the method further including;

receiving, by the mobile device, a control signal indicating a power compensation to apply to the one or more imbalanced receiver chains in response to the indication; and

disregarding, by the mobile device, the control signal.

12. The method of claim 1, further including:

precoding additional SRS targeting downlink operations for each reference signal for which interference is estimated; and

transmitting the additional precoded SRS.

13. The method of claim 1, further including:

receiving, from a base station, a precoded SRS vector indicating the precoding to apply to the precoded SRS.

14. The method of claim 13, further including:

receiving a plurality of aperiodic SRS triggers in a single subframe, wherein the precoded SRS vector are received with the plurality of aperiodic SRS triggers; and

indicating an error when the plurality of aperiodic SRS triggers indicate different precoded SRS vectors.

15. The method of claim 13, further including:

receiving a plurality of aperiodic SRS triggers in a single subframe, wherein the precoded SRS vector are received with the plurality of aperiodic SRS triggers; and

selecting the precoded SRS vector associated with the last of the plurality of aperiodic SRS triggers received in the same subframe.

16. The method of claim 1, wherein the transmitting includes:

transmitting the precoded SRS over a plurality of subframes.

17. The method of claim 16, wherein the precoded SRS is transmitted using the same transmission parameters for each of the plurality of subframes.

18. The method of claim 16, wherein a portion of the precoded SRS is transmitted over each of a plurality of subframes.

19. The method of claim 16, wherein the plurality of subframes are one of:

configurable and predetermined.

20. The method of claim 16, wherein the plurality of subframes are linked with transmission time interval (TTI) bundling operations for physical uplink shared channel (PUSCH).

21. The method of claim 16, wherein the precoded SRS includes demodulation reference signals (DM-RS) used for sounding.

22. A method of wireless communication, comprising:

determining, by a base station, a precoded sounding reference signal (SRS) vector for one or more user equipments (UEs), wherein the determined precoded SRS vector includes one of;

determining the precoded SRS vector on a per UE basis;

enabling the precoded SRS vector for at least one of;

a frequency division duplex (FDD) system or a time division duplex (TDD) system; and

enabling the precoded SRS vector for aperiodic SRS only; and

transmitting the determined precoded SRS vector from the base station to at least one of the one or more UEs.

23. The method of claim 22, wherein the precoded SRS vector targets downlink operations.

24. The method of claim 22, wherein the base station determines a single precoded SRS vector.

25. The method of claim 22, wherein the base station dynamically determines a plurality of precoded SRS vectors.

26. The method of claim 25, wherein each of the plurality of precoded SRS vectors is assigned to one of a plurality of aperiodic SRS sets.

27. The method of claim 26, further including:

determining a downlink control information (DCI) format; and

transmitting from the base station to the mobile device the precoded SRS vector assigned to the one of the plurality of aperiodic SRS set corresponding to the determined DCI format.

28. The method of claim 22, wherein the precoded SRS vector is implicitly selected for use based on an operating condition.

29. The method of claim 28, wherein the operation condition includes one of:

a subframe index;

an aggregation level;

a decoding candidate;

a search space; and

a channel type.

30. The method of claim 22, wherein the precoded SRS vector is selected for use based on one of:

a precoded SRS vector assignment indication; and

information included in a downlink control information (DCI) message.

31. The method of claim 22, wherein precoded SRS vector is selected for use according to a precoding used for the physical uplink shared channel (PUSCH).

32. The method of claim 22, wherein the determined precoded SRS vector instructs transmission of a precoded SRS over a plurality of subframes.

33. The method of claim 32, wherein the determined precoded SRS vector instructs the precoded SRS to be transmitted using the same transmission parameters for each of the plurality of subframes.

34. The method of claim 32, wherein the determined precoded SRS vector instructs a portion of the precoded SRS to be transmitted over each of a plurality of subframes.

35. The method of claim 32, wherein the plurality of subframes are one of:

configurable and predetermined.

36. The method of claim 32, wherein the plurality of subframes are linked with transmission time interval (TTI) bundling operations for physical uplink shared channel (PUSCH).

37. The method of claim 32, wherein the precoded SRS includes demodulation reference signals (DM-RS) used for sounding.

38. A method of wireless communication, comprising:

determining, at a mobile device, a density of sounding reference signal (SRS) transmissions; and

transmitting SRS by the mobile device based at least in part on the determined density.

39. The method of claim 38, wherein the determining the density is based at least in part on a channel condition or an interference condition including one of:

a number of antennas at a serving base station exceeding a threshold antenna value; and

detecting inaccuracy of the downlink communications over a predetermined time period.

40. The method of claim 38, wherein the determining the density is based at least in part on a configuration signal received from a base station.

41. The method of claim 38, wherein the density of SRS transmissions includes one or more additional SRS transmissions in a same subframe as a first SRS transmission.

42. The method of claim 38, wherein the density of SRS transmissions includes an SRS transmission across a bundled number of subframes, wherein the bundled number of subframes includes two or more subframes.

43. The method of claim 42, wherein the SRS transmission across the bundled number of subframes includes one of:

repeating the SRS transmission across the bundled number of subframes; and

transmitting a portion of the SRS transmission across each of the bundled number of subframes.

44. The method of claim 42, wherein the bundled number subframes are one of:

consecutive and non-consecutive.

45. The method of claim 42, wherein the bundled number of subframes are one of:

predetermined and configurable.

46. The method of claim 38, wherein the density of SRS transmissions includes one SRS transmission in a same subframe.

47. The method of claim 38, wherein the transmission of SRS is triggered based at least in part on at least one of a higher layer configuration or an information field in a control channel.

48. A method of wireless communication, comprising:

determining, at a base station, a density of sounding reference signal (SRS) transmissions for a user equipment (UE);

indicating the density of SRS transmissions to the UE; and

receiving, at the base station, the SRS transmissions from the UE.

49. The method of claim 48, further comprising:

determining a channel estimation for downlink multiple input, multiple output (MIMO) operations to the mobile device based on the SRS transmissions; and

transmitting downlink data to the mobile device using the determined channel estimation.

50. The method of claim 48, wherein the SRS transmissions include one of:

a single SRS received in a single subframe; and

a plurality of SRS are received in a single subframe.

51. The method of claim 48, wherein the SRS transmissions include a plurality of SRS received across a bundled number of subframes, wherein the bundled number of subframes includes two or more subframes.

52. The method of claim 51, wherein the plurality of SRS are received including one of:

a repetition of a same SRS transmission from the mobile device; and

a portion of the same SRS transmission.

53. The method of claim 51, wherein the bundled number subframes are one of:

consecutive and non-consecutive.

54. The method of claim 51, wherein the bundled number of subframes are one of:

predetermined and configurable.

55. The method of claim 48, wherein the density of SRS transmissions includes one SRS transmission in a same subframe.

56. The method of claim 48, wherein the SRS transmissions received are triggered based at least in part on at least one of a higher layer configuration or an information field in a control channel.

57. An apparatus configured for wireless communication, comprising:

means for detecting, at a mobile device, an observed interference level for each one of a plurality of receiver chains of the mobile device;

means, executable in response to detecting an imbalance in the observed interference level for the plurality of receiver chains, for precoding a sounding reference signal (SRS) to indicate the imbalance; and

means for transmitting the precoded SRS.

58. The apparatus of claim 57, wherein the means for precoding the SRS targets downlink operations.

59. The apparatus of claim 57, wherein the precoding further includes an indication to compensate a transmit power for one or more imbalanced receiver chains of the plurality of receiver chains, wherein the indication is based on the detected imbalance.

60. The apparatus of claim 57, wherein the precoded SRS is processed using a first virtual antenna port while an SRS targeting uplink operations is processed using a second virtual antenna port, wherein the first and second virtual antenna ports are separate.

61. The apparatus of claim 57, wherein the precoding is also applied to a physical uplink shared channel when the precoded SRS and an SRS targeting uplink operations are processed using a same virtual antenna port.

62. The apparatus of claim 57, further including:

means for detecting, at the mobile device, transmit power within a threshold level of maximum power; and

means, executable in response to the means for detecting, for disabling the precoding at the mobile device.

63. The apparatus of claim 57, further including:

means for precoding additional SRS targeting downlink operations for each reference signal for which interference is estimated; and

means for transmitting the additional precoded SRS.

64. The apparatus of claim 57, further including:

means for receiving, from a base station, a precoded SRS vector indicating the precoding to apply to the precoded SRS.

65. An apparatus configured for wireless communication, comprising:

means for determining, by a base station, a precoded sounding reference signal (SRS) vector for one or more user equipments (UEs), wherein the determined precoded SRS vector includes one of;

means for determining the precoded SRS vector on a per UE basis;

means for enabling the precoded SRS vector for at least one of;

a frequency division duplex (FDD) system or a time division duplex (TDD) system; and

means for enabling the precoded SRS vector for aperiodic SRS only; and

means for transmitting the determined precoded SRS vector from the base station to at least one of the one or more UEs.

66. The apparatus of claim 65, wherein the precoded SRS vector targets downlink operations.

67. The apparatus of claim 65, wherein the precoded SRS vector is implicitly selected for use based on one of:

a subframe index;

an aggregation level;

a decoding candidate;

a search space; and

a channel type.

68. The apparatus of claim 65, wherein the precoded SRS vector is selected for use based on one of:

a precoded SRS vector assignment indication; and

information included in a downlink control information (DCI) message.

69. The apparatus of claim 65, wherein the precoded SRS vector is selected for use according to a precoding used for the physical uplink shared channel (PUSCH).

70. The apparatus of claim 65, wherein the determined precoded SRS vector instructs transmission of a precoded SRS over a plurality of subframes.

71. An apparatus configured for wireless communication, comprising:

means for determining, at a mobile device, a density of sounding reference signal (SRS) transmissions; and

means for transmitting SRS by the mobile device based at least in part on the determined density.

72. The apparatus of claim 71, wherein the means for determining the density is based at least in part on a channel condition or an interference condition including one of:

a number of antennas at a serving base station exceeding a threshold antenna value; and

detecting inaccuracy of the downlink communications over a predetermined time period.

73. The apparatus of claim 71, wherein the means for determining the density is based at least in part on a configuration signal received from a base station.

74. The apparatus of claim 71, wherein the means for transmitting SRS includes one or more additional SRS transmissions in a same subframe as a first SRS transmission.

75. The apparatus of claim 71, wherein the means for transmitting SRS includes an SRS transmission across a bundled number of subframes, wherein the bundled number of subframes includes two or more subframes.

76. The apparatus of claim 71, wherein the density of SRS transmissions includes one SRS transmission in a same subframe.

77. The apparatus of claim 71, wherein the transmission of SRS is triggered based at least in part on at least one of a higher layer configuration or an information field in a control channel.

78. An apparatus configured for wireless communication, comprising:

means for determining, at a base station, a density of sounding reference signal (SRS) transmissions for a user equipment (UE);

means for indicating the density of SRS transmissions to the UE; and

means for receiving, at the base station, the SRS transmissions from the UE.

79. The apparatus of claim 78, further comprising:

means for determining a channel estimation for downlink multiple input, multiple output (MIMO) operations to the mobile device based on the SRS transmissions; and

means for transmitting downlink data to the mobile device using the determined channel estimation.

80. The apparatus of claim 78, wherein the SRS transmissions include one of:

a single SRS received in a single subframe and a plurality of SRS received in a single subframe.

81. The apparatus of claim 78, wherein the SRS transmissions include a plurality of SRS received across a bundled number of subframes, wherein the bundled number of subframes includes two or more subframes.

82. The apparatus of claim 78, wherein the density of SRS transmissions includes one SRS transmission in a same subframe.

83. The apparatus of claim 78, wherein the SRS transmissions received are triggered based at least in part on at least one of a higher layer configuration or an information field in a control channel.

84. A computer program product for wireless communications in a wireless network, comprising:

a non-transitory computer-readable medium having program code recorded thereon, the program code including;

program code for causing at least one computer to detect, at a mobile device, an observed interference level for each one of a plurality of receiver chains of the mobile device;

program code, executable in response to detecting an imbalance in the observed interference level for the plurality of receiver chains, for causing at least one computer to precode a sounding reference signal (SRS) to indicate the imbalance; and

program code for causing at least one computer to transmit the precoded SRS.

85. A computer program product for wireless communications in a wireless network, comprising:

a non-transitory computer-readable medium having program code recorded thereon, the program code including;

program code for causing at least one computer to determine, by a base station, a precoded sounding reference signal (SRS) vector for one or more user equipments (UEs), wherein the determined precoded SRS vector includes one of;

program code for causing at least one computer to determine the precoded SRS vector on a per UE basis;

program code for causing at least one computer to enable the precoded SRS vector for at least one of;

a frequency division duplex (FDD) system or a time division duplex (TDD) system; and

program code for causing at least one computer to enable the precoded SRS vector for aperiodic SRS only; and

program code for causing at least one computer to transmit the determined precoded SRS vector from the base station to at least one of the one or more UEs.

86. A computer program product for wireless communications in a wireless network, comprising:

a non-transitory computer-readable medium having program code recorded thereon, the program code including;

program code for causing at least one computer to determine, at a mobile device, a density of sounding reference signal (SRS) transmissions; and

program code for causing at least one computer to transmit SRS by the mobile device based at least in part on the determined density.

87. A computer program product for wireless communications in a wireless network, comprising:

a non-transitory computer-readable medium having program code recorded thereon, the program code including;

program code for causing at least one computer to determine, at a base station, a density of sounding reference signal (SRS) transmissions for a user equipment (UE) served by the base station;

program code for causing at least one computer to indicate the density of SRS to the UE; and

program code for causing at least one computer to receive, at the base station, the SRS transmissions from the UE.

88. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured;

to detect, at a mobile device, an observed interference level for each one of a plurality of receiver chains of the mobile device;

to precode a sounding reference signal (SRS) to indicate the imbalance in response to detecting an imbalance in the observed interference level for the plurality of receiver chains; and

to transmit the precoded SRS.

89. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured;

to determine, by a base station, a precoded sounding reference signal (SRS) vector for one or more user equipments (UEs), wherein the determined precoded SRS vector includes one of;

to determine the precoded SRS vector on a per UE basis;

to enable the precoded SRS vector for at least one of;

a frequency division duplex (FDD) system or a time division duplex (TDD) system; and

to enable the precoded SRS vector for aperiodic SRS only; and

to transmit the determined precoded SRS vector from the base station to at least one of the one or more served UEs.

90. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured;

to determine, at a mobile device, a density of sounding reference signal (SRS) transmissions; and

to transmit SRS by the mobile device based at least in part on the determined density.

91. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured;

to determine, at a base station, a density of sounding reference signal (SRS) transmissions for a user equipment (UE);

to indicate the density of SRS transmissions to the UE; and

to receive, at the base station, the SRS transmissions from the UE.