Techniques for transmitting and receiving synchronization signals over an unlicensed radio frequency spectrum band

1. A method for wireless communication, comprising:

receiving at a user equipment (UE) over an unlicensed radio frequency spectrum band an indication of a time window associated with a transmission of a synchronization signal;

waking up a receiver of the UE from a sleep state prior to the time window;

monitoring the unlicensed radio frequency spectrum band during the time window to receive the synchronization signal from a base station, wherein the time window is during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

receiving the synchronization signal from the base station during the time window.

2. The method of claim 1 , further comprising:

receiving, during the time window, timing information in the synchronization signal from the base station, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

3. The method of claim 2 , further comprising:

synchronizing the UE with the base station based at least in part on the timing information.

4. The method of claim 1 , wherein the indication of the time window is received in a system information block or a master information block.

5. The method of claim 1 , wherein the indication of the time window is received in a radio resource control (RRC) message.

6. The method of claim 1 , further comprising:

receiving system information for the base station during the time window, the system information received in a system information block or a master information block.

7. The method of claim 1 , further comprising:

performing radio resource management measurements on the synchronization signal.

8. The method of claim 1 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

9. An apparatus for wireless communication, comprising:

means for receiving at a user equipment (UE) over an unlicensed radio frequency spectrum band an indication of a time window associated with a transmission of a synchronization signal;

means for waking up a receiver of the UE from a sleep state prior to the time window;

means for monitoring the unlicensed radio frequency spectrum band during the time window to receive the synchronization signal from a base station, wherein the time window is during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

means for receiving the synchronization signal from the base station during the time window.

10. The apparatus of claim 9 , further comprising:

means for receiving, during the time window, timing information in the synchronization signal from the base station, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

11. The apparatus of claim 10 , further comprising:

means for synchronizing the UE with the base station based at least in part on the timing information.

12. The apparatus of claim 9 , wherein the indication of the time window is received in a system information block or a master information block.

13. The apparatus of claim 9 , wherein the indication of the time window is received in a radio resource control (RRC) message.

14. The apparatus of claim 9 , further comprising:

means for receiving system information for the base station during the time window, the system information received in a system information block or a master information block.

15. The apparatus of claim 9 , further comprising:

means for performing radio resource management measurements on the synchronization signal.

16. The apparatus of claim 9 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

17. An apparatus for wireless communication, comprising:

a processor; and

memory coupled to the processor, wherein the processor is configured to:

receive at a user equipment (UE) over an unlicensed radio frequency spectrum band an indication of a time window associated with a transmission of a synchronization signal;

wake up a receiver of the UE from a sleep state prior to the time window;

monitor the unlicensed radio frequency spectrum band during the time window to receive the synchronization signal from a base station, wherein the time window is during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

receive the synchronization signal from the base station during the time window.

18. The apparatus of claim 17 , wherein the processor is configured to:

receive, during the time window, timing information in the synchronization signal from the base station, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

19. The apparatus of claim 18 , wherein the processor is configured to:

synchronize the UE with the base station based at least in part on the timing information.

20. The apparatus of claim 17 , wherein the processor is configured to:

receive system information for the base station during the time window, the system information received in a system information block or a master information block.

21. The apparatus of claim 17 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

22. A non-transitory computer-readable medium for storing instructions executable by a processor, comprising:

instructions to receive at a user equipment (UE) over an unlicensed radio frequency spectrum band an indication of a time window associated with a transmission of a synchronization signal;

instructions to wake up a receiver of the UE from a sleep state prior to the time window;

instructions to monitor the unlicensed radio frequency spectrum band during the time window to receive the synchronization signal from a base station, wherein the time window is during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

instructions to receive the synchronization signal from the base station during the time window.

23. The non-transitory computer-readable medium of claim 22 , further comprising:

instructions to receive, during the time window, timing information in the synchronization signal from the base station, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

24. The non-transitory computer-readable medium of claim 22 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

25. A method for wireless communication, comprising:

transmitting, by a transmitter of a base station, an indication of a time window associated with a transmission of a synchronization signal;

performing a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band during the time window; and

transmitting, by the transmitter, the synchronization signal over the unlicensed radio frequency spectrum band at a transmission time during a periodic fixed subframe location within the time window, wherein the transmission time is based at least in part on a result of at least one of the CCAs.

26. The method of claim 25 , wherein performing the number of CCAs on the unlicensed radio frequency spectrum band during the time window comprises:

identifying a first successful one of the CCAs during the time window;

wherein the transmission time follows the first successful one of the CCAs during the time window.

27. The method of claim 25 , wherein performing the number of CCAs on the unlicensed radio frequency spectrum band during the time window comprises:

determining that none of the CCAs performed during the time window were successful;

wherein the transmission time occurs at an end of the time window.

28. The method of claim 25 , further comprising:

transmitting timing information during the time window, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

29. The method of claim 25 , further comprising:

transmitting the synchronization signal over the unlicensed radio frequency spectrum band during a clear channel assessment (CCA)-exempt transmission (CET).

30. The method of claim 25 , further comprising:

transmitting downlink control information (DCI) for a subframe in which the synchronization signal is transmitted, the DCI signaling at least one resource used to transmit the synchronization signal in the subframe.

31. The method of claim 25 , further comprising:

transmitting the synchronization signal over the unlicensed radio frequency spectrum band opportunistically.

32. The method of claim 31 , wherein the time window is associated with a different set of subcarrier frequencies of the unlicensed radio frequency spectrum band than the opportunistically transmitted synchronization signal.

33. The method of claim 31 , wherein the time window overlaps in time with the periodic fixed subframe location of the base station.

34. The method of claim 25 , wherein the time window replaces at least one clear channel assessment (CCA)-exempt transmission (CET) of the base station.

35. The method of claim 25 , wherein the number of CCAs comprises a plurality of CCAs.

36. The method of claim 25 , wherein the indication of the time window is transmitted in a system information block or a master information block.

37. The method of claim 25 , wherein the indication of the time window is transmitted in a radio resource control (RRC) message.

38. The method of claim 25 , further comprising:

transmitting system information for the base station during the time window, the system information being transmitted in a system information block or a master information block.

39. The method of claim 25 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

40. An apparatus for wireless communication, comprising:

means for transmitting, by a transmitter of a base station, an indication of a time window associated with a transmission of a synchronization signal;

means for performing a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band during the time window; and

means for transmitting, by the transmitter, the synchronization signal over the unlicensed radio frequency spectrum band at a transmission time during a periodic fixed subframe location within the time window, wherein the transmission time is based at least in part on a result of at least one of the CCAs.

41. The apparatus of claim 40 , wherein the means for performing the number of CCAs on the unlicensed radio frequency spectrum band during the time window comprises:

means for identifying a first successful one of the CCAs during the time window;

wherein the transmission time follows the first successful one of the CCAs during the time window.

42. The apparatus of claim 40 , wherein the means for performing the number of CCAs on the unlicensed radio frequency spectrum band during the time window comprises:

means for determining that none of the CCAs performed during the time window were successful;

wherein the transmission time occurs at an end of the time window.

43. The apparatus of claim 40 , further comprising:

means for transmitting timing information during the time window, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

44. The apparatus of claim 40 , further comprising:

means for transmitting the synchronization signal over the unlicensed radio frequency spectrum band during a clear channel assessment (CCA)-exempt transmission (CET).

45. The apparatus of claim 40 , further comprising:

means for transmitting downlink control information (DCI) for a subframe in which the synchronization signal is transmitted, the DCI signaling at least one resource used to transmit the synchronization signal in the subframe.

46. The apparatus of claim 40 , further comprising:

means for transmitting the synchronization signal over the unlicensed radio frequency spectrum band opportunistically.

47. The apparatus of claim 46 , wherein the time window is associated with a different set of subcarrier frequencies of the unlicensed radio frequency spectrum band than the opportunistically transmitted synchronization signal.

48. The apparatus of claim 46 , wherein the time window overlaps in time with the periodic fixed subframe location of the base station.

49. The apparatus of claim 40 , wherein the time window replaces at least one clear channel assessment (CCA)-exempt transmission (CET) of the base station.

50. The apparatus of claim 40 , wherein the number of CCAs comprises a plurality of CCAs.

51. The apparatus of claim 40 , wherein the indication of the time window is transmitted in a system information block or a master information block.

52. The apparatus of claim 40 , wherein the indication of the time window is transmitted in a radio resource control (RRC) message.

53. The apparatus of claim 40 , further comprising:

means for transmitting system information for the base station during the time window, the system information being transmitted in a system information block or a master information block.

54. The apparatus of claim 40 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

55. An apparatus for wireless communication, comprising:

a processor; and

memory coupled to the processor, wherein the processor is configured to:

transmit, by the transmitter of a base station, an indication of a time window associated with a transmission of a synchronization signal;

perform a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band during the time window; and

transmit, by the transmitter, the synchronization signal over the unlicensed radio frequency spectrum band at a transmission time a periodic fixed subframe location within during the time window, wherein the transmission time is based at least in part on a result of at least one of the CCAs.

56. The apparatus of claim 55 , wherein the processor is configured to:

transmit timing information during the time window, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

57. The apparatus of claim 55 , wherein the processor is configured to:

transmit downlink control information (DCI) for a subframe in which the synchronization signal is transmitted, the DCI signaling at least one resource used to transmit the synchronization signal in the subframe.

58. The apparatus of claim 55 , wherein the number of CCAs comprises a plurality of CCAs.

59. The apparatus of claim 55 , wherein the indication of the time window is transmitted in a system information block or a master information block.

60. The apparatus of claim 55 , wherein the indication of the time window is transmitted in a radio resource control (RRC) message.

61. The apparatus of claim 55 , wherein the processor is configured to:

transmit system information for the base station during the time window, the system information being transmitted in a system information block or a master information block.

62. The apparatus of claim 55 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

63. A non-transitory computer-readable medium for storing instructions executable by a processor, comprising:

instructions to transmit, by a transmitter of a base station, an indication of a time window associated with a transmission of a synchronization signal;

instructions to perform a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band during the time window; and

instructions to transmit, by the transmitter, the synchronization signal over the unlicensed radio frequency spectrum band at a transmission time during a periodic fixed subframe location within the time window, wherein the transmission time is based at least in part on a result of at least one of the CCAs.

64. The non-transitory computer-readable medium of claim 63 , further comprising:

instructions to transmit timing information during the time window, the timing information comprising an indication of one from a group consisting of: a current frame of the base station, a current subframe of the base station, or a current symbol.

65. The non-transitory computer-readable medium of claim 63 , wherein the number of CCAs comprises a plurality of CCAs.

66. The non-transitory computer-readable medium of claim 63 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

67. A method for wireless communication, comprising:

monitoring an unlicensed radio frequency spectrum band, at a receiver of a user equipment (UE), to receive a transmission of a synchronization signal from a base station during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

receiving, at the receiver, the synchronization signal from the base station.

68. The method of claim 67 , wherein receiving the synchronization signal comprises receiving the synchronization signal with timing information.

69. The method of claim 68 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

70. The method of claim 68 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

71. The method of claim 68 , further comprising:

synchronizing the UE with the base station based at least in part on the timing information.

72. The method of claim 67 , further comprising:

receiving system information for the base station with the synchronization signal, the system information being received in a system information block or a master information block.

73. The method of claim 67 , further comprising:

performing radio resource management measurements on the synchronization signal.

74. The method of claim 67 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

75. An apparatus for wireless communication, comprising:

means for monitoring an unlicensed radio frequency spectrum band, at a receiver of a user equipment (UE), to receive a transmission of a synchronization signal from a base station during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

means for receiving, at the receiver, the synchronization signal from the base station.

76. The apparatus of claim 75 , wherein the means for receiving the synchronization signal comprises means for receiving the synchronization signal with timing information.

77. The apparatus of claim 76 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

78. The apparatus of claim 76 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

79. The apparatus of claim 76 , further comprising:

means for synchronizing the UE with the base station based at least in part on the timing information.

80. The apparatus of claim 75 , further comprising:

means for receiving system information for the base station with the synchronization signal, the system information being received in a system information block or a master information block.

81. The apparatus of claim 75 , further comprising:

means for performing radio resource management measurements on the synchronization signal.

82. The apparatus of claim 75 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

83. An apparatus for wireless communication, comprising:

a processor; and

memory coupled to the processor, wherein the processor is configured to:

monitor an unlicensed radio frequency spectrum band, at a receiver of a user equipment (UE), to receive a transmission of a synchronization signal from a base station during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

receive, at the receiver, the synchronization signal from the base station.

84. The apparatus of claim 83 , the processor configured to receive the synchronization signal comprises the processor configured to:

receive the synchronization signal with timing information.

85. The apparatus of claim 84 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

86. The apparatus of claim 84 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

87. The apparatus of claim 84 , wherein the processor is configured to:

synchronize the UE with the base station based at least in part on the timing information.

88. The apparatus of claim 83 , wherein the processor is configured to:

perform radio resource management measurements on the synchronization signal.

89. The apparatus of claim 83 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

90. A non-transitory computer-readable medium for storing instructions executable by a processor, comprising:

instructions to monitor an unlicensed radio frequency spectrum band, at a receiver of a user equipment (UE), to receive a transmission of a synchronization signal from a base station during a clear channel assessment (CCA)-exempt transmission (CET) of the base station; and

instructions to receive, at the receiver, the synchronization signal from the base station.

91. The non-transitory computer-readable medium of claim 90 , wherein the instructions to receive the synchronization signal comprise:

instructions to receive the synchronization signal with timing information.

92. The non-transitory computer-readable medium of claim 90 , further comprising:

instructions to perform radio resource management measurements on the synchronization signal.

93. The non-transitory computer-readable medium of claim 90 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

94. A method for wireless communication, comprising:

performing, at a base station, a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band; and

transmitting, by a transmitter of the base station, a synchronization signal with timing information over the unlicensed radio frequency spectrum band, at a transmission time during a periodic fixed subframe based at least in part on a result of at least one of the CCAs.

95. The method of claim 94 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

96. The method of claim 94 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

97. The method of claim 94 , wherein performing the number of CCAs on the unlicensed radio frequency spectrum band comprises:

identifying a first successful one of the CCAs;

wherein the transmission time follows the first successful one of the CCAs.

98. The method of claim 94 , wherein performing the number of CCAs on the unlicensed radio frequency spectrum band comprises:

determining that none of the CCAs were successful;

wherein the transmission time following a performance of a last unsuccessful one of the number of CCAs.

99. The method of claim 94 , wherein the number of CCAs comprises a plurality of CCAs.

100. The method of claim 94 , further comprising:

transmitting system information for the base station with the synchronization signal, the system information being transmitted in a system information block or a master information block.

101. The method of claim 94 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

102. An apparatus for wireless communication, comprising:

means for performing, at a base station, a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band; and

means for transmitting, by a transmitter of the base station, a synchronization signal with timing information over the unlicensed radio frequency spectrum band, at a transmission time during a periodic fixed subframe based at least in part on a result of at least one of the CCAs.

103. The apparatus of claim 102 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

104. The apparatus of claim 102 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

105. The apparatus of claim 102 , wherein the means for performing the number of CCAs on the unlicensed radio frequency spectrum band comprises:

means for identifying a first successful one of the CCAs;

wherein the transmission time follows the first successful one of the CCAs.

106. The apparatus of claim 102 , wherein the means for performing the number of CCAs on the unlicensed radio frequency spectrum band comprises:

means for determining that none of the CCAs were successful;

wherein the transmission time following a performance of a last unsuccessful one of the number of CCAs.

107. The apparatus of claim 102 , wherein the number of CCAs comprises a plurality of CCAs.

108. The apparatus of claim 102 , further comprising:

means for transmitting system information for the base station with the synchronization signal, the system information being transmitted in a system information block or a master information block.

109. The apparatus of claim 102 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

110. An apparatus for wireless communication, comprising:

a processor; and

memory coupled to the processor, wherein the processor is configured to:

perform, at a base station, a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band; and

transmit, by a transmitter of the base station, a synchronization signal with timing information over the unlicensed radio frequency spectrum band, at a transmission time during a periodic fixed subframe based at least in part on a result of at least one of the CCAs.

111. The apparatus of claim 110 , wherein the timing information comprises an indication of a current frame of the base station and a current subframe of the base station.

112. The apparatus of claim 110 , wherein the timing information comprises an indication of a current frame of the base station, a current subframe of the base station, and a current symbol.

113. The apparatus of claim 110 , wherein the number of CCAs comprises a plurality of CCAs.

114. The apparatus of claim 110 , wherein the processor is configured to:

transmit system information for the base station with the synchronization signal, the system information being transmitted in a system information block or a master information block.

115. The apparatus of claim 110 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).

116. A non-transitory computer-readable medium for storing instructions executable by a processor, comprising:

instructions to perform, at a base station, a number of clear channel assessments (CCAs) on an unlicensed radio frequency spectrum band; and

instructions to transmit, by a transmitter of the base station, a synchronization signal with timing information over the unlicensed radio frequency spectrum band, at a transmission time during a periodic fixed subframe based at least in part on a result of at least one of the CCAs.

117. The non-transitory computer-readable medium of claim 116 , wherein the number of CCAs comprises a plurality of CCAs.

118. The non-transitory computer-readable medium of claim 116 , wherein the synchronization signal comprises one from a group consisting of:

a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS), and a channel state information reference signal (CSI-RS).