Preambles in Ofdma System

• US 20080039107A1
• Filed: 06/23/2005
• Published: 02/14/2008
• Est. Priority Date: 06/24/2004
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Zhang, Hang, Tong, Wen, Ma, Jianglei, Zhu, Peiying, Jia, Ming, Fong, Mo-Han
• Granted Patent: US 7,961,696 B2
• Time in Patent Office: Days
• US Class Current: 455/450
• CPC Class Codes: H04B 7/02 Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas RAKE receivers H04B1/7115
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/265 Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators H04L27/26524 takes precedence
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2686 Range of frequencies or delays tested
• CPC Class Codes: H04L 27/2692 with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 7/043 Pseudo-noise [PN] codes variable during transmission synchronisation of spread spectrum receivers H04B1/69
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition

Abstract

The present invention provides a preamble that is inserted into an OFDMA frame and has a common sequence for all the base stations participating in a transmission. The subscriber station performs fine synchronization using the common sequence on the common preamble, and the resulting peaks will provide the locations of candidate base stations. The base station specific search is then performed in the vicinities of those peaks by using base station specific pseudo-noise sequences. With this two stage cell search, the searching window is drastically reduced. The preamble is matched to known values by a respective receiver to decode the signals and permit multiple signals to be transferred from the transmitter to the receiver. The preamble may comprise two parts, Preamble-1 and Preamble-2, which may be used in different systems, including multioutput, multi-input (MIMO) systems.

Claims

1. A method for accessing an orthogonal frequency division multiplexing access (OFDMA) system comprising the steps of:

a) constructing an OFDMA frame having a training sequence;

b) assigning said training sequence for use in a plurality of base stations,

c) transmitting said training sequence by said plurality of base stations; and

d) detecting said training sequence at said subscriber station;

e) performing synchronization at said subscriber station using said training sequence.

2. The method according to claim 1, wherein said training sequence is a preamble having a common synchronization channel comprising common synchronization subcarriers, said common synchronization subcarriers carrying a common sequence;

said common sequence providing locations of candidate base stations, and reducing a search window for base station specific preamble.

3. The method according to claim 2, wherein said common sequence has a repeated time domain structure.

4. The method according to claim 2, wherein said common synchronization subcarriers comprises pseudo-noise codes.

5. The method according to claim 2, wherein a length of said common sequence is scalable with a bandwidth of a channel, thus providing same synchronization performance for all bandwidth.

6. The method according to claim 1, wherein said training sequence is located in a zone comprising a first dimension of subchannels and a second dimension of said time division and multiplex OFDM symbols;

said zone being defined by a subcarrier allocation method.

7. The method according to claim 1, wherein said training sequence is located in a fully utilized subchannel (FUSC) zone.

8. The method according to claim 1, wherein said training sequence is for a partially utilized subchannel (PUSC) zone.

9. The method according to claim 1, wherein said common sequence results a low peak to average power ratio (PAPR).

10. The method according to claim 2, wherein said common synchronization subcarriers are separated by null-subcarriers.

11. The method according to claim 2, further comprising the step of carrying additional signaling information in a second common channel.

12. The method according to claim 1, wherein said OFDMA system is selected from the group consisting of single-input, single-output (SISO) system, multiple-input, single-output (MISO) system, and a multiple-input, multiple-output (MIMO) system.

13. The method according to claim 2, wherein said OFDMA system is a multi-input, single-output (MISO) system, further comprising the step of transmitting said preamble in a cyclic delay diversity (CDD) on a plurality of outputs.

14. The method according to claim 1, wherein said training sequence is at a flexible location being indicated by a preceding zone in said OFDMA frame.

15. The method according to claim 11, wherein said additional signaling information identifies a segment.

16. The method according to claim 1, wherein said training sequence is a preamble, said preamble comprising cell-specific synchronization subcarriers;

further comprising the step of assigning said preamble for use in said plurality of base stations and performing cell search at said subscriber station.

17. The method according to claim 16, wherein said OFDMA system is multiple-input, multiple-output (MIMO) system, further comprising the step of assigning said cell-specific synchronization subcarriers to a plurality of antennas according to a predefined antenna mapping pattern.

18. The method according to claim 17, wherein a defined set of said cell-specific synchronization subcarriers is used for MIMO systems with various numbers of antennas.

19. The method according to claim 17, wherein said predefined antenna mapping pattern is based on time division, further comprising the steps of dividing said cell-specific synchronization subcarriers of said preamble into a plurality of groups, and transmitting each of said plurality of groups at a predefined time.

20. The method according to claim 17, wherein said predefined antenna mapping pattern is based on code division.

21. The method according to claim 20, further comprising the steps of mapping Walsh codes to said plurality of antennas, and mapping Walsh chips to said cell-specific synchronization subcarriers of said preamble.

22. The method according to claim 21, further comprising the steps of mapping Walsh chips to said cell-specific synchronization subcarriers of said preamble in both time direction and frequency direction.

23. The method according to claim 16, further comprising the step of using Steiner approach for cyclic shift in time to separate different transmit antennas and to achieve a low peak to average power ratio (PAPR) or a low cross correlation.

24. The method according to claim 17, wherein said predefined antenna mapping pattern includes mapping pattern for null-subcarriers, said null-subcarriers providing interference avoidance and carrier interference ratio (CIR) estimation.

25. The method according to claim 16, wherein said cell-specific synchronization subcarriers of second preamble have same subchannel permutation and grouping as data subcarriers.

26. The method according to claim 16, wherein only a part of said cell-specific synchronization subcarriers of said preamble is used by a sector.

27. The method according to claim 2, wherein said preamble is a first preamble, and said OFDMA frame has a second preamble, said second preamble comprising cell-specific synchronization subcarriers, further comprising the step of assigning said second preamble for use in said plurality of base stations and performing cell search at said subscriber station.

28. The method according to claim 27, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

29. The method according to claim 27, wherein said first preamble and said second preamble are inserted in alternating frames.

30. The method according to claim 27, wherein said first preamble or second preamble is located at a predefined location.

32. The method according to claim 27, wherein said first preamble or said second preamble coexists with a legacy preamble.

33. The method according to claim 27, wherein said second preamble is at a flexible location being indicated by a preceding zone in said OFDMA frame.

34. The method according to claim 27, wherein said OFDMA frame has a plurality of second preambles.

31. The method according to claim 31, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

35. An orthogonal frequency division multiplexing access (OFDMA) system comprising:

a) a base station controller adapted to schedule data being transmitted;

b) a plurality of base stations operatively associated with said base station controller, each base station being adapted to receive at least a portion of scheduled data from said base station controller, and to transmit a plurality of orthogonal frequency division multiplexing (OFDM) symbols to said subscriber station;

said plurality of base stations transmitting an OFDMA frame having a training sequence;

c) a subscriber station using said training sequence to provide locations of candidate base stations.

36. The OFDMA system according to claim 35, wherein said training sequence is a preamble having a common synchronization channel comprising common synchronization subcarriers, said common synchronization subcarriers carrying a common sequence, said common sequence providing locations of candidate base stations, and reducing a search window for base station specific preamble.

37. The OFDMA system according to claim 36, wherein said common sequence comprises pseudo-noise codes.

38. The OFDMA system according to claim 36, wherein said common sequence results a low peak to average power ratio (PAPR).

39. The OFDMA system according to claim 36, wherein said common synchronization channel is separated by null-subcarriers.

40. The OFDMA system according to claim 36, wherein said preamble has a second common channel carrying additional signaling information.

41. The OFDMA system according to claim 35, wherein the OFDMA system is selected from the group consisting of single-input, single-output (SISO) system, multiple-input, single-output (MISO) system, and a multiple-input, multiple-output (MIMO) system.

42. The OFDMA system according to claim 35, wherein said training sequence is at a flexible location being indicated by a preceding zone in said OFDMA frame.

43. The OFDMA system according to claim 35, wherein said training sequence is a preamble, said preamble comprising cell-specific synchronization subcarriers, said preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

44. The OFDMA system according to claim 43, wherein said OFDMA system is multiple-input, multiple-output (MIMO) system, said common synchronization channels subcarriers being assigned to a plurality of antennas according to a predefined antenna mapping pattern.

45. The OFDMA system according to claim 44, wherein said predefined antenna mapping pattern is based on time division, wherein said cell-specific synchronization subcarriers of said second preamble are devised into a plurality of groups, and each of said plurality of groups is transmitted at a predefined time.

46. The OFDMA system according to claim 44, wherein said predefined antenna mapping pattern is based on code division.

47. The OFDMA system according to claim 44, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.

48. The OFDMA system according to claim 36, wherein said preamble is a first preamble, and said OFDMA frame has a second preamble, said second preamble comprising cell-specific synchronization subcarriers, said second preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

49. The OFDMA system according to claim 48, wherein said first preamble or said second preamble is for a fully utilized subchannel (FUSC) zone.

50. The OFDMA system according to claim 48, wherein said first preamble or said second preamble is for a partially utilized subchannel (PUSC) zone.

51. The OFDMA system according to claim 48, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

52. The OFDMA system according to claim 48, wherein said first preamble or said second preamble coexists with a legacy preamble.

53. The OFDMA system according to claim 48, wherein said first preamble or second preamble is located at a predefined location.

54. The OFDMA system according to claim 53, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

55. A base station in an orthogonal frequency division multiplexing access (OFDMA) system comprising:

a) a training sequence configuring logic for generating a training sequence, said training sequence having a plurality of subcarriers;

b) Inverse Fourier Transform (IFT) logic adapted to provide an IFT on each of said subcarriers to generate a plurality of OFDM symbols; and

c) transmit circuitry having transmitting said plurality of OFDM signals for reception by a subscriber station;

said subscriber station performing synchronization using said training sequence.

56. The base station according to claim 55, wherein said training sequence is a preamble having a common synchronization channel comprising common synchronization subcarriers, said common synchronization subcarriers carrying a common sequence;

said common sequence providing locations of candidate base stations, and reducing a search window for base station specific preamble.

57. The base station according to claim 56, wherein said common sequence comprises pseudo-noise codes.

58. The base station according to claim 56, wherein said common sequence results a low peak to average power ratio (PAPR).

59. The base station according to claim 56, wherein said common synchronization channel is separated by null-subcarriers.

60. The base station according to claim 55, wherein said OFDMA system is selected from the group consisting of single-input, single-output (SISO) system, multiple-input, single-output (MISO) system, and a multiple-input, multiple-output (MIMO) system.

61. The base station according to claim 55, wherein said training sequence is at a flexible location being indicated by a preceding zone in said OFDMA frame.

62. The base station according to claim 55, wherein said training sequence is a preamble, said preamble comprising cell-specific synchronization subcarriers, said preamble being assigned for use in said base station and performing cell search at said subscriber station.

63. The base station according to claim 62, wherein said OFDMA system is multiple-input, multiple-output (MIMO) system, said common synchronization channels subcarriers being assigned to a plurality of antennas according to a predefined antenna mapping pattern.

64. The base station according to claim 63, wherein said predefined antenna mapping pattern is based on time division, wherein said cell-specific synchronization subcarriers of said second preamble are devised into a plurality of groups, and each of said plurality of groups of said cell-specific synchronization subcarriers is transmitted at a predefined time.

65. The base station according to claim 63, wherein said predefined antenna mapping pattern is based on code division.

66. The base station according to claim 65, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.

67. The base station according to claim 56, wherein said preamble is a first preamble, and said OFDMA frame has a second preamble, said second preamble comprising cell-specific synchronization subcarriers, said second preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

68. The base station according to claim 67, wherein said first preamble or said second preamble is located in a fully utilized subchannel (FUSC) zone.

69. The base station according to claim 67, wherein said first preamble or said second preamble is located a partially utilized subchannel (PUSC) zone.

70. The base station according to claim 67, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

71. The base station according to claim 67, wherein said first preamble or said second preamble coexists with a legacy preamble.

72. The base station according to claim 67, wherein said first preamble or second preamble is located at a predefined location.

73. 72. The base station according to claim 72, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

75. The subscriber station according to claim 73, wherein said training sequence is a preamble having a common synchronization channel comprising common synchronization subcarriers, said common synchronization subcarriers carrying a common sequence;

said common sequence providing locations of candidate base stations, and reducing a search window for base station specific preamble.

76. The subscriber station according to claim 75, wherein said common sequence comprises pseudo-noise codes.

77. The subscriber station according to claim 75, wherein said common sequence results a low peak to average power ratio (PAPR).

78. The subscriber station according to claim 75, wherein said common synchronization channel is separated by null-subcarriers.

80. The subscriber station according to claim 75, wherein said preamble is at a flexible location being indicated by a preceding zone in said OFDMA frame.

86. The subscriber station according to claim 75, wherein said preamble is a first preamble, and said OFDMA frame has a second preamble, said second preamble comprising cell-specific synchronization subcarriers, said second preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

87. The subscriber station according to claim 86, wherein said first preamble or said second preamble is for a fully utilized subchannel (FUSC) zone.

88. The subscriber station according to claim 86, wherein said first preamble or said second preamble is for a partially utilized subchannel (PUSC) zone.

89. The subscriber station according to claim 86, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

90. The subscriber station according to claim 86, wherein said first preamble or said second preamble coexists with a legacy preamble.

91. The subscriber station according to claim 86, wherein said first preamble or second preamble is located at a predefined location.

92. The subscriber station according to claim 91, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

74. A subscriber station in an orthogonal frequency division multiplexing access (OFDMA) system comprising:

a) receive circuitry adapted to receive and downconvert a plurality of OFDM signals, said plurality of OFDM symbols forming an OFDMA frame having a training sequence;

b) Fourier Transform (FT) logic adapted to provide a FT on each of said plurality of OFDM signals to generate a plurality of divided-multiplexed coded signals, and

b) decoder logic adapted to provide division-multiplexing decoding on said plurality of divided-multiplexed coded signals to recover data from a plurality of base stations.

79. The subscriber station according to claim 74, wherein said OFDMA system is selected from the group consisting of single-output, single-output (SISO) system, multiple-input, single-output (MISO) system, and a multiple-input, multiple-output (MIMO) system.

81. The subscriber station according to claim 74, wherein said training sequence is a preamble, said preamble comprising cell-specific synchronization subcarriers, said preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

82. The subscriber station according to claim 74, wherein said OFDMA system is multiple-input, multiple-output (MIMO) system, said common synchronization channels subcarriers being assigned to a plurality of antennas according to a predefined antenna mapping pattern.

83. The subscriber station according to claim 82, wherein said predefined antenna mapping pattern is based on time division, wherein said cell-specific synchronization subcarriers of said second preamble are divided into a plurality of groups, and each of said plurality of groups of said subcarriers is transmitted at a predefined time.

84. The subscriber station according to claim 82, wherein said predefined antenna mapping pattern is based on code division.

85. The subscriber station according to claim 84, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.