PREAMBLES IN OFDMA SYSTEM

• US 20110222504A1
• Filed: 05/24/2011
• Published: 09/15/2011
• 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 8,340,072 B2
• Time in Patent Office: Days
• US Class Current: 370/330
• 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-I and Preamble-2, which may be used in different systems, including multioutput, multi-input (MIMO) systems.

Claims

1. 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.

2. The OFDMA system 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 OFDMA system according to claim 2, wherein said common sequence comprises pseudo-noise codes.

4. The OFDMA system according to claim 2, wherein said common sequence results a low peak to average power ratio (PAPR).

5. The OFDMA system according to claim 2, wherein said common synchronization channel is separated by null-subcarriers.

6. The OFDMA system according to claim 2, wherein said preamble has a second common channel carrying additional signaling information.

7. The OFDMA system according to claim 1, 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.

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

9. The OFDMA system according to claim 1, 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.

10. The OFDMA system according to claim 9, 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.

11. The OFDMA system according to claim 10, 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.

12. The OFDMA system according to claim 10, wherein said predefined antenna mapping pattern is based on code division.

13. The OFDMA system according to claim 10, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.

14. The OFDMA system 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, said second preamble being assigned for use in said plurality of base stations and performing cell search at said subscriber station.

15. The OFDMA system according to claim 14, wherein said first preamble or said second preamble is for a fully utilized subchannel (FUSC) zone.

16. The OFDMA system according to claim 14, wherein said first preamble or said second preamble is for a partially utilized subchannel (PUSC) zone.

17. The OFDMA system according to claim 14, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

18. The OFDMA system according to claim 14, wherein said first preamble or said second preamble coexists with a legacy preamble.

19. The OFDMA system according to claim 14, wherein said first preamble or second preamble is located at a predefined location.

20. The OFDMA system according to claim 19, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

21. 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.

22. The base station according to claim 21, 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.

23. The base station according to claim 22, wherein said common sequence comprises pseudo-noise codes.

24. The base station according to claim 22, wherein said common sequence results a low peak to average power ratio (PAPR).

25. The base station according to claim 22, wherein said common synchronization channel is separated by null-subcarriers.

26. The base station according to claim 21, 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.

27. The base station according to claim 21, wherein said training sequence is at a flexible location being indicated by a preceding zone in said OFDMA frame.

28. The base station according to claim 21, 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.

29. The base station according to claim 28, 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.

30. The base station according to claim 29, 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.

31. The base station according to claim 29, wherein said predefined antenna mapping pattern is based on code division.

32. The base station according to claim 31, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.

33. The base station according to claim 22, 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.

34. The base station according to claim 33, wherein said first preamble or said second preamble is located in a fully utilized subchannel (FUSC) zone.

35. The base station according to claim 33, wherein said first preamble or said second preamble is located a partially utilized subchannel (PUSC) zone.

36. The base station according to claim 33, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

37. The base station according to claim 33, wherein said first preamble or said second preamble coexists with a legacy preamble.

38. The base station according to claim 33, wherein said first preamble or second preamble is located at a predefined location.

39. The base station according to claim 38, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.

40. 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.

41. The subscriber station according to claim 40, 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.

42. The subscriber station according to claim 41, wherein said common sequence comprises pseudo-noise codes.

43. The subscriber station according to claim 41, wherein said common sequence results a low peak to average power ratio (PAPR).

44. The subscriber station according to claim 41, wherein said common synchronization channel is separated by null-subcarriers.

45. The subscriber station according to claim 40, 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.

46. The subscriber station according to claim 41, wherein said preamble is at a flexible location being indicated by a preceding zone in said OFDMA frame.

47. The subscriber station according to claim 40, 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.

48. The subscriber station according to claim 40, 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.

49. The subscriber station according to claim 48, 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.

50. The subscriber station according to claim 48, wherein said predefined antenna mapping pattern is based on code division.

51. The subscriber station according to claim 50, wherein Walsh codes are mapped to said plurality of antennas, and wherein Walsh chips are mapped to subcarriers of said second preamble.

52. The subscriber station according to claim 41, 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.

53. The subscriber station according to claim 52, wherein said first preamble or said second preamble is for a fully utilized subchannel (FUSC) zone.

54. The subscriber station according to claim 52, wherein said first preamble or said second preamble is for a partially utilized subchannel (PUSC) zone.

55. The subscriber station according to claim 52, wherein said first preamble and said second preamble are inserted alternately in a number of frames.

56. The subscriber station according to claim 52, wherein said first preamble or said second preamble coexists with a legacy preamble.

57. The subscriber station according to claim 52, wherein said first preamble or second preamble is located at a predefined location.

58. The subscriber station according to claim 57, wherein said first preamble or second preamble is located at an end of an OFDMA subframe.