Systems and Methods for Satellite Forward Link Transmit Diversity Using Orthagonal Space Coding

• US 20070184849A1
• Filed: 01/18/2007
• Published: 08/09/2007
• Est. Priority Date: 01/20/2006
• Status: Active Grant

• Current Assignee: ATC Technology Corporation (FedEx Corporation)
• Original Assignee: AC Technologies SA
• Inventors: Zheng, Dunmin
• Granted Patent: US 7,979,024 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: H04B 7/06 at the transmitting station
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/18545 Arrangements for managing station mobility, i.e. for station registration or localisation
• CPC Class Codes: H04L 1/0606 Space-frequency coding
• CPC Class Codes: H04L 1/0625 Transmitter arrangements
• CPC Class Codes: H04L 1/0643 block codes
• CPC Class Codes: H04L 1/0668 Orthogonal systems, e.g. using Alamouti codes

Abstract

Methods of transmitting communications signals from a satellite to a wireless terminal include determining a location of the wireless terminal, selecting a plurality of antenna feed elements at the satellite in response to the determined location of the wireless terminal, block coding a plurality of symbols into a number of transmit streams equal to the number of selected antenna feed elements, and transmitting the transmit streams over the selected plurality of antenna feed elements. Block coding the plurality of symbols may include space-code, space-time and/or space-frequency encoding the plurality of symbols. Related satellites, satellite gateways and satellite communications systems are also disclosed.

Claims

1. A method of transmitting communications signals from a satellite to a wireless terminal, comprising:

determining a location of the wireless terminal;

selecting a plurality of antenna feed elements at the satellite in response to the determined location of the wireless terminal;

block coding a plurality of symbols into a number of transmit streams equal to the number of selected antenna feed elements; and

transmitting the transmit streams over the selected plurality of antenna feed elements.

2. The method of claim 1, further comprising demultiplexing an information signal to provide the plurality of symbols.

3. The method of claim 1, further comprising selecting a transmit frequency in response to the location of the wireless terminal, wherein transmitting the transmit streams comprises transmitting the transmit streams over the selected transmit frequency.

4. The method of claim 1, wherein determining the location of the wireless terminal comprises receiving an indication of the location of the wireless terminal from the wireless terminal over a return link frequency.

5. The method of claim 1, wherein block coding the plurality of symbols comprises space-code encoding the plurality of symbols.

6. The method of claim 5, wherein space-code encoding the plurality of symbols comprises generating a transmission matrix using the plurality of symbols and combining the transmission matrix with a plurality of pseudonoise codes to generate the transmit streams.

7. The method of claim 5, further comprising:

generating a plurality of extended pseudonoise codes w_L based on a pseudonoise code w associated with the wireless terminal, wherein the extended pseudonoise codes w_L have a length that is m-times longer than the pseudonoise code w;

repeating the symbols m times; and

constructing a transmission matrix using the repeated symbols;

wherein block coding the transmit streams comprises combining the extended pseudonoise codes with the transmission matrix.

8. The method of claim 7, wherein the pseudonoise code w comprises a Walsh code, and wherein generating the extended pseudonoise codes comprises generating extended Walsh codes.

9. The method of claim 8, wherein generating the extended Walsh codes comprises constructing a matrix M from the Walsh code having the following form:

10. The method of claim 7, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

11. The method of claim 7, wherein the transmission matrix has a form such that the product of the transmission matrix and its transpose conjugate is equal to the sum of the squares of the plurality of symbols used to generate the transmission matrix multiplied by a diagonal unity matrix.

12. The method of claim 1, wherein selecting a plurality of feed elements at the satellite comprises selecting a first feed element at a first satellite and selecting a second feed element at a second satellite, and wherein transmitting the transmit streams over the selected plurality of feed elements comprises transmitting a first of the transmit streams to the wireless terminal from the first feed element at the first satellite and transmitting a second of the transmit streams to the wireless terminal from the second feed element at the second satellite.

13. The method of claim 12, further comprising:

determining a difference in propagation delay between the first and second satellites and the wireless terminal; and

selectively delaying the first or second transmit stream by a delay time in response to the determined difference in propagation delay.

14. The method of claim 13, wherein the delay time is selected such that signals transmitted by the first and second satellites arrive at the wireless terminal within a coherence time of a receiver in the wireless terminal.

15. The method of claim 1, wherein block coding the plurality of symbols comprises space-time encoding the plurality of symbols.

16. The method of claim 15, wherein space-time encoding the plurality of symbols comprises generating a transmission matrix using the plurality of symbols, and wherein transmitting the transmit streams over the selected plurality of antenna feed elements comprises transmitting the transmit streams at time intervals specified by a time scheduler.

17. The method of claim 16, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

18. The method of claim 16, wherein the transmission matrix has a form such that the product of the transmission matrix and its transpose conjugate is equal to the sum of the squares of the plurality of symbols used to generate the transmission matrix multiplied by a diagonal unity matrix.

19. The method of claim 1, wherein block coding the plurality of symbols comprises space-frequency encoding the plurality of symbols.

20. The method of claim 19, wherein space-frequency encoding the plurality of symbols comprises generating a transmission matrix using the plurality of symbols, and wherein transmitting the transmit streams over the selected plurality of antenna feed elements comprises transmitting the transmit streams over orthogonal subcarriers.

21. The method of claim 20, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

22. The method of claim 20, wherein the transmission matrix has a form such that the product of the transmission matrix and its transpose conjugate is equal to the sum of the squares of the plurality of symbols used to generate the transmission matrix multiplied by a diagonal unity matrix.

23. A satellite configured to transmit communications signals to a wireless terminal, comprising:

an antenna including a plurality of feed elements;

a controller configured to obtain a location of the wireless terminal and configured to select a plurality of the antenna feed elements in response to the obtained location of the wireless terminal, and configured to block code a plurality of symbols into a number of transmit streams equal to the number of selected antenna feed elements; and

a transmitter configured to transmit the transmit streams over the selected plurality of antenna feed elements.

24. The satellite of claim 23, wherein the controller is further configured to demultiplex an information signal to provide the plurality of symbols.

25. The satellite of claim 23, wherein the controller is further configured to select a transmit frequency in response to the location of the wireless terminal, and wherein the transmitter is further configured to transmit the transmit streams over the selected transmit frequency.

26. The satellite of claim 23, wherein the controller is configured to receive an indication of the location of the wireless terminal from the wireless terminal over a return link frequency.

27. The satellite of claim 23, wherein the controller is configured to block code the plurality of symbols by space-code encoding the plurality of symbols.

28. The satellite of claim 27, wherein the controller is configured to space-code encode the plurality of symbols by generating a transmission matrix using the plurality of symbols and combining the transmission matrix with a plurality of pseudonoise codes to generate the transmit streams.

29. The satellite of claim 27, wherein the controller is configured to generate a plurality of extended pseudonoise codes w_L based on a pseudonoise code w associated with the wireless terminal, wherein the extended pseudonoise codes w_L have a length that is m-times longer than the pseudonoise code w.

30. The satellite of claim 29, wherein the controller is further configured to repeat the symbols m times, to construct a transmission matrix using the repeated symbols, and to combine the extended pseudonoise codes with the transmission matrix to generate the transmit streams.

31. The satellite of claim 30, wherein the pseudonoise code w comprises a Walsh code, and wherein the extended pseudonoise codes comprise extended Walsh codes.

32. The satellite of claim 31, wherein the extended Walsh codes comprises a matrix M having the form:

33. The satellite of claim 30, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

34. The satellite of claim 23, wherein the controller is configured to block code the plurality of symbols by space-time encoding the plurality of symbols.

35. The satellite of claim 34, further comprising a time scheduler, wherein the controller is configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over the selected plurality of antenna feed elements at time intervals specified by the time scheduler.

36. The satellite of claim 35, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

37. The satellite of claim 23, wherein the controller is configured to block code the plurality of symbols by space-frequency encoding the plurality of symbols.

38. The satellite of claim 37, wherein the controller is further configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over orthogonal subcarriers.

39. The satellite of claim 38, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

40. A satellite gateway configured to transmit communications signals to a wireless terminal via a satellite including an antenna having a plurality of feed elements, comprising:

a controller configured to obtain a location of the wireless terminal and configured to select a plurality of the antenna feed elements in response to the obtained location of the wireless terminal and configured to block code a plurality of symbols into a number of transmit streams equal to the number of selected antenna feed elements; and

a transmitter configured to transmit the transmit streams to the satellite for transmission over the selected plurality of antenna feed elements.

41. The satellite gateway of claim 40, wherein the controller is further configured to demultiplex an information signal to provide the plurality of symbols.

42. The satellite gateway of claim 40, wherein the controller is configured to receive an indication of the location of the wireless terminal from the wireless terminal.

43. The satellite gateway of claim 40, wherein the controller is configured to block code the plurality of symbols by space-code encoding the plurality of symbols.

44. The satellite gateway of claim 43, wherein the controller is configured to space-code encode the plurality of symbols by generating a transmission matrix using the plurality of symbols and combining the transmission matrix with a plurality of pseudonoise codes to generate the transmit streams.

45. The satellite gateway of claim 43, wherein the controller is configured to generate a plurality of extended pseudonoise codes w_L based on a pseudonoise code w associated with the wireless terminal, wherein the extended pseudonoise codes w_L have a length that is m-times longer than the pseudonoise code w.

46. The satellite gateway of claim 45, wherein the controller is further configured to repeat the symbols m times, to construct a transmission matrix using the repeated symbols, and to combine the extended pseudonoise codes with the transmission matrix to generate the transmit streams.

47. The satellite gateway of claim 46, wherein the pseudonoise code w comprises a Walsh code, and wherein the extended pseudonoise codes comprise extended Walsh codes.

48. The satellite gateway of claim 47, wherein the extended Walsh codes comprises a matrix M having the form:

49. The satellite gateway of claim 46, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

50. The satellite gateway of claim 40, wherein the controller is configured to block code the plurality of symbols by space-time encoding the plurality of symbols.

51. The satellite gateway of claim 50, further comprising a time scheduler, wherein the controller is configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over the selected plurality of antenna feed elements at time intervals specified by the time scheduler.

52. The satellite gateway of claim 51, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

53. The satellite gateway of claim 40, wherein the controller is configured to block code the plurality of symbols by space-frequency encoding the plurality of symbols.

54. The satellite gateway of claim 53, wherein the controller is further configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over orthogonal subcarriers.

55. The satellite gateway of claim 54, wherein the number of selected antenna feed elements is four, and wherein the transmission matrix has the form:

56. The satellite gateway of claim 40, wherein the satellite comprises a first satellite, and wherein the controller is further configured to select a first feed element at the first satellite and to select a second feed element at a second satellite, and wherein the transmitter is configured to transmit a first of the transmit streams to the first satellite for transmission to the wireless terminal from the first feed element at the first satellite and to transmit a second of the transmit streams to the second satellite for transmission to the wireless terminal from the second feed element at the second satellite.

57. The satellite gateway of claim 56, wherein the controller is further configured to determine a difference in propagation delay between the first and second satellites and the wireless terminal, and to selectively delay the first or second transmit stream by a delay time in response to the determined difference in propagation delay.

58. The satellite gateway of claim 57, wherein the delay time is selected such that signals transmitted by the first and second satellites arrive at the wireless terminal within a coherence time of a receiver in the wireless terminal.

59. A satellite communications system, comprising:

a satellite including an antenna having a plurality of antenna feed elements; and

a satellite gateway comprising;

a controller configured to obtain a location of a wireless terminal within a geographic footprint of the satellite, and configured to select a plurality of the antenna feed elements in response to the obtained location of the wireless terminal and configured to block code a plurality of symbols into a number of transmit streams equal to the number of selected antenna feed elements; and

a transmitter configured to transmit the transmit streams to the satellite for transmission over the selected plurality of antenna feed elements.

60. The satellite communications system of claim 59, wherein the controller is further configured to demultiplex an information signal to provide the plurality of symbols.

61. The satellite communications system of claim 59, wherein the controller is configured to receive an indication of the location of the wireless terminal from the wireless terminal.

62. The satellite communications system of claim 59, wherein the controller is configured to block code the plurality of symbols by space-code encoding the plurality of symbols.

63. The satellite communications system of claim 62, wherein the controller is configured to space-code encode the plurality of symbols by generating a transmission matrix using the plurality of symbols and combining the transmission matrix with a plurality of pseudonoise codes to generate the transmit streams.

64. The satellite communications system of claim 62, wherein the controller is configured to generate a plurality of extended pseudonoise codes w_L based on a pseudonoise code w associated with the wireless terminal, wherein the extended pseudonoise codes w_L have a length that is m-times longer than the pseudonoise code w.

65. The satellite communications system of claim 64, wherein the controller is further configured to repeat the symbols m times, to construct a transmission matrix using the repeated symbols, and to combine the extended pseudonoise codes with the transmission matrix to generate the transmit streams.

66. The satellite communications system of claim 65, wherein the pseudonoise code w comprises a Walsh code, and wherein the extended pseudonoise codes comprise extended Walsh codes.

67. The satellite communications system of claim 59, wherein the controller is configured to block code the plurality of symbols by space-time encoding the plurality of symbols.

68. The satellite communications system of claim 67, further comprising a time scheduler, wherein the controller is configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over the selected plurality of antenna feed elements at time intervals specified by the time scheduler.

69. The satellite communications system of claim 59, wherein the controller is configured to block code the plurality of symbols by space-frequency encoding the plurality of symbols.

70. The satellite communications system of claim 69, wherein the controller is further configured to generate a transmission matrix using the plurality of symbols, and wherein the transmitter is configured to transmit the transmit streams over orthogonal subcarriers.

71. The satellite communications system of claim 59, wherein the satellite comprises a first satellite, the system further comprising a second satellite comprising an antenna having a plurality of antenna feed elements;

wherein the controller is further configured to select a first feed element at the first satellite and to select a second feed element at the second satellite, and wherein the transmitter is configured to transmit a first of the transmit streams to the first satellite for transmission to the wireless terminal from the first feed element at the first satellite and to transmit a second of the transmit streams to the second satellite for transmission to the wireless terminal from the second feed element at the second satellite.

72. The satellite communications system of claim 71, wherein the controller is further configured to determine a difference in propagation delay between the first and second satellites and the wireless terminal, and to selectively delay the first or second transmit stream by a delay time in response to the determined difference in propagation delay.

73. The satellite communications system of claim 72, wherein the delay time is selected such that signals transmitted by the first and second satellites arrive at the wireless terminal within a coherence time of a receiver in the wireless terminal.