Methods and apparatus for efficient digital broadcast signaling in a wireless communications system

• US 20060223520A1
• Filed: 03/07/2006
• Published: 10/05/2006
• Est. Priority Date: 03/08/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Das, Arnab, Laroia, Rajiv, Li, Junyi
• Granted Patent: US 7,990,840 B2
• Time in Patent Office: Days
• US Class Current: 455/422.100
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0491 using two or more sectors, i.e. sector diversity
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04H 20/22 Arrangements for broadcast of identical information via plural broadcast systems
• CPC Class Codes: H04H 20/26 Arrangements for switching distribution systems
• CPC Class Codes: H04H 20/72 of terrestrial networks
• CPC Class Codes: H04L 27/2604 Multiresolution systems by means of multiresolution subcarriers H04L27/183, H04L27/3488
• CPC Class Codes: H04W 52/143 Downlink power control
• CPC Class Codes: H04W 52/322 Power control of broadcast channels
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity
• CPC Class Codes: H04W 52/54 Signalisation aspects of the TPC commands, e.g. frame structure

Abstract

First and second transmitters transmit signals communicating the same information, e.g., program segment, but at different times. Different carriers may, but need not be, used by the different transmitters. If a wireless terminal can not recover broadcast segment information from one carrier, the wireless terminal can switch to another transmitter and recover the information, e.g., on another carrier, since the broadcasts are intentionally offset in time. In some embodiments, the timing is offset such that a single channel receiver is able to recover signals corresponding to the same program segment from two sources, and perform a decoding and information recovery using input from both sources, where recovery using input from a single source is not possible. Symbol level timing synchronization of base stations is not required thereby allowing for simpler implementations and/or lower overhead, as compared to systems which require base stations to be synchronized to the symbol timing level.

Claims

1. A communications method comprising:

operating a first base station transmitter to transmit program segments corresponding to a first program; and

operating a second base station transmitter, located adjacent said first base station transmitter, to transmit the same program segments of said first program as said first base station but with segments having the same information content being transmitted by said first and second base stations at different times.

2. The communications method of claim 1, wherein said first and second base station transmitters are transmitters located in adjacent single sector cells.

3. The communications method of claim 1, wherein said first and second base station transmitters are sector transmitters located in adjacent sectors and wherein the communications method is used in a system with multi-sector cells, said adjacent sectors being sectors of the same cell or sectors of adjacent multi-sector cells.

4. The communications method of claim 1, wherein operating the first base station transmitter to transmit program segments corresponding to the first program includes transmitting the program segments corresponding to the first program using a first carrier;

and

wherein operating the second base station transmitter to transmit program segments corresponding to the same program segments includes transmitting the program segments corresponding to the first program using a second carrier which has a different frequency from said first carrier.

5. The communications method of claim 1, wherein operating the first base station transmitter to transmit program segments corresponding to the first program includes using a first carrier and a first transmission power level for transmission of said program segments;

and

wherein operating the second base station transmitter to transmit program segments corresponding to the first program includes using a second carrier which has a different frequency from said first carrier and a second transmission power level than said first power level to transmit said the first program segments.

6. The communications method of claim 5, wherein the first and second base station transmitters correspond to different cells, the method further and are not timing synchronized to within a cyclic prefix duration.

7. The communications method of claim 1, wherein operating a second base station transmitter, located adjacent said first base station transmitter, to transmit the same program segments of said first program includes operating the second base station transmitter to transmit program segments having the same information content as program segments transmitted by the first base station transmitter at a time which is offset from the time at which the first base station transmitter transmits the program segments having the same information content.

8. The communications method of claim 7, wherein said information program segments are transmitted using OFDM symbols which are transmitted with cyclic prefixes, the transmission timing offset between program segments having the same information content by said first and second base station transmitters being greater than the duration of a cyclic prefix.

9. The communications method of claim 8, wherein said first and second base station transmitters are not synchronized to within a cyclic prefix duration and wherein said transmission off between program segments transmitted by said first and second base stations with the same information content exceeds the duration of a symbol transmission time period which includes the time used to transmit one OFDM symbol and a corresponding cyclic prefix.

10. The communications method of claim 9, wherein the time offset between transmission of a program segment by said first base station and the transmission of a program segment having the same program content by the second base station at least equals the amount of time used to transmit said program segment.

11. The communications method of claim 9, wherein the time offset, between transmission of a program segment by said first base station and the transmission of a program segment having the same program content by the second base station, at least equals the amount of time used to transmit said program segment by the first base station.

12. The communications method of claim 11, wherein the first base station does not transmit a program segment corresponding to the first program when said second base station transmits a program segment corresponding to the first program, the first and second base station transmitting program segments corresponding to the first program on an interleaved basis.

13. The communications method of claim 12, wherein said interleaved program segments are transmitted on a periodic basis by said first and second base stations with the transmission time between program segments corresponding to said first program being less than 5 seconds.

14. The communications method of claim 1, wherein the first and second base stations each transmit signals using multiple carrier frequencies, adjacent base stations using different transmission power levels for the same carrier frequency.

15. The communications method of claim 14, wherein each carrier frequency corresponds to a different OFDM tone block, the tones of each different OFDM tone block being non-overlapping in terms of frequency.

16. A communications system comprising:

at least one set of stored program segments corresponding to a first program;

a first base station transmitter to transmit program segments corresponding to the first program;

a second base station transmitter, located adjacent said first base station transmitter, for transmitting at least some of the program segments of the first program transmitted by said first base station; and

a transmission time control module for controlling at least the second base station transmitter to transmit program segments at times which are different from the times at which program segments having the same information content are transmitted by said first base station transmitter.

17. The system of claim 16, wherein said first and second base station transmitters are transmitters in single sector cells.

18. The system of claim 16, wherein said first and second base station transmitters are sector transmitters and wherein at least one of said first and second transmitters are located in a multi-sector cell.

19. The system of claim 16, further comprising:

stored transmission scheduling information indicating when program segments corresponding to the first program are to be transmitted by the first base station transmitter using a first carrier; and

indicating when program segments corresponding to the first program are to be transmitted by the second base station transmitter using a second carrier which has a carrier frequency which is different from a carrier frequency of the first carrier.

20. The system of claim 16, stored transmission power level information corresponding to the first base station transmitter indicating a first transmission power level at which the program segments corresponding to the first program are to be transmitted from the first base station transmitter using a first carrier;

and

additional stored transmission power level information corresponding to the second base station transmitter indicating a second transmission power level at which the program segments corresponding to the first program are to be transmitted from the second base station transmitter, the second transmission power level being different from the first transmission power level.

21. The system of claim 20, wherein the first and second base stations are not timing synchronized to within a cyclic prefix duration.

22. The system of claim 16, further comprising:

a timing synchronization module for maintaining timing synchronization between said first and second base station transmitter to maintain a level of timing synchronization which is within a maximum tolerance, said maximum timing tolerance being greater than an OFDM cyclic preface duration of OFDM symbol transmitted by said first base station transmitter.

23. The system of claim 16, wherein said transmission time control module controls at least the second base station transmitter to transmit program segments having the same information content as program segments being transmitted by said first base station transmitter, at a different non-overlapping times from the times at which the same program segments are transmitted by the first base station transmitter.

24. A communications system, comprising:

first base station transmitter means for transmitting program segments corresponding to a first program; and

second base station transmitter means, located adjacent said first base station transmitter, to transmit the same program segments of said first program as said first base station but with segments having the same information content being transmitted by said first and second base station transmitter means at different times.

25. The communications system of claim 24, wherein said first and second base station transmitter means are transmitters located in adjacent single sector cells.

26. The communications system of claim 24, wherein said first and second base station transmitter means are sector transmitters located in adjacent sectors of a multi-sector cell.

27. A method operating a wireless terminal, comprising:

receiving a first broadcast signal corresponding to a first program on a first carrier;

performing a first decoding operation on the first received broadcast signal;

determining if said first decoding operation was unsuccessful; and

if it is determined that said decoding operation was unsuccessful, tuning to a second carrier which is different from said first carrier.

28. The method of claim 27, further comprising:

operating the wireless terminal to receive a second broadcast signal corresponding to the first program on the second carrier.

29. The method of claim 28, further comprising:

performing a decoding operation on the received second broadcast signal.

30. The method of claim 29, further comprising:

determining if said second decoding operation was unsuccessful; and

if it is determined that said decoding operation was unsuccessful, tuning to the first carrier.

31. The method of claim 30, further comprising:

switching between the first and second carriers on an ongoing basis when a received signal can not be decoded.

32. The method of claim 27, where the first carrier corresponds to a first base station transmitter and the second carrier corresponds to a second base station transmitter, said first and second base station transmitters being located in adjacent cells or sectors.

33. The method of claim 27, wherein said first and second received signals include the same program content but are received at different times.

34. The method of claim 33, further comprising:

combining the signals received on said first and second carriers to generate a presentable copy of said first program.

35. A wireless terminal, comprising:

a receiver for receiving broadcast signals transmitted on first and second carriers at different times;

a decoder coupled to said receiver for performing decoding operations on the received broadcast signals;

an decoding operation evaluation module for determining if decoding of a broadcast signal was unsuccessful; and

a control module for controlling said receiver to switch between said first and second carriers in response to said decoding operation evaluation module determining that a decoding operation was unsuccessful.

36. The wireless terminal of claim 35, further comprising:

a program segment combining module for combining program segments generated by decoding signals received on different carriers to generate a presentable copy of said broadcast program.

37. The wireless terminal of claim 35, wherein the same program segments can be recovered from signals transmitted on both the first and second carriers but at different times, said control module including switching functionally which switches within a period of time which is less than a time offset between segment transmission having the same information content.

38. The wireless terminal of claim 36, further comprising:

a carrier strength monitoring module for checking the strength of signals indicative of the received strength of said first and second carrier signals; and

a carrier selection module for performing a carrier selection operation as a function of the relative received strengths of the first and second carriers as determined by the carrier strength monitoring module.

39. The wireless terminal of claim 36, wherein said receiver is a single carrier receiver capable of receiving a single carrier at a time.

40. The wireless terminal of claim 35, where the first carrier corresponds to a first base station transmitter and the second carrier corresponds to a second base station transmitter, said first and second base station transmitters being located in adjacent cells or sectors.

41. A wireless terminal, comprising:

receiver means for receiving broadcast signals transmitted on first and second carriers at different times;

decoder means coupled to said receiver for performing decoding operations on the received broadcast signals;

decoding operation evaluation means for determining if decoding of a broadcast signal was unsuccessful; and

control means for controlling said receiver to switch between said first and second carriers in response to said decoding operation evaluation module determining that a decoding operation was unsuccessful.

42. The wireless terminal of claim 41, further comprising:

program segment combining means for combining program segments generated by decoding signals received on different carriers to generate a presentable copy of said broadcast program.

43. The wireless terminal of claim 41, wherein the same program segments can be recovered from signals transmitted on both the first and second carriers but at different times, said control means including means for switching between the first and second carriers within a period of time which is less than a time offset between segment transmission having the same information content.

44. The wireless terminal of claim 42, further comprising:

carrier strength monitoring means for checking the strength of signals indicative of the received strength of said first and second carrier signals; and

a carrier selection means for performing a carrier selection operation as a function of the relative received strengths of the first and second carriers as determined by the carrier strength monitoring module.

45. A communications method comprising:

operating a first base station to transmit information; and

operating a second base station, located adjacent said first base station, to transmit said information transmitted by said first base station, the information transmitted by said second base station being transmitted such that the same information is transmitted by said first and second base stations at different times.

46. The communications method of claim 45, wherein operating the first base station to transmit information includes transmitting said information using a first carrier;

and

wherein operating the second base station to transmit information includes transmitting said information using a second carrier, said second carrier having a different frequency than said first carrier.

47. The communications method of claim 46, wherein said first and second base stations transmit said information at different power levels.

48. The method of claim 46, wherein transmitting said information from said first base station includes transmitting said first information using at least one OFDM symbol and a cyclic prefix having a cyclic prefix duration, said first and second base stations not being synchronized to within the cyclic prefix duration.

49. The communications method of claim 45, wherein said information corresponds to a program segment of a program being transmitted by said first and second base stations, the method further comprising:

operating the first base station to transmit a plurality of different program segments corresponding to said program; and

operating the second base station to transmit the same plurality of different program segments but with segments having the same information content being transmitted with a time offset from the segment having the same information content transmitted by said first base station.

50. A communications system comprising:

a first base station including a first transmitter for transmitting information;

a second base station, located adjacent said first base station, including second transmitter for transmitting the same information transmitted by said first base station; and

a transmission time control module for controlling at least the second base transmitter to transmit the same information transmitted by said first base station transmitter but with a time difference from transmission by said first transmitter so that portions of said same information which have the same content are transmitted by said first and second transmitters at different times.

51. The system of claim 50, wherein said first transmitter is a first carrier transmitter which transmits on a first carrier;

and

wherein said second transmitter is a second carrier transmitter which transmits on the second carrier, said first and second carriers having different carrier frequencies.

52. The system of claim 51, further comprising:

a power control module for controlling the second transmitter to transmit said information at a different power level than a power level at which said information is transmitted by the first transmitter.

53. The system of claim 51, wherein said first and second transmitter are OFDM transmitters which are timing synchronized to a level greater than a cyclic prefix duration but less than the transmission timing difference between transmissions by said first and second transmitters of portions of said information having the same information content.

54. The system of claim 50, wherein said information corresponds to video program, and wherein said portions of information are program segments.

55. A computer readable medium embodying instructions for performing a method of operating a first base station transmitter and a second base station transmitter, the method comprising:

operating the first base station transmitter to transmit program segments corresponding to a first program; and

operating the second base station transmitter, located adjacent said first base station transmitter, to transmit the same program segments of said first program as said first base station but with segments having the same information content being transmitted by said first and second base stations at different times.

56. The computer readable medium of claim 55, wherein said first and second base station transmitters are transmitters located in adjacent single sector cells.

57. The computer readable medium of claim 55, wherein said first and second base station transmitters are sector transmitters located in adjacent sectors and wherein the communications method is used in a system with multi-sector cells, said adjacent sectors being sectors of the same cell or sectors of adjacent multi-sector cells.

58. The computer readable medium of claim 55, further embodying instructions for:

transmitting the program segments corresponding to the first program using a first carrier as part of said step of operating the first base station transmitter to transmit program segments corresponding to the first program includes; and

transmitting the program segments corresponding to the first program using a second carrier which has a different frequency from said first carrier as part of operating the second base station transmitter to transmit program segments corresponding to the same program segments.

59. The computer readable medium of claim 55, further embodying instructions for:

using a first carrier and a first transmission power level for transmission of said program segments as part of said step of operating the first base station transmitter to transmit program segments corresponding to the first program includes; and

using a second carrier which has a different frequency from said first carrier and a second transmission power level than said first power level to transmit said the first program segments as part of said step of operating the second base station transmitter to transmit program segments corresponding to the first program.

60. A computer readable medium embodying instructions for performing a method of operating a wireless terminal, the method comprising:

receiving a first broadcast signal corresponding to a first program on a first carrier;

performing a first decoding operation on the first received broadcast signal;

determining if said first decoding operation was unsuccessful; and

if it is determined that said decoding operation was unsuccessful, tuning to a second carrier which is different from said first carrier.

61. The computer readable medium of claim 60, further embodying instructions for:

operating the wireless terminal to receive a second broadcast signal corresponding to the first program on the second carrier.

62. The computer readable medium of claim 61, further embodying instructions for:

performing a decoding operation on the received second broadcast signal.

63. The computer readable medium of claim 62, further embodying instructions for:

determining if said second decoding operation was unsuccessful; and

if it is determined that said decoding operation was unsuccessful, tuning to the first carrier.

64. The computer readable medium of claim 63, further embodying instructions for:

switching between the first and second carriers on an ongoing basis when a received signal can not be decoded.

65. A computer readable medium embodying instructions for performing a method of operating a first base station transmitter and a second base station transmitter, the method comprising:

operating the first base station to transmit information; and

operating the second base station, located adjacent said first base station, to transmit said information transmitted by said first base station, the information transmitted by said second base station being transmitted such that the same information is transmitted by said first and second base stations at different times.

66. The computer readable of claim 65, further embodying instructions for:

transmitting said information using a first carrier as part of said step of operating the first base station to transmit information; and

transmitting said information using a second carrier as part of said step of operating the second base station to transmit information, said second carrier having a different frequency than said first carrier.

67. The computer readable medium of claim 66, further embodying instructions for:

controlling first and second base stations to transmit said information at different power levels.

68. The computer readable medium of claim 66, further embodying instruction for:

transmitting said first information using at least one OFDM symbol and a cyclic prefix having a cyclic prefix duration as part of said step of transmitting said information from said first base station, said first and second base stations not being synchronized to within the cyclic prefix duration.

69. The computer readable medium of claim 65, wherein said information corresponds to a program segment of a program being transmitted by said first and second base stations, the computer readable medium further embodying instructions for:

operating the first base station to transmit a plurality of different program segments corresponding to said program; and

operating the second base station to transmit the same plurality of different program segments but with segments having the same information content being transmitted with a time offset from the segment having the same information content transmitted by said first base station.