Beacon signals facilitating signal detection and timing synchronization

• US 20060083267A1
• Filed: 10/14/2005
• Published: 04/20/2006
• Est. Priority Date: 10/17/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Uppala, Sathyadev Venkata, Laroia, Rajiv, Li, Junyi, Parizhsky, Vladimir
• Granted Patent: US 7,941,173 B2
• Time in Patent Office: Days
• US Class Current: 370/503
• CPC Class Codes: H04B 1/40 Circuits
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically

Abstract

Improved beacon signaling methods are described. Beacon signals are transmitted on the same tone in at least two consecutive symbol periods facilitating accurate energy measurements over a symbol period even if timing synchronization with the transmitter is not maintained. A low power wideband signal is also combined with the beacon signal to facilitate channel estimation and other operations such as timing synchronization operations.

Claims

1. A communications method comprising:

operating a first transmitter in a first cell to transmit on a recurring schedule, for at least two consecutive symbol time periods, a narrowband beacon signal, said narrowband beacon signal including at least 60 percent of the power transmitted by said first transmitter during said two consecutive time periods.

2. The communication method of claim 1, further comprising:

periodically operating a second transmitter located adjacent said first transmitter, to transmit, for at least two consecutive symbol time periods, a narrowband beacon signal, said narrowband beacon signal including at least 60 percent of the power transmitted by said second transmitter during said two consecutive time periods.

3. The communication method of claim 2, wherein said first and second transmitters are located in adjacent cells of a communications system and wherein said first and second transmitters transmit beacon signals during different non-overlapping symbol time periods.

4. The communications method of claim 1, further comprising:

operating the first transmitter to transmit a wideband signal during at least one of said at least two consecutive symbol time periods, said wideband signal using less than 40 percent of the power transmitted by said first transmitter during said at least one of said at least two consecutive symbol time periods.

5. The method of claim 4, wherein the wideband signal has the same duration as said beacon signal.

6. The method of claim 5, wherein said beacon signal and said wideband signal occupy two consecutive symbol transmission time periods.

7. The method of claim 6, wherein said beacon signal uses a single physical tone which is the same for each of said at least two consecutive symbol transmission time periods.

8. The method of claim 7, wherein said wideband signal uses a plurality of physical tones, said plurality including the same physical tones during each of said at least two consecutive symbol transmission time periods.

9. The method of claim 7, wherein said wideband signal uses at least 30 percent of the tones used by said first transmitter to transit symbols in a symbol transmission time period immediately following said at least two consecutive symbol transmission time periods.

10. The method of claim 7, wherein at least 50 tones are used out of 113 tones for transmission of said wideband signal.

11. The communications method of claim 4, wherein said beacon signal uses at least 80% of the transmitter power during said at least two consecutive symbol time periods.

12. The communications method of claim 11, wherein said wideband signal uses 20% or less of the transmitter power during one of said at least two consecutive symbol time periods.

13. The communications method of claim 11, wherein the wideband signal is at least 5 times wider than the narrowband beacon signal in terms of frequency width.

14. The communications method of claim 11, where the wideband signal is at least 10 times wider than the narrowband beacon signal in terms of frequency width.

15. The communications method of claim 11, where the wideband signal is at least 20 times wider than the narrowband beacon signal in terms of frequency width.

16. The communications method of claim 12, wherein said beacon signal is less than 3 tones wide.

17. The communications method of claim 16, wherein said beacon signal is a single tone and wherein said transmitter transmits during each symbol time using at least 100 tones.

18. The communications method of claim 17, wherein said transmitter is an OFDM transmitter and where a symbol time is the time used to transmit a single OFDM symbol.

19. The method of claim 2, wherein said first and second transmitters are transmitters corresponding to different sectors of a basestation located in a cell.

20. The method of claim 2, wherein said first and second transmitters are transmitters corresponding to different basestations located in adjacent cells.

21. The method of claim 2, further comprising:

operating a wireless terminal to receive beacon signals transmitted by said first and second base transmitters and to measure at least one beacon signal received from each of the transmitters to obtain for at least one beacon signal from each of the transmitters the energy received during a symbol time during which the beacon signal is received for the entire symbol time.

22. The method of claim 21, further comprising:

operating the wireless terminal to compare the energy measured from the received first base station beacon signal during a symbol transmission time period in which the first base station beacon signal was received during the full symbol time in which energy was measured to the energy measured from the received second base station beacon signal during a symbol transmission time period in which the second base station beacon signal was received during the full symbol time in which energy was measured.

23. The method of claim 22, further comprising:

making a selection of which transmitter the wireless terminal is to interact with based on the measured beacon signal energy.

24. The method of claim 22, further comprising:

operating the wireless terminal to make a timing signal adjustment based on a wideband signal received during the same symbol time period as a beacon signal.

26. The method of claim 24, wherein said wireless terminal uses said wideband signal for channel estimation.

27. The method of claim 26, wherein said wideband signal includes multiple tones spaced over a frequency band at least 15 tones wide.

25. The method of claim 25, wherein said timing signal adjustment is made after the wireless terminal determines that it should interact with a transmitter with which it does not already have timing synchronization, said wideband signal used to make said timing signal adjustment being from the transmitter which said wireless terminal is to interact.

28. A communications system comprising:

a first base station including;

a first transmitter for transmitting on a plurality of tones;

stored transmission schedule information; and

a first transmitter control module for controlling said first transmitter to transmit on a recurring basis in accordance with said stored schedule information, for at least two consecutive symbol time periods, a narrowband beacon signal, said narrowband beacon signal including at least 60 percent of the power transmitted by said first transmitter during said two consecutive time periods.

29. The system of claim 28, further comprising:

a second transmitter located adjacent said first transmitter for transmitting on said plurality of tones; and

a second transmitter control module for controlling said second transmitter to transmit, for at least two consecutive symbol time periods, another narrowband beacon signal, said another narrowband beacon signal including at least 60 percent of the power transmitted by said second transmitter during said two consecutive time periods.

30. The system of claim 29, wherein said second transmitter is located in a second base station, said first and second transmitters being located in adjacent cells of a communications system.

31. The system of claim 28, wherein said first base station further comprises:

a wideband signal generating module for generating a wideband signal to be transmitted during at least one of said at least two consecutive symbol time periods, said wideband signal using less than 40 percent of the power transmitted by said first transmitter during said at least one of said at least two consecutive symbol time periods.

32. The system of claim 31, wherein the wideband beacon signal has the same duration as said beacon signal.

33. The system of claim 32, wherein said beacon signal and said wideband signal occupy two consecutive symbol transmission time periods.

34. The system of claim 33, wherein said beacon signal uses a single physical tone which is the same for each of said two consecutive symbol transmission time periods.

35. The system of claim 34, wherein said wideband signal uses a plurality of physical tones, said plurality including the same physical tones during each of said two consecutive symbol transmission time periods.

36. The system of claim 34, wherein said wideband signal uses at least 30 percent of the tones used by said first transmitter to transit symbols in a symbol transmission time period immediately following said two consecutive symbol transmission time periods.

37. The system of claim 34, wherein at least 50 tones are used out of 113 tones for transmission of said wideband signal.

38. The system of claim 31, wherein said control module includes a transmission power control module for controlling the transmitter to supply at least 80% of the transmitter transmission power used during said two consecutive symbol time periods to said beacon signal.

39. A method of operating a wireless terminal, comprising:

receiving beacon signals transmitted by first and second transmitters;

measuring the amount of received energy in a first beacon signal received from the first transmitter during a first measurement time interval in which the first beacon signal is received from the first transmitter for the full duration of said first measurement time interval to produce a first measured signal energy value; and

measuring the amount of received energy in a second beacon signal received from the second transmitter during a second measurement time interval in which the second beacon signal is received from the second transmitter for the full duration of said second measurement time interval to produce a second measured signal energy value.

40. The method of claim 39, wherein said first and second measurement time intervals are different.

41. The method of claim 40, wherein said first and second measurement time intervals are non overlapping with each other.

42. The method of claim 39, further comprising:

comparing the first and second measured signal energy values.

43. The method of claim 42, further comprising:

making a selection between an attachment point corresponding to said first transmitter and an attachment point corresponding to said second transmitter based on the result of said comparison of the first and second measured signal energy values.

44. The method of claim 42, further comprising:

making a transmitter timing signal adjustment based on a wideband signal received during the same symbol time period as a beacon signal.

45. The method of claim 44, wherein said transmitter timing signal adjustment is made after the wireless terminal determines that it should interact with an attachment point with which the wireless terminal does not already have timing synchronization.

46. The method of claim 44, further comprising:

performing a channel estimation operation based on said received wideband signal received with a beacon signal from a transmitter at an attachment point to which the terminal is seeking to attach.

47. The method of claim 46, wherein said wideband signal includes multiple tones spaced over a frequency band at least 15 tones wide.

48. A wireless terminal comprising:

a beacon signal measurement module; and

a wideband signal evaluation module for processing said wideband synchronization signal to produce a timing adjustment control signal.

49. The wireless terminal of claim 48, further comprising:

a channel estimation module for performing a channel estimate based on said received wideband signal and NULL tones included with said wideband signal.

50. The wireless terminal of claim 49, further comprising:

a handoff control module for changing attachment points and adjusting transmitter timing using information supplied by said wideband signal evaluation module.

51. The wireless terminal of claim 50, wherein said handoff control module uses said channel estimate based on said wideband signal to initialize another channel estimate that is to be used when attaching to the point from which the wideband signal used to generate said channel estimate was transmitted.

52. A communications method comprising:

operating a first transmitter in a first cell to transmit, during a first recurring beacon signal transmission time period a narrowband beacon signal, said narrowband beacon signal being transmitted in two consecutive symbol transmission time periods occurring within said first recurring beacon signal transmission time period, said narrowband beacon signal occupying a signal tone transmitted by said transmitter at a higher power level than any non-beacon signal tone transmitted during said at least two consecutive symbol transmission time periods.

53. The method of claim 52, further comprising:

operating the first transmitter to transmit signals for at least 50 symbol transmission time periods between each of said recurring first beacon signal transmission time periods without transmitting any signals with a per tone energy equal to or exceeding said at least one signal tone transmitted at said higher power level.

54. The method of claim 53, wherein said narrowband beacon signal includes a single signal tone having said higher power level, the frequency of said tone being the same for the two consecutive symbol transmission time periods.

55. The method of claim 54, wherein said narrowband beacon signal corresponds to less than 2 percent of the downlink tones used by said first transmitter during and between at least one occurrence of said first recurring beacon signal transmission time period.

56. The method of claim 54, further comprising operating said first transmitter to transmit null values on more than 40 percent of the total number of downlink tones in a downlink tone block corresponding to said first transmitter and including the tone on which said single high power tone is transmitted.

57. The method of claim 54, further comprising operating said first transmitter to transmit null values on more than 50 percent of the total number of downlink tones in a downlink tone block corresponding to said first transmitter and including the tone on which said single high power tone is transmitted.

58. The method of claim 57, wherein the number of tones in said downlink tone block includes 113 tones.

59. The method of claim 57, further comprising operating said first transmitter to transmit a wideband synchronization signal during said consecutive symbol transmission time periods.

60. The method of claim 59, wherein said wideband synchronization signal includes at least 50 non-zero signal values, each non-zero signal value being transmitted on a different one tone in said downlink tone block.