BEACON ASSISTED CELL SEARCH IN A WIRELESS COMMUNICATION SYSTEM

• US 20080095108A1
• Filed: 09/11/2007
• Published: 04/24/2008
• Est. Priority Date: 09/14/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: LI, Junyi, MONTOJO, Juan, MALLADI, Durga
• Granted Patent: US 8,665,799 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04J 11/0069 Cell search, i.e. determining cell identity [cell-ID] design of multiplexing codes H04J13/00; processing access restriction or access information H04W48/16; discovery of network devices for network data management H04W8/005; sounding signals for channel estimation H04L25/0226; structure of reference signals in multicarrier modulation systems H04L27/2613; frame, time or carrier synchronisation in multicarrier modulation systems H04L27/2655
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• 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 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04L 5/0064 Rate requirement of the data, e.g. scalable bandwidth, data priority
• CPC Class Codes: H04W 48/12 using downlink control channel
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 56/001 Synchronization between nodes

Abstract

Techniques for transmitting synchronization signals to assist user equipments (UEs) perform cell searches are described. In one design, a base station for a cell may generate and transmit a primary synchronization signal and a secondary synchronization signal, which may be used by the UEs for initial cell search at power up. The base station may also generate and transmit one or more beacon signals, which may be used by the UEs for neighbor cell search to detect for neighbor cells. The number of beacon signals to transmit and the set of subcarriers usable for each beacon signal may be determined based on the system bandwidth. Each beacon signal may be mapped to one subcarrier in the set of subcarriers in each beacon symbol period. This one subcarrier may be determined based on a beacon hopping pattern or a beacon code and may be dependent on a cell identifier (ID).

Claims

1. An apparatus for wireless communication, comprising:

at least one processor configured to determine system bandwidth from a set of possible system bandwidths, to determine a set of subcarriers usable for a beacon signal based on the system bandwidth, and to generate the beacon signal based on the set of subcarriers; and

a memory coupled to the at least one processor.

2. The apparatus of claim 1, wherein the at least one processor is configured to map the beacon signal to one subcarrier in the set of subcarriers in each symbol period in which the beacon signal is transmitted.

3. The apparatus of claim 2, wherein the at least one processor is configured to determine a beacon hopping pattern based on a cell identifier (ID), and to select the one subcarrier from the set of subcarriers based on the beacon hopping pattern.

4. The apparatus of claim 2, wherein the at least one processor is configured to select the one subcarrier from the set of subcarriers based on a beacon code indicating which subcarrier to use for the beacon signal in each symbol period in which the beacon signal is transmitted.

5. The apparatus of claim 1, wherein the subcarriers usable for the beacon signal have a predetermined spacing, and wherein the number of subcarriers usable for the beacon signal is variable and determined based on the system bandwidth.

6. The apparatus of claim 1, wherein the number of subcarriers usable for the beacon signal is fixed, and wherein the subcarriers usable for the beacon signal have variable spacing determined based on the system bandwidth.

7. The apparatus of claim 1, wherein the at least one processor is configured to determine the number of beacon signals to transmit based on the system bandwidth.

8. The apparatus of claim 1, wherein the at least one processor is configured to generate one beacon signal if the system bandwidth is equal to or less than a predetermined value, and to generate multiple beacon signals if the system bandwidth is greater than the predetermined value.

9. A method for wireless communication, comprising:

determining system bandwidth from a set of possible system bandwidths;

determining a set of subcarriers usable for a beacon signal based on the system bandwidth; and

generating the beacon signal based on the set of subcarriers.

10. The method of claim 9, wherein the generating the beacon signal comprises mapping the beacon signal to one subcarrier in the set of subcarriers in each symbol period in which the beacon signal is transmitted.

11. The method of claim 10, wherein the generating the beacon signal further comprises

determining a beacon hopping pattern based on a cell identifier (ID), and

selecting the one subcarrier from the set of subcarriers based on the beacon hopping pattern.

12. The method of claim 9, further comprising:

determining the number of beacon signals to transmit based on the system bandwidth.

13. An apparatus for wireless communication, comprising:

means for determining system bandwidth from a set of possible system bandwidths;

means for determining a set of subcarriers usable for a beacon signal based on the system bandwidth; and

means for generating the beacon signal based on the set of subcarriers.

14. The apparatus of claim 13, wherein the means for generating the beacon signal comprises means for mapping the beacon signal to one subcarrier in the set of subcarriers in each symbol period in which the beacon signal is transmitted.

15. The apparatus of claim 14, wherein the means for generating the beacon signal further comprises

means for determining a beacon hopping pattern based on a cell identifier (ID), and

means for selecting the one subcarrier from the set of subcarriers based on the beacon hopping pattern.

16. A machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform operations including:

determining system bandwidth from a set of possible system bandwidths;

determining a set of subcarriers usable for a beacon signal based on the system bandwidth; and

generating the beacon signal based on the set of subcarriers.

17. The machine-readable medium of claim 16 which, when executed by the machine, cause the machine to perform operations further including:

mapping the beacon signal to one subcarrier in the set of subcarriers in each symbol period in which the beacon signal is transmitted.

18. The machine-readable medium of claim 17 which, when executed by the machine, cause the machine to perform operations further including:

determining a beacon hopping pattern based on a cell identifier (ID), and

selecting the one subcarrier from the set of subcarriers based on the beacon hopping pattern.

19. An apparatus for wireless communication, comprising:

at least one processor configured to determine system bandwidth from a set of possible system bandwidths, to determine a set of subcarriers usable for beacon signals based on the system bandwidth, and to detect for the beacon signals based on the set of subcarriers; and

a memory coupled to the at least one processor.

20. The apparatus of claim 19, wherein the at least one processor is configured to perform demodulation for each symbol period in which the beacon signals are transmitted to obtain received symbols, to determine candidate subcarriers with received signal quality exceeding a threshold based on the received symbols, and to identify cells transmitting the beacon signals based on the candidate subcarriers.

21. The apparatus of claim 20, wherein the at least one processor is configured to identify the cells transmitting the beacon signals further based on beacon hopping patterns for different possible cell identifiers (IDs).

22. The apparatus of claim 20, wherein the at least one processor is configured to identify the cells transmitting the beacon signals further based on a beacon code indicating which subcarrier to use for a beacon signal in each symbol period for each possible cell identifier (ID).

23. The apparatus of claim 19, wherein the at least one processor is configured to detect for beacon signals received from an entire system bandwidth if the system bandwidth is equal to or less than a predetermined value, and to detect for beacon signals received from a portion of the system bandwidth if the system bandwidth is greater than the predetermined value.

24. The apparatus of claim 19, wherein the at least one processor is configured to perform initial cell search based on synchronization signals transmitted by cells, and to determine the system bandwidth based on system information received from a cell detected by the initial cell search.

25. The apparatus of claim 19, wherein the at least one processor is configured to periodically perform neighbor cell search while operating in an idle state or an active state to detect for beacon signals from neighbor cells.

26. A method for wireless communication, comprising:

determining system bandwidth from a set of possible system bandwidths;

determining a set of subcarriers usable for beacon signals based on the system bandwidth; and

detecting for the beacon signals based on the set of subcarriers.

27. The method of claim 26, wherein the detecting for the beacon signals comprises

performing demodulation for each symbol period in which the beacon signals are transmitted to obtain received symbols,

determining candidate subcarriers with received signal quality exceeding a threshold based on the received symbols, and

identifying cells transmitting the beacon signals based on the candidate subcarriers.

28. The method of claim 27, wherein the detecting for the beacon signals further comprises identifying the cells transmitting the beacon signals further based on beacon hopping patterns for different possible cell identifiers (IDs).

29. The method of claim 26, wherein the detecting for the beacon signals comprises

detecting for beacon signals received from an entire system bandwidth if the system bandwidth is equal to or less than a predetermined value, and

detecting for beacon signals received from a portion of the system bandwidth if the system bandwidth is greater than the predetermined value.

30. An apparatus for wireless communication, comprising:

means for determining system bandwidth from a set of possible system bandwidths;

means for determining a set of subcarriers usable for beacon signals based on the system bandwidth; and

means for detecting for the beacon signals based on the set of subcarriers.

31. The apparatus of claim 30, wherein the means for detecting for the beacon signals comprises

means for performing demodulation for each symbol period in which the beacon signals are transmitted to obtain received symbols,

means for determining candidate subcarriers with received signal quality exceeding a threshold based on the received symbols, and

means for identifying cells transmitting the beacon signals based on the candidate subcarriers.

32. The apparatus of claim 31, wherein the means for detecting for the beacon signals further comprises means for identifying the cells transmitting the beacon signals further based on beacon hopping patterns for different possible cell identifiers (IDs).

33. A machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform operations including:

determining system bandwidth from a set of possible system bandwidths;

determining a set of subcarriers usable for beacon signals based on the system bandwidth; and

detecting for the beacon signals based on the set of subcarriers.

34. The machine-readable medium of claim 33 which, when executed by the machine, cause the machine to perform operations further including:

performing demodulation for each symbol period in which the beacon signals are transmitted to obtain received symbols;

determining candidate subcarriers with received signal quality exceeding a threshold based on the received symbols; and

identifying cells transmitting the beacon signals based on the candidate subcarriers.

35. The machine-readable medium of claim 34 which, when executed by the machine, cause the machine to perform operations further including:

identifying the cells transmitting the beacon signals further based on beacon hopping patterns for different possible cell identifiers (IDs).

36. An apparatus for wireless communication, comprising:

at least one processor configured to generate a wideband synchronization signal used by user equipments (UEs) for initial cell search, to generate a narrowband beacon signal used by the UEs for neighbor cell search, and to send the wideband synchronization signal and the narrowband beacon signal; and

a memory coupled to the at least one processor.

37. The apparatus of claim 36, wherein the at least one processor is configured to map the wideband synchronization signal to a fixed portion of system bandwidth, and to map the narrowband beacon signal to different subcarriers in different symbol periods in which the narrowband beacon signal is transmitted.

38. The apparatus of claim 36, wherein the wideband synchronization signal comprises a secondary synchronization signal, and wherein the at least one processor is configured to generate the secondary synchronization signal based on a pseudo-random sequence for a cell identifier (ID), and to generate the narrowband beacon signal based on a beacon hopping pattern for the cell ID.

39. The apparatus of claim 36, wherein the wideband synchronization signal comprises a primary synchronization signal used by the UEs for cell detection during initial cell search.

40. An apparatus for wireless communication, comprising:

at least one processor configured to perform initial cell search based on wideband synchronization signals transmitted by cells in a wireless communication system, and to perform neighbor cell search based on narrowband beacon signals transmitted by the cells; and

a memory coupled to the at least one processor.

41. The apparatus of claim 40, wherein the at least one processor is configured to receive the wideband synchronization signals from a fixed portion of system bandwidth, and to receive the narrowband beacon signals from different subcarriers in different symbol periods in which the narrowband beacon signals are transmitted.

42. The apparatus of claim 40, wherein the wideband synchronization signals comprise secondary synchronization signals, and wherein the at least one processor is configured to detect for the secondary synchronization signals based on pseudo-random sequences for a set of possible cell identifiers (IDs), and to detect for the narrowband beacon signals based on a set of beacon hopping patterns for the set of possible cell IDs.

43. The apparatus of claim 40, wherein the wideband synchronization signals comprise primary synchronization signals, and wherein the at least one processor is configured to detect for cells during initial cell search based on the primary synchronization signals transmitted by the cells.

44. An apparatus for wireless communication, comprising:

at least one processor configured to generate a beacon signal, to generate at least one other signal, and to frequency division multiplex the beacon signal and the at least one other signal on different parts of system bandwidth; and

a memory coupled to the at least one processor.

45. The apparatus of claim 44, wherein the at least one other signal comprises a secondary synchronization signal used for initial cell search.

46. The apparatus of claim 44, wherein the at least one other signal comprises a primary synchronization signal used for cell detection during initial cell search.

47. The apparatus of claim 44, wherein the at least one processor is configured to map the beacon signal to different subcarriers in a first part of the system bandwidth in different symbol periods in which the beacon signal is transmitted, and to map the at least one other signal to a second part of the system bandwidth in the symbol periods in which the beacon signal is transmitted.

48. The apparatus of claim 47, wherein the at least one processor is configured to determine a first fraction of total transmit power to use for the beacon signal based on the first part of the system bandwidth, and to determine a second fraction of the total transmit power to use for the at least one other signal based on the second part of the system bandwidth.

49. The apparatus of claim 44, wherein the at least one processor is configured to determine the system bandwidth from a set of possible system bandwidths, and to determine bandwidth of the beacon signal based on the system bandwidth.

50. An apparatus for wireless communication, comprising:

at least one processor configured to receive beacon signals from a first part of system bandwidth, and to receive other signals from a second part of the system bandwidth, the beacon signals and the other signals being frequency division multiplexed; and

a memory coupled to the at least one processor.

51. The apparatus of claim 50, wherein the other signals comprise secondary synchronization signals, and wherein the at least one processor is configured to perform initial cell search based on the secondary synchronization signals and to perform neighbor cell search based on the beacon signals.

52. The apparatus of claim 50, wherein the other signals comprise primary synchronization signals, and wherein the at least one processor is configured to detect for cells during initial cell search based on the primary synchronization signals, and to perform neighbor cell search based on the beacon signals.

53. The apparatus of claim 50, wherein the at least one processor is configured to receive the beacon signals from different subcarriers in a first part of the system bandwidth in different symbol periods in which the beacon signals are transmitted, and to receive the other signals from a second part of the system bandwidth in the symbol periods in which the beacon signals are transmitted.

54. The apparatus of claim 50, wherein the at least one processor is configured to determine the system bandwidth from a set of possible system bandwidths, and to determine bandwidth of the beacon signals based on the system bandwidth.