Synchronization signal design for wireless devices in a long range extension mode

• US 9,917,616 B2
• Filed: 01/16/2014
• Issued: 03/13/2018
• Est. Priority Date: 01/17/2013
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Baldemair, Robert, Bergman, Johan, Dimou, Konstantinos, Frenger, Pl
• Primary Examiner(s): Thier, Michael
• Assistant Examiner(s): Islam, Rownak
• Application Number:
  US14/156,730
• Publication Number:
  US 20140198772A1
• Time in Patent Office: 1,517 Days
• Field of Search: 370229, 370335
• CPC Class Codes: H04B 1/7073 Synchronisation aspects
• CPC Class Codes: H04L 27/26132 using repetition
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• 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 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 56/001 Synchronization between nodes
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others

Abstract

Systems and methods related to a synchronization signal particularly well suited for wireless devices in an extended coverage area of a cell of a cellular communications network are disclosed. In one embodiment, a base station transmits a synchronization signal including multiple repetitions of a basic synchronization block during a coherence time of a downlink channel over which the synchronization signal is transmitted. The multiple repetitions of the basic synchronization block during the coherence time enable coherent combining during detection of the synchronization signal at wireless devices located in the cellular communications network. This coherent combining enables, for example, wireless devices located in an extended coverage area of a cell served by the base station to synchronize to the cell using a shorter synchronization signal than that which would be required if only non-coherent combining were used.

Claims

1. A method of operation of a base station of a cellular communications network, comprising:

transmitting a synchronization signal comprising a plurality of repetitions of a basic synchronization block during a coherence time of a downlink channel over which the synchronization signal is transmitted, where the coherence time is defined as T_c=1/f_d, where f_d is the Doppler frequency, which is defined as f_d=v. f/c where v is speed in m/s, f is carrier frequency in Hertz (Hz), and c is the speed of light.

2. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal according to a multi-subcarrier transmission scheme, and the basic synchronization block comprises a sequence of symbols transmitted over at least a subset of a plurality of subcarriers in a downlink bandwidth of the base station.

3. The method of claim 2 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the coherence time is one subframe.

4. The method of claim 2 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the coherence time is two subframes.

5. The method of claim 1 wherein the synchronization signal spans less than a full bandwidth of the downlink channel.

6. The method of claim 1 wherein the synchronization signal spans a full bandwidth of the downlink channel.

7. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal such that the plurality of repetitions of the basic synchronization block comprises a first instance of the basic synchronization block and a second instance of the basic synchronization block that immediately follows the first instance of the basic synchronization block in time.

8. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal such that the plurality of repetitions of the basic synchronization block comprises a first instance of the basic synchronization block and a second instance of the basic synchronization block that is separated from the first instance of the basic synchronization block in time.

9. The method of claim 1 further comprising transmitting a primary synchronization signal and a secondary synchronization signal in addition to the synchronization signal.

10. The method of claim 9 wherein:

transmitting the primary synchronization signal and the secondary synchronization signal comprises transmitting the primary synchronization signal and the secondary synchronization signal at a first periodicity; and

transmitting the synchronization signal comprises transmitting the synchronization signal at a second periodicity that is different than the first periodicity.

11. The method of claim 10 wherein the second periodicity is less than the first periodicity.

12. The method of claim 1 wherein transmitting the synchronization signal comprises block spreading the plurality of repetitions of the basic synchronization block.

13. The method of claim 12 wherein:

transmitting the synchronization signal comprises transmitting the synchronization signal according to a multi-subcarrier signal based transmission scheme such that each repetition of the basic synchronization block of the plurality of repetitions is in a different multi-subcarrier signal symbol period; and

block spreading the plurality of repetitions of the basic synchronization block comprises applying a different element from a block spreading sequence to each repetition of the basic synchronization block of the plurality of repetitions of the basic synchronization block.

14. The method of claim 13 wherein the block spreading sequence is different than that used in at least one other cell of the cellular communications network.

15. The method of claim 13 wherein the block spreading sequence is the same as that used in all other cells of the cellular communications network.

16. The method of claim 1 wherein the synchronization signal further comprises a second plurality of repetitions of a second basic synchronization block during a second coherence time of the downlink channel over which the synchronization signal is transmitted.

17. The method of claim 16 wherein the second basic synchronization block is different than the basic synchronization block.

18. The method of claim 16 wherein the second basic synchronization block is the same as the basic synchronization block.

19. The method of claim 16 wherein transmitting the synchronization signal comprises applying a block spreading sequence to the synchronization signal such that a first element from the block spreading sequence is applied to the plurality of repetitions of the basic synchronization block and a second element from the block spreading sequence is applied to the second plurality of repetitions of the second basic synchronization block.

20. The method of claim 16 wherein transmitting the synchronization signal comprises:

applying a first block spreading sequence to the synchronization signal such that a first element from the first block spreading sequence is applied to the plurality of repetitions of the basic synchronization block and a second element from the first block spreading sequence is applied to the second plurality of repetitions of the second basic synchronization block; and

applying a second block spreading sequence to the plurality of repetitions of the basic synchronization block such that a different element from the second block spreading sequence is applied to each repetition of the basic synchronization block in the plurality of repetitions of the basic synchronization block.

21. The method of claim 20 wherein transmitting the synchronization signal further comprises:

applying the second block spreading sequence to the second plurality of repetitions of the second basic synchronization block such that a different element from the second block spreading sequence is applied to each repetition of the second basic synchronization block in the second plurality of repetitions of the second basic synchronization block.

22. The method of claim 16 wherein the second coherence time immediately follows the coherence time in time.

23. The method of claim 16 wherein the coherence time and the second coherence time are separated in time.

24. The method of claim 16 wherein transmitting the synchronization signal comprises transmitting the synchronization signal according to a frequency-hopping scheme.

25. The method of claim 24 wherein transmitting the synchronization signal according to the frequency-hopping scheme comprises transmitting the synchronization signal such that the plurality of repetitions of the basic synchronization block during the coherence time are transmitted on a first set of sub-carrier frequencies and the second plurality of repetitions of the second basic synchronization block during the second coherence time are transmitted on a second set of sub-carrier frequencies that is at least partly different than the first set of sub-carrier frequencies.

26. The method of claim 1 wherein the synchronization signal further comprises a second part having a wider bandwidth than the plurality of repetitions of the basic synchronization block.

27. The method of claim 1 wherein transmitting the synchronization signal comprises puncturing the synchronization signal to transmit one or more other signals within time and frequency resources that would otherwise be used for the synchronization signal.

28. The method of claim 27 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the one or more other signals comprise one or more of a group consisting of:

a control signal, a common reference signal, a channel state information reference signal, and an enhanced synchronization signal.

29. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal using time and frequency resources mapped around time and frequency resources used for one or more other signals.

30. The method of claim 29 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the one or more other signals comprise one or more of a group consisting of:

a control signal, a common reference signal, a channel state information reference signal, and an enhanced synchronization signal.

31. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal using a power boosting scheme.

32. The method of claim 31 wherein the cellular communications network utilizes a multi-subcarrier transmission scheme, and transmitting the synchronization signal using the power boosting scheme comprises transmitting the synchronization signal while at least some of a plurality of subcarriers in a downlink bandwidth of the base station are unused or transmitted with reduced power.

33. The method of claim 1 wherein transmitting the synchronization signal comprises transmitting the synchronization signal using a beamforming transmission scheme.

34. The method of claim 33 wherein the beamforming transmission scheme is a blind beamforming transmission scheme.

35. A base station for a cellular communications network, comprising:

a transceiver; and

a processor associated with the transceiver and configured to transmit, via the transceiver, a synchronization signal comprising a plurality of repetitions of a basic synchronization block during a coherence time of a downlink channel over which the synchronization signal is transmitted, where the coherence time is defined as T_c=1/f_d, where f_d is the Doppler frequency, which is defined as f_d=v. f/c where v is speed in m/s, f is carrier frequency in Hertz (Hz), and c is the speed of light.

36. The base station of claim 35 wherein the synchronization signal further comprises a second plurality of repetitions of a second basic synchronization block during a second coherence time of the downlink channel over which the synchronization signal is transmitted.

37. A method of operation of a wireless device in a cellular communications network, comprising:

detecting a synchronization signal in a downlink from a base station of the cellular communications network, the synchronization signal comprising a plurality of repetitions of a basic synchronization block during a coherence time of a downlink channel over which the synchronization signal is transmitted, where the coherence time is defined as T_c=1/f_d, where f_d is the Doppler frequency, which is defined as f_d=v. f/c where v is speed in m/s, f is carrier frequency in Hertz (Hz), and c is the speed of light.

38. The method of claim 37 further comprising connecting to a cell served by the base station upon detecting the synchronization signal.

39. The method of claim 37 wherein the wireless device is a Machine Type Communication, MTC, device.

40. The method of claim 39 wherein the MTC device is located in an extended coverage area of a cell served by the base station.

41. The method of claim 37 wherein the basic synchronization block comprises a sequence of symbols transmitted over at least a subset of a plurality of subcarriers in a downlink bandwidth of the base station.

42. The method of claim 41 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the coherence time is one subframe.

43. The method of claim 41 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the coherence time is two subframes.

44. The method of claim 37 wherein the synchronization signal spans less than a full bandwidth of the downlink channel.

45. The method of claim 37 wherein the synchronization signal spans a full bandwidth of the downlink channel.

46. The method of claim 37 wherein the synchronization signal comprises a first instance of the basic synchronization block and a second instance of the basic synchronization block that immediately follows the first instance of the basic synchronization block in time.

47. The method of claim 37 wherein the synchronization signal comprises a first instance of the basic synchronization block and a second instance of the basic synchronization block that is separated from the first instance of the basic synchronization block in time.

48. The method of claim 37 further comprising detecting a primary synchronization signal and a secondary synchronization signal in addition to the synchronization signal.

49. The method of claim 37 wherein detecting the synchronization signal comprises detecting the synchronization signal according to a block spreading sequence applied to the plurality of repetitions of the basic synchronization block such that a different element from the block spreading sequence is applied to each repetition of the basic synchronization block in the plurality of repetitions of the basic synchronization block.

50. The method of claim 37 wherein the synchronization signal further comprises a second plurality of repetitions of a second basic synchronization block during a second coherence time of the downlink channel over which the synchronization signal is transmitted.

51. The method of claim 50 wherein detecting the synchronization signal comprises detecting the synchronization signal according to a block spreading sequence applied to the synchronization signal such that a first element from the block spreading sequence is applied to the plurality of repetitions of the basic synchronization block and a second element from the block spreading sequence is applied to the second plurality of repetitions of the second basic synchronization block.

52. The method of claim 50 wherein detecting the synchronization signal comprises detecting the synchronization signal according to:

a first block spreading sequence applied to the synchronization signal such that a first element from the first block spreading sequence is applied to the plurality of repetitions of the basic synchronization block and a second element from the first block spreading sequence is applied to the second plurality of repetitions of the second basic synchronization block; and

a second block spreading sequence applied to the plurality of repetitions of the basic synchronization block such that a different element from the second block spreading sequence is applied to each repetition of the basic synchronization block in the plurality of repetitions of the basic synchronization block.

53. The method of claim 50 wherein detecting the synchronization signal comprises detecting the synchronization signal according to a frequency-hopping scheme utilized to transmit the synchronization signal.

54. The method of claim 37 wherein the synchronization signal further comprises a second part having a wider bandwidth than the plurality of repetitions of the basic synchronization block.

55. The method of claim 37 wherein detecting the synchronization signal comprises detecting the synchronization signal using time and frequency resources mapped around time and frequency resources used for one or more other signals.

56. The method of claim 55 wherein the cellular communications network is a Long Term Evolution, LTE, cellular communications network, and the one or more other signals comprise one or more of a group consisting of:

a control signal, a common reference signal, a channel state information reference signal, and an enhanced synchronization signal.

57. The method of claim 37 further comprising, prior to detecting the synchronization signal:

detecting a primary synchronization signal and a secondary synchronization signal in the downlink from the base station;

wherein detecting the synchronization signal comprises, subsequent to detecting the primary synchronization signal and the secondary synchronization signal and after losing synchronization with the base station, detecting the synchronization signal but not at least one of the primary synchronization signal and the secondary synchronization signal such that synchronization with the base station is re-established.

58. A wireless device configured for operation in a cellular communications network, comprising:

a transceiver; and

a processor associated with the transceiver and configured to detect, via the transceiver, a synchronization signal comprising a plurality of repetitions of a basic synchronization block during a coherence time of a downlink channel over which the synchronization signal is transmitted, where the coherence time is defined as T_c=1/f_d, where f_d is the Doppler frequency, which is defined as f_d=v. f/c where v is speed in m/s, f is carrier frequency in Hertz (Hz), and c is the speed of light.

59. The wireless device of claim 58 wherein the synchronization signal further comprises a second plurality of repetitions of a second basic synchronization block during a second coherence time of the downlink channel over which the synchronization signal is transmitted.