Acquisition of sychronization in a spread spectrum communications transceiver

• US 6,727,790 B2
• Filed: 08/20/2001
• Issued: 04/27/2004
• Est. Priority Date: 08/20/2001
• Status: Expired due to Fees

• Current Assignee: Yitran Communications Ltd. (Allalouf Capital Ltd.)
• Original Assignee: Yitran Technologies Ltd.
• Inventors: Raphaeli, Dan, Kaufman, Oren, Bassin, Evgeny, Zarud, Boris
• Primary Examiner(s): Corrielus, Jean B.
• Application Number:
  US09/933,065
• Publication Number:
  US 20040042534A1
• Time in Patent Office: 981 Days
• Field of Search: 375/130, 375/140, 375/142, 375/145, 375/149, 375/150, 375/354, 375/363, 375/365, 375/367, 370/503, 370/504, 370/509, 370/512, 370/515
• US Class Current: 375/363
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/7095 Sliding correlator type
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A novel and useful acquisition and synchronization mechanism for spread spectrum communication systems whereby a synchronization sequence comprising a plurality of known symbols spaced apart by predefined time delay intervals is transmitted as the start of packet signal. At the receiver, the received signal is correlated against the synchronization sequence using the predefined gaps or time delay intervals inserted between the symbols. The received signal is linearly correlated to generate a correlation peak for each symbol received. The expected position of each correlation peak is calculated and compared to the positions of the correlation peaks received. If the number of matches exceeds a threshold, synchronization is declared.

Claims

1. A method of acquiring synchronization on a start of packet signal comprising a plurality of symbols generated in accordance with a predefined synchronization sequence template, said method comprising the steps of:

correlating a receive signal to generate a plurality of received correlation peaks;

calculating an expected position of each received correlation peak in accordance with said predefined synchronization sequence template;

determining a correlation qualities at said expected position of said each received correlation peak; and

evaluating said correlation qualities and declaring synchronization if said evaluation exceeds predetermined criteria.

2. The method according to claim 1, wherein said correlation quality is determined in accordance with the distance of each received correlation peak from said expected position in addition to the height of said received correlation peak.

3. The method according to claim 1, wherein said correlation quality is set to a match if the position of a received correlation peak is within a predetermined distance of said corresponding expected position, and is set to no match otherwise.

4. The method according to claim 3, wherein said predetermined criteria comprises the number of matches exceeding a threshold, and wherein said threshold is set as a function of the heights of said correlation peaks.

5. The method according claim 1, wherein said step of determining said correlation quality comprises determining the value of the correlation at the expected position of said each received correlator peak and wherein said step of evaluating comprises summing said correlation quality values.

6. The method according to claim 1, wherein information related to acquisition is conveyed in predefined time delays or gaps between transmitted symbols.

7. The method according to claim 1, wherein each of said plurality of symbols comprises a zero shifted code shift keying (CSK) modulated symbol.

8. The method according to claim 1, wherein said step of correlating comprises performing linear correlation on said receive signal.

9. The method according to claim 1, wherein said plurality of symbols as sent by a transmitter comprises a start of packet synchronization sequence including seven zero shift symbols with predefined delay inserted after each symbol.

10. The method according to claim 1, wherein the position of each received correlation peak is stored in a table.

11. The method according to claim 1, wherein said predefined synchronization sequence template is stored in a table.

12. The method according to claim 3, wherein said predetermined distance comprises a plurality of phase units to the left of each received correlation peak.

13. The method according to claim 4, wherein said threshold comprises a majority of said plurality of symbols.

14. The method according to claim 1, wherein the position of the last received correlation peak is assumed to be correct.

15. The method according to claim 1, wherein said expected position is calculated with reference to the last received correlation peak.

16. The method according to claim 1, further comprising the step of assuming the correlation peak previous to the last received correlation peak is correct and repeating said steps of calculating wherein the expected positions are calculated with reference to the previous to the last received correlation peak.

17. The method according to claim 1, further comprising the step of repeating said steps of calculating, determining and evaluating in search for matches with different synchronization sequence delay templates.

18. The method according to claim 3, wherein synchronization is declared, in the event of a borderline number of matches, only if the sum of matching correlation peaks exceeds a peak value threshold.

19. The method according to claim 3, further comprising the step of determining a synchronization point as a function of the average of the differences between the expected position and the position of the received correlation peak of each matching correlation peak.

20. The method according to claim 1, further comprising the step of calculating a synchronization quality factor whereby the reception of a new packet with an associated higher synchronization quality factor causes a receiver to drop the packet previously being received and immediately receive the new packet.

21. The method according to claim 1, wherein said method is implemented in an Application Specific Integrated Circuit (ASIC).

22. The method according to claim 1, wherein said method is implemented in a Field Programmable Gate Array (FPGA).

23. An apparatus for acquiring synchronization in a communications network on a start of packet synchronization sequence comprising a plurality of symbols, each pair of symbols spaced apart in accordance with the predetermined synchronization template, comprising:

a correlator adapted to generate a correlation peak in response to each received symbol in said synchronization sequence;

an acquisition circuit comprising;

means for calculating an expected position of each received correlation peak in accordance with said predefined synchronization template;

means for determining a correlation quality at said expected position of said each received correlator peak; and

means for evaluating said correlation qualities and declaring synchronization if said evaluation exceeds predetermined criteria.

24. The apparatus according to claim 23, wherein said correlation quality is determined in accordance with the distance of each received correlation peak from said expected position in addition to the height of said received correlation peak.

25. The apparatus according to claim 23, wherein said correlation quality is set to a match if the position of a received correlation peak is within a predetermined distance of said corresponding expected position, and is set to no match otherwise.

26. The apparatus according to claim 25, wherein said predetermined criteria comprises the number of matches exceeding a threshold, and wherein said threshold is set as a function of the heights of said correlation peaks.

27. The apparatus according claim 23, wherein said means for determining sad correlation quality comprise means for determining the value of the correlation at the expected position of each said received correlator peak and wherein said step of evaluating comprises summing said correlation quality values.

28. The apparatus according to claim 23, wherein said predetermined synchronization template comprises a sequence of time delays.

29. The apparatus according to claim 23, wherein said correlator is adapted to perform linear correlation on a receive signal.

30. The apparatus according to claim 25, wherein said predetermined distance comprises a number of phase units to the left of each received correlation peak.

31. The apparatus according to claim 26, wherein said threshold comprises a majority of said plurality of symbols.

32. The apparatus according to claim 23, wherein the position or the last received correlation peak is assumed to be correct.

33. The apparatus according to claim 23, wherein said expected position is calculated with reference to the last received correlation peak.

34. The apparatus according to claim 23, further comprising means for assuming the correlation peak previous to the last received correlation peak is correct and repeatedly calculating said expected positions with reference to the previous to the last received correlation peak.

35. The apparatus according to claim 23, further comprising means for repeatedly calculating and comparing in search for synchronization matches utilizing multiple predefined synchronization time delay templates.

36. The apparatus according to claim 25, wherein synchronization is declared, in the event of a borderline number of matches is, only if the sum of he values of each matching correlation peaks exceeds a peak value threshold.

37. The apparatus according to claim 25, further comprising means for determining a synchronization point as a function of the average of the differences between the expected position and the position of the received correlation peak of each matching correlation peak.

38. The apparatus according to claim 23, further comprising means for calculating a synchronization quality factor whereby the reception of a new packet with an associated higher synchronization quality factor causes a receiver to drop the packet previously being received and immediately receive the new packet.

39. The apparatus according to claim 23, wherein said apparatus is implemented in an Application Specific Integrated Circuit (ASIC).

40. The apparatus according to claim 23, wherein said apparatus is implemented in a Field Programmable Gate Array (FPGA).

41. A method of acquiring synchronization in a communications network, said method comprising the steps of:

receiving a synchronization sequence at the beginning of a packet sent by a transmitting station, the transmitted synchronization sequence comprising a plurality of symbols wherein each symbol is separated by a predetermined time delay;

correlating said received synchronization sequence to generate a plurality of correlation peaks;

searching for the presence of correlation peaks in expected positions within a predefined range of phase units wherein said expected positions correspond to said predetermined time delays inserted between symbols by said transmitting station;

declaring synchronization if the number of correlation peaks found in corresponding expected positions within said predefined range of phase units exceeds a threshold; and

determining a synchronization time point as a function of the distances between the positions of the received correlation peaks and their corresponding expected positions.

42. The method according to claim 41, wherein each said predetermined signal comprises a particular time delay or gap in transmission.

43. The method according to claim 41, wherein data decoding of said packet begins a predetermined fixed distance after said synchronization time point.

44. The method according to claim 41, further comprising the step of determining a synchronization point as a function of the average of the differences between the expected position and the position of the received correlation peak of each matching correlation peak.

45. The method according to claim 41, further comprising the step of calculating a synchronization quality factor whereby the reception of a new packet with an associated higher synchronization quality factor causes a receiver to drop the packet previously being received and immediately receive the new packet.

46. The method according to claim 41, wherein said method is implemented in an Application Specific Integrated Circuit (ASIC).

47. The method according to claim 41, wherein said method is implemented in a Field Programmable Gate Array (FPGA).

48. An Application Specific Integrated Circuit (ASIC) for acquiring synchronization in a communication network on a transmission signal including a start of packet synchronization sequence of a plurality of symbols, each pair of symbols with a predetermined gap inserted therebetween in accordance with a predetermined synchronization sequence gap template, said ASIC comprising:

receiving means adapted to generate a receive signal from said communications network;

correlator means adapted to generate a correlation peak from said receive signal in response to each received symbol in said synchronization sequence;

calculating means for calculating an expected position of each received correlation peak in accordance with said predefined synchronization gap template;

determining means for generating a correlation quality at said expected positions; and

means for evaluating said correlation qualities and declaring synchronization if said evaluation exceeds predetermined criteria.

49. The ASIC according to claim 48, wherein said correlation quality is determined in accordance with the distance of each received correlation peak from said expected position in addition to the height of said received correlation peak.

50. The ASIC according to claim 48, wherein said correlation quality is set to a match if the position of a received correlation peak is within a predetermined distance of said corresponding expected position, and is set to no match otherwise.

51. The ASIC according to claim 50, wherein said predetermined criteria comprises the number of matches exceeding a threshold, and wherein said threshold is set as a function of the height of aid correlation peaks.

52. The ASIC according claim 48, wherein said determining means comprises determining the value of the correlation at the expected position and wherein said means for evaluating comprises means for summing said correlation quality values.

53. The ASIC according to claim 48, further comprising mean for assuming the correlation peak previous to the last received correlation peak its correct and repeatedly calculating said expected positions with reference to the previous to the last received correlation peak.

54. The ASIC according to claim 48, further comprising means for repeatedly calculating said expected positions in search for synchronization matches utilizing multiple predefined synchronization sequence gap templates.

55. The ASIC according to claim 50, wherein synchronization is declared, in the event of a borderline number of matches, only if the sum of matching correlation peak exceeds a peak value threshold.

56. The ASIC according to claim 50, further comprising means for determining a synchronization point as a function of the average of the differences between the expected position and the position of the received correlation peak of each matching correlation peak.

57. The ASIC according to claim 48, further comprising means for calculating a synchronization quality factor whereby the reception of a new packet with in associated higher synchronization quality factor causes a receiver to drop the packet previously being received and immediately receive the new packet.

58. A communications station for transmitting and receiving signals to and from other stations connected over a shared communications media based network, comprising:

a coupling circuit for generating a receive signal received over said network and for outputting a transmit signal onto said network;

a transmitter adapted to modulate a synchronization sequence and data to be transmitted in accordance with a modulation scheme so as to generate said transmit signal therefrom, said synchronization sequence comprising a plurality of symbols wherein each symbol is separated by a first signal in accordance with a predetermined synchronization sequence template;

a receiver adapted to demodulate said receive signal in accordance with said modulation scheme so as to generate a receive data signal therefrom, said receiver comprising an acquisition circuit comprising;

means for correlating said receive signal to generate a plurality of received correlation peaks therefrom;

means for calculating an expected position of each received correlation peak in accordance with said predetermined synchronization sequence template;

means for comparing the position of each received correlation peak with a corresponding expend position and declaring a match if the position of a received correlation peak is within a predetermined distance of said corresponding expected position;

means for declaring synchronization if the number of matches exceeds a threshold;

a media access control (MAC) circuit adapted to interface an application processor to said shared communications media; and

said application processor adapted to control the operation of said transmitter, receiver and MAC and to provide an interface between said MAC and an external host.

59. The communications station according to claim 58, wherein said first signal comprises a series of time delays in accordance with said predetermined synchronization sequence template.

60. The communications station according to claim 58, wherein said modulation scheme comprises code shift keying (CSK) modulation.

61. The communications station according to claim 58, further comprising means for assuming the correlation peak previous to the last received correlation peak is correct and repeatedly calculating said expected positions with reference to the previous to the last received correlation peak.

62. The communications station according to claim 58, further comprising means for repeatedly calculating said expected positions in search for synchronization matches utilizing multiple predefined synchronization sequence gap templates.

63. The communications station according to claim 58, wherein synchronization is declared in the event the number of matches is borderline, only if the sum of the vagus of each matching correlation peak exceeds a peak value threshold.

64. The communications station according to claim 58, further comprising means for determining a synchronization point as a function of the average of the differences between the expected position and the position of the received correlation peak of each matching correlation peak.

65. The communications station according to claim 58, further comprising means for calculating a synchronization quality actor whereby the reception of a new packet with an associated higher synchronization quality factor causes a receiver to drop the packet previously being received and immediately receive the new packet.

66. The communication station according to claim 58, wherein said transmitter and receiver are implemented in an Application Specific Integrated Circuit (ASIC).

67. The communications station according to claim 58, wherein said transmitter and receiver are implemented in a Field Programmable Gate Array (FPGA).