Synchronizer

• US 6,009,131 A
• Filed: 07/25/1997
• Issued: 12/28/1999
• Est. Priority Date: 08/29/1996
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hiramatsu, Katsuhiko
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Fan, Chieh M.
• Application Number:
  US08/900,862
• Time in Patent Office: 886 Days
• Field of Search: 375/275, 375/344, 375/354, 375/356, 375/357, 375/364, 375/365, 375/366, 370/324, 370/462
• US Class Current: 375/354
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15

Abstract

A detection circuit of a synchronizer detects a difference between a reference timing of a transmitter and a reference timing of a receiver based on a time of receiving a known transmission pattern sent from the transmitter. An average value calculation circuit calculates an average value of the difference detected by the detection circuit. An integration circuit determines an integrated value by integrating the average value each time of interrupting the receiver. A correction value calculation circuit calculates a correction value to correct the reference timing of the receiver in forward direction in the case where the integrated value exceeds a predetermined first threshold level and to correct the reference timing of the receiver backward in the case where the integrated value is reduced below a predetermined second threshold level.

Claims

1. A synchronizer comprising:

a transmission pattern detection circuit for detecting a known transmission pattern transmitted from a transmitter and generating a transmission pattern detection information signal upon detection of said known transmission pattern;

a difference detection circuit for detecting a difference between a reference timing of said transmitter and a reference timing of a receiver on the basis of a receiving time of said known transmission pattern;

an average value calculation circuit for calculating an average value of said difference detected in said difference detection circuit and updating said calculated average value only upon receipt of said transmission pattern detection information signal from said transmission pattern detection circuit;

an integration circuit for determining an integrated value by integrating said average value for each time of interrupting said receiver; and

a correction value calculation circuit for calculating a correction value used to correct the reference timing of said receiver in a forward direction in the case where said integrated value exceeds a predetermined first threshold level, and to correct the reference timing of said receiver backward in the case where said integrated value is reduced below a predetermined second threshold level.

2. A synchronizer according to claim 1, further comprising a timing counter to be corrected in timing,

wherein the difference between the reference timing of said transmitter and the reference timing of said receiver is calculated using said timing counter, and

in the case where a frame length of the reference timing of said receiver is shortened by said correction value in order to deviate the timing in a forward direction by said timing correction in said timing counter, said correction value is added to the receiving time of said known transmission pattern, and in the case where the frame length of the reference timing of said receiver is lengthened by said correction value in order to deviate the timing backward by said timing correction in said timing counter, said correction value is subtracted from the receiving time of said known transmission pattern, thereby to calculate the receiving time of said known transmission pattern.

3. A synchronizer according to claim 1, further comprising a counter having a counting period shorter than a period of receiving said known transmission pattern,

wherein an operation of said counter is started before receiving said known transmission pattern, and the operation of said counter is stopped after time when said known transmission pattern is assumed to be received, thereby to calculate the receiving time of said known transmission pattern.

4. A synchronizer according to claim 1, further comprising a counter having a counting period shorter than a period of receiving said known transmission pattern,

wherein an operation of said counter is started before receiving said known transmission pattern, the operation of said counter is stopped upon receipt of said known transmission pattern, and in the case where said known transmission pattern is not received, the operation of said counter is stopped before time when said known transmission pattern is to be received, thereby to calculate the receiving time of said known transmission pattern.

5. A synchronizer according to claim 1, further comprising a symbol clock reproduction circuit for reproducing an optimum symbol clock using a clock representing an integer multiple of said symbol clock, and a timing circuit having a time accuracy equivalent to a symbol time accuracy,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver with an accuracy an integer multiple of said symbol time accuracy.

6. A synchronizer according to claim 1, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

7. A synchronizer according to claim 1, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said detection circuit detects the difference between the reference timing of said difference transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

8. A synchronizer according to claim 1, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

9. A synchronizer according to claim 8, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

10. A synchronizer according to claim 1, further comprising:

a histogram calculation circuit for calculating a histogram of the receiving time of said known symbol pattern and calculating the difference between the reference timing of said transmitter and the reference timing of said receiver, and

a second correction value calculation circuit for calculating a timing correction value based on said calculated histogram.

11. A synchronizer according to claim 1, further comprising:

a histogram calculation circuit for calculating a histogram of the difference of the receiving time of said known symbol pattern to calculate the difference between the reference timing of said transmitter and the reference timing of said receiver, and

a second correction value calculation circuit for calculating a timing correction value based on said calculated histogram.

12. A synchronizer according to claim 1, further comprising:

a high-accuracy reference clock oscillator;

a low-accuracy reference clock oscillator;

a timing correction circuit for correcting various timings using said high-accuracy reference clock and calculating an average value of the difference between the reference clock of said transmitter and the reference clock of said receiver using said low-accuracy reference clock in a continuous receiving mode; and

a timing control circuit for controlling said various timings based on said average value calculated using said low-accuracy reference clock in an intermittent receiving mode.

25. A synchronizer according to claim 2, further comprising a counter having a counting period shorter than a period of receiving said known transmission pattern,

wherein an operation of said counter is started before receiving said known transmission pattern, and the operation of said counter is stopped after time when said known transmission pattern is assumed to be received, thereby to calculate the receiving time of said known transmission pattern.

26. A synchronizer according to claim 2, further comprising a counter having a counting period shorter than a period of receiving said known transmission pattern,

wherein an operation of said counter is started before receiving said known transmission pattern, the operation of said counter is stopped upon receipt of said known transmission pattern, and in the case where said known transmission pattern is not received, the operation of said counter is stopped before time when said known transmission pattern is to be received, thereby to calculate the receiving time of said known transmission pattern.

27. A synchronizer according to claim 2, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

28. A synchronizer according to claim 3, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

29. A synchronizer according to claim 4, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

30. A synchronizer according to claim 5, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

31. A synchronizer according to claim 25, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

32. A synchronizer according to claim 26, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number.

33. A synchronizer according to claim 2, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

34. A synchronizer according to claim 3, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

35. A synchronizer according to claim 4, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

36. A synchronizer according to claim 5, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

37. A synchronizer according to claim 25, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

38. A synchronizer according to claim 26, further comprising a selection circuit for selecting a reference time by a channel type and a slot number, and a memory for storing a reference time determined by said channel type and said slot number,

wherein said difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver without regard to said channel type and said slot number, and

said average value calculation circuit calculates the average value of said difference using the number of slots as counted from a previous receiving time of the known symbol string.

39. A synchronizer according to claim 2, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

40. A synchronizer according to claim 3, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

41. A synchronizer according to claim 4, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

42. A synchronizer according to claim 5, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

43. A synchronizer according to claim 6, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

44. A synchronizer according to claim 7, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

45. A synchronizer according to claim 25, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

46. A synchronizer according to claim 26, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

47. A synchronizer according to claim 27, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

48. A synchronizer according to claim 28, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

49. A synchronizer according to claim 29, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

50. A synchronizer according to claim 30, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

51. A synchronizer according to claim 31, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

52. A synchronizer according to claim 32, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

53. A synchronizer according to claim 33, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

54. A synchronizer according to claim 34, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

55. A synchronizer according to claim 35, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

56. A synchronizer according to claim 36, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

57. A synchronizer according to claim 37, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

58. A synchronizer according to claim 38, further comprising:

a memory for storing the differences between the reference clock of said transmitter and the reference clock of said receiver over all frames based on the detection time of the known symbol pattern at time of achieving a frame synchronism, and

an initial value calculation circuit for calculating an initial average value of said differences upon complete achievement of said frame synchronism.

59. A synchronizer according to claim 39, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

60. A synchronizer according to claim 40, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

61. A synchronizer according to claim 41, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

62. A synchronizer according to claim 42, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

63. A synchronizer according to claim 43, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

64. A synchronizer according to claim 44, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

65. A synchronizer according to claim 45, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

66. A synchronizer according to claim 46, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

67. A synchronizer according to claim 47, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

68. A synchronizer according to claim 48, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

69. A synchronizer according to claim 49, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

70. A synchronizer according to claim 50, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

71. A synchronizer according to claim 51, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

72. A synchronizer according to claim 52, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

73. A synchronizer according to claim 53, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

74. A synchronizer according to claim 54, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

75. A synchronizer according to claim 55, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

76. A synchronizer according to claim 56, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

77. A synchronizer according to claim 57, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

78. A synchronizer according to claim 58, further comprising an updating circuit for updating said difference by receiving the known symbol pattern of an arbitrary slot after complete achievement of said frame synchronism.

13. A synchronizer provided in a receiver, comprising:

a transmission pattern detection circuit for detecting a known transmission pattern transmitted from a transmitter and generating a transmission pattern detection information signal upon detection of said transmission pattern;

a timing difference detection circuit for detecting a difference between a reference timing of said transmitter and a reference timing of said receiver on the basis of a receiving time of said transmission pattern;

an average value calculation circuit for calculating an average value of said detected difference and updating said calculated average value only upon receipt of said transmission pattern detection information signal from said transmission pattern detection circuit;

an integration circuit for determining an integrated value by integrating said average value for each time of interrupting said receiver; and

a correction value calculation circuit for calculating a correction value to correct the reference timing of said receiver in forward direction in the case where said integrated value exceeds a predetermined first threshold level and to correct the reference timing of said receiver backward in the case where said integrated value is reduced below a predetermined second threshold level.

14. A synchronizer according to claim 13, further comprising a timing counter with an initial value set in accordance with said correction value;

wherein said timing difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver on the basis of a count value of said timing counter, and

said average value calculation circuit correcting said detected difference in accordance with said correction value and then calculating the average value of said corrected difference.

15. A synchronizer according to claim 13, further comprising:

a reference timer having a counting period shorter than a period of receiving said transmission pattern and for detecting the receiving time of said transmission pattern; and

a reference timer control circuit for starting an operation of said reference timer before receiving said transmission pattern and stopping the operation of said reference timer after time when said transmission pattern is assumed to be received.

16. A synchronizer according to claim 15, wherein said reference timer control circuit stops the operation of said reference timer upon detection of said transmission patter by said transmission pattern detection circuit.

17. A synchronizer according to claim 13, further comprising a symbol synchronization circuit for determining an absolute value of said transmission pattern at a period an integer multiple of a symbol period of said transmission pattern, adding said absolute value for each symbol period, and deciding on a symbol identification point from the added absolute value;

wherein said timing difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver based on the receiving time of said transmission pattern and said symbol identification point.

18. A synchronizer according to claim 13, further comprising a memory for storing a reference time determined by a channel type and a slot number,

wherein said timing difference detection circuit detects the difference between the reference timing of said transmitter and the reference timing of said receiver on the basis of the receiving time of said transmission pattern and said reference time read out of said memory.

19. A synchronizer according to claim 18, wherein said average value calculation circuit calculates the average value of said difference divided by said reference time.

20. A synchronizer according to claim 13, further comprising:

a memory for storing the differences between the reference timing of said transmitter and the reference timing of said receiver based on the receiving time of said transmission pattern over all frames at time of achieving a frame synchronism;

a back-end protection circuit for generating a frame synchronism establishment signal upon complete achievement of said frame synchronism; and

an initial value calculation circuit for reading the differences stored in said memory to calculate an initial average value of said differences upon receipt of said frame synchronism establishment signal from said back-end protection circuit.

21. A synchronizer according to claim 20, further comprising a switch for preventing the difference between the reference timing of said transmitter and the reference timing of said receiver from being applied to said initial value calculation circuit upon receipt of said frame synchronism establishment signal from said back-end protection circuit.

22. A synchronizer according to claim 13, further comprising:

a histogram calculation circuit for calculating a histogram of the receiving time of said transmission pattern; and

a second correction value calculation circuit for calculating a second correction value for correcting the reference timing of said receiver on the basis of said calculated histogram.

23. A synchronizer according to claim 13, further comprising:

a histogram calculation circuit for calculating a histogram of the difference between the reference timing of said transmitter and the reference timing of said receiver detected by said timing difference detection circuit; and

a second correction value calculation circuit for calculating a second correction value to correct the reference timing of said receiver on the basis of said calculated histogram.

24. A synchronizer provided in a receiver, comprising:

a transmission pattern detection circuit for detecting a known transmission pattern transmitted from a transmitter and generating a transmission pattern detection information signal upon detection of said transmission pattern;

a first timing difference detection circuit for detecting a first difference between the reference timing of said transmitter and the reference timing of said receiver on the basis of the receiving time of said transmission pattern using a high-accuracy reference clock;

a first average value calculation circuit for calculating a first average value of said detected first difference;

a first integration circuit for determining a first integrated value by integrating said first average value for each time of interrupting said receiver;

a first correction value calculation circuit for calculating a first correction value to correct the reference timing of said receiver in forward direction in the case where said first integrated value exceeds a predetermined first threshold level and to correct the reference timing of said receiver backward in the case where said first integrated value is reduced below a predetermined second threshold level;

a second timing difference detection circuit for detecting a second difference between the reference timing of said transmitter and the reference timing of said receiver based on the receiving time of said transmission pattern using a low-accuracy reference clock;

a second average value calculation circuit for calculating a second average value of said detected second difference;

a second integration circuit for determining a second integrated value by integrating said second average value for each time of interrupting said receiver; and

a second correction value calculation circuit for calculating a second correction value to correct the reference timing of said receiver in forward direction in the case where said second integrated value exceeds a predetermined third threshold level and to correct the reference timing of said receiver backward in the case where said second integrated value is reduced below a predetermined fourth threshold level;

wherein the reference timing of said receiver is corrected based on said first correction value and said second correction value is calculated by said second correction value calculation circuit in a continuous receiving mode, and

the reference timing of said receiver is corrected based on said second correction value in an intermittent receiving mode.