Radio-controlled timepiece, method of obtaining date/time information, and recording medium

Patent metadata

Field	Value
Publication number	US-9766598-B2
Application number	US-201514963459-A
Country	US
Kind code	B2
Filing date	Dec 9, 2015
Priority date	Dec 24, 2014
Publication date	Sep 19, 2017
Grant date	Sep 19, 2017

Abstract

A radio-controlled timepiece, including: a radio wave reception unit that receives satellite waves and extracts an incoming code sequence formatted in a prescribed format from the received satellite waves; and a processor that generates in advance an expected code sequence that is expected to be part of the incoming code sequence and detects a matching code sequence segment, within the incoming code sequence, that has a degree of match with the expected code sequence that satisfies a prescribed matching condition, the processor determining a present date/time, as indicated by the satellite waves, in accordance with a timing at which the detected matching code sequence segment occurs within the incoming code sequence as measured by time kept by the timepiece.

First claim

What is claimed is:

1. A radio-controlled timepiece, comprising:
a radio wave reception unit that receives satellite waves and extracts an incoming code sequence formatted in a prescribed format from said received satellite waves; and
a processor that generates in advance an expected code sequence that is expected to be part of said incoming code sequence and detects a matching code sequence segment, within said incoming code sequence, that has a degree of match with the expected code sequence that satisfies a prescribed matching condition, the processor determining a present date/time, as indicated by the satellite waves, in accordance with a timing at which said detected matching code sequence segment occurs within said incoming code sequence as measured by time kept by the timepiece.

2. The radio-controlled timepiece according to claim 1 , wherein said degree of match is determined by comparing respective code bits in said expected code sequence with corresponding code bits in said incoming code sequence and determining a mismatch count in said comparison.

3. The radio-controlled timepiece according to claim 2 , wherein said prescribed matching condition is such that said mismatch count for said matching code sequence segment, which is defined as a first mismatch count, is less than or equal to a prescribed maximum value, and that a quotient obtained by dividing a first probability of occurrence, as defined below, by a second probability of occurrence, as defined below, is less than or equal to a first reference value,
wherein said first probability of occurrence is defined as a probability that an arbitrarily chosen code sequence segment with a same length as the expected code sequence has said first mismatch count with respect to the expected code sequence, and said second probability of occurrence is defined as a probability that an arbitrarily chosen code sequence segment with a same length as the expected code sequence has a second mismatch count, as defined below, with respect to the expected code sequence, and
wherein said second mismatch count is a smallest one among a plurality of mismatch counts of code sequence segments that are compared with the expected code sequence within a prescribed range in said incoming code segment from the said matching code sequence segment that has said first mismatch count.

4. The radio-controlled timepiece according to claim 3 , wherein said first probability of occurrence and said second probability of occurrence are calculated by assuming that, in each of binary codes that constitute said incoming code sequence, a probability that 0 occurs and a probability that 1 occurs are 1/2, respectively.

5. The radio-controlled timepiece according to claim 3 , wherein said processor instructs, when said quotient obtained by dividing said first probability of occurrence by said second probability of occurrence is not less than or equal to said first reference value for the matching code sequence segment that has said first mismatch count less than the prescribed maximum value, said radio wave reception unit to receive subsequent satellite waves during a portion or portions of a next transmission period such that a resultant newly extracted incoming code sequence or sequences include a first code sequence that corresponds to a code sequence segment in a current incoming code sequence from which said first mismatch count is obtained and a second code sequence segment that corresponds to a code segment in the current incoming code sequence from which said second mismatch count is obtained, and wherein said processor compares said expected code sequence with said first code sequence segment and said second code sequence segment, respectively, and determines whether said prescribed condition is satisfied for the first and second code sequence segments included in the newly extracted incoming code sequence or sequences.

6. The radio-controlled timepiece according to claim 5 , wherein said processor instructs said radio wave reception unit to receive said subsequence satellite waves during said portion or portions of said next transmission period when a third probability of occurrence, as defined below, is greater than a second reference value, and
wherein said third probability of occurrence is defined as a probability that an arbitrarily chosen code sequence segment with a same length as the expected code sequence has a third mismatch count with respect to the expected code sequence, said third mismatch count being defined as a second smallest one among the plurality of mismatch counts of the code sequence segments that are compared with the expected code sequence within the prescribed range in said incoming code sequence from the said matching code sequence segment that has said first mismatch count.

7. The radio-controlled timepiece according to claim 6 , wherein said second reference value is a value obtained by multiplying said second probability of occurrence by a prescribed number.

8. The radio-controlled timepiece according to claim 2 , wherein said prescribed matching condition is that said mismatch count is less than or equal to a prescribed upper limit.

9. The radio-controlled timepiece according to claim 8 , wherein said upper limit for said mismatch count is determined such that a probability that an arbitrarily chosen code sequence segment with a same length as the expected code sequence has a mismatch count equal to said upper limit with respect to the expected code sequence is less than or equal to a prescribed reference value.

10. The radio-controlled timepiece according to claim 9 , wherein said probability of occurrence is computed by assuming that, in each of binary codes that constitute said incoming code sequence, a probability that 0 occurs and a probability that 1 occurs are 1/2, respectively.

11. The radio-controlled timepiece according to claim 1 , further comprising:
a counter unit that counts a date/time of said radio-controlled timepiece, wherein said processor generates, based on said date/time counted by said counter unit, said expected code sequence that includes a prescribed number of lower bits, inclusive of a least significant bit, of a series of bits that represent, in said prescribed format, a present time that is updated at each transmission period.

12. The radio-controlled timepiece according to claim 11 , wherein said processor determines that said degree of match between said incoming code sequence and said expected code sequence does not satisfy said prescribed matching condition when a mismatch occurs in any one of said prescribed number of lower bits of the series of bits that represent the present time.

13. The radio-controlled timepiece according to claim 11 , wherein said processor updates said expected code sequence in accordance with changes in said present time as updated when a code sequence segment that satisfies the prescribed matching condition is not found by shifting a beginning of a candidate code sequence segment that is compared with the expected code sequence until said shift is greater than or equal to a number of code bits that corresponds to said transmission period.

14. The radio-controlled timepiece according to claim 1 , wherein said processor generates said expected code sequence that includes an invariant code sequence that does not change with transmission period, set forth by the prescribed format.

15. The radio-controlled timepiece according to claim 1 , further comprising:
a storage unit that stores a reception history of most recently received satellite waves and a code sequence that is obtained from said most recently received s

Assignees

• Casio Computer Co Ltd

Inventors

• Matsue Takeshi
• Abe Hideo
• Abe Kazuaki

Classifications

• G04R20/06 Primary

  Decoding time data; Circuits therefor · CPC title