Nippon Telegraph and Telephone Corporation

Ryuta Sugiyama

Kaoru Arai

Hiroki Sakuma

Osamu Kurokawa

Kazuyuki Matsumura

Shunichi Tsuboi

Takaaki Hisashima

A management apparatus in a time synchronization system includes a time variation information receiving unit configured to acquire time variation information and position information of a time synchronization apparatus, a position information classifying unit configured to classify time synchronization apparatuses into predetermined categories based on the acquired position information, a time variation analysis configured to determine majority based on whether patterns of time variation of the time synchronization apparatuses belonging to an identical category are identical to each other, and to analyze the time variation based on the determined results, and a filtering and delivery unit configured to output an instruction to block the time information received from the positioning satellite, to the time synchronization apparatus having abnormal time variation. A GPS-FW includes a filtering determination unit configured to blocks the time information received from a GPS satellite in a case where a block instruction is received from the management apparatus.

Time synchronization system, management device, time synchronization method, and program

A second transceiver () includes a guide light source (), a photorefractive crystal (), and a frequency control unit (). The guide light source () emits guide light (Y). A double phase conjugate mirror () is formed in a crystal () by scattering of reference signal light (Y), which has a frequency different from that of the guide light and is incident on the crystal via space () after being transmitted from a first transceiver () which is a transceiver on the other side, and the guide light that is incident on the crystal in a reverse direction to that of the reference signal light. A frequency control unit () couples the reference signal light emitted from the crystal (), which is phase-conjugate light of the guide light generated by the mirror (), to an optical fiber ().

Transceiver, spatial light frequency transmission system and spatial light frequency transmission method

[Problem] To monitor a frequency difference between an input clock and a synchronous clock synchronized with the input clock. [Solution] A clock frequency monitoring apparatus that monitors the frequency of an input clockincludes a phase comparatorthat compares a phase of a synchronous clockphase-synchronized with the input clockor a first frequency-divided clockobtained by frequency-dividing the synchronous clockwith the phase of the input clock, a filterthat low-pass filters an output signal of the phase comparator, an oscillatorthat generates the synchronous clockhaving a frequency corresponding to a control value from the filter, and a determinerthat determines that the frequency of the input clockis abnormal when the variation amplitude of the output signal of the filteris equal to or more than a predetermined range.

Clock frequency monitoring device and clock frequency monitoring method

[Problem] To determine a time difference between clocks which, for example, are placed far apart from each other with high accuracy at low cost. [Solution] In a time comparison system, an intermediate stationdisperses a single optical signalin the spatial region using the optical complex amplitude modulation to simultaneously transmit the optical signalto a plurality of comparative stationsandapart from each other. The intermediate stationtransmits the optical signalwhile changing the transmission angle using phase modulation, performs intensity scanning for the reflected light cof the optical signal, and detects the peak intensity to determine the directions of the comparative stationsand. The reflected light cof the optical signaltransmitted to the comparative stationsandof which the direction have been determined, is detected to determine a round-trip propagation delay time between the intermediate stationand each of the comparative stationsand. The difference calculation unitcalculates a sum of time difference between each of times to and tb associated with the comparative stationsandand the time tc associated with the intermediate station, and the determined propagation delay time to determine time information of each of the comparative stationsand. Based on the result of subtracting, from the time information of the comparative stations, the time information of the comparative stations, the time difference between the comparative stationsandis determined.

Time comparison system, time comparison device, and time comparison method

[Problem] To select an optimal transmission path having a minimum total MTIE value of total MTIE values between a plurality of master apparatuses configured to transmit time information serving as a reference and a specific relay apparatus configured to receive the time information via a plurality of relay apparatuses to achieve time synchronization. [Solution] A time path selection apparatusselects a transmission path employed for time synchronization, on the basis of a MTIE value evaluated in each of relay apparatusesto, between master apparatusesandconfigured to transmit time information serving as a reference and a relay apparatusorat an edge configured to receive the time information via a relay apparatusorto achieve the time synchronization. The time path selection apparatusincludes a time information reception unitconfigured to receive the MTIE value evaluated in each of the relay apparatusesto, and an optimal path derivation unitconfigured to evaluate, on the basis of the received MTIE value, a total MTIE value for every transmission path in transmission paths between the relay apparatusand the master apparatusesandand to select and derive, as the transmission path employed for the transmission path for time synchronization, a transmission path where the total MTIE value is a minimum (170 ns).

Time path selection device and time path selection method

[Problem] It is possible to improve the quality of time information by suppressing a jump in time which arises when switching a transfer path in a BC apparatus to which transfer paths of time information of at least 2 systems are connected to an input side. [Solution] A time synchronization apparatusis mounted on a BC apparatusin which two systems of at least a 0-system route (0-system) and a 1-system route (1-system) are connected to an input side, and includes a time correction value holding unitconfigured to hold a 0-system correction value in which a time error resulting from delay of UTC due to performance inherent to the BC apparatus is the same value as a time error accumulated on the 0-system side and a 1-system correction value in which the time error is the same value as a time error accumulated on the 1-system side. Further, a failure restoration detection unitconfigured to detect a failure in the 0-system or the 1-system, a time calculation unitconfigured to perform correction by subtracting a 1-system correction value relating to a normal 1-system from UTC having time error accumulated on the normal 1-system side, when a failure in the 0-system is detected, and a path switching unitconfigured to switch to the normal 1-system side such that the UTC after correction is transferred, when the failure is detected, are included.

Time synchronization device and time synchronization method

[Problem] To synchronize timings of transmitting and receiving a pulse signal (1 PPS signal) at a constant interval between communication apparatuses even in a case where an optical fiber connecting the communication apparatuses fluctuates in an optical characteristic and an optical fiber length. [Solution] The time synchronization systemtransmits and receives a pulse signal at a constant interval between a local apparatus L (apparatus L) and a remote apparatus R (apparatus R) connected through the two-core bidirectional optical fibers Fand Fto synchronize time. A propagation delay amount &#x3c4;in the fiber Fis calculated, from a proportional relationship between Tand Tand a proportional relationship of &#x3c4;ud and &#x3c4;, where Trepresents a propagation delay time difference between a pulse signals Pand Pof an identical wavelength &#x3bb;returned after transmitting a pulse signal Pof wavelength &#x3bb;and a pulse signal Pof wavelength &#x3bb;different from &#x3bb;to the remote apparatus R, Trepresents a propagation delay time difference between the pulse signal Pof wavelength &#x3bb;and a pulse signal Pof wavelength &#x3bb;, and &#x3c4;ud represents the round-trip delay time between the apparatuses L and R. The pulse signals Pand Pare transmitted with a time difference td corresponding to a difference between the current and last calculated propagation delay amounts &#x3c4;being set so that the difference is zero.

Time synchronization system and time synchronization method

A local device of a time synchronization system includes a path switching unit that connects respective remote devices using individual optical fibers and switches the respective optical fibers sequentially in a cyclic order, a counter unit, a phase difference memory unit, and a table unit. The counter unit counts a pulse signal Pdemodulated by a PPS demodulation unit to obtain a count value. The phase difference memory unit stores the count value as path information in association with a phase difference detected by a phase detection unit, and outputs the phase difference associated with this path information indicated by the count value to the variable delay unit. When the count value is input, the table unit outputs a path switching signal for switching to the next optical fiber in the cyclic order to the path switching unit and the path switching unit performs switching to the next optical fiber.

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Tokyo, Japan

Ryuta Sugiyama