JP2014060637A - Frequency synchronization accuracy monitoring device, transmission/reception system, frequency synchronization accuracy monitoring method, and transmission/reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To steadily and stably monitor frequency synchronization accuracy between clocks of a transmitter and a receiver without depending on change in the weather or an installation position of the receiver.SOLUTION: A frequency synchronization accuracy monitoring device monitors a precedent packet (for example, K-th packet) and a succeeding packet (for example, N-th packet) from a transmitter 1 to a receiver 2, and measures frequency synchronization accuracy, where the frequency synchronization accuracy is a deviation of difference between an interval between transmission time Tand Tmeasured by the transmitter 1 and an interval between reception time T' and T' measured by the receiver 2 from 0 which is a value of the difference in the case of complete establishment of frequency synchronization. When synchronization accuracy of a clock frequency deteriorates more than a preset accuracy threshold, the frequency synchronization accuracy monitoring device generates information on the deterioration. Propagation delay between the transmitter 1 and the receiver 2 is approximately constant from transmission of the precedent packet (for example, K-th packet) by the transmitter 1 to reception of the succeeding packet (for example, N-th packet) by the receiver 2.

Description

  The present invention relates to a technique for monitoring whether synchronization accuracy is deteriorated between a clock frequency of a receiving apparatus and a clock frequency of a transmitting apparatus.

  When only a data signal is transmitted between the transmission device and the reception device and no clock signal is transmitted, in order to obtain a clock synchronized with the internal clock of the transmission device in the reception device, for example, a known PLL (Phase Locked Loop) circuit is used. Therefore, it is necessary to extract a clock from the transmission signal. A configuration of a conventional PLL circuit P is shown in FIG.

  The phase comparator C performs phase comparison between the data string and the divided clock, detects a phase error, and outputs an error signal having a pulse width proportional to the phase error. The filter F flattens an error signal having a pulse width proportional to the phase error, and outputs a control signal having an amplitude proportional to the magnitude of the phase error. A VCO (Voltage Controlled Oscillator) circuit V adjusts the frequency and phase of an output clock in accordance with an input control signal. The frequency divider D changes the frequency by multiplying the output clock to a frequency suitable for phase comparison. The clock output from the frequency divider D is input again to the phase comparator C and phase-compared with the data string.

  A series of these loops synchronize the frequency and phase of the clock of the receiving apparatus with the frequency and phase of the input data signal. In this way, the clock of the receiving device can be synchronized with the internal clock of the transmitting device by frequency synchronization by the known PLL circuit P.

JP 2010-288085 A

  Here, for example, the frequency of the clock of the reception device regenerated by the PLL circuit P is transmitted due to device performance degradation caused by aging degradation such as degradation of the performance of transistors included in the VCO circuit V and the phase comparator C. It can be considered that the frequency of the internal clock of the device is deviated. A control method of the VCO circuit V of the prior art is shown in FIG.

  The output frequency of the VCO circuit V is uniquely determined by a certain characteristic with respect to the control voltage of the VCO circuit V, for example, as shown in FIG. The control voltage of the VCO circuit V is mainly determined by the phase comparator C and the filter F, and can be changed only within a certain range.

  When the device is normal without deterioration over time, the control voltage of the VCO circuit V corresponding to the desired output frequency of the VCO circuit V is included in the adjustable range of the control voltage of the VCO circuit V. A desired frequency is output from the PLL circuit P by appropriately adjusting the control voltage by the unit C and the filter F (for example, in the case of FIG. 2, the operation is performed under the condition of the point A).

  However, for example, when the performance of the transistors in the VCO circuit V deteriorates, the characteristics of the output frequency of the VCO circuit V with respect to the control voltage of the VCO circuit V may change.

  Here, when the control voltage of the VCO circuit V corresponding to the desired output frequency of the VCO circuit V is within the adjustable range of the control voltage of the VCO circuit V (for example, in the case of the first abnormality in FIG. 2), Since negative feedback is applied by the feedback loop of the PLL circuit P, the desired output frequency of the VCO circuit V is output (for example, in the case of FIG. 2, the operation is performed under the condition of point B).

  However, when the control voltage of the VCO circuit V corresponding to the desired output frequency of the VCO circuit V is not within the adjustable range of the control voltage of the VCO circuit V due to, for example, significant device performance degradation (for example, in the second example of FIG. 2), even if negative feedback is applied by the feedback loop of the PLL circuit P, the control voltage cannot be adjusted beyond the adjustable range of the control voltage, so the desired output frequency of the VCO circuit V May not be output, resulting in a frequency shift, which may degrade the synchronization accuracy of the output frequency of the VCO circuit V.

  For frequency synchronization that may be deteriorated due to such performance degradation of the device, as one method for monitoring the frequency synchronization accuracy between two clocks, the frequency between the clocks of the transmission device and the reception device is used. There are methods to measure synchronization accuracy.

  As a method of calculating the frequency synchronization accuracy between two clocks, for example, there is a method of measuring the MTIE (Maximum Time Interval Error) of two clocks and calculating the frequency synchronization accuracy from the value (Patent Document 1).

TIE (Time Interval Error) represents a phase difference between the rising edges of two clocks, and represents a maximum variation in TIE as MTIE at a certain measurement time. When the MTIE is A at the measurement time T, the frequency synchronization accuracy at the measurement time T can be evaluated as A / T (for example, when the measurement time T is 100 seconds and the MTIE is 1 ns). The frequency synchronization accuracy can be calculated as 1 × 10 ⁻¹¹ ).

  When considering the frequency synchronization accuracy between the clocks of the transmission device and the reception device by this method in the reception device, the internal clock of the transmission device, which is a comparison target with the clock of the reception device in the MTIE measurement. Another clock synchronized with the clock or a clock whose temporal frequency stability is equal to or higher than the internal clock of the transmitting apparatus is required in the receiving apparatus.

  As a clock whose temporal frequency stability is equal to or higher than the internal clock of the transmitter, for example, a clock provided by GPS (Global Positioning System) and synchronized with UTC (Coordinated Universal Time) may be used. It is done. In this case, it is necessary to install a GPS signal receiver in the receiving device and receive the GPS signal.

  However, the reception status of the GPS signal receiver may deteriorate due to weather changes such as lightning strikes, and there is a problem that it is difficult to monitor the frequency synchronization accuracy stably and stably. Also, if it is necessary to install the receiver in the basement, etc., and it is difficult to install a GPS signal receiver in an environment where GPS signals can be received, a clock synchronized with UTC cannot be obtained, and frequency synchronization accuracy can be monitored. There is a problem that it is difficult to do.

  Therefore, in order to solve the above-mentioned problem, the present invention constantly and stably monitors the frequency synchronization accuracy between the clocks of the transmission device and the reception device without depending on the weather change or the installation location of the reception device. For the purpose.

  In order to achieve the above object, the difference between the transmission time interval measured by the transmission device and the reception time interval measured by the reception device for the preceding packet and the subsequent packet addressed from the transmission device to the reception device is completely frequency-synchronized. The degree of deviation from 0, which is the difference when the frequency is established, is measured as frequency synchronization accuracy.

  Specifically, the present invention relates to a transmission / reception time information acquisition unit that acquires information on a transmission time measured by the transmission device and information on a reception time measured by the reception device for a packet addressed to the reception device from the transmission device; The transmission clock referred to by the transmission device and the reception device are referred to by calculating the degree of difference between the transmission time interval and the reception time interval from 0 for the preceding packet and the subsequent packet among the packets. A frequency synchronization accuracy monitoring apparatus comprising: a frequency synchronization accuracy measurement unit that measures a clock frequency synchronization accuracy for a reception clock to be received.

  The present invention also relates to a transmission device that measures the transmission time of the packet by referring to the transmission clock and transmits information on the packet and the transmission time of the packet, and the transmission time of the packet and the packet. A transmission / reception system comprising: a reception device that receives information and refers to the reception clock to measure the reception time of the packet; and the frequency synchronization accuracy monitoring device.

  In addition, the present invention relates to a transmission / reception time information acquisition step for acquiring transmission time information measured by the transmission device and reception time information measured by the reception device for a packet addressed to the reception device from the transmission device; Of the preceding packet and the subsequent packet, the transmission clock referred to by the transmission device and the reception clock referred to by the reception device are calculated by calculating the degree of difference between the transmission time interval and the reception time interval from 0. Is a frequency synchronization accuracy monitoring method for measuring the synchronization accuracy of the clock frequency in order.

  According to the present invention, the transmitting device measures the transmission time of the packet by referring to the transmission clock, and transmits the packet and information on the transmission time of the packet. Receiving the packet and information on the transmission time of the packet and referring to the reception clock to measure the reception time of the packet and the frequency synchronization accuracy monitoring method in order This is a characteristic transmission / reception method.

  According to this configuration, it is possible to constantly and stably monitor the frequency synchronization accuracy between the clocks of the transmission device and the reception device without depending on the weather change or the installation location of the reception device.

  In addition, the present invention further includes a frequency synchronization accuracy degradation information generation unit that generates information to that effect when the synchronization accuracy of the clock frequency deteriorates below a preset accuracy threshold. It is a monitoring device.

  The present invention further includes a frequency synchronization accuracy degradation information generation step after the frequency synchronization accuracy measurement step for generating information to that effect when the synchronization accuracy of the clock frequency is degraded below a preset accuracy threshold. This is a frequency synchronization accuracy monitoring method.

  According to this configuration, it is possible to notify the transmission device, the reception device, and these management devices that the frequency synchronization accuracy between the clocks of the transmission device and the reception device has deteriorated.

  Further, the present invention is characterized in that a propagation delay between the transmission device and the reception device is substantially constant from the transmission of the preceding packet at the transmission device to the reception of the subsequent packet at the reception device. This is a frequency synchronization accuracy monitoring device.

  Further, the present invention is characterized in that a propagation delay between the transmission device and the reception device is substantially constant from the transmission of the preceding packet at the transmission device to the reception of the subsequent packet at the reception device. This is a frequency synchronization accuracy monitoring method.

  According to this configuration, the calculated difference is caused by a frequency shift between the clocks of the transmission device and the reception device, and is not caused by time variation of the propagation delay between the transmission device and the reception device. Therefore, the frequency synchronization accuracy between the clocks of the transmission device and the reception device can be monitored more stably and stably.

  The present invention can constantly and stably monitor the frequency synchronization accuracy between the clocks of the transmission device and the reception device without depending on the weather change or the installation location of the reception device.

It is a figure which shows the structure of the PLL circuit of a prior art. It is a figure which shows the control method of VCO of a prior art. It is a figure which shows the measuring method of the frequency synchronization precision of this invention. It is a figure which shows the structure of the 1st receiver of this invention. It is a figure which shows the structure of the 2nd receiver of this invention. It is a flowchart which shows the transmission process of this invention. It is a flowchart which shows the 1st reception process of this invention. It is a flowchart which shows the 2nd reception process of this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Measurement method of frequency synchronization accuracy)
The frequency synchronization accuracy measuring method of the present invention is shown in FIG. The transmission device 1 transmits a packet and a time stamp to the reception device 2. The clock frequencies of the transmission device 1 and the reception device 2 are f1 and f2, respectively. If the frequency f2 is equal to the frequency f1, the receiving device 2 can establish frequency synchronization with the transmitting device 1. If the frequency f2 is significantly different from the frequency f1, the receiving device 2 cannot establish frequency synchronization with the transmitting device 1.

K is an integer from 1 to N−1 (N will be described later). First, the transmission apparatus 1, when sending the K-th packet, measures the transmission time T _K of K-th packet by referring to the clock frequency f1, the time stamp information of the transmission time T _K of K-th packet As shown in FIG. Next, the receiving apparatus 2, upon receipt of the K-th packet, received from the transmitting apparatus 1 information transmission time T _K of K-th packet as a time stamp, the K-th packet by referring to the clock frequency f2 _'measures the reception time T _K of K-th _packet' reception time T _K embossing information as a time stamp.

Consider a case in which when the transmitting apparatus 1 transmits an Nth packet and a time stamp to the receiving apparatus 2, it is monitored whether the receiving apparatus 2 has established frequency synchronization with the transmitting apparatus 1. Here, the reception time of the measured packet differs depending on whether the frequency synchronization is established or not. In other words, a _{T K '(f1 = f2)} ≠ T K' (f1~f2), a _{T N '(f1 = f2)} ≠ T N' (f1~f2). However, for the first packet, T ₁ ′ (f1 = f2) = T ₁ ′ (f1 to f2).

  When there is no time variation of the propagation delay between the transmission device 1 and the reception device 2, the reception intervals of the Kth and Nth packets at the reception device 2 are the transmission intervals of the Kth and Nth packets at the transmission device 1. Should be equal to As a case where there is no time variation of the propagation delay between the transmission device 1 and the reception device 2, there is a case where a switch or a router is not interposed between the transmission device 1 and the reception device 2. There is a case where a PON (Passive Optical Network) is applied in which the receiving apparatus 2 is an ONU (Optical Network Unit). The PON has a small propagation delay time variation due to factors other than the temperature time variation.

Then, if you are able to establish frequency synchronization, interval _{T K} which is measured by the receiving apparatus 2 '(f1 = f2), and _{T N'} (f1 = f2) is, _{T K} and measured by the transmitter 1 Should be equal to the interval of _TN . However, if not able to establish frequency synchronization, interval _{T K} which is measured by the receiving apparatus 2 '(f1 to f2) and _{T N'} (f1~f2) is, _{T K} and measured by the transmitter 1 This is different from the interval of _TN . That is, the spacing between different degrees of _{T K} and _{T N} interval is measured by the transmission device 1 of _{T K} which is measured by the receiving apparatus 2 '(f1 to f2) and _{T N'} (f1 to f2) is, frequency synchronization Corresponding to the degree of failure to establish.

As the degree that is not able to establish frequency synchronization, the ratio of the frequency difference (f2-f1) / f1, the frequency difference f2-f1, the phase difference _{2πf1 {(T N '-T K} ') - (T N -T K)} , Etc. Here, the frequency f1 is proportional to 1 / (T _N −T _K ), and the frequency f2 is proportional to 1 / (T _N ′ −T _K ′). Therefore, the ratio of the frequency difference can be calculated as _{(f2-f1) / f1 =} (T N -T K) / (T N '-T K') -1. If the transmission-side frequency f1 is known, the frequency difference f2-f1 can be calculated by multiplying the frequency difference ratio (f2-f1) / f1 by the frequency f1.

  In the above, it has been described that there is no time variation of the frequency difference ratio, the frequency difference, the phase difference, and the propagation delay between the transmission device 1 and the reception device 2. However, there may be a time variation in propagation delay between the transmission device 1 and the reception device 2 to the extent that it can be determined without error whether frequency synchronization is established. Therefore, how much time variation of the propagation delay between the transmission apparatus 1 and the reception apparatus 2 may be described will be described.

  In order to determine whether or not frequency synchronization has been established, a determination threshold is preset for the degree to which frequency synchronization has not been established. Here, the frequency difference ratio (f2−f1) / f1 is considered as the degree of frequency synchronization not being established. Here, the frequency difference ratio (f2-f1) / f1 can be either positive or negative. Therefore, t (> 0) is selected as the determination threshold for the absolute value | (f2-f1) / f1 | of the frequency difference ratio.

For the K-th and N-th packets, when the propagation delay time variation T _V ′ is not considered, the frequency difference ratio (f2−f1) / f1 is (T _N −T _K ) / (T _N ′ −T _K ') -1 is calculated. For the Kth and Nth packets, when considering the time variation T _V ′ of propagation delay, the frequency difference ratio (f2−f1) / f1 is (T _N −T _K ) / (T _N ′ −T _K '−T _V ′) −1. However, the sign of T _V ′ is positive when the propagation delay increases, and is negative when the propagation delay decreases.

Here, when the time variation T _V ′ of the propagation delay is not considered, the calculated frequency difference ratio (f2−f1) / f1 is 0 when the frequency synchronization is established, but the time variation T of the propagation delay _V 'when considering the absolute value of the ratio of the frequency difference | (f2-f1) / f1 | is for more than a determination threshold value _{t (> 0), T V} ' consider the conditions. That is, it is determined that the frequency synchronization is established when the time variation T _V ′ of the propagation delay is not considered, but it is determined that the frequency synchronization is not established when the time variation T _V ′ of the propagation delay is considered. For this reason, the condition of T _V ′ is considered.

_{(T N -T K) / (} T N '-T K') -1 = 0 and _{| (T N -T K) /} (T N '-T K' -T V ') -1 |> t is It is established. Then, when T _V ′> 0, T _V ′> {t / (1 + t)} (T _N −T _K ) to t (T _N −T _K ). When T _V ′ <0, T _V ′ <− {t / (1−t)} (T _N −T _K ) to −t (T _N −T _K ). Here, it was assumed that t << 1. Thus, in order to determine without error whether or not frequency synchronization is established, the time variation T _V ′ of the propagation delay between the transmission device 1 and the reception device 2 has never exceeded, but its absolute values may be equal to or less than about _{t (T} N -T _K).

  In the above, it has been described that the frequency synchronization accuracy is monitored by using the values of the variables K and N. However, the frequency synchronization accuracy may be monitored without necessarily using the values of the variables K and N. That is, in monitoring the frequency synchronization accuracy, if the transmission time T measured by the transmission device 1 and the reception time T ′ stamped by the reception device 2 are linked one-to-one in the reception device 2. It is enough. Then, when the reception device 2 receives the packet, the transmission time T measured by the transmission device 1 and the reception time T ′ stamped by the reception device 2 are stored together in the reception device 2. , Without using the variables K and N.

  In the above, an example in which there is no correlation between the values indicated by the counters of the transmission device 1 and the reception device 2 has been described. However, the present invention can also be implemented when the counter value of the receiving device 2 is matched with the counter value of the transmitting device 1 when the counter value of the transmitting device 1 is sent. Only the difference between the two counter values is necessary, not both counter values themselves.

(Receiver configuration)
The configuration of the first receiving apparatus of the present invention is shown in FIG. The configuration of the second receiving apparatus of the present invention is shown in FIG. The first receiving device 2 includes a data reading unit 21, a time stamp reading unit 22, a time stamp holding unit 23, a clock extracting unit 24, a counter 25, a time stamp generating unit 26, and a frequency difference detecting unit 27. The second receiving device 2 includes a data reading 21, a time stamp reading unit 22, an internal clock 28, a counter 25, a time stamp generation unit 26, and a frequency difference detection unit 27.

  In the first receiving device 2 and the second receiving device 2, the time stamp reading unit 22 and the time stamp generating unit 26 correspond to a transmission / reception time information acquiring unit. The component acquires information on the transmission time T measured by the transmission device 1 and information on the reception time T ′ measured by the reception device 2 for the packet addressed to the reception device 2 from the transmission device 1.

In the first receiving device 2 and the second receiving device 2, the frequency difference detecting unit 27 corresponds to a frequency synchronization accuracy measuring unit. The component includes the transmission time T _N , the interval of T _K and the reception time for the preceding packet (for example, the Kth packet in FIG. 3) and the subsequent packet (for example, the Nth packet in FIG. 3) among the received packets. By calculating the degree to which the difference between the intervals of T _N ′ and T _K ′ is separated from 0, the synchronization accuracy of the clock frequency is measured for the transmission clock referred to by the transmission device 1 and the reception clock referred to by the reception device 2. .

  In the first receiving device 2 and the second receiving device 2, the frequency difference detection unit 27 corresponds to a frequency synchronization accuracy deterioration information generation unit. When the clock frequency synchronization accuracy deteriorates from a preset accuracy threshold (for example, the determination threshold t in FIG. 3), the component generates information to that effect.

As described above, from the transmission of the preceding packet (for example, the Kth packet in FIG. 3) at the transmission device 1 to the reception of the subsequent packet (for example, the Nth packet in FIG. 3) at the reception device 2. The absolute value of the time variation T _V ′ of the propagation delay between 1 and the receiving apparatus 2 is about t (T _N −T _K ) or less, and the propagation delay between the transmitting apparatus 1 and the receiving apparatus 2 is substantially constant. .

  The time stamp reading unit 22, the time stamp generating unit 26, and the frequency difference detecting unit 27 constitute a frequency synchronization accuracy monitoring device. As shown in FIGS. 4 and 5, the frequency synchronization accuracy monitoring device may be provided in the reception device 2, or may be provided outside the reception device 2 as a modification.

Next, details of the first receiving device 2 will be described. The data reading unit 21 receives the data signal transmitted from the transmission device 1, reads the data transmitted from the transmission device 1, and outputs the data to the outside of the reception device 2. Time stamp reading unit 22 is input to the time stamp transmitted from the transmitting apparatus 1, reads the time stamp value T _K transmitted from the transmitting device 1 and outputs it to the time stamp holding unit 23. Further, the time stamp read part 22, upon receiving the time stamp value T _K transmitted from the transmitting apparatus 1, and outputs a control signal of the time stamp generating to time stamp generating unit 26.

The time stamp generation unit 26 generates a time stamp value T _K ′ based on the local time obtained from the counter 25 and outputs it to the time stamp holding unit 23. The time stamp holding unit 23 holds the time stamp values in the transmission device 1 and the reception device 2 so far, and outputs the time stamp value to the frequency difference detection unit 27 as necessary.

  The frequency difference detection unit 27 is necessary to determine whether or not the frequency synchronization accuracy such as the frequency difference ratio, the frequency difference, and the phase difference has deteriorated based on the combination of the time stamp values output from the time stamp holding unit 23. The correct value is calculated. Further, the frequency difference detection unit 27 determines whether or not the frequency synchronization accuracy is deteriorated by comparing with a predetermined threshold value, and outputs the frequency error and the synchronization accuracy deterioration information to the outside of the receiving device 2.

  Here, the clock obtained from the clock extraction unit 24 is used as the operation clock of the counter 25 that sends the local time to the time stamp generation unit 26. For example, the clock extraction unit 24 reproduces a clock that is frequency-synchronized with a PLL circuit or the like with respect to the data signal or time stamp sent from the transmission device 1 and sends it to the counter 25. Alternatively, when the frequency of the clock synchronized with the data signal or the time stamp is different from the frequency of the clock to be output to the counter 25, the clock extraction unit 24 uses a multiplier or a frequency divider, etc. The clock frequency to be output to 25 may be converted to a clock frequency that is frequency-synchronized with the data signal or time stamp.

  It is desirable that the clock frequency synchronization monitoring is started after the frequency of the clock extraction unit 24 is stabilized. For example, when the clock is extracted by the PLL circuit, the time until the clock is stabilized by the filter in the PLL circuit can be designed (for example, about several tens of ms). By waiting for a sufficiently long time compared to the time when the clock is stabilized, the clock inside the receiving apparatus 2 can be stabilized.

  Next, details of the second receiving device 2 will be described. The difference between the second receiving device 2 and the first receiving device 2 is that the part that generates the clock to be sent to the counter 25 is not the clock extracting unit 24 but the internal clock 28.

  For example, as the internal clock 28, it is conceivable to use an oven controlled Xtal Oscillator (OCXO). The clock obtained by the internal clock 28 has a frequency synchronization accuracy lower than that of the clock obtained by the clock extraction unit 24, but the frequency can be synchronized with a certain degree of accuracy.

  In the case of the internal clock 28 as well, it is desirable to start the synchronization monitoring of the clock frequency after the frequency is stabilized, similarly to the clock extraction unit 24. For example, in the case of OCXO, the output clock is stabilized by warming the thermostat, so that the internal clock of the receiver 2 can be stabilized by waiting for a sufficiently long time compared to the time taken to warm the thermostat. it can.

  According to such a receiving apparatus 2, the difference in the clock recovery method between the transmitting and receiving apparatuses when the synchronization accuracy of the clock frequency is monitored and corrected between the transmitting and receiving apparatuses that transmit the data signal but not the clock signal. It is not affected by the jitter caused by.

(Contents of transmission processing)
A flowchart of the transmission process of the present invention is shown in FIG. The transmitting apparatus 1 substitutes 1 for the variable K (step S1), waits for a certain time (step S2), sends a time stamp (step S3), and substitutes K + 1 for K (step S4). ) Repeat.

  Here, the waiting time is a parameter corresponding to the time stamp transmission interval, and may be a fixed time or a random time. K corresponds to the total number of time stamps sent from the start of transmission until the time stamp is sent.

(Contents of reception processing)
FIG. 7 shows a flowchart of the first reception process of the present invention. The time stamp generator 26 substitutes 1 for the variable K (step S11), and waits until a time stamp is received from the transmission device 1 (step S12). Here, K corresponds to the total number of time stamps received from the start of reception to the time when the corresponding time stamp is received. When the transmission apparatus 1 and the reception apparatus 2 are started at the same time and all the transmitted time stamps are received without loss, the values of K managed by the transmission apparatus 1 and the reception apparatus 2 match.

Time stamp reading unit 22 receives a time stamp T ₁ from the transmitting apparatus 1, the time stamp generating unit 26 _'to emboss the, T ₁ and T _1' timestamp T ₁ of the receiving apparatus 2 is stored (Step S13). The time stamp generation unit 26 substitutes K + 1 for K (step S14), and waits until a time stamp is received from the transmission device 1 (step S15). Time stamp reading unit 22 receives the time stamp T _K from the transmitting apparatus 1, the time stamp generating unit 26 _'to emboss the, T _K and T _K' timestamp T _K of the receiving apparatus 2 is stored (Step S16).

Frequency difference detector _{27, T K + 1 ', T} K', based on _{T K} + 1, _{T K,} for the transmitter 1 and the receiver 2 clocks, to notify by calculating the ratio or frequency difference of the frequency difference (step S17, S18). Then, the frequency difference detection unit 27 compares the calculated frequency difference ratio or the frequency difference with a frequency difference ratio threshold (for example, 5 × 10 ⁻⁸ ) or a frequency difference threshold (for example, 5 Hz). It is determined whether it is small (step S19).

  When the calculated frequency difference ratio or frequency difference is smaller than the frequency difference ratio threshold or the frequency difference threshold (YES in step S19), the frequency difference detection unit 27 has degraded frequency synchronization accuracy. Judge that there is no. The time stamp generation unit 26 substitutes K + 1 for K (step S14), and waits again until the next time stamp is received.

  When the calculated frequency difference ratio or frequency difference is larger than the frequency difference ratio threshold or the frequency difference threshold (NO in step S19), the frequency difference detection unit 27 determines that the frequency synchronization accuracy has deteriorated. Judgment is made (step S20), the fact that the frequency synchronization accuracy has deteriorated is notified to the outside of the receiving apparatus 2 (step S21), and the reception process is terminated.

  FIG. 8 shows a flowchart of the second reception process of the present invention. The difference between the second reception process and the first reception process is that when the frequency synchronization accuracy deteriorates, the fact is notified to the outside of the receiving apparatus 2 and then the reception process is not terminated and the monitoring is continuously performed. In the point. Thereby, even if the frequency synchronization accuracy is once deteriorated, the frequency synchronization accuracy can be continuously monitored thereafter.

  According to such reception processing, due to the difference in the clock recovery method between the transmission / reception devices when monitoring and correcting the synchronization accuracy of the clock frequency between the transmission / reception devices that transmit the data signal but not the clock signal. It is not affected by jitter.

  The frequency synchronization accuracy monitoring device, the transmission / reception system, the frequency synchronization accuracy monitoring method, and the transmission / reception method according to the present invention can be generally applied to a transmission / reception device in which a clock signal is not included in the transmission / reception signal, and in particular, propagation between the transmission / reception devices. The present invention can be applied to a communication system with a small delay time variation (for example, a communication system or a PON not via a switch or a router).

P: PLL circuit C: Phase comparator F: Filter V: VCO circuit D: Frequency divider 1: Transmission device 2: Reception device 21: Data reading unit 22: Time stamp reading unit 23: Time stamp holding unit 24: Clock extraction Unit 25: Counter 26: Time stamp generation unit 27: Frequency difference detection unit 28: Internal clock

Claims (8)

A transmission / reception time information acquisition unit that acquires information on a transmission time measured by the transmission device and information on a reception time measured by the reception device for a packet addressed to the reception device from the transmission device;
The transmission clock referred to by the transmission device and the reception device are referred to by calculating the degree of difference between the transmission time interval and the reception time interval from 0 for the preceding packet and the subsequent packet among the packets. A frequency synchronization accuracy measuring unit that measures the clock frequency synchronization accuracy,
A frequency synchronization accuracy monitoring apparatus comprising: When the synchronization accuracy of the clock frequency has deteriorated below a preset accuracy threshold, a frequency synchronization accuracy deterioration information generation unit that generates information to that effect,
The frequency synchronization accuracy monitoring apparatus according to claim 1, further comprising:   The propagation delay between the transmission device and the reception device is substantially constant from the transmission of the preceding packet at the transmission device to the reception of the subsequent packet at the reception device. The frequency synchronization accuracy monitoring apparatus described. A transmission device that measures the transmission time of the packet by referring to the transmission clock, and transmits information on the packet and the transmission time of the packet;
Receiving the packet and information on the transmission time of the packet and referring to the reception clock to measure the reception time of the packet;
A frequency synchronization accuracy monitoring device according to any one of claims 1 to 3,
A transmission / reception system comprising: Transmission / reception time information acquisition step for acquiring transmission time information measured by the transmission device and reception time information measured by the reception device for a packet addressed to the reception device from the transmission device;
The transmission clock referred to by the transmission device and the reception device are referred to by calculating the degree of difference between the transmission time interval and the reception time interval from 0 for the preceding packet and the subsequent packet among the packets. A frequency synchronization accuracy measurement step for measuring the clock frequency synchronization accuracy for the received clock;
Are provided in order.   When the clock frequency synchronization accuracy is deteriorated below a preset accuracy threshold, a frequency synchronization accuracy degradation information generation step for generating information to that effect is further provided after the frequency synchronization accuracy measurement step. Item 6. The frequency synchronization accuracy monitoring method according to Item 5.   The propagation delay between the transmission device and the reception device is substantially constant from the transmission of the preceding packet at the transmission device to the reception of the subsequent packet at the reception device. The frequency synchronization accuracy monitoring method described. The transmitting device measures the transmission time of the packet by referring to the transmission clock, and transmits the packet and information on the transmission time of the packet;
The reception step of receiving the packet and information on the transmission time of the packet and measuring the reception time of the packet by referring to the reception clock;
A frequency synchronization accuracy monitoring method according to any one of claims 5 to 7,
In order.

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