JP7683737B2 - Time stamp correction system, sensor system, and time stamp correction method - Google Patents

Description

The present invention relates to a timestamp correction system, a sensor system, and a timestamp correction method for transmitting and receiving data.

In IoT (Internet of Things) networks, various sensors are connected to collect a large amount of data of various types, and it is expected that useful information will be extracted by analyzing the data. Therefore, terminals that house sensors are required to be able to respond to various use cases and needs, and it is necessary to reduce power consumption during long-term measurements (Non-Patent Document 1).

In particular, in sensors, intermittent operation can be achieved by appropriately putting the MPU (Micro-Processing Unit), which consumes more power than other elements, into sleep mode, and only the analog front end (AFE) operates continuously, thereby reducing costs and power consumption (Non-Patent Document 2).

Kenichi Matsunaga et al., "Proposal of a multi-sensor data collection technology suitable for IoT," 2016 IEICE Communication Society Conference, B-18-56. "Development of a low-power, small-sized wearable sensor capable of measuring electrocardiogram, acceleration, temperature, and humidity for smart healthcare," NTT Technical Journal, Focus on the NEWS, March 2020, pp. 57-58.

However, when time stamping is performed on the data collection terminal, the delay time involved in communication between the sensor and the data collection terminal cannot be canceled, resulting in errors in the time stamp.

Furthermore, even if the interval at which the MPU wakes up is accurate, there will be constant errors in the clock installed in the AFE, causing fluctuations in the interval between packets being sent and errors in the timestamps.

In addition, external noise entering the radio section can cause the reception timing to shift, resulting in errors in the timestamp.

In order to solve the above-mentioned problems, a time stamp correction system according to the present invention is a time stamp correction system that corrects time stamps assigned to each of a plurality of packets transmitted at a predetermined transmission interval time when the plurality of packets are received, and includes a delay circuit that delays the time stamp of one of the plurality of packets, a subtraction unit that calculates a difference between a time stamp of another packet received subsequent to the one packet and the delayed time stamp of the one packet as an arrival interval time, a packet number estimation unit that quantizes the arrival interval time by comparing it with the transmission interval time , calculates a sum of quantization numbers of the quantized arrival interval times in a predetermined period, calculates an average value of the quantization numbers by dividing the calculated sum of quantization numbers by the number of packets arriving in the predetermined period, and sets the average value of the quantization numbers as an estimate of the number of packets, a calculation unit that multiplies the estimate of the number of packets by the transmission interval time to calculate a dequantized arrival interval time, a moving average filter that performs a moving average on the dequantized arrival interval time, and an addition unit that adds the time stamp of the one packet to the value obtained by the moving average.

A timestamp correction method according to the present invention is a method for correcting timestamps added to a plurality of packets transmitted at a predetermined transmission interval when the plurality of packets are received, the method comprising the steps of: a delay circuit delaying a timestamp of one of the plurality of packets; a subtraction unit calculating a difference between a timestamp of another packet received subsequent to the one packet and a timestamp of the delayed one packet as an arrival interval; a packet number estimation unit quantizing the arrival interval by comparing it with the transmission interval ; The method includes the steps of: calculating a sum of quantized numbers of quantized arrival interval times; calculating an average value of the quantized numbers by dividing the calculated sum of quantized numbers by the number of packets arriving in a predetermined period; and setting the average value of the quantized numbers as an estimate of the number of packets; a calculation unit multiplying the estimate of the number of packets by the transmission interval time to calculate a dequantized arrival interval time; a moving average filter performing a moving average on the dequantized arrival interval time; and an addition unit adding a timestamp of the one packet to the value obtained by the moving average.

The present invention provides a timestamp correction system, a sensor system, and a timestamp correction method that reduce errors in timestamps assigned to packets.

FIG. 1 is a block diagram showing a configuration of a sensor system according to a first embodiment of the present invention. FIG. 2A is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 2B is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a time stamp correction system according to a first embodiment of the present invention. FIG. 4 is a flow chart showing a time stamp correction method according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 6A is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 6B is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 6C is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 6D is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 7 is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 8 is a diagram for explaining the operation of the time stamp correction system according to the first embodiment of the present invention. FIG. 9 is a block diagram showing a configuration of a time stamp correction system according to the second embodiment of the present invention. FIG. 10 is a flow chart showing a time stamp correction method according to the second embodiment of the present invention. FIG. 11 is a schematic diagram showing the configuration of a sensor system according to the third embodiment of the present invention. FIG. 12 is a schematic diagram showing the configuration of a sensor system according to the fourth embodiment of the present invention.

First Embodiment
A time stamp correction system, a sensor system, and a time stamp correction method according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIG.

<Sensor system configuration>
1, a sensor system 10 according to this embodiment includes a sensor 11 and a receiver 12. Signals are transmitted and received between the sensor 11 and the receiver 12 wirelessly or via wires.

The sensor 11 operates intermittently and includes an AFE 111, a memory 112, an MPU 113, and a transmission unit 114. It also includes an AFE clock 115 connected to the AFE 111, and a packet clock 116 connected to the MPU 113.

The AFE 111 samples and quantizes the measurement signal 1 at time T _AFE counted by the AFE clock 115 .

The memory 112 stores the quantized measurement signal 1 as sensor data 2.

Here, one packet 3 consists of a predetermined number of sensor data 2.

The MPU 113 is activated at a predetermined interval T _packet counted by a packet clock 116, and checks the memory 112. When the sensor data 2 to be stored in one packet 3 is stored in the memory 112, a wireless circuit (e.g., BLE, Bluetooth Low Energy) is activated, and the packet 3 is transmitted from the transmission unit 114. In this manner, the packet transmission interval time is T _packet .

The receiver 12 includes a time stamp correction system 121 according to the present embodiment, a time stamp assignment unit 122, and a receiving unit 123. It also includes a time stamp clock 125.

After receiving a packet at the receiving unit 123, the time stamp adding unit 122 according to this embodiment adds to the packet a time stamp T _stamp that is counted by the time stamp clock 125 and provided via the receiver's OS 124. Here, the time stamp is synchronized with the Global Positioning System (GPS), the Network Time Protocol (NTP), the Network Identity and Time Zone (NITZ), or the like.

The timestamp correction system 121 corrects the timestamp assigned to the packet input by the timestamp assignment unit 122, as described below.

<Configuration and operation of timestamp correction system>
The configuration and operation of the time stamp adding unit 122 according to this embodiment will be described below.

First, a case where a time stamp correction system is not provided will be described. In this configuration, the _TAFE in the AFE clock 115 has a large error due to low power consumption and cost reduction, and may deviate by up to several minutes per day. This error is a problem for a biosensor that performs measurement for a day or more. Details will be described below.

Figures 2A and 2B show examples of packet transmission modes 131_1, 132_1 and reception modes 131_2, 132_2 when timestamp correction is not performed. Here, the length Lp of one packet corresponds to eight pieces of sensor data 2. White circles 3_1 to 3_4 indicate packets, and T1 to T4 indicate the arrival interval times of the packets.

When the AFE clock 115 is faster than the startup interval of the MPU 113, as shown in Figure 2A, there are cases where the AFE has two or more packets of data (e.g., packets 3_2 and 3_3) at startup (131_1). In this case, packets 3_2 and 3_3 are transmitted consecutively, so the packet arrival interval time T2 becomes very short on the receiver side (132_1).

Also, if the AFE clock is slower than the MPU startup interval, as shown in Figure 2B, the amount of data in the packets sent at startup will be insufficient (dotted white circle 3'). In this case, no packets will be sent (131_2). In this case, the packet arrival interval time T4 on the receiver side will be longer (132_2).

In this way, in a configuration that does not have a timestamp correction system, the arrival interval of packets varies greatly depending on the AFE clock, and errors also occur due to transmission errors during wireless transmission, so if the timestamp at the time of reception is used as is, the error increases.

Next, the time stamp correction system 121 and the time stamp correction system according to this embodiment will be described. Figure 3 shows the configuration of the time stamp correction system 121 according to this embodiment. Figure 4 shows a flowchart of the time stamp correction method according to this embodiment.

As shown in FIG. 3, the timestamp correction system 121 includes a delay circuit 1211, a subtraction unit 1212, a packet number estimation unit 1213, a calculation unit 1214, a moving average filter 1215, and an addition unit 1216.

Here, the time stamp correction system 121 acquires and holds the transmission interval time T _packet in advance. The transmission interval time T _packet may be stored in the time stamp correction system 121 in advance, or may be transmitted from the sensor 11.

The arrival time T _arrival given to the packet is input to the time stamp correction system 121. Here, the arrival time T _arrival is the same as the time stamp T _stamp .

The delay circuit 1211 is configured as a one-stage delay circuit, and delays the arrival time T _arrival (time stamp T _stamp ) of a received packet (one packet), for example, T _arrival [i-1].

The subtraction unit 1212 calculates the difference (e.g., T arrival [i]-T _arrival [i-1]) between the arrival _time T _arrival (e.g., T _arrival [i]) of the subsequently received packet (other packet) and the T _arrival delayed by the delay circuit (e.g., T _arrival [i-1]) (step S11). This difference in arrival time T _arrival (time stamp T _stamp ) is the arrival interval time T _interval [i].

The packet number estimation unit 1213 estimates the number of packets from the arrival interval T _interval [i].

Here, the arrival interval is distributed with noise for integer multiples (n) of the transmission interval T _packet of packets from the sensor, as shown in Fig. 5. Therefore, in order to cancel this noise, the estimated value of T _packet is set to n = 1, and quantized by the number of packets estimated to have been sent within the transmission interval, such as n = 0, 1, 2, ... (step S12).

Quantization by packet number is explained with reference to Figures 6A to 6D, using as an example packets received when the AFE clock is faster than the MPU wake-up interval.

Packets P(i) to P(i-5) are received, and their respective inter-arrival times are designated as T _interval (i) to T _interval (i-4) (FIG. 6A).

First, the time between received packets is set as a transmission interval time T _packet .

The arrival intervals T _interval (i) to T _interval (i-4) of the actually received packets are compared with T _packet , and when the arrival intervals T _interval (i) to T _interval (i-4) of the packets correspond to n times T _packet , the quantization number is set to n (FIG. 6B).

Specifically, since T _interval (i) is equal to T _packet , the quantization number is "1". Similarly, since T _interval (i-1) is equal to T _packet , the quantization number is "1". Next, since T _interval (i-2) is shorter than T _packet , the quantization number is "0". Next, since T _interval (i-3) is equal to T _packet , the quantization number is "1". Similarly, since T _interval (i-4) is equal to T _packet , the quantization number is "1".

In this way, the quantized inter-arrival time varies from 1 → 1 → 0 → 1 → 1 (Figure 6C).

Next, the quantized number of the quantized arrival interval times, i.e., the total number of packets, is calculated (step S13). In this case, it is 1+1+0+1+1=4. Next, the average of the quantized arrival interval times is calculated as an estimate of the number of packets (step S14). In this case, the number of arriving packets is 5, so the average value is 4/5. In this way, the quantized arrival interval times are smoothed and fluctuations in the arrival interval times are suppressed (Figure 6D).

This converts the real value of the inter-arrival time into an integer value, reducing noise.

Next, the calculation unit 1214 converts the quantized arrival interval time (integer value) back into a real value. In other words, inverse quantization is performed. Specifically, the quantized arrival interval time (integer value) is multiplied by the transmission interval time T _packet (step S15). In the above example, (4/5)×T _packet is calculated.

Next, the dequantized arrival interval is input to the moving average filter 1215 to perform moving average calculation (step S16). Here, the moving average value is calculated by using the average value of T _interval and the average value of T _interval that is subsequently obtained.

For example, as shown in FIG. 7, a moving average is calculated for the arrival interval times from an arbitrary (i-th) arrival interval time T _interval [i] to the N-1th previous arrival interval time T _interval [i-N+1].

Here, the moving average can be a simple moving average, a weighted moving average, an exponential moving average, etc.

The effect of the processing (moving average) of the moving average filter 1215 is described below.

The cutoff frequency Fc of the moving average filter 1215 is designed to be lower than the Nyquist frequency, which is a frequency expressed as f _packet /2, where 1/T _packet =f _packet .

As shown in Figure 8, quantization noise 151 is distributed across the entire frequency range during the quantization and inverse quantization processes. The quantization noise 151 is noise caused by information (analog values) that is lost during quantization.

In addition, when sensor data is actually transmitted in packets, the packets have a high-frequency signal 152 such as a measurement signal, and a low-frequency signal 153 including information related to a timestamp. Here, the high-frequency signal 152 varies on a second-by-second basis, and the low-frequency signal 153 varies on a minute-by-minute basis.

By setting the cutoff frequency Fc of the moving average filter 1215 lower than the Nyquist frequency, the moving average filter 1215 functions as a low-pass filter, blocking the high-frequency signal 152 and transmitting the low-frequency signal 153, thereby correcting the timestamp contained in the low-frequency signal 153.

Here, since the high frequency signal 152 fluctuates in units of seconds while the low frequency signal 153 fluctuates in units of minutes, it is effective to set the cutoff frequency Fc to 1/60 or less of the frequency of the high frequency signal 152.

Furthermore, since the quantization noise 151 is uniformly distributed with respect to frequency, the noise can be reduced by f _packet /2Fc.

Finally, the adder 1216 adds the initial time T ₀ , which is an offset, to the calculated moving average value of the arrival interval, thereby obtaining a time stamp correction value T _correct (step S17).

Here, when determining the initial time _T0 , even if the first arrival time is used or it is estimated using the least squares method or the like, an absolute time error of only a few tens of ms occurs, so the impact is smaller than before the application, when a deviation of seconds or more occurs.

Furthermore, in the time stamp correction system 121, by configuring the moving average filter 1215 in multiple stages, the slope 154 of the low-pass filter characteristic of the moving average filter 1215 becomes steeper, the jitter component can be reduced, and high frequency signals can be cut off more accurately and stably. On the other hand, a delay occurs in tracking the fluctuation of T _packet , but this delay is not so large that it causes any trouble in a biological data measurement system that cuts off the DC component.

Furthermore, since the rate of change of T _packet is very slow depending on temperature changes and aging, there is little effect of narrowing the bandwidth of the filter.

In addition, in the time stamp correction method, the output of the moving average filter 1215 may be fed back to the step of quantizing the arrival interval (step S12) to calculate the moving average again (dotted arrow in FIG. 4). This causes T _packet to change over time, so the time stamp can be corrected with higher accuracy by performing calculation again using the updated T _packet .

According to the timestamp correction system of this embodiment, a moving average filter can remove noise, mitigate delays, and reduce timestamp errors.

Furthermore, if a packet transmission error occurs, two or more packets are transmitted in succession immediately afterwards, so T _interval contains noise that is correlated in time, and this noise can be easily removed by the moving average filter 1215. In other words, using the transmission interval time T _packet as a reference can reduce jitter and obtain a time stamp with high accuracy, rather than using the arrival time containing noise and delay as is.

It is also useful in systems where packets arrive on a stream and require real-time correction. It is also useful in that it has a wider range of applicable applications than systems that perform batch processing on a server.

In addition, since signal processing is basically composed of delay and multiply-and-accumulate operations, acceleration processing using a DSP (digital signal processor) can be applied, making it suitable for real-time data processing.

In addition, corrections are performed using a clock synchronized with GPS, NIP, NITZ, etc., allowing for highly accurate corrections.

Second Embodiment
A time stamp correction system, a sensor system, and a time stamp correction method according to a second embodiment of the present invention will be described with reference to FIGS.

<Configuration and operation of timestamp correction system>
The sensor system 20 according to this embodiment has a configuration substantially similar to that of the first embodiment, but differs in the configuration of a timestamp correction system 221 .

Figure 9 shows the configuration of a timestamp correction system 221 according to this embodiment. Figure 10 shows a flowchart of a timestamp correction method according to this embodiment.

As shown in FIG. 9, the timestamp correction system 221 includes a multi-stage delay circuit 2211, a subtraction unit 2212, a packet number estimation unit 2213, a calculation unit 2214, a moving average filter 2215, and an addition unit 2216.

The time stamp correction system 221 receives the arrival time T _arrival (time stamp T _stamp ) assigned to the packet.

The delay circuit 2211 is composed of M-stage delay circuits, and delays the input T _arrival (for example, T _arrival [i-1]), where T _arrival is the same as T _stamp .

The subtraction unit 2212 uses the outputs of the M-stage delay circuit to calculate the difference in arrival time, i.e., the arrival interval time (step S21). As a result, M arrival interval times are obtained.

The packet number estimation unit 2213 quantizes the arrival interval time and calculates the average value of this quantized number as an estimate of the packet number (steps S22 to S24).

Next, the calculation unit 2214 multiplies the quantized arrival interval time by the transmission interval time T _packet to perform inverse quantization and convert it into a real value (step S25).

As described above, since the arrival interval time is multiplied by M times by the M-stage delay circuits, the quantized arrival interval time is multiplied by the T _packet value and divided by M (step S26).

Next, the inversely quantized arrival interval time divided by M is input to the moving average filter 2215 to perform moving averaging (step S27).

Finally, the adder 2216 adds the initial time T ₀ , which is an offset, to the calculated moving average value of the arrival interval, thereby obtaining a time stamp correction value T _correct (step S28).

Here, as in the first embodiment, the output of the moving average filter 2215 may be fed back to the quantization step of the arrival interval time (step S22) to calculate the moving average value again (dotted arrow in Figure 10).

According to the timestamp correction system of this embodiment, a moving average filter can remove noise, mitigate delays, and reduce timestamp errors.

Furthermore, by using multiple delay circuits, correlated noise can be removed before the number of packets is quantized. Also, since the M-times multiplied data is multiplied by 1/M during inverse quantization, the noise caused by inverse quantization itself can be reduced.

In addition, since the time stamp correction system requires a delay of M stages in the process of estimating the number of packets, the noise is reduced as the number of stages (M stages) of the delay circuit increases, but the real-time performance decreases. Therefore, the number of stages (M stages) of the delay circuit needs to be adjusted depending on the application. However, since the fluctuation of the T _packet to be tracked is in minutes, a delay of about 10 seconds is thought to have no effect on the real-time performance.

Third Embodiment
A time stamp correction system and a sensor system according to a third embodiment of the present invention will be described with reference to FIG.

<Sensor system configuration>
11, the sensor system 30 according to the present embodiment includes sensors 31_1 to 31_M and mobile information terminals 32_1 to 32_M such as smartphones, and each of the mobile information terminals 32_1 to 32_M includes the time stamp correction system according to the first embodiment and a time stamp providing unit. Here, the time stamp correction system according to the second embodiment may be included.

In the sensor system 30, data acquired by the sensors 31_1 to 31_M is collected by the mobile information terminals 32_1 to 32_M. The collected data is assigned a timestamp by the mobile information terminals 32_1 to 32_M, the timestamp is corrected, and the data is transmitted to the network system 4, where it is handled in the form of a cloud or the like.

According to the sensor system of this embodiment, the timestamp correction system can eliminate noise, mitigate delays, and reduce timestamp errors. In addition, since correction is performed using a clock synchronized with GPS, NIP, NITZ, etc., correction can be performed with high accuracy.

Furthermore, for example, in Android and iOS, which are typical operating systems for smartphones, the resolution of the timestamp is limited to 1 ms, which may limit the achievable jitter value. With the sensor system of this embodiment, the accuracy is reduced to the number of arriving packets in any time interval, and the accuracy of the timestamp itself is not an issue. Therefore, the sensor system of this embodiment is effective when performing software processing on the OS of a smartphone.

In addition, in the sensor system according to this embodiment, one smartphone may be configured to connect to multiple sensors and provide timestamps. In this configuration, the effect of delay is large, and the effect on other applications is also large. Therefore, a configuration in which one sensor is connected to one smartphone is more preferable than a configuration in which multiple sensors are connected to one smartphone.

<Fourth embodiment>
A time stamp correction system and a sensor system according to a fourth embodiment of the present invention will be described with reference to FIG.

<Sensor system configuration>
12, the sensor system 40 according to the present embodiment includes sensors 41_1 to 41_M, data collection terminals 42_1 to 42_N, and a server 43. Here, the data collection terminals 42_1 to 42_N include a time stamp providing unit, and the server 43 includes the time stamp correction system according to the first embodiment. Here, the server 43 may include the time stamp correction system according to the second embodiment.

In the sensor system 40, data acquired by sensors 41_1 to 42_M is collected by data collection terminals 42_1 to 42_N and time stamped. The time stamped data is sent to the server 43, where the time stamp is corrected, and the data is sent to the network system 4, where it is handled in the form of a cloud or the like.

In this way, the sensor system 40 is configured such that the data collection terminals 42_1 to 42_N only assign timestamps, and the server 43 corrects the timestamps.

According to the sensor system of this embodiment, the timestamp correction system can remove noise, mitigate delays, and reduce timestamp errors. Furthermore, since the data collection terminal can allocate resources only to providing timestamps, it is possible to prevent degradation of timestamp accuracy due to calculations in an environment where multiple sensors are connected to the data collection terminal.

In addition, in a typical sensor network, the higher the server (closer to the network system) the higher its computing power, while the lower the sensor (further away from the network system) the lower its computing power. Therefore, correcting the timestamp on a server with high computing power is useful in that it allows resources to be concentrated.

In particular, in the sensor system of the second embodiment, packet transmission failures increase when multiple sensors are connected, but since the timestamp can be corrected and transmitted again after a packet transmission failure, noise becomes correlated and accuracy can be maintained.

In the embodiment of the present invention, an example of the structure, dimensions, etc. of each component in the configuration of the timestamp correction system and sensor system, the timestamp correction method, etc. is shown, but it is not limited to this. It is sufficient if the configuration of the timestamp correction system and sensor system, and the timestamp correction method can exhibit the functions and effects.

The present invention relates to a timestamp correction system, a sensor system and a timestamp correction method, and can be applied to systems and communication systems that transmit and receive data acquired by sensors.

121 time stamp correction system 1211 delay circuit 1212 subtraction unit 1213 packet number estimation unit 1214 calculation unit 1215 moving average filter 1216 addition unit

Claims (6)

1. A time stamp correction system for correcting a time stamp assigned to each of a plurality of packets when the plurality of packets are received, the time stamp correction system comprising:
a delay circuit for delaying a timestamp of one of the plurality of packets;
a subtraction unit that calculates a difference between a timestamp of another packet received after the one packet and a timestamp of the delayed one packet as an arrival interval;
a packet number estimation unit that quantizes the arrival interval time by comparing it with the transmission interval time , calculates a sum of quantized numbers of the quantized arrival interval time in a predetermined period, calculates an average value of the quantized numbers by dividing the calculated sum of the quantized numbers by the number of packets arriving in the predetermined period , and sets the average value of the quantized numbers as an estimate of the number of packets;
a calculation unit that calculates an inverse quantized arrival interval by multiplying the estimated value of the number of packets by the transmission interval;
a moving average filter that performs a moving average on the dequantized inter-arrival times;
an adding unit that adds a timestamp of the one packet to the value obtained by the moving average. 2. The time stamp correction system according to claim 1, wherein the delay circuit is a multi-stage circuit. a sensor that transmits packets generated from a measurement signal at a transmission interval;
a time stamp assignment unit that receives the packet and assigns a time stamp to the packet;
A sensor system comprising: the time stamp correction system according to claim 1 or 2 . The sensor;
The sensor system according to claim 3 , further comprising: a portable information terminal comprising the time stamp providing unit and the time stamp correction system, and configured to transmit the corrected time stamp over a network. The sensor;
a data collection terminal including the time stamp assignment unit;
The sensor system of claim 3 , further comprising: a server comprising the time stamp correction system and configured to transmit the corrected time stamp to a network. 1. A method for correcting timestamps added to a plurality of packets when the plurality of packets are received, the timestamps being corrected when the plurality of packets are received, the method comprising the steps of:
a delay circuit delaying a timestamp of one of the plurality of packets;
A subtraction unit calculates a difference between a timestamp of another packet received after the one packet and a timestamp of the delayed one packet as an arrival interval;
a packet number estimation unit quantizing the arrival interval time by comparing it with the transmission interval time ;
a step in which the packet number estimation unit calculates a sum of quantized numbers of the quantized arrival intervals in a predetermined period, calculates an average value of the quantized numbers by dividing the calculated sum of the quantized numbers by the number of packets arriving in the predetermined period , and sets the average value of the quantized numbers as an estimate of the number of packets;
a calculation unit multiplying the estimated value of the number of packets by the transmission interval time to calculate an inverse quantized arrival interval time;
a moving average filter performing a moving average on the dequantized inter-arrival times;
an adding unit adding a timestamp of the one packet to the value obtained by the moving average.

Images