JP7808331B2 - Delay Time Measurement System - Google Patents

Description

This invention relates to a delay time measurement system that uses GPS (Global Positioning System) to accurately measure the time required for a series of operations to be performed between remote locations in a measurement target that captures, transmits, and displays video and other data. Measurement targets are not limited to video; audio and haptics can also be measured.

There are many ways to measure video latency, including inserting a timestamp, capturing and displaying a clock, and measuring the round-trip time using the ICMP protocol on an IP network.

The method using timestamps involves sending information with a precise time stamp attached from the video sending side along with the video signal, transmitting it through the system under test, and then analyzing it on the receiving side. For example, details of this method are described in Patent Document 1. However, this method cannot measure the delay of the video cameras and displays included in the system under test, and can only measure the delay time of part of the system. Furthermore, in addition to the original video signal, a signal with a timestamp attached must be inserted on the video sending side and extracted on the receiving side, making the measurement system complicated.

A method for capturing and displaying a clock is described, for example, in Patent Document 2, in which an image of the clock is captured using a video camera in the system under test, and the image displayed on the display of the system under test after transmission is compared with the image of the clock at that time to calculate the delay time. While this system is capable of measuring delay times including the video camera and display, it has the drawback of being inaccurate because it cannot accurately capture changes in the clock display.

Measurements using the ICMP protocol on IP networks, i.e., measuring latency using the so-called ping command, are widely performed, and there is no need to refer to the literature. However, this only targets round-trip latency, and measurements are limited to transmissions over IP networks. Furthermore, it cannot measure latency including video cameras and displays.

Another method is shown in Non-Patent Document 1. In this method, a light source blinks using a measuring device, and the image is captured and transmitted using a video camera in the system under test. The blinking image displayed on the display is then converted into an electrical signal using an optical sensor, and the delay time is measured from the response.

Figure 1 shows the configuration. In Figure 1, 1 is a light source, such as a light-emitting diode (LED), and 2 is an optical sensor, such as a photodiode (PD). 3 is a reference signal generator that outputs a predetermined rectangular wave under the control of controller 7. 4 is a light source driver that generates a signal to drive light source 1 from the signal from reference signal generator 3. 5 is a trigger signal generator that inputs the signal from reference signal generator 3 and generates a signal to be applied to waveform measurement unit 6. The timing of signal changes from light source driver 4 and trigger generator 5 is identical. Waveform measurement unit 6 measures the waveforms of the signal from optical sensor 2 and the signal from trigger generator 5. The waveform acquired by waveform measurement unit 6 is sent to controller 7, where it is analyzed and the delay time is calculated. Controller 7 is, for example, a personal computer, and the delay time calculation result is displayed on its display. 10 is the system under test, which includes a video camera 11, a video transmission system 12, and a display 13.

This operation is shown in the timing chart of Figure 2. When the light source drive signal, i.e., the trigger signal, is low level, light source 1 is turned off, and when it is high level, the light source is turned on. The output of video camera 11 of system under test 10, which captures an image of the light source, is displayed on display 13 via video transmission system 12. The delay time of this operation is a delay in the light intensity signal output from optical sensor 2, as shown in Figure 2, and the delay time can be measured by analyzing it in controller 7, such as the time indicated by T1 when light source 1 goes from off to on, and the time indicated by T2 when it goes from on to off.

The configuration in Figure 1 does not use timestamps, so the video signal under test is left untouched, and it can measure all delays from the video camera to the display. Furthermore, it uses two values, the on/off state of the light source, so it can simply calculate delay time. Unlike the ICMP protocol, it can evaluate one-way delays in any video transmission system, not limited to IP networks.

The delay time measurement system in Figure 1 assumes that the video camera 11 and display 13 of the system under test 10 are located close to each other, at a distance that allows the measurement signals to be connected appropriately via cable. However, if the video camera 11 and display 13 of the system under test 10 are installed in remote locations and it is desired to measure the delay time between them, it is common to synchronize the time using GPS, as shown in Figure 3.

In Figure 3, GPS receiver 21 and GPS receiver 31 are installed at different locations. When receiving signals from a location with good signal reception, the GPS receiver's time accuracy typically achieves an error of approximately ±10 nanoseconds relative to absolute time. On the other hand, if the system under test has a video signal frame rate of, say, 60 Hz, the period should preferably be shorter than 16.7 milliseconds. The signal from the GPS receiver has sufficient accuracy. Based on the signal from the GPS, controllers 23 and 24 control reference signal generators 22 and 32 to generate predetermined square waves. The output of reference signal generator 22 drives light source 2 via light source driver 4. Meanwhile, the output of reference signal generator 32 is applied to waveform measurement unit 6 via trigger generator 5. The outputs of reference signal generator 22 and 32 are precisely synchronized by the GPS function, and are considered identical signals, as if generated by a single reference signal generator. This configuration achieves the same operation as the timing chart shown in Figure 2, enabling delay measurements between remote locations.

Patent No. 3892844 Patent No. 5553409

Taro Ogawa and Hiroyuki Matsuura, "Zero-Delay Optical Video Transmission Technology and Its Applications," Large Display & Digital Signage Overview 2020, pp. 12-22, Japan Social Systems Laboratory, 2020.

In the configuration shown in Figure 3, controllers 23 and 33 must communicate with each other and control the entire measurement system to ensure consistent operation. This communication can be achieved, for example, using the Internet, but it is cumbersome. Furthermore, it is necessary to have reference signal generators 22 and 32, respectively, and the control of these is also cumbersome.

Furthermore, when measuring delay times at remote locations, the configuration shown in Figure 3 is used, and when measuring delay times at short distances, the configuration shown in Figure 1 is used, but each requires appropriate controller control software. This requires both hardware and software switching depending on the distance, which is cumbersome. It would be desirable to be able to measure delay times even when synchronized with GPS by using the same software used for short-distance measurements without modification, without creating software compatible with GPS.

In order to solve these problems, a device is provided which turns on and off a light source installed at a first location using a light source drive signal, converts the light source image into a video signal using a video camera in the system under test, transmits the video signal, and then converts the image of the light source displayed on a display of the system under test into an electrical signal using an optical sensor at a second location, and measures the time difference between the change in the light source drive signal and the electrical signal from the optical sensor,
When the first point and the second point are located far apart, a first GPS receiver is installed at the first point and a second GPS receiver is installed at the second point, and the signals from the first GPS receiver and the second GPS receiver are used as the time reference at each point; when the first point and the second point are located close to each other, no GPS receivers are used, and the signal from a single reference signal generator connected by electrical wiring is used as the time reference;
Even when the first and second GPS receivers are used, a controller that controls the entire system is installed only at the second location, and control of time synchronization at the first location is not performed by instructions from the controller via communication, but is performed solely by signals from the first GPS receiver installed at the first location;
The controller software uses the same software as that which operates without signals from the first and second GPS receivers, and establishes a delay time measurement system that measures a predetermined time difference.

Because the first GPS receiver and the second GPS receiver are configured to appear as a single reference signal generator, it is easy to switch between a configuration using GPS when measuring delay times between distant locations and the configuration shown in Figure 1 when measuring delay times over short distances without GPS. Furthermore, there is no need to switch software. The same software used for short-distance measurements can be used without modification when using GPS to measure delay times. Furthermore, instructions for measurement from the controller are not sent to remote locations; that is, no communication for measurement is performed from point 2, where the controller is installed, to point 1, where the controller is not installed, making for a simple system.

1 is a diagram illustrating a conventional example of a delay time measurement system that does not use GPS. 2 is a timing chart showing the operation of FIG. 1; 1 is a diagram illustrating a conventional delay time measurement system using GPS. 1 is a diagram showing a first embodiment of the present invention; FIG. 4 is an explanatory diagram of when GPS is used. FIG. 10 is a diagram illustrating a second embodiment of the present invention. FIG. 10 is a diagram illustrating a third embodiment of the present invention.

The first embodiment is shown in Figure 4. Here, the output signals of GPS receiver 21 and GPS receiver 31 are signals with an accurate 1-second period known as 1PPS (Pulse Per Second), and the timing of their changes matches the absolute time with an error of, for example, ±10 nanoseconds. This 1PPS signal is often output as standard from components and devices sold commercially as ordinary GPS receivers. However, the output of GPS receiver 21 is configured to output a signal with a predetermined duty cycle, for example a 50% duty cycle. If the components used do not have this, the above can be achieved by adding appropriate circuitry.

At the location where the video camera 11 of the system under test 10 is installed, the output of the GPS receiver 21 is connected to the light source driver 25 via the selector switch 24. When explaining the measurement operation at a remote location using GPS, the selector switch 24 is set to connection A. By doing this, the light source 1 repeatedly turns on and off with a duty cycle of 50% at a one-second interval precisely synchronized with absolute time.

At the point where the display 13 of the system under test 10 is installed, the output of the GPS receiver 31 is connected to the trigger generator 35 via the selector switch 34. The selector switch 34 is set to the A connection, and a trigger signal with a 50% duty cycle is output from the trigger generator 5 at a 1-second cycle synchronized with the flashing of the light source. The selector switch 34 is set to the A connection, and the reference signal generator 3 is not used for measurement. Similarly, in Figure 4, the selector switch 24 is set to the A side, so the output of the reference signal generator 3 is not used by the selector switch 24, and no wiring is required.

The waveform measurement unit 5 receives signals from the optical sensor 2 and trigger generator 5, sends the data to the controller, and analyzes the waveform and measures the delay time in the same way regardless of whether GPS is present or not.

Figure 5 is an explanatory diagram of the first embodiment, which is the same as Figure 4, with switches 24 and 34 flipped to position A and the unused reference signal generator 3 removed. GPS receiver 21 and GPS receiver 31 are used in place of reference signal generator 3, and it can be seen that, despite being in a remote location, the system operates as if it were using a signal from a single reference signal generator. At this time, the signal from the GPS receiver is based on a 1PPS signal, and operates in no way differently from a reference signal generator with a 1-second cycle and a 50% duty cycle. Software operation with a 1-second cycle is assumed to be realized in a system without GPS, and the control software for controller 7 can be used without modification even when GPS is not used. This is a significant advantage.

Next, we will describe the case where GPS is not used and a video camera and display are installed in close proximity. In this case, selector switch 24 in Figure 4 is connected to side B, and selector switch 34 is also connected to side B. In this case, the outputs of GPS receiver 21 and GPS receiver 31 are not used. This results in exactly the same connection relationship as in Figure 1, and its operation is as described above, allowing the desired delay time to be measured. These selector switches 24 and 34 are not only mechanical switches, but also have low switching frequency, so the same can be achieved by simply plugging and unplugging the connector. The same applies to the selector switches below.

In Figure 6, which shows the second embodiment, two light source drivers and two trigger generators are depicted, and the positions of the selector switches are different from those in Figure 4, which shows the first embodiment.

At the point where the video camera 11 of the system under test 10 is installed, the output of the GPS receiver 21 is connected to the changeover switch 26 via the light source driver 25. If the changeover switch 26 is connected to side A, the light source will repeatedly turn on and off with a duty cycle of 50% in one-second cycles in accordance with the 1 PPS signal from the GPS receiver 21.

At the point where the display 13 of the system under test 10 is installed, the output of the GPS receiver 31 is connected to the selector switch 36 via the trigger generator 35. The selector switch 36 is set to the A connection, and a trigger signal with a 50% duty cycle is output from the trigger generator 37 at a 1-second cycle synchronized with the blinking of the light source. Because the selector switch 36 is set to the A connection, the signal from the reference signal generator 3 via the trigger generator 3 is not used for measurement. Similarly, in Figure 6, the selector switch 26 is set to the A side, so the signal from the output of the reference signal generator 3 via the light source driver 4 is not used by the selector switch 26, and no wiring is required.

In Figure 6, the waveform measurement unit 5 receives a signal from the optical sensor 2 trigger generation 37, sends the data to the controller, and analyzes the waveform and measures the delay time in the same way regardless of whether GPS is present or not.

In this way, if you flip switches 26 and 36 to side A and remove the unused reference signal generator 3, light source driver 3, and trigger generator 3, the system will look the same as Figure 5. Instead of the reference signal generator 3, GPS receiver 21 and GPS receiver 31 are used, and even in this case, despite being in remote locations, it can be seen that the system is operating as if it were using a signal from a single reference signal generator.

Next, we will describe the case where a video camera and display are installed in close proximity without using GPS. In this case, the selector switch 26 in Figure 6 is connected to side B, and the selector switch 36 is also connected to side B. In this case, the outputs of the GPS receiver 21, light source driver 25, GPS receiver 31, and trigger generator 37 are not used. This results in exactly the same connection relationship as in Figure 1, and its operation is as described above, allowing the desired delay time to be measured.

A third embodiment of the present invention is shown in Figure 7. This is a GPS module that houses the GPS receiver, light source driver, and trigger generation in a single housing. That is, GPS module 28 consists of GPS receiver 21, light source driver 25, and trigger generation 27. Only the output of light source driver 25 is connected to switch 26, and the output of trigger generation 27 is not used. Similarly, GPS module 38 consists of GPS receiver 31, light source driver 35, and trigger generation 37. Only the output of trigger generation 37 is connected to switch 36, and the output of light source driver 35 is not used. The operation in this case is the same as that already described.
Although the number of blocks increases and it may seem more complex, the size of each individual circuit block is small and not a problem. For example, the light source driver is a single transistor, and the trigger is generated by a voltage divider circuit using two resistors. By configuring it in this way, GPS module 28 and GPS module 38 are the same, so users do not need to use them differently, and manufacturers also have the great advantage of not having to manufacture and stock separate modules.

So far, we have been explaining how to measure video delay. The object of measurement is not limited to video; it can also be audio, for example. In this case, what is turned on and off is the sound from the speaker instead of the light source, a microphone instead of a video camera in the system being measured, and a speaker instead of a display. The microphone receives the sound on the measurement system side. In this case, too, the present invention can be applied in the same way, converting the audio into an electrical signal, detecting it, and converting it into an electrical signal of audio intensity.

Haptics can also be measured. Haptics is a technology that obtains tactile feedback by applying force, vibration, movement, etc. to the user. In other words, the system under test has a vibration-sensing sensor instead of a video camera, and a vibration-generating actuator instead of a display. On the measurement side, an actuator that generates vibrations is installed instead of a light source, and a vibration-sensing sensor is installed instead of an optical sensor, and the intensity of the vibrations is used to measure delay.

The symbols in Figures 1 to 7 are as follows:
1 --- Light source
2 --- Optical sensor
3 --- Reference signal generator
4 --- Light source driver
5 --- Trigger occurs
6 --- Waveform measurement section
7 --- Controller
10 --- System under test
11 --- Video camera
12 --- Video transmission system
13 --- Display
21 --- GPS receiver
22 --- Reference signal generator
23 --- Controller
24 --- Changeover switch
25 --- Light source driver
26 --- Changeover switch
27 --- Trigger occurs
28 --- GPS module
31 --- GPS receiver
32 --- Reference signal generator
33 --- Controller
34 --- Changeover switch
35 --- Light source driver
36 --- Changeover switch
37 --- Trigger occurs
38 --- GPS module

Claims (4)

An apparatus for driving an actuator installed at a first point by an electric drive signal to turn it on and off, sensing and transmitting the signal in a system under test, and then converting a physical quantity output from a second point of the system under test into an electric signal by a sensor, and measuring the time difference between the change in the electric drive signal and the change in the electric signal from the sensor, comprising:
When the first point and the second point are located far apart, a first GPS receiver is installed at the first point and a second GPS receiver is installed at the second point, and the signals from the first GPS receiver and the second GPS receiver are used as the time reference at each point; when the first point and the second point are located close to each other, no GPS receivers are used, and the signal from a single reference signal generator connected by electrical wiring is used as the time reference;
Even when the first and second GPS receivers are used, a controller that controls the entire system is installed only at the second location, and control of time synchronization at the first location is not performed by instructions from the controller via communication, but is performed solely by signals from the first GPS receiver installed at the first location;
The controller software is the same as that which operates without signals from the first and second GPS receivers, and is used to measure a predetermined time difference.
The delay time measurement system according to claim 1, wherein the system under test comprises a video camera, a video transmission unit, and a display, the actuator is a light source, and the sensor is an optical sensor.
The delay time measurement system according to claim 1, wherein the system under test comprises a first microphone, an audio signal transmission unit, and a first speaker, the actuator is a second speaker, and the sensor is a second microphone.
The delay time measurement system according to claim 1, wherein the system under test comprises a first vibration sensor, a vibration signal transmission unit, and a first vibration actuator, the actuator being a second vibration actuator, and the sensor being a second vibration sensor.