Signal synchronization methods and signal transmission systems

Abstract

Regardless of whether or not they share a common protocol, they synchronize data signals transmitted and received between devices via telecommunication lines. [Solution] A reference signal is converted into a packet signal and transmitted via a telecommunication line to a data transmitting device and a data receiving device that transmit and receive data signals. Both devices generate a synchronization clock signal whose clock rate, frequency, time, phase, etc., are synchronized with the received reference signal, and this synchronization clock signal enables synchronization of the data signals transmitted and received between the two devices. If the reference signal is lost due to packet loss, both devices generate dummy data to serve as the reference signal, and the synchronization of the data signals is maintained by synchronizing this dummy data with the synchronization clock signal.

Description

Technical Field

[0001] The present invention relates to a signal synchronization method capable of synchronizing clock devices, times, frequencies, phases, etc. of a transmission-side device and a reception-side device (terminal device: hereinafter simply referred to as "device") communicated via a network (telecommunication line) such as Ethernet, and a signal transmission system capable of realizing the synchronization method.

Background Art

[0002] Signal transmission systems are roughly classified into wireless systems and wired systems. In a wireless system, devices such as televisions and mobile phones receive signals from satellites and base stations to receive video, audio, etc. In recent years, it has become common to receive various signals. In a wired system, various telecommunication lines using cable television, analog optical lines, Ethernet, etc. have become widespread, and it is possible to transmit and receive high-frequency signals (data signals) such as video signals, audio signals, and data signals. In Ethernet, reliable data signal transmission has become possible by using a communication protocol (TCP / IP: Transmission Control Protocol / Internet Protocol).

[0003] When transmitting and receiving data signals between a plurality of devices connected to a telecommunication line, information on when the data signal was transmitted may be important. In this case, there is a method of synchronizing the time between a plurality of devices to confirm the transmission time. In a system that performs time synchronization using radio waves such as Japanese standard time represented by a radio-controlled clock, there is also a method of adjusting to the accurate time when it becomes the reference time. As an example, there is a method of synchronizing time using a satellite positioning system (GPS) or the like. There are Patent Documents 1 to 5 as patent documents related to synchronization.

[0004] In a synchronization system between devices connected via a telecommunication line, the IEEE1588 standard is widespread as a means for high-precision time synchronization.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-17057 [Patent Document 2] Japanese Patent Publication No. 2021-169962 [Patent Document 3] Patent No. 5650072 [Patent Document 4] Patent No. 6607627 [Patent Document 5] Patent No. 6879750

[0006] (Problems with conventional technology) Standard time synchronization methods using GPS or IEEE 1588 are intermittent, meaning that devices at multiple transmission / reception points cannot be constantly synchronized in real time. A certain degree of clock deviation between devices must be tolerated until the next synchronization timing. This leads to problems such as the need for complex systems when reception conditions are unstable, and the assumption that all terminal devices operate under the same protocol, resulting in high costs and complexity for the system. Furthermore, the longer the reception interval, the more difficult it becomes to maintain accurate synchronization.

[0007] In systems where a signal contains multiple channels, a method of synchronization has been disclosed in which each channel is transmitted individually to prevent interference with others. However, this synchronization method has problems such as high cost and large size, as it requires individual equipment to be synchronized to each channel, and individual transmitting and receiving terminals are needed.

[0008] Synchronization methods and systems for devices connected to telecommunication lines include methods and systems that synchronize clock rate, time, frequency, and phase. However, these methods and systems had to sacrifice real-time capabilities to ensure reliable data transmission due to data signal loss caused by jitter and packet loss present in telecommunication lines. Furthermore, the synchronization accuracy of clock devices, time, and frequency / phase deteriorated to several hundred milliseconds, resulting in a significant increase in the time required for synchronization.

[0009] Methods such as forward error correction and retransmission exist to recover lost data signals due to jitter and packet loss in telecommunication lines. However, these methods have problems such as increasing the information transmission capacity because they add extra data signals during transmission, the inability to synchronize unless the telecommunication line is bidirectional, and the inability to maintain real-time performance until retransmission.

[0010] In transmission systems that send and receive continuous data signals, such as those sampled in real time, over one or more channels via telecommunications lines, there was a problem in environments where devices on the telecommunications line did not have protocols for synchronizing between devices. Even if packet loss, jitter, etc., occurred, it was not possible to synchronize multiple devices in real time with low transmission capacity. When synchronizing high-frequency signals, if synchronization was attempted again, it took time for the receiving side to synchronize, which caused the data signal to break down. [Overview of the project] [Problems that the invention aims to solve]

[0011] The problem to be solved by the present invention is to provide a signal synchronization method and signal transmission system that can transmit and receive analog and digital image signals, audio signals, and other signals in real time between transmitting and receiving devices connected via a telecommunications line, and can synchronize data signals transmitted between devices with reduced delay time, regardless of whether or not they have a time synchronization means using GPS or a common protocol such as the IEEE 1588 standard (regardless of the presence or absence of an external synchronization signal).

[0012] Furthermore, when transmitting discretely sampled data signals in real time between devices communicating via telecommunication lines, even if all devices do not operate on the same protocol or if the telecommunication line is not bidirectional and does not allow mutual communication, the aim is to enable high-precision and high-speed synchronization between devices, for example, on the order of femtoseconds, regardless of the presence or absence of an external synchronization signal such as GPS. By achieving femtosecond-order synchronization, the signal-to-noise ratio (SNR) does not deteriorate even when high-frequency signals are generated using the synchronization signal, thereby providing a signal synchronization method and signal transmission system that enables the generation of high-frequency signals and their application to high-frequency devices. [Means for solving the problem]

[0013] The signal synchronization method of the present invention generates a reference signal (synchronization information: clock signal) which serves as the reference signal for the signal synchronization method, in a reference transmitting device, converts the reference signal into a packet signal, and transmits it to a data transmitting device and a data receiving device via a telecommunication line. The data transmitting device and the data receiving device can send and receive analog and digital image signals, audio signals, and other high-frequency signals (hereinafter collectively referred to as "data signals") via the telecommunication line. Each of the data transmitting device and the data receiving device generates synchronization information (synchronization clock signal) in which the clock rate, time, frequency, phase, etc., are synchronized with the received reference signal, and the data signals transmitted and received between the data transmitting device and the data receiving device via the telecommunication line are synchronized by this synchronization clock signal.

[0014] The signal synchronization method of the present invention can also maintain the synchronized state of data signals transmitted and received between the data transmission device and the data reception device by generating dummy data that serves as the reference signal in each data transmission device and data reception device when the reference signal transmitted through the telecommunication line is lost due to packet loss, and by synchronizing the dummy data with the synchronization clock signal.

[0015] The signal synchronization method of the present invention can also be configured such that, if the jitter of a reference signal transmitted through a telecommunications line continues for a certain period of time, it is considered a packet loss, dummy data is generated to replace the reference signal, a synchronization clock signal is generated based on the dummy data, and the synchronization state of the data signals transmitted and received between the data transmitting device and the data receiving device can be maintained based on the synchronization clock signal.

[0016] The signal transmission system of the present invention comprises a reference transmitter, a data transmitter, and a data receiver. The reference transmitter generates a reference signal (clock signal) that serves as the basis for the signal synchronization method, converts this reference signal into a packet signal, and can send it over a telecommunications line. The data transmitter can transmit data signals to the data receiver through the telecommunications line. The data transmitter and data receiver generate synchronization information (synchronization clock signal) in which the clock rate, time, frequency, phase, etc., are synchronized with the received reference signal, and this synchronization clock signal enables synchronization of data signals transmitted and received between the data transmitter and data receiver over the telecommunications line.

[0017] The reference transmitter, data transmitter, and data receiver, which are connected via a telecommunications line, can also be configured in a redundant configuration.

[0018] The reference transmission device can be installed separately from the data transmission device and data reception device, either externally (as an add-on), or internally (built-in) within the data transmission device and data reception device.

Advantages of the Invention

[0019] The signal synchronization method of the present invention has the following effects. (1) Synchronization information (synchronization clock signal) synchronized with a reference signal, clock rate, time, frequency, phase, etc. is generated, and based on the synchronization clock signal, synchronization of data signals transmitted and received between a data transmission device and a data reception device through a telecommunication line is achieved. Therefore, synchronization can be achieved regardless of whether it has a time synchronization means using GPS or a common protocol such as the IEEE 1588 standard. Also, even when all data transmission devices and data reception devices do not operate based on the same protocol, when the telecommunication line has no bidirectionality and mutual communication is impossible, or when there is no external synchronization signal such as GPS, synchronization can be achieved with high precision and high speed by the synchronization clock signal. For example, synchronization can be achieved on the order of femtoseconds.

[0020] (2) Since the synchronization clock signal is generated based on dummy data replacing the reference signal, even if there is an obstacle in the transmission of the reference signal due to packet loss or jitter, the synchronization clock signal can be generated and the synchronization of the data signal can be maintained.

[0021] (3) Time, frequency, phase, etc. can be synchronized at high speed without retransmission or adding extra data, so the time until synchronization is shortened (synchronization can be achieved at high speed).

[0022] The signal transmission system of the present invention has the following effects. (1) Synchronization of data signals transmitted and received by a data transmission device and a data reception device can be achieved based on a reference signal generated by a reference device.

[0023] (2) If the reference transmitter, data transmitter, and data receiver connected via a telecommunications line are configured in a redundant configuration, the reference signal and data signal can be transmitted and received using the normally functioning redundant line. Therefore, even if one of the redundant components fails, the transmission and reception of the reference signal and data signal can be maintained.

[0024] (3) Since one or more data transmission devices and data receiving devices that transmit one or more channels can simultaneously receive a reference signal within the telecommunications line, various signals including multiple channels can be configured with fewer transmission devices, thereby reducing the overall cost of the transmission system. [Brief explanation of the drawing]

[0025] [Figure 1] A first configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Figure 2] Figure 1 shows the configuration diagram of the reference signal generation unit included in the reference transmitting device. [Figure 3] Figure 2 shows the first configuration diagram of the timing signal generation unit. [Figure 4] Figure 2 shows the second configuration diagram of the timing signal generation unit. [Figure 5] Figures 1, 9 through 13 show the configuration diagrams of the receiving sections in the data transmission device and the data reception device, respectively. [Figure 6] A diagram illustrating the jitter in the signal synchronization method of the present invention. [Figure 7] Diagram illustrating packet loss in the signal synchronization method of the present invention. [Figure 8] This diagram illustrates the arrival timing of packet data signals in the signal synchronization method and signal transmission system of the present invention. [Figure 9] A second configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Figure 10] A third configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Figure 11] A fourth configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Figure 12] A fifth configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Figure 13] A sixth configuration diagram of the signal synchronization method and signal transmission system of the present invention. [Modes for carrying out the invention]

[0026] (Embodiment 1) The signal synchronization method and signal transmission system of the present invention will be described below, using Figures 1 to 4 as an example.

[0027] [Signal transmission system] The signal transmission system in Figure 1 comprises a reference transmitter 1001, a data transmitter 1002, a data receiver 1003, and a telecommunications line 1006. The telecommunications line 1006 is a general-purpose telecommunications line that utilizes cable television, analog optical lines, Ethernet, etc. The data transmitter 1002 and the data receiver 1003 can transmit and receive data signals B (Figure 1), such as analog and digital image signals, audio signals, and other high-frequency signals, through the telecommunications line 1006.

[0028] [Reference transmitter, reference signal generator] The reference transmitter 1001 in Figure 1 includes a reference signal generation unit 1004. As shown in Figure 2, the reference signal generation unit 1004 includes a clock signal generation unit 2002, a timing signal generation unit 2003, and an IP packetization unit 2004.

[0029] [Clock signal generation unit] The clock signal generation unit 2002 in Figure 2 is composed of high-precision GPS, rubidium, cesium, TCXO, OCXO, etc., and can generate a constant and stable clock signal (reference signal).

[0030] [Timing signal generation unit] The timing signal generation unit 2003 in Figure 2 comprises a frequency divider 3004, a zero-crossing determination unit 3005, and the timing signal generation unit 2003, as shown in Figure 3.

[0031] [Frequency dividing section] The frequency divider 3004 in Figure 3 controls the frequency, phase, clock rate, timing, etc. of the clock signal by dividing or multiplying the clock-like reference signal (hereinafter, "reference signal" may be referred to as "clock signal" for easier understanding of the explanation) generated by the clock signal generation unit 2002, thereby reducing the transmission rate of the clock signal. If the reference signal clock is counted 1000 times, for example, and a pulse is output, then a 1-bit data signal can be output as a 1000-division frequency of the clock signal generation unit 2002, thereby reducing the transmission rate of the clock signal. Hereafter, the divided clock signal may be referred to as the reference signal or the clock signal.

[0032] The frequency divider 3004 in Figure 3 includes a step constant unit 3001 that determines the frequency division step, a data delay unit 3003 having a memory that stores an initial value, an adder unit (adder 3002) that calculates the sum of the data delay unit 3003 and the step constant unit 3001, a zero-crossing determination unit 3005 that detects when the output of the data signal delay unit 3003 becomes zero or reaches a specific value, and a timing signal generation unit 3006 that stores the determination timing of the zero-crossing determination unit 3005.

[0033] [IP Packetization Section] The IP packetization unit 2004 in Figure 2 can convert the reference signal, whose transmission rate has been reduced by the timing signal generation unit 2003 (Figures 2 and 3), into a packet signal (packetize it) and transmit it to the telecommunications line 1006 at regular intervals. In the following description, the packetized reference signal may also be referred to as reference signal A or packet signal A.

[0034] [Packet signal transmission] The reference signal A (Figure 1), sent from the IP packetization unit 2004 in Figure 2 to the telecommunications line 1006, is transmitted to the data transmission device 1002 and the data receiving device 1003 through the telecommunications line 1006, as shown by the solid line in Figure 1.

[0035] [Data transmission device and data reception device] The data transmission device 1002 and the data receiving device 1003 are in a master / slave relationship with each other. The data transmission device 1002 can transmit analog and digital image signals, audio signals, digital data signals, and various other high-frequency signals received from the outside, or signals (data signals) B generated internally by the data transmission device 1002, to the data receiving device 1003 via the telecommunications line 1006, as shown by the dashed line in Figure 1.

[0036] [Data transmission device and data receiving device's receiving section] The data transmission device 1002 and data reception device 1003 in Figure 1 each have a receiving unit 1007. Both receiving units 1007 (Figure 1) have the same configuration and can generate a clock signal (synchronization information: synchronization clock signal) synchronized with the clock rate, time, frequency, phase, etc. of the reference signal, based on the reference signal received from the reference transmission device 1001 via the telecommunication line 1006.

[0037] [Receiving section] Figure 5 shows an example of the receiving unit 1007 of the data transmission device 1002 and data receiving device 1003 shown in Figure 1. The receiving unit 1007 includes an IP packet data signal receiving unit 5002, a redundancy selection unit 5003, a clock signal holding unit 5004, a timing calculation unit 5005, a jitter / packet loss prediction unit 5010, a dummy data generation unit 5006, a storage unit 5007, a filter unit 5008, a synchronization determination unit 5009, a data signal generation unit 5013, a variable clock signal generation unit 5012, a clock signal conversion unit 5011, and a clock signal generation unit 5014. The dummy data generation unit 5006 has an internal storage unit (not shown).

[0038] [IP packet data receiving unit] The IP packet data receiving unit 5002 in Figure 5 releases the packet signal received through the telecommunications line 1006 and extracts the reference signal.

[0039] [Redundancy Selection Section] In this invention, a packet signal (reference signal) A can be transmitted through a redundant telecommunications line 1006. The packet signal may be interrupted or fail to recover after being interrupted due to packet loss, packet jitter, or other causes resulting from abnormalities in the telecommunications line 1006. The redundancy selection unit 5003 in Figure 5 selects a redundant line that can operate normally when an abnormality occurs in the telecommunications line 1006. The packet signal is transmitted through the selected redundant line, preventing interruption of the packet signal A transmitted to the data transmission device 1002 and the data receiving device 1003.

[0040] [Clock signal holding unit] The clock signal holding unit 5004 in Figure 5 holds the timing of the received reference signal A. Furthermore, when the reference signal that should have arrived has not arrived due to, for example, packet loss or jitter, and then arrives after the packet loss or jitter is resolved, it can return the synchronization timing from the time when the reference signal was not yet arrived to the time when it has arrived. It can also correct the clock frequency error that occurs when the timing is switched back to the correct timing when the reference signal arrives.

[0041] [Timing Calculation Unit] The timing calculation unit 5005 in Figure 5 calculates the synchronization timing, such as the clock rate, time, frequency, and phase of the synchronous clock signal generated by the variable clock signal generation unit 5012.

[0042] [Jitter / Packet Loss Prediction Unit] In this invention, if the reference signal transmitted through the telecommunications line 1006 does not arrive properly, the variable clock signal generation unit 5012 will not operate properly, and the synchronization clock signal will not be generated properly. The jitter / packet loss prediction unit 5010 in Figure 5 predicts or estimates the arrival of jitter and packet loss of the reference signal (packet signal) received from the reference transmitter through the telecommunications line, constantly checking whether the reference signal is being received properly. If the reference signal cannot be received properly (if it cannot be received as predicted), the dummy data generation unit 5006 (Figure 5) generates dummy data to replace the reference signal.

[0043] [Dummy Data Generation Unit] The dummy data generation unit 5006 in Figure 5 generates dummy data in place of the reference signal when the reference signal is not received, thereby maintaining the arrival timing of the reference signal as if the reference signal had arrived normally.

[0044] [Storage] The memory unit 5007 in Figure 5 can store (store) the calculation results of the timing calculation unit 5005 and the reference signal, including the transmission rate and transmission timing of the data signal B (Figure 1) transmitted and received between the data transmission device 1002 and the data reception device 1003, for each arrival time.

[0045] [Functional part] The filter unit 5008 in Figure 5 can smooth the signal (sawtooth wave signal) output from the memory unit 5007.

[0046] [Synchronization Determination Unit] The synchronization determination unit 5009 in Figure 5 determines whether synchronization is achieved by differentiating the output of the filter unit 5008 and checking whether it falls below a predetermined threshold within a given time period.

[0047] [Data signal generation unit] The data signal generation unit 5013 in Figure 5 receives the output of the synchronization determination unit 5009 and generates a control signal to change the output frequency of the variable clock signal generation unit 5012.

[0048] [Variable clock signal generation unit] The variable clock signal generation unit 5012 in Figure 5 is equipped with a high-precision freely oscillating clock oscillator, such as a voltage-controlled oscillator that oscillates in response to a control signal such as voltage. The oscillation frequency of the synchronous clock signal generated from this variable clock signal generation unit 5012 is varied by the control signal generated by the data signal generation unit 5013 (Figure 5).

[0049] [Clock signal conversion unit] The clock signal conversion unit 5011 in Figure 5 controls the bit rate and timing of the synchronous clock signal oscillated from the variable clock signal generation unit 5012.

[0050] [Clock signal generation unit] The clock signal generation unit 5014 in Figure 5 can generate a clock signal of any frequency using the clock signal generated by the variable clock signal conversion unit 5012 as a reference signal. The generated clock signal becomes a reference signal and can be converted to the frequency required by other ICs such as PLLs and frequency dividers (such as RF AD converters and DA converters), and can be used to generate a clock signal used by other ICs mounted on the data transmission device 1002 (Figure 1) and the data receiving device 1003 (Figure 1).

[0051] [Signal transmission and synchronization methods] In the signal transmission system shown in Figure 1, the reference signal (clock signal) generated by the reference signal generation unit 1004 of the reference transmission device 1001 is converted into a packet signal (packetized) by the IP packetization unit 2004 (Figure 2), and the packetized reference signal (packet signal) A is transmitted to the data transmission device 1002 and the data receiving device 1003 via the telecommunication line 1006. Specifically, the clock signal is generated by the clock signal generation unit 2002 in Figure 2, divided by the frequency divider unit 3004 (Figure 3) of the timing signal generation unit 2003, packetized by the IP packetization unit 2004 in Figure 2, and output to the telecommunication line 1006.

[0052] [Generating a synchronous clock signal] The reference signal (packet signal) A output to the telecommunications line 1006 is received by the IP packet data receiving unit 5002 (Figure 5) of the receiving unit 1007 of the data receiving device 1003 and the data transmitting device 1002 shown in Figure 1. The received reference signal is processed within the receiving unit 1007 (Figure 5), and based on the reference signal A, the variable clock signal generating unit 5012 generates a synchronous clock signal that is synchronized with the reference signal A in terms of clock rate, time, frequency, phase, etc.

[0053] [Data signal synchronization] The generated synchronization clock signal is used to synchronize the time, frequency, phase, etc., of the data signal B (Figure 1) transmitted and received between the data transmission device 1002 and the data reception device 1003.

[0054] [Processing of the reference signal within the receiver] The reference signals received by the IP packet data receiving unit 5002 of the receiving unit 1007 (Figure 5) of the data transmission device 1002 and data receiving device 1003 in Figure 1 are written (stored) in the storage unit 5007 (Figure 5) in the order they were received, via the redundancy selection unit 5003, clock signal holding unit 5004, and timing calculation unit 5005 in Figure 5. For example, if one packet is 1500 bytes (let's call it P), and the IP packet data signal is 1 bit, it is written to the storage unit 5007 until 12000 bits (let's call it A) of data signals have been accumulated. If one sample is 16 bits, it is written to the storage unit 5007 until 750 samples (let's call it B) of bit data signals have been accumulated. Once writing is complete, the next IP packet data signals are periodically transmitted through the telecommunication line 1006 within the period during which they can be stored in the storage unit 5007.

[0055] [Packet loss, jitter] The reference signal A, transmitted through the telecommunications line 1006 and received by the IP packet data receiving unit 5002 (Figure 5) of the receiving unit 1007, may experience packet loss (Figure 7) or jitter 6001 (Figure 6) in the telecommunications line 1006.

[0056] Figure 6 is an explanatory diagram of jitter, with the horizontal axis representing time and the vertical axis representing the packet arrival interval. Figure 6 shows the time difference and the difference in arrival interval between the jitter 6001 that arrived first and the jitter 6003 that arrived later. In Figure 6, the reception timing (arrival timing) of jitter 6001 and jitter 6003 is not constant because it is delayed or accelerated relative to the average arrival time (TA) 6002. The average arrival time (TA) 6002 in Figure 6 represents the average delay in the telecommunications line that occurs when a packet signal is transmitted periodically at a predetermined interval (storage interval) and arrives at the receiving unit 1007 of the data transmission device 1002 and data receiving device 1003.

[0057] Figure 7 is an explanatory diagram of packet loss, with the horizontal axis representing time and the vertical axis representing the packet arrival interval. Packet loss 7001 is the time when the reference signal (packet signal) does not reach the receiving unit 1007 of the data transmitting device 1002 and data receiving device 1003 for some reason (i.e., there is no packet signal). In Figure 7, the time from when the packet signal disappears until the packet signal recovers is shown as packet loss 7001.

[0058] [Packet signal reception prediction] When jitter 6001, 6003 (Figure 6) or packet loss 7001 (Figure 7) occurs, the arrival interval of the reference signal may become unstable or the reference signal may be interrupted, which may result in the reference signal not being accumulated at all or being excessively accumulated in the IP packet data receiver 5002 (Figure 5). However, since the reference signal is transmitted at a constant interval during transmission, the timing of receiving the next reference signal 8002 (Figure 8) can be predicted from the timing of receiving the previous reference signal 8001 (Figure 8). Specifically, if we let the timing of receiving the first reference signal 8001 as T0, the timing of receiving it after T0 8002 as T1, and the timing of the next reception 8003 as T2, then T1-T0 ≈ T2-T1, and T1 can be predicted.

[0059] Even if the reference signal transmitted from the reference transmitter 1001 is output at regular intervals, the arrival time fluctuates (disperses) due to fluctuations in the telecommunications line 1006, so the interval between jitter 6001 and jitter 6003 (Figure 6) is not constant. It may be delayed compared to the average arrival time (TA) 6002 (Figure 6). In this case, the arrival interval becomes longer as shown in Figure 6 (jitter 6001 is above the average arrival time (TA) 6002 on the vertical axis, indicating a delay in the arrival interval).

[0060] If a buffer of ±t time is provided in the reception time relative to the average arrival time (TA) of the jitter, and the reference signal is not received during TA±t, it is impossible to distinguish whether this is due to packet loss 7001 (Figure 7) or jitter 6001, 6003 (Figure 6). If jitter 6001, 6003 are also considered as packet loss, then in both cases of jitter and packet loss, the reference signal received by the receiving unit 1007 (Figure 1) of the data transmission device 1002 and data receiving device 1003 (Figure 1) is discarded and lost on the telecommunication line 1006 (Figure 1) (Figure 7). In this invention, this loss can be predicted and avoided in the following way.

[0061] [Predicting and avoiding the loss of reference signals] The IP packet data receiving unit 5002 (Figure 5) acquires two or more reference signals (packet signals) A. The packet signals received by the IP packet data receiving unit 5002 are signals obtained by dividing the frequency of the clock signal generated by the clock signal generating unit 2002 (Figure 2).

[0062] The upper part of Figure 8 shows the input to the internal memory unit (not shown) of the clock signal holding unit 5004 (Figure 5), and the lower part shows the output from the clock signal holding unit 5004. Instead of using the signal in the upper part as the reference signal, the delayed signal in the lower part is always input to the timing calculation unit 5005 (Figure 5) as the reference signal, regardless of whether or not there is packet loss. In the upper part of Figure 8, the case where packet signal A was received within the arrival timing 8001 to 8003 (TA±t) is shown with a solid line, and the case where it was not received due to packet loss is shown with a dotted line.

[0063] Even if packet loss 7001 (Figure 7) occurs at packet arrival timing 8002 in the upper part of Figure 8, there are still reference signals stored in memory unit 5007 (Figure 5). Therefore, even if the reference signals stored in memory unit 5007 are read out at the same timing, the reference signals will not be depleted. In effect, the read-out reference signals will arrive at arrival timings 8004, 8005, and 8006 in the lower part of Figure 8. Even if the reference signal does not arrive at arrival timing 8002, the following operations will prevent the reference signals from being actually depleted and maintain synchronization.

[0064] Even if packet loss occurs, the period until the signal in the lower part of Figure 8 reaches the timing calculation unit (Figure 5) (the period during which it is held in the internal memory of the clock signal holding unit 5004) can be avoided from being synchronized with the missing reference signal. During this period, packet loss is predicted by the signal in the upper part of Figure 8, and if there is a loss of the reference signal due to packet loss at arrival timing 8002, synchronization can be maintained by switching to (compensating for) dummy data at arrival timing 8002 of the lower part. This timing adjustment is performed by the jitter / packet loss prediction unit 5010 in Figure 5.

[0065] Even with a reference signal that has experienced packet loss 7001 (Figure 7), the output frequency of the variable clock signal generation unit 5012 (Figure 5) of the receiving unit 1007 (Figure 4) is stabilized, and packet loss 7001 is predicted so that the reference signal is not lost even if packet loss occurs. In order to achieve this, the receiving unit 1007 (Figure 5) is equipped with a jitter / packet loss prediction unit 5010, a clock signal holding unit 5004, a dummy data generation unit 5006, and a timing calculation unit 5005.

[0066] [Readout of reference signal] The data transmission device 1002 (Figure 1) and the data receiving device 1002 (Figure 1) can read out the reference signal A for synchronous operation of the clock signal generation unit 2002 (Figure 2) as follows.

[0067] The initial signal of the variable clock signal generator 5012 of the receiver 1007 in Figure 5 is generated by the data signal generation unit 5013 (Figure 5), and is therefore determined by the initial value of the data signal generation unit 5013 (the initial value that determines the initial frequency of the voltage-controlled oscillator). Before synchronization, the frequency values ​​of the clock signal generated by the clock signal generator 2002 and the initial signal oscillated by the variable clock signal generator 5012 are slightly different from the reference signal. In the figure, the variable clock signal generator 5012 is controlled by the storage unit 5007, the filter unit 5008, and the data signal generation unit 5013 to control the synchronization clock signal oscillated by the variable clock signal generator 5012 so that it has the same frequency as the reference signal (to synchronize).

[0068] The reference signal is read from a redundant line within the telecommunications line 1006 selected by the redundant selection unit 5003 (Figure 5) and transmitted to the clock signal holding unit 5004. The timing of the reference signal read from the internal storage unit (not shown) of the clock signal holding unit 5004 is input to the timing calculation unit 5005. Simultaneously, a synchronous clock signal generated by the variable clock signal generation unit 5012 and converted by the clock signal conversion unit 5011 is input to the timing calculation unit 5005.

[0069] The timing calculation unit 5005 calculates how much the timing of the reference signal deviates from the timing of the synchronous clock signal, that is, how much the frequencies differ. The dummy data generation unit 5006 (Figure 5) generates a signal with the same frequency as the deviated frequency as dummy data. Either the generated dummy data or the reference signal output from the clock signal holding unit 5004 (Figure 5) is selected and held by the jitter / packet loss prediction unit 5010 (Figure 5).

[0070] The reference signal stored in the memory unit 5007 (Figure 5) is read out using a synchronous clock signal synchronized with the clock signal generated by the clock signal generation unit 2002 (Figure 2). The reference signal is input to the memory unit 5007 at the timing of the timing calculation unit 5005 (Figure 5). If the synchronous clock signal generated by the variable clock signal generation unit 5012 is slightly faster than the reference signal stored in the memory unit 5007, the stored reference signal will be depleted. If it is slightly slower, the stored reference signal will be saturated. However, if the speeds are the same, the amount of reference signal stored in the memory unit 5007 will stabilize and will not increase or decrease. This is considered a constant value. Therefore, by reading out the reference signal stored in the memory unit 5007 so that it becomes a constant value, the timing of the received reference signal can be measured.

[0071] The output timing of the clock signal conversion unit 5011 in Figure 5 is the same as the reference signal in the telecommunications line 1006, and the synchronous clock signal generated by the variable clock signal generation unit 5012 is the same as the clock signal generated by the reference signal generation unit 1004 (Figure 1) of the data transmission device 1002 or data reception device 1003 in Figure 1. Based on this synchronous clock signal, the clock signal generation unit 5014 (Figure 5) generates a clock signal of a different frequency using a phase-locked loop (PLL) or the like. The output of the variable clock signal generation unit 5012 and the clock signal generation unit 5014 may be an analog signal or a digital signal.

[0072] [Dummy data] Dummy data serves as a substitute for the reference signal. Dummy data is generated in packet format from the dummy generation unit 5006. It is generated at the timing of the synchronous clock signal generated from the variable clock signal generation unit 5012 (Figure 5).

[0073] Typically, when packet loss 7001 (Figure 7) occurs frequently, the transmission of the reference signal itself is often not functioning correctly. When the clock signal generated by the clock signal generator 2002 (Figure 2) and the synchronous clock signal generated by the variable clock signal generator 5012 (Figure 4) are not synchronized, dummy data in packet format is generated at the timing of the synchronous clock signal.

[0074] [Synchronization of dummy data and reference signal] Dummy data is received at T0=0 in Figure 8 and stored in the memory unit 5007 (Figure 5) for a certain period of time. After the dummy data is stored, the reference signal is received normally, so the reference signal and the synchronization clock signal output from the clock signal conversion unit 5011 are at the same timing, and synchronization is completed. At this point, the dummy data is also generated using the synchronized synchronization clock signal. Therefore, the dummy data is data that is at the same timing as the reference signal.

[0075] With a tolerance of ±t above the jitter 6001 (Figure 6), packets are received at the timing T shown in the upper part of Figure 8, and synchronization is achieved using a reference signal delayed from the arrival timing T0 of the first received packet to the arrival timing T1 of the next received packet. The delay of the reference signal in Figure 8 is performed internally by the clock signal holding unit 5004. The input to the timing calculation unit 5005 is always the delayed reference signal shown in the lower part. Even if packet loss occurs at the packet arrival timing T1 in the upper part of Figure 8, the packet arrival timing in the lower part is still T0, so the packet loss at the packet arrival timing T1 in the upper part can be observed before the packet loss due to the lower part affects the timing calculation unit 5005 (Figure 5). In addition, jitter exceeding a preset threshold t can also be treated as packet loss. In this case, to mitigate the effect of synchronization deviation due to packet loss, dummy data is used instead of the delayed reference signal. Incidentally, if the reference signal for arrival timing T1 in the lower part of Figure 8 is input to the timing calculation unit 5005, it will synchronize with the missing reference signal. However, if packet loss is observed at arrival timing T1 in the upper part of Figure 8, the effect of synchronization drift can be mitigated by switching from the reference signal for arrival timing T1 in the lower part of Figure 8 to dummy data.

[0076] When packet loss occurs at timing T1 (8002) in the upper part of Figure 8, the jitter / packet loss prediction unit 5010 (Figure 5) instructs the clock signal holding unit 5004 (Figure 5) to hold the reference signal at this timing, and the clock signal holding unit 5004 holds the reference signal.

[0077] For the time period beyond timing T2 (8003) in the upper part of Figure 8, dummy data is always used to generate a synchronization clock signal in the variable clock signal generator 5012 (Figure 5) of the receiver 1007 (Figure 1). Since this synchronization clock signal already has a frequency synchronized with the clock signal generated by the clock signal generator 2002 (Figure 2), even if the timing of the synchronization clock signal and the timing of the dummy data that replaces the reference signal are synchronized, the frequency will not shift. In addition, because the jitter / packet loss prediction unit 5010 (Figure 5) predicts and controls packet loss, even if packet loss occurs, the dummy data and reference signal can be switched while maintaining the clock frequency.

[0078] [Other examples of packet loss detection] To determine packet loss, when transmitting a reference signal generated by the reference signal generation unit 1004 (Figure 2) and packetized by the IP packetization unit 2004 (Figure 2), each packet of the reference signal can be numbered 1, 2, 3, 4, etc., and packet loss can be determined if the packets do not reach the receiving end in that order.

[0079] If a reference signal is lost (fails to arrive), does not arrive at the expected time, or arrives earlier than expected, the system checks how much the arrival time deviates from the average arrival time when the reference signal arrives normally. If this deviation exceeds a predetermined threshold, it is considered a packet loss.

[0080] [Packet loss recovery] After packet loss is recovered, it is possible to predict whether packet loss will occur again. If packet loss occurs again, the dummy packet is not returned to the original reference signal. If packet loss does not occur again, the system is restored to synchronize with the reference signal. In other words, if the reference signal arrives without packet loss or jitter for the same amount of time that the reference signal arrival timing was delayed due to packet loss, synchronization with the reference signal is resumed.

[0081] [Other examples of timing signal generation units] The timing signal generation unit 2003 in Figure 2 may have the configuration shown in Figure 4. The timing signal generation unit 2003 in Figure 4 includes a numerically controlled oscillator unit 4004, a differentiation unit 4005, a zero-crossing determination unit 3005, and a timing signal generation unit 3006.

[0082] The numerically controlled oscillator 4004 in Figure 4 includes an accumulator 4002 that operates based on a reference signal (clock signal) generated by the reference signal generation unit 1004 in Figure 2, a timing constant setting unit 4001 that determines the update timing and update constants of the accumulator 4002, a data memory unit 4003 that generates sine waves and cosine waves based on the results of the accumulator 4002, a differentiation unit 4005 that stores the phase change state of the sine wave output of the data signal memory unit 4003, a zero-crossing determination unit 3005 that detects when the output of the differentiation unit 4005 (the output of the accumulator or the output of the data signal memory unit that generates the sine wave) reaches a specific value, compares the state before differentiation with the state after differentiation and records the specific value, and a timing signal generation unit 3006.

[0083] (Embodiment 2) The present invention is not limited to Embodiment 1, and other configurations are also possible. An example of Embodiment 2 (second configuration) is shown in Figure 9. In Figure 9, the reference signal generation unit 1004 of the reference transmission device 1001 (Figure 1) is built into (loaded) the data transmission device 1002. The reference signal generation unit 1004 in Figure 9 has the same configuration as the reference signal generation unit 1004 in Figure 1, and is configured as shown in Figure 2 or Figure 4.

[0084] In Figure 9, the receiving unit 1007 (Figure 1) of the data receiving device 1003 can reproduce and output data signals B, such as video signals, audio signals, and other frequency signals, in synchronization with the reference signal A generated by the clock signal generation unit 2002 (Figure 2) of the reference signal generation unit 1004. Even with this configuration, the data signals B transmitted and received between the data transmission device 1002 and the data receiving device 1003 can be synchronized, just as in Embodiment 1, and the same effects as in Embodiment 1 can be obtained.

[0085] (Embodiment 3) The signal transmission system of the present invention can also be configured as shown in Figure 10 (third configuration). Figure 10 shows the reference signal generation unit 1004 of the reference generation device 1001 in Figure 1 built into (loaded) the data receiving device 1003. In Figure 10, the receiving unit 1007 (Figure 1) of the data transmission device 1003 can reproduce and output data signals B such as video signals, audio signals, and other high-frequency signals in synchronization with the reference signal A generated by the clock signal generation unit 2002 (Figure 2) of the reference signal generation unit 1004. Even with this configuration, the data signals B transmitted and received between the data transmission device 1002 and the data receiving device 1003 can be synchronized, as in Embodiment 1, and the same effects as in Embodiment 1 can be obtained.

[0086] (Embodiment 4) The signal transmission system of the present invention can also be configured as shown in Figure 11 (the fourth configuration). In Figure 11, similar to Figure 1, a reference generation device 1001 (including a reference signal generation unit 1004) is provided separately from the data transmission devices 1002-1, 1002-2 and the data receiving devices 1003-1, 1003-2. Multiple data transmission devices 1002-1, 1002-2 and multiple data receiving devices 1003-1, 1003-2 are connected via a telecommunications line 1006. The telecommunications line 1006 is a redundant line. Each of the data transmission device 1002 and data receiving device 1003 is provided with receiving units 1007-1, 1007-2 similar to the receiving unit 1007 in Figure 1, and a transmission unit 1008 for retransmitting reference signal A and data signal B.

[0087] With the configuration shown in Figure 11, the reference signal A from the reference generation device 1001 can be transmitted via the telecommunications line 1006 to multiple data transmission devices 1002-1, 1002-2 and multiple data receiving devices 1003-1, 1003-2. In addition, data signals B can be transmitted and received between multiple data transmission devices 1002-1, 1002-2 and multiple data receiving devices 1003-1, 1003-2 (N to N) connected via the telecommunications line 1006.

[0088] In the transmission system shown in Figure 11, for example, if a reference signal cannot be received via the telecommunications line 1006 due to a failure of the receiving units 1007-1, 1007-2 or transmission units 1008-1, 1008-2 of the data transmitting devices 1002-1, 1002-2 or data receiving devices 1003-1, 1003-2, or for any other reason, the transmission unit 1008 of any of the data transmitting devices 1002-1, 1002-2 or data receiving devices 1003-1, 1003-2 can transmit reference signal A to the other data transmitting devices 1002-1, 1002-2 or data receiving devices 1003-1, 1003-2 via the redundant telecommunications line 1006. Furthermore, synchronized transmission and reception of data signals B can be performed between the data transmitting devices 1002-1, 1002-2 and the data receiving devices 1003-1003-2.

[0089] (Embodiment 5) The signal transmission system of the present invention can also be configured as shown in Figure 12 (the fifth embodiment). In Figure 12, in addition to the reference transmitter 1001, a sub-reference transmitter 12002 is provided, and the sub-reference transmitter 12002 is connected to the telecommunications line 1006. This sub-reference transmitter 12002 includes a reference signal generation unit (not shown) similar to the reference signal generation unit 1004 in Figures 1 and 2, and a receiving unit 12003 similar to the receiving unit 1007 in Figure 1.

[0090] With the configuration shown in Figure 12, if the reference transmitter 1001 fails to transmit the reference signal A due to a malfunction or other reason, and the receiving units 1007 of the data transmitters 1002-1 and 1002-2, and the receiving units 1007 of the data receivers 1003-1 and 1003-2 are unable to receive the reference signal A properly, the sub-reference transmitter 12002 can become a new reference transmitter and output a sub-reference signal A1, which is then transmitted via the telecommunication line 1006 to multiple data transmitters 1002-1 and 1002-2 and multiple data receivers 1003-1 and 1003-2, enabling communication that synchronizes the transmitted and received data signals B between the data transmitters 1002-1 and 1002-2 and the data receivers 1003-1 and 1003-2.

[0091] (Embodiment 6) The signal transmission system of the present invention can also be configured as shown in Figure 13 (sixth embodiment). In Figure 13, the reference transmitter 1001 of Figure 1 is omitted, and multiple (two in Figure 13, but more) data transmitters 1002-1, 1002-2 and multiple (two in Figure 13, but more) data receivers 1003-1, 1003-2 are provided on the telecommunications line 1006. These data transmitters 1002-1, 1002-2 and data receivers 1003-1, 1003-2 can transmit and receive data signals B through the telecommunications line 1006. Each of the multiple data receivers 1003-1, 1003-2 has a built-in receiver 1007 with the same configuration as the receiver 1007 of Figure 1.

[0092] Furthermore, one data transmission device 1002-1 in Figure 13 is equipped with a reference signal generation unit 1004-1 similar to the reference signal generation unit 1004 in Figure 2, and the other data transmission device 1002-2 is equipped with a reference signal generation unit 1002-2 similar to the reference signal generation unit 1004 in Figure 2, thus providing a redundant configuration. This redundant configuration allows for redundancy by transmitting the reference signal A from both the reference signal generation unit 1002-1 and 1002-2 to the telecommunications line 1006. Synchronized transmission and reception of data signals B between N-to-N data transmission devices 1002 and data receiving device 1003 is also possible. The data transmission devices 1003-1 and 1003-2 in Figure 13 are equipped with a receiving unit 1007 with the same configuration as the receiving unit 1007 in Figure 1.

[0093] In Figure 13, data transmission device 1002-1 is provided with a reference signal generation unit 1004-1, data transmission device 1002-2 is provided with a reference signal generation unit 1004-2 and a receiving unit 1007, and data receiving devices 1003-1 and 1003-2 are provided with a receiving unit 1007. Reference signal generation units 1004-1 and 1004-2 have the same configuration and functions as reference signal generation unit 1004 in Figure 2. The receiving unit 1007 has the same configuration and functions as the receiving unit 1007 in Figure 5. In Figure 13, data receiving devices 1003-1 and 1003-2 may also be provided with a reference signal generation unit (not shown) having the same configuration and functions as reference signal generation units 1004-1 and 1004-2. [Industrial applicability]

[0094] Embodiments 1 to 6 described above are the main examples of the signal synchronization method and signal transmission system of the present invention. The present invention is not limited to these embodiments, and the design can be modified to the extent that the problem can be solved. Since there are many configurations that utilize the telecommunications line 1006, the design can be similarly modified for wireless communication and broadcasting systems other than those in the embodiments. The means for transmitting data signals to the telecommunications line 1006 of the present invention includes, but is not limited to, multicast, unicast, wireless communication, etc. [Explanation of Symbols]

[0095] 1001 Reference Transmitter 1002 Data transmission device 1002-1 Data transmission device 1002-2 Data transmission device 1003 Data receiving device 1003-1 Data receiving device 1003-2 Data receiving device 1004 Reference signal generation unit 1004-1 Reference signal generation unit 1004-2 Reference signal generation unit 1006 Telecommunication lines 1007 Receiving section of data transmission device and data reception device 1007-1 Receiving section of data transmission device and data reception device 1007-2 Receiving section of data transmission device and data reception device 1008-1 Transmission section 1008-2 Transmission section 2002 Clock signal generation unit 2003 Timing signal generation unit 2004 IP Packetization Section 3001 Step constant section 3002 Adder 3003 Data Delay Device 3004 Frequency divider 3005 Zero-crossing determination unit 3006 Timing signal generation unit 4001 Timing constant setting section 4002 Accumulator 4003 Data memory section for generating sine waves and cosine waves 4004 Numerical Control Transmitter 4005 Differential part 5002 IP Packet Data Receiver 5003 Redundancy Selection Section 5004 Clock signal holding unit 5005 Timing Calculation Unit 5006 Dummy Data Generation Unit 5007 Storage section 5008 Filter section 5009 Synchronization Determination Unit 5010 Jitter / Packet Loss Prediction Unit 5011 Clock signal conversion unit 5012 Variable Clock Signal Generator 5013 Data signal generation unit 5014 Clock signal generation unit 6001 Jitter 6002 Average arrival time (TA) 6003 Jitter 7001 Packet Loss 7002 Packet signal (reference signal) 8001 Packet signal (reference signal) arrival timing (T0) 8002 Packet signal (reference signal) arrival timing (T1) 8003 Packet signal (reference signal) arrival timing (T2) 8004 Packet signal (reference signal) arrival timing (T0) 8005 Packet signal (reference signal) arrival timing (T1) 8006 Packet signal (reference signal) arrival timing (T2) 12002 Subreference Transmitter 12003 Sub-reference transmitting device receiving unit A (packetized) reference signal A1 (packetized) subreference signal B Data signal

Claims

1. Data signals such as image signals, audio signals, and various other data are transmitted from a data transmission device to a data receiving device via a telecommunications line. The reference signal generated by the reference transmitter is converted into packet format and transmitted via the telecommunications line to the data transmitter and data receiver. The data transmission device transmits data signals based on the received reference signal. The data receiving device receives data signals based on the received reference signal. The data transmission device and the data reception device generate a synchronization clock signal synchronized with the received reference signal, The aforementioned synchronization clock signal synchronizes the data signals transmitted and received between the data transmission device and the data reception device via the telecommunications line. A signal synchronization method characterized by the following features.

2. Data signals such as image signals, audio signals, and various other data are transmitted from a data transmission device to a data receiving device via a telecommunications line. The reference signal generated by the reference transmitter is converted into packet format and transmitted via the telecommunications line to the data transmitter and data receiver. The data transmission device transmits data signals based on the received reference signal. The data receiving device receives data signals based on the received reference signal. The data transmission device and the data reception device generate a synchronization clock signal synchronized with the received reference signal, Even if the reference signal from the reference transmitter is no longer received by either or both the data transmitter and the data receiver, the reference signal is transmitted through a redundant line, and the data transmitter and data receiver generate a synchronized clock signal based on the received reference signal. This synchronization clock signal ensures that the data signals transmitted and received between the data transmission device and the data reception device remain synchronized. A signal synchronization method characterized by the following features.

3. In the signal synchronization method according to claim 1 or claim 2, Even if the reference signal is lost due to packet loss and cannot be received by the data transmitter and data receiver, dummy data is generated to replace the reference signal. Based on this dummy data, the data transmitter and data receiver generate a synchronization clock signal, and this synchronization clock signal allows the synchronization of the data signals transmitted and received between the data transmitter and data receiver to be maintained. A signal synchronization method characterized by the following features.

4. In the signal synchronization method according to claim 1 or claim 2, If packet jitter persists for a certain period of time, dummy data is generated to replace the reference signal. Based on this dummy data, a synchronization clock signal is generated in the data transmitter and data receiver. This synchronization clock signal allows the synchronization of the data signals transmitted and received between the data transmitter and data receiver to be maintained. A signal synchronization method characterized by the following features.

5. In the signal synchronization method according to claim 1 or claim 2, In the data transmission and data reception devices, the arrival of a reference signal is predicted. If the reference signal does not arrive at the predicted time, dummy data is generated in place of the reference signal. A synchronization clock signal synchronized with this dummy data is then generated by both the data transmission and reception devices, enabling synchronization of the data signals transmitted and received between the data transmission and reception devices. A signal synchronization method characterized by the following features.

6. In the signal synchronization method according to claim 1 or claim 2, The reference signal is generated from a reference transmitter located outside the data transmitter and data receiver, or from a reference transmitter built into the data transmitter or data receiver. A signal synchronization method characterized by the following features.

7. A data transmission device and a data reception device capable of sending and receiving data signals such as image signals, audio signals, and data, A reference transmission device provided outside the data transmission device and data reception device, There is a telecommunications line connecting the reference transmitter, the data transmitter, and the data receiver. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. The data transmission device and data reception device each include a receiving unit, which can generate a synchronization clock signal synchronized with the reference signal received from the reference transmission device via a telecommunications line, and can synchronize the data signals transmitted and received between the data transmission device and the data reception device based on that synchronization clock signal. A signal transmission system characterized by the following features.

8. A data transmission device and a data reception device capable of sending and receiving data signals such as image signals, audio signals, and data, A telecommunications line connecting a data transmission device and a data reception device, The data transmission device has a built-in reference transmission device. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. The data receiving device includes a receiving unit, which receives a reference signal output from the reference transmitting device and transmitted through a telecommunications line, generates a synchronization clock signal synchronized with the reference signal based on that reference signal, and synchronizes the data signals transmitted and received between the data transmitting device and the data receiving device based on that synchronization clock signal. A signal transmission system characterized by the following features.

9. A data transmission device and a data reception device capable of sending and receiving data signals such as image signals, audio signals, and data, A telecommunications line connecting a data transmission device and a data reception device, The data receiving device has a built-in reference transmitting device. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. A data receiving device has a receiving unit, which receives a reference signal output from the reference transmitting device and transmitted through a telecommunications line. Based on this reference signal, it can generate a synchronization clock signal synchronized with the reference signal, and based on this synchronization clock signal, it can synchronize the data signals transmitted and received between the data transmitting device and the data receiving device. A signal transmission system characterized by the following features.

10. Multiple data transmission devices and multiple data receiving devices capable of sending and receiving data signals such as image signals, audio signals, and data, A reference transmission device provided outside the data transmission device and data reception device, The reference transmitting device, multiple data transmission devices, and multiple data receiving devices are connected by multiple telecommunications lines, and these devices are configured with redundancy. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. Multiple data transmission devices and multiple data receiving devices each consist of a receiving unit and a transmission unit, and the receiving unit is equipped with a redundant selection unit. The transmission unit can transmit data signals from the data transmission device to the data receiving device. Multiple data transmitting devices and the receiving units of multiple data receiving devices operate based on a reference signal received from a reference transmitting device via a telecommunications line, can generate a synchronization clock signal synchronized with that reference signal, and can synchronize the data signals transmitted and received between the multiple data transmitting devices and the multiple data receiving devices based on that synchronization clock signal. The redundancy selection unit, when the reference signal is no longer transmitted through the telecommunications line to either or both the data transmission device and the data reception device, selects a telecommunications line that is functioning normally, and ensures that the reference signal is transmitted through the selected telecommunications line to the receiving section of either the data transmission device or the data reception device. A signal transmission system characterized by the following features.

11. Multiple data transmission devices and multiple data receiving devices capable of sending and receiving data signals such as image signals, audio signals, and data, A reference transmission device located outside of multiple data transmission devices and multiple data receiving devices, A sub-reference transmitting device is provided separately from the aforementioned reference transmitting device, Multiple data receiving devices, multiple data receiving devices, a reference transmitting device, and a sub-reference transmitting device are connected by multiple telecommunications lines, and the devices are configured in a redundant manner. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. The subreference transmission device includes a reference signal generation unit capable of generating a subreference signal, and a packetization unit capable of converting the subreference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. Each of the multiple data receiving devices has a receiving unit, which receives a reference signal from a reference transmitting device or a sub-reference signal from a sub-reference transmitting device transmitted via a telecommunication line. Based on the received reference signal or sub-reference signal, it can generate a synchronization clock signal synchronized with the reference signal or sub-reference signal, and based on that synchronization clock signal, it can synchronize the data signals transmitted and received between the multiple data transmitting devices and the multiple data receiving devices. If the reference signal from the reference transmitting device is not received by the receiving units of any or multiple data transmitting devices and data receiving devices via the telecommunications line, a sub-reference signal from a sub-reference transmitting device is transmitted to the multiple data transmitting devices and multiple data receiving devices via the telecommunications line. The receiving units of the multiple data transmitting devices and multiple data receiving devices that receive the sub-reference signal generate a synchronization clock signal synchronized with the sub-reference signal, and based on that synchronization clock signal, the data signals transmitted and received between the multiple data transmitting devices and multiple data receiving devices can be synchronized. A signal transmission system characterized by the following features.

12. Multiple data transmission devices and multiple data receiving devices capable of sending and receiving data signals such as image signals, audio signals, and data, Multiple data transmission devices and multiple data reception devices are connected by multiple telecommunication lines in a redundant configuration. Multiple data transmission devices have a built-in reference transmission device. The reference transmission device includes a reference signal generation unit capable of generating a reference signal, and a packetization unit capable of converting the reference signal generated by the reference signal generation unit into a packet signal and sending it over a telecommunications line. Multiple data receiving devices have a receiving unit, which receives a reference signal transmitted from a reference transmitter built into one of the data transmitting devices via a telecommunications line. Based on this reference signal, it can generate a synchronization clock signal synchronized with the reference signal, and based on this synchronization clock signal, it can synchronize the data signals transmitted and received between the multiple data transmitting devices and the multiple data receiving devices. If the reference signal from a reference device built into one of the data transmitting devices becomes unreceivable by other data transmitting devices and other data receiving devices, the reference signal generated from the reference transmission device built into another data transmitting device is received by the receiving unit of the data receiving device via the telecommunications line. The receiving unit then operates based on the received reference signal and generates a synchronization clock signal synchronized with that reference signal. Based on this synchronization clock signal, the data signals transmitted and received between multiple data transmitting devices and multiple data receiving devices can be synchronized. A signal transmission system characterized by the following features.

13. In the signal transmission system according to any one of claims 7 to 12, The data transmission device and the data reception device, or the receiving section of either one of them, have a dummy data generation unit. The dummy data generation unit generates dummy data to replace the reference signal when packet loss occurs or packet jitter persists for a predetermined time or longer in the reference signal transmitted from the reference transmitter to the data transmitter and data receiver, or in the sub-reference signal transmitted from the sub-reference transmitter to the data transmitter and data receiver. Based on this dummy data, it generates a synchronization clock signal, and based on this synchronization clock signal, it enables synchronization of data signals transmitted and received between the data transmitter and multiple data receivers. A signal transmission system characterized by the following features.

14. In the signal transmission system according to any one of claims 7 to 12, The receiving section of the data transmission device and the data reception device includes a jitter / packet loss prediction unit that predicts the arrival of a reference signal, and a dummy data generation circuit. If the reference signal does not arrive during prediction by the prediction unit, a dummy data generation circuit generates dummy data in place of the reference signal. Based on this dummy data, a synchronization clock signal is generated, and based on this synchronization clock signal, the data signals transmitted and received between the data transmission device and multiple data reception devices can be synchronized. A signal transmission system characterized by the following features.

15. In the signal transmission system according to any one of claims 7 to 12, The receiving unit is equipped with a variable clock signal generator that can vary the oscillation frequency of the synchronous clock signal it generates. A signal transmission system characterized by the following features.

16. In the signal transmission system according to any one of claims 7 to 12, The receiving unit includes a variable clock signal generator that can vary the oscillation frequency of the synchronous clock signal it generates. The reference transmission device comprises a clock signal generation unit that generates a reference signal, and a timing signal generation unit that can control at least one of the phase, frequency, bit rate, or timing of the generated reference signal. A signal transmission system characterized by the following features.

17. In the signal transmission system according to any one of claims 7 to 12, The receiving unit includes a variable clock signal generator capable of varying the oscillation frequency of the generated synchronous clock signal, and a timing calculation unit capable of calculating at least the phase, frequency, bit rate, timing, and time of the synchronous clock signal generated by the variable clock signal generator. A signal transmission system characterized by the following features.

18. In the signal transmission system according to any one of claims 7 to 12, The receiving unit includes a variable clock signal generation unit that can vary the oscillation frequency of the generated synchronous clock signal, and a clock conversion unit that can control at least the rate or timing of the synchronous clock signal generated by the variable clock signal generation unit. A signal transmission system characterized by the following features.

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