JPH0360306A - Train data transmission system - Google Patents

Abstract

PURPOSE:To facilitate high speed data transmission with a metallic wire by a method wherein the lower limit of the frequency of a signal used for a train transmission system is selected to be higher than the frequency of a track circuit of the section and the upper limit is obtained by dividing 1Mbps by the maximum number of vehicles of which the train is composed. CONSTITUTION:Signal transmitters 1 are mounted on respective vehicles of which a train is composed and connected to a metallic transmission line 3 by a multi-drop method and both the ends of the transmission line 3 are grounded through terminal resistors R0. The lower limit of the frequency of a carrier wave transmitting the signal is selected to be higher than the frequency of a track circuit signal of the section, for instance 15kHz. On the other hand, the upper limit of the carrier wave frequency is predetermined by dividing 1Mbps by the maximum number of vehicles in one train. If the number of the vehicles is 16, for instance, the upper limit frequency is 62.5kbps. With this constitution, even if a transmission line which is not shielded sufficiently is used, induction interference against the track circuit can be suppressed and, even if the resistance of the terminal resistor R0 is not matched with the characteristic impedance of the transmission line, the transmission error caused by a reflective wave can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data transmission system for trains, and particularly to a system for transmitting data using metal wires.

[Conventional technology]

As the demand for monitoring various devices on trains and various information services increases, the demand for on-board information transmission systems is increasing. The transmission lines of this type of system that have been put into practical use so far use optical fiber cables for high speed systems, and twisted pair cables or metal wires such as backup lines for existing through lines for low speed systems. By the way, recently, the aim is to increase transportation efficiency through flexible operation of train configurations.

It has become more common to change train lengths from time to time. As a result, jumper couplers between cars need to be connected and disconnected more frequently, but fiber optic cables are susceptible to dirt at the ends and must be handled with care, so in the case of trains where jumper couplers are often connected and disconnected, transmission lines that run the length of the train are conventional. It can be said that metal wires, which have a proven track record, are preferable in terms of reliability.

Now, the data transmission speed of the train transmission system using metal wires that has been put into practical use is at most 9,600 bits/second in the FSX modulation method, and 1,000 bits/second in the baseband method (FFI Kisha no Kagaku van 39. & 8p. 3
4) In the former case, the value is determined mainly because the upper limit of the carrier frequency that can be transmitted by a twisted pair cable is IM Hz or less.

The latter low transmission speed is due to the use of low-speed, high-power switching elements in order to improve noise resistance when using ordinary lead-through lines.

[Problem to be solved by the invention]

It is clear that metal wire transmission lines are more convenient in terms of flexibility in train organization, but if the transmission speed remains this low, the amount of information on trains will increase in the future. ,
There is a problem in that the metal wire method cannot cope with the increasing sophistication of control.

An object of the present invention is to solve the problems of the conventional transmission system using metal wires and to provide a system capable of higher-speed transmission.

[Means to solve the problem]

Therefore, in the present invention, the lower limit of the bit rate frequency is set higher than the track circuit frequency of the relevant line section, while the upper limit is roughly determined by the number of vehicles on which the longest transmission line that directly connects the transmission devices is installed. A method of dividing IMbps was used.

[Effect]

The present invention will be briefly explained with reference to FIG. Generally, if the characteristic impedance of the transmission line and the value of the # end resistor do not match,
Reflected waves occur, disrupting the signal waveform on the transmission path, and causing transmission errors (
0,1 read error). According to the present invention, in the case shown in FIG. 1 (1), I Mbps is divided by the number of vehicles (4) to obtain a value of 250 Kbps. If this is taken as the bit rate frequency, the time length of one bit is 4 microseconds.

Generally, the wave speed of a traveling wave in a metal transmission cable is approximately 200,000 km/sec, and the length of a typical train car is 20 m, and the length of 4 cars is 80 m, so the round trip The time it takes to pass 160m (the time the reflected wave returns) is 0.8 microseconds.

This corresponds to 20% of the 1-bit time length as shown in FIG. 1(2), and the influence of reflection appears after this point. In particular, when transmission is performed using a normal lead-through line, the reflected waveform becomes disordered due to the nonlinear effects of the metal of the vehicle body, and the negative effects of reflection appear after this point. However, normally only the influence of the first-order reflection is large, and the influence of the second and subsequent reflections is small, so in the end, the duration of the influence of reflection is 4
It is within 0%.

In the case of baseband transmission without modulation, since the truth value determination for each bit is performed approximately at the center of the bits, that is, at the 50% position, the waveform has already stabilized and there is no possibility of reception errors occurring.

On the other hand, in the case of a drop-in line, there is no shielding, so in order to prevent the transmitted signal from affecting the ground track circuit, the lower limit of the data signal frequency is set higher than the ground track circuit frequency in the present invention.

〔Example〕

FIG. 2 shows an embodiment of the first step of the present invention. 3 is a multi-drop transmission line. This example is for a normal train with a maximum length of 16 cars, and the bit rate frequency is
By dividing Mbps by 16 to 62.5Xbps, reliable transmission as described above is possible without matching the value of the terminating resistor to the transmission path characteristic impedance.

Furthermore, the signal format of this embodiment is bipolar transmission, as shown in Figure 2 (
The data signal waveform shown in 2) is used, and 1 bit of information is .

It is represented by a half wave of the carrier signal of 1/2 of the bit rate frequency, that is, 31.25 KHz.

For example, at this transmission speed, information of l word 8 bits (2
), the time required to send 13 bits including the control bit is 208 microseconds, but with the conventional 9600 bps, it takes 1354 microseconds and 1200 bps.
In the case of s, it takes 10833 microseconds. Trains are equipped with many devices that generate powerful noise, and the shorter the time it takes to transfer a unit of information, the lower the probability of collision with noise. The present invention can also be said to be more preferable than conventional methods in this respect.

Next, the relationship with the track circuit will be described. Typically, the carrier frequency of the track circuit signal is within 15 KHz. Assuming that the track circuit frequency of the relevant railway is ↓5KHz,
According to the present invention, in the case of bipolar baseband transmission,
The range from 15 KHz to 31.25 KHz is appropriate as a carrier frequency band, and the upper limit was used in the first embodiment, but the bit rate is between 30 and 62.5 Kbps.
It can be selected depending on the circumstances of the transmission equipment design.

Next, FIG. 3 shows an embodiment of a loop type transmission mode.

In this example, the transmission devices were arranged in each vehicle, and in order to equalize the distances between the transmission devices as much as possible, they were arranged in a zigzag pattern as shown in the figure. Therefore, the longest transmission line spans three cars. Therefore, in this example, IMbps is divided by 3.
250 Kbps was set as a value within 33 Kbps.

This value is a cost-effective transmission speed that can take full advantage of the capabilities of a relatively small microprocessor circuit, including peripheral input/output processing, when one communication process is performed in a transmission device using a relatively small-scale microprocessor circuit. The hardware is also small.

〔Effect of the invention〕

As described above, according to the present invention, the reliability of data waveforms can be improved even in transmission systems that use metal wires as transmission paths, such as train lead-in wires, where it is difficult to specify the transmission characteristic impedance. transmission at the maximum possible speed, and the influence of radiation from unshielded or insufficiently shielded transmission paths on the track circuit can be suppressed. Here, we have explained an example in which a normal electric wire is used as the transmission path, but when using other metal wires such as twisted pair cables and coaxial cables, the value and characteristics of the terminating resistor may be affected due to the design of the transmission device. It goes without saying that the present invention is effective when it is difficult to match impedances.

[Brief explanation of drawings]

Claims (1)

[Claims] 1. A plurality of data transmission devices are provided on the train, and these are connected using ordinary electric wires or electric wires and car body grounding,
The lower limit of the bit rate frequency is higher than the track circuit frequency of the line concerned, and the upper limit is approximately 1 Mbps based on the number of cars installed on the longest transmission line that directly connects the transmission equipment.
A data transmission system for trains characterized by a frequency divided by . 2. A data transmission system for a train, wherein the electric wire according to claim 1 is a through line for controlling a train. 3. A train data transmission system characterized in that the system configuration according to claim 1 or 2 is of a multi-drop type. 4. A train data transmission system, wherein the system configuration according to claim 1 or 2 is a loop-shaped transmission line.