JPH01181353A - Bi-directional signal transmission system - Google Patents

Abstract

PURPOSE:To improve the transmission efficiency by forming a reflecting end to other end of a transmission line and using a directional coupler for a coupling circuit in a way that a signal is reflected in the reflecting end and then sent so as to couple the signal to the transmission line. CONSTITUTION:A reflecting end 6 is provided to other end of an incoming transmission line 3 and branch connection circuits 7a-7n connected to the said incoming transmission line 3 include a directional coupler sending an output signal of a transmission circuit T of slave sets 2a-2n toward the reflecting end 6. A resistive terminator 5 absorbing and terminating a signal of an outgoing transmission line 3 is provided to other end of the outgoing transmission line 3. Even when the distance of the slave sets 2a-2n is long and the propagation time between the slave sets 2a-2n is large, the transmission signal of the slave sets 2a-2n is arranged correctly on the incoming transmission line 3 and it is not required to provide a guard time to its time slot. Thus, the transmission efficiency is kept high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is used in digital communications. The present invention is utilized in a wired transmission system. The present invention can be used with either optical fiber cables or metallic cables. The present invention is suitable for use in local area networks that perform high-speed communications.

The present invention is based on one main station device, and a branch connection circuit connected to the downlink transmission path and uplink transmission path through a downlink transmission path and an uplink transmission path each having one end connected to its transmitting circuit output and receiving circuit input. The present invention relates to an improvement in a bidirectional signal transmission system in which a plurality of slave devices connected via a time-division communication are performed.

[Conventional technology]

FIG. 4 is a block diagram of a conventional system.

This method uses one main station device 1 and multiple slave devices 2a.
12b...2n. One end is connected to the transmitting circuit (T) output of the master station device 1, and the slave station devices 2a12b...
・One downlink transmission line 3 to which each of the 2n receiving circuit (R) inputs are connected via a branch connection circuit, and the main station device 1
The upstream transmission line 4 is provided with one end connected to the receiving circuit (R) input of the slave station device, and to which each transmitting circuit output of the slave station device is connected via a branch connection circuit. Furthermore, the transmission circuit of the main station device 1 connects each slave device 2a1 to this downlink transmission path 3.
The signals addressed to 2b...2n are divided and transmitted by time slots, and the transmitting circuit of each slave station receives the time assigned to it in synchronization with the above time slot received by the receiving circuit of that slave station. A signal addressed to the main station device 1 is transmitted to the slot.

That is, in this system, for example, the slave station device 2n synchronizes with the received signal arriving at the downlink transmission path 3, and sends a transmission signal to the uplink transmission path 4 in the time slot assigned to its own station.

The slave station device 2a also synchronizes with the received signal arriving on the downlink transmission path 3, and sends a transmission signal to the uplink transmission path 4 in the time slot assigned to the slave station. At this time, if the distance between the slave station device 2n and the slave station bag 2a is smaller than the signal propagation time of the transmission path, there is no problem since the timings of the received signal and the transmitted signal are slightly different from each other.

However, if this distance is large, the received signal will be shifted by the signal propagation time during that time, and furthermore, when the transmitted signal from the slave device 2a reaches the connection point of the slave device 2n, the position of the time slot will be shifted by the signal propagation time during that time. As a result, the respective transmission signals of the slave station device 2n and the slave station device 2a are not arranged correctly. In order to prevent transmission signals from overlapping due to shifts in the positions of the time slots, it becomes necessary to provide a guard time in which no signals are transmitted in the time slots assigned to each slave station, which reduces transmission efficiency.

In order to improve this, a structure as shown by the broken line in FIG. 4 was proposed (see Japanese Patent Laid-Open No. 17753/1983). That is, in addition to the upstream transmission line 4, another upstream transmission line 4' is provided as indicated by a broken line, and the other end of this transmission line is connected back, and the transmission signals from each slave station device 2as2b...2n are transmitted as indicated by the broken line. The signal is transmitted as shown by the arrow, and the receiving circuit of the main station device 1 receives not the signal on the uplink transmission path 4 but the signal on the uplink transmission path 4' shown by the broken line. With this configuration, if the signals transmitted from each slave station device 2a12b...2n are transmitted in synchronization with the reception timing received by that slave station device, they will be correctly arranged in their assigned time slots without overlapping. will be done.

[Problem that the invention seeks to solve]

However, this method requires a double transmission line as an upstream transmission line, which requires an extra number of lines. Particularly, when the distance of the transmission path is long, this method has the disadvantage of becoming uneconomical.

The present invention improves this, and allows signals on the uplink transmission path transmitted from each slave station device to be correctly arranged in the assigned time slots without providing a guard time.
The purpose is to provide a system that does not require dual transmission lines.

[Means for solving problems]

The present invention is characterized in that a reflection end is formed at the other end of the transmission path, and a directional coupler is used in the coupling circuit to couple the signal to the transmission path so that the signal is reflected at the reflection end and transmitted. shall be.

That is, in the first method, the other end of the upstream transmission path is formed as a reflective end, and the branch connection circuit connected to the upstream transmission path transmits the output signal of the transmitting circuit of each slave station toward the reflective end. This uses a directional coupler.

In the second method, the other end of the downlink transmission path is formed as a reflection end, and the branch connection circuit connected to the downlink transmission path receives the signal arriving from the reflection end as an input signal to the receiving circuit of each slave station. This uses a directional coupler that takes in the signal.

Furthermore, in this method, the content of the signal flowing into the transmission circuit of the slave device from the transmission path connected to that transmission circuit is compared with the content of the signal sent by the transmission circuit to that transmission path, and the contents do not match. Therefore, it is desirable to provide a circuit for detecting transmission conflicts.

[Effect]

In the first method, the transmission signal transmitted from each slave station device is first transmitted toward the reflection end, reflected at the reflection end, and directed to the main station device along the same transmission path. Therefore, the time required for a signal transmitted from the master station device to reach the slave device via the downlink transmission path, and the time it takes for the signal transmitted from the slave device to travel up the uplink transmission path toward the reflection end and be reflected at the reflection end. The sum of the time it takes to propagate through the upstream transmission path and reach the main station device is the same for all slave devices, so as long as each slave device sends out a transmission signal in synchronization with its received signal, the time slot No deviation will occur.

The same applies to the second system, in which the signal transmitted from the main station device is transmitted via the downlink transmission path, and after being reflected at the reflection end, it is sequentially taken into each station device.

Signals transmitted from each slave station device reach the main station device via an uplink transmission path. Therefore, the sum of the time for a signal transmitted from the master station device to reach the slave station device via the downlink transmission path and the time for the signal transmitted from the slave station device to propagate through the uplink transmission path and reach the master station device is: Since the time slots are the same for all slave devices, as long as each slave device sends out a transmission signal in synchronization with its received signal, no time slot deviation will occur.

Providing a circuit for detecting a collision of transmitted signals is advantageous when transmission is initiated from the slave device side.

That is, in the access method known as C3MA/CD, there is no signal from the master station, and the slave station can start transmission at random. In this access method, slave devices on two sides may start transmitting almost simultaneously, and in this case, transmission signals will conflict on the upstream transmission path, causing confusion.

In order to avoid this, the signal flowing in from the transmission line to which the output of the transmitting circuit is connected is detected and compared with the signal transmitted from the transmitting circuit, and if they do not match, it is determined that there is a conflict. When it is determined that there is a conflict, transmission is temporarily stopped and measures are taken such as retransmitting the transmitted signal. This collision detection circuit is very advantageous when implemented in the first mode of the invention.

〔Example〕

FIG. 1 is a block diagram of a method according to an embodiment of the present invention. This embodiment system includes one main station device 1, and a plurality of slave devices 2a%2b...2n, one end of which is connected to the transmitting circuit (T) output of the main station device 1. 2b-
...2n receiving circuit (R) inputs are respectively connected to one down transmission line 3 via a branch connection circuit, and one end is connected to the receiving circuit (R) input of the master station device l, and each slave station device 2
Each transmission circuit (T) output of as2b...2n is provided with one uplink transmission line 4 connected via a branch connection circuit.

The transmitting circuit of the main station device 1 connects each slave device 2 to the downlink transmission path 3.
a12b...2n includes means for segmenting and transmitting signals addressed to each slave station device 2a12b...2n by time slot.
・The 2n transmitting circuit (T) is the receiving circuit (T) of its slave station.
R) includes means for transmitting a signal addressed to the main station device in a time slot assigned to the own device in synchronization with the time slot received at R).

Here, the feature of the present invention is that a reflection end 6 is provided at the other end of the upstream transmission line 3, and branch connection circuits 7a, 7b, . The configuration includes a directional coupler that transmits the output signal of the circuit toward the reflective end 6. A non-reflection end 5 is provided at the other end of the down transmission line 3 for absorbing and terminating the signal of the down transmission line 3.

In the case of an optical fiber cable, the reflective end 6 can be realized by forming a cut surface, or by forming a cut surface and plating the cut surface with metal. In the case of a metallic cable, this can be realized by forming an open end or a short-circuited end.

The directional coupler can be realized by selecting known elements suitable for the transmission path and frequency used. In the case of optical fiber cable, star coupler, half mirror 1
It can be realized using other known elements. Further, in the case of a metallic cable, it can be realized using a hybrid transformer, an echo canceller, or other known circuits.

A non-reflective end can be realized in an optical fiber cable by arranging a black body. For metallic cables, this can be achieved by connecting a resistor with the same characteristic impedance to the cable.

Each slave station device 2a12b...2n has its receiving circuit (R
) is synchronized with a signal received from the downlink transmission path 3, identifies the time slot assigned to the own station, and transmits a signal from the transmitting circuit (T) to the uplink transmission path 4 in that time slot. In other words, from the main station device 1 to the downlink transmission path 3
It sequentially transmits frame signals addressed to the subordinate station devices 2a, 2b, . . . 2n. A destination code is arranged in the header of each frame signal, and each slave station device 2as2b...2n identifies and captures a signal addressed to its own station by identifying this destination code. Each slave station device 2. a, 2b...2
It is set in common for n.

Therefore, in the system configured in this way, the main station device 1
The time T for a signal to reach the slave device via the downlink transmission path 3, and the signal transmitted from the slave device to the uplink transmission path 4 is reflected at the reflection end 6, further propagates through the uplink transmission path, and reaches the master station device 1. The sum (T+t) of the time t reaching the
, 2b...2n all have the same value. In other words, as long as each slave station device 2a, 2b, . , whose time slots do not overlap.

This method does not require a separate line like the conventional method described above.

FIG. 2 is a block diagram of another embodiment of the present invention. In this example, a reflective end 8 is provided at the other end of the down transmission line 3, and a branch connection circuit 10a connected to the down transmission line 3,
10b...1on is characterized in that it includes a directional coupler that takes in the signal arriving from the reflecting end 8 as an input signal to the receiving circuit (R) of each slave station device 2a, 2b...2n. A non-reflection end 9 is connected to the other end of the upstream transmission line 4 .

Even in this configuration, each element can be realized in the same manner as in the example shown in FIG. 1 above.

In this configuration, all signals transmitted from the transmission circuit (T) of the main station device 1 to the downlink transmission path 3 are once reflected at the reflection end 8, propagated in the direction of the main station device l, and are transmitted to each slave device 2a12b. ...2n via a directional coupler. The transmission signal of each slave station device 2a12b...2n is identified from the timing of the signal received by the receiving circuit (R), and is transmitted in the time slot assigned to that station. Therefore, the time T' when a signal transmitted from the main station device 1 to the downlink transmission path 3 is reflected at the reflection end 8 and reaches each slave station device 2a12b...2n, and the time T' when the signal is transmitted from the main station device 1 to the downlink transmission path 3, respectively, and the time T' when the signal transmitted from the main station device 1 to the downlink transmission path 3 is reflected at the reflection end 8 and reach each slave station device 2a, 2b... 2n to the upstream transmission path 4 reaches the main station device 1 (
T'+t') is all the slave devices 2a12b...2
Since n is equal, the transmission signals of each slave device 2a12b...2n are correctly arranged at the connection point of the slave device 2n on the upstream transmission path 4.

Even with this configuration, there is no need to provide duplicate transmission paths.

FIG. 3 is a diagram illustrating an example of a configuration in which a circuit for identifying collision of transmission signals is included. A signal arriving at the transmission input 21 is amplified by the transmission driver 22 and transmitted from the coupling circuit 23 to the transmission line as a transmission signal.

A signal arriving from the transmission path is branched by this coupling circuit 23, amplified by an amplifier 26, and applied to one input of a comparison circuit 27. On the other hand, the signal of the transmission input 21 is input to the storage circuit 25 via the buffer 24 and temporarily stored.
The stored contents are read out in synchronization with the output of the amplifier 26 and applied to the other input of the comparison circuit 27. The coupling circuit 23 is a directional coupler, and is configured so that the output signal of the transmission driver 22 is sent out as a transmission signal, but does not appear at the input of the amplifier 26.

If the output signal of the amplifier 26 is the signal transmitted by the transmission driver 22 and reflected at the reflection end, the two input signals of the comparator circuit 27 match, so that a matching output is obtained. However, the output signal of the amplifier 26 is
2 is different from the transmitted signal, no coincidence output is sent to the comparison circuit 27.

In this case, it is determined that there is a signal conflict on the transmission path to which the transmitted signal is connected. If a conflict is identified, the operation of the transmitting circuit can be prohibited and the transmitted signal can be controlled to be retransmitted.

Providing this equilibrium identification circuit is a method (CS MA/
This is extremely advantageous for CDs, etc.).

In addition, by providing this balancing identification circuit, it is possible to prevent the system from operating normally, such as during a transient state until synchronization is established or when there is an error in time slot assignment changes due to changes in the connection of slave devices. Even in such a case, collision with signals from other slave devices can be avoided and the normal operating state can be quickly converged.

In the above example, it has been explained that the wavelength of the signal propagating through the transmission path is one type, but the present invention can be implemented in the same way even if the signal propagating through the transmission path is a wavelength multiplexed signal.

That is, the transmitting circuit and receiving circuit of the main station device and each slave station device can be circuits that can transmit or receive wavelength-multiplexed signals.

〔Effect of the invention〕

As explained above, according to the present invention, even if the distance between each slave device is long and the propagation time between slave devices becomes long,
The transmission signals of each slave station device are correctly arranged on the uplink transmission path, and there is no need to provide a guard time in the time slot, and the transmission efficiency can be maintained at a high level. Furthermore, the system of the present invention does not require a separate transmission path, and can be implemented economically.

Furthermore, if a circuit for identifying signal conflict is provided in the transmission circuit of the slave station device, the system of the present invention becomes extremely advantageous in a system in which access is initiated from the slave station device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the system according to the first embodiment of the present invention. FIG. 2 is a block diagram of a system according to a second embodiment of the present invention. FIG. 3 is a diagram showing a configuration example in the case where a circuit for identifying signal conflict is connected to a transmitting circuit of a slave station device. FIG. 4 is a block diagram of a conventional system. DESCRIPTION OF SYMBOLS 1...Main station device, 2a, 2b...2n...Slave station device, 3...Downward transmission line, 4...Uplink transmission line, 5...
・Non-reflective end, 6...Reflective end, ? a, 7b...7n.
...Branch connection circuit, 8...Reflection end, 9...Non-reflection end, 10a, 10b...10n...Branch connection circuit.

Claims (1)

[Scope of Claims] 1. A master station device and a plurality of slave station devices, one end of which is connected to the transmitting circuit output of the master station device, and each receiving circuit input of the slave device connected to a branch connection circuit. and one uplink transmission line, one end of which is connected to the receiving circuit input of the master station device and each of the transmitting circuit outputs of the slave station device are connected to each other via a branch connection circuit. The transmitting circuit of the master station device includes means for dividing and transmitting signals addressed to each slave device on the downlink transmission path by time slots, and the transmitting circuit of the slave device transmits a signal addressed to each slave device on the downlink transmission path, and the transmitting circuit of the slave station device includes a receiving circuit of the slave device. In a two-way signal transmission method, the other end of the uplink transmission path is a reflection end, and the other end of the uplink transmission path is a reflection end. The bidirectional signal transmission system is characterized in that the branch connection circuit formed and connected to the upstream transmission path includes a directional coupler that transmits the output signal of the transmission circuit of each slave station toward the reflection end. . 2. A device comprising one master station device and a plurality of slave station devices, one end of which is connected to the transmitting circuit output of the master station device and each receiving circuit input of the slave device connected via a branch connection circuit. and one uplink transmission path, one end of which is connected to the receiving circuit input of the master station device, and one upstream transmission path, one end of which is connected to the receiving circuit input of the master station device, and each transmitting circuit output of the slave station device is connected via a branch connection circuit, The transmitting circuit of the device includes means for transmitting signals addressed to each slave device on the downlink transmission path by dividing them into time slots, and the transmitting circuit of the slave device transmits the signals addressed to each slave device to the receiving circuit of the slave device. In a bidirectional signal transmission method including means for transmitting a signal addressed to a main station device in a time slot assigned to the own device in synchronization with a slot, the other end of the downlink transmission path is formed as a reflective end, and the downlink transmission 2. A bidirectional signal transmission system, characterized in that said branch connection circuit connected to said reflection end includes a directional coupler that takes in a signal arriving from said reflection end as an input signal to a reception circuit of each slave station device. 3. The transmitting circuit of the slave device includes means for receiving a signal arriving from the transmission path to which the output of the transmitting circuit is connected, and a comparing circuit that compares the signal with the transmitting signal of the transmitting circuit. 2. The bidirectional signal transmission system according to claim 1, further comprising means for identifying a conflict in transmitted signals based on a mismatch in circuit outputs.