JPH1141159A - Communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove interference without deteriorating the transmission quality of a signal from a slave station by branching and delaying a base band signal to be used at the time of transmission, and generating the replica of the transmission signal of a master station without any error. SOLUTION: A master station 1 is provided with a replica generating circuit 6 for generating the transmission signal replica of its own station. Then, a synthesizing circuit 9 anti-phase synthesizes the replica of the transmission signal of its own station with a signal received by a receiving circuit 8, eliminates the transmission signal of its own station, and extracts the transmission signals of slave stations 2-1 to 2-n. This master station 1 is provided with a delay circuit 5 as a means for delaying a base band signal outputted to the modulation input of its own station, and the replica generating circuit 6 generates the replica of the transmission of the master station 1 from the output signal of the delay circuit 5. Moreover, this master station 1 includes a synchronizing circuit 11 as a means for reading the signal delayed by the delay circuit 5 synchronously with the output of the receiving circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a multiple access superposed transmission system in which one master station and a plurality of slave stations at least partially communicate in the same frequency band. The present invention relates to a technique for canceling a signal of a master station itself that causes interference when the master station receives a signal from a slave station. The present invention is suitable for use in communication via a relay station such as the same communication satellite (transponder).

[0002]

2. Description of the Related Art A multiple access communication system is known in which one master station and a plurality of slave stations communicate at least partially using the same frequency band via a relay station such as a communication satellite. In this way, when one master station and a plurality of slave stations at least partially communicate via the same frequency band, when the master station receives a signal from the slave station, it is looped back from the relay station. The signal of the master station itself causes interference.

Therefore, the master station demodulates the transmission signal (modulated signal) transmitted by the own station from the received signal to extract a baseband signal as a modulation signal, and furthermore, regenerates the reproduced carrier into the baseband signal. To generate a replica of the modulation signal of the master station, and by combining the generated replica with the received signal in reverse phase, interference is removed.

[0004] This conventional example will be described with reference to FIGS. 5 to 7. FIG. 5 is a block diagram showing a general configuration of a conventional communication apparatus and a master station. FIG. 6 is a diagram showing the spectrum of the received signal at the master station. FIG. 7 is a diagram illustrating a spectrum of a signal output from the combining circuit. As shown in FIG. 5, the master station 1 inputs a baseband signal as a modulation signal including information to be transmitted by the master station 1 to a modulation input of the modulation transmission circuit 4. The modulation transmission circuit 4 modulates the carrier supplied from the carrier generation circuit 12 according to the input baseband signal to generate a transmission signal. This transmission signal is transmitted to the communication satellite 3.

A plurality (n) of slave stations 2-1 to 2-n transmit a transmission signal from the slave stations 2-1 to 2-n to the same communication satellite 3. The master station 1 receives a signal having the spectrum shown in FIG.
The received signal includes the transmission signal of the master station 1 and the slave stations 2-1 to 2-
n is included. The reception signal received by the reception circuit 8 is input to the delay circuit 66, and a delay time equal to the transmission delay of the master station transmission signal extraction circuit 67, demodulation circuit 68, remodulation circuit 69, and replica control circuit 7 is added. The output of the delay circuit 66 is input to the synthesis circuit 9.

[0006] The received signal received by the receiving circuit 8 is input to the parent transmission modulation signal extraction circuit 67, and the transmission signal of the parent station 1 is extracted. The output of the master station transmission signal extraction circuit 67 is the demodulation circuit 6
8, a carrier and a clock whose frequency and phase are synchronized with the transmission signal of the master station 1 are reproduced, and the baseband signal is demodulated. Here, the clock is a clock in which a baseband signal which is a digital signal is synchronized.

The reproduced carrier generated by the demodulation circuit 68,
The clock and demodulated baseband signal are re-modulated 69
The carrier is modulated using the demodulated baseband signal, and a replica of the transmission signal of the master station 1 is generated.

The replica of the transmission signal of the master station 1 generated by the re-modulation circuit 69 is controlled by the replica control circuit 7 for its propagation path characteristics such as its amplitude, phase, and nonlinearity of the satellite channel.
A replica of the transmission signal of the master station 1 in which only the carrier phase of the reception signal input to the synthesis circuit 9 is opposite to that of the transmission signal of the master station 1 and all other phases are equal is generated.

[0009] The output of the replica control circuit 7 is input to the synthesizing circuit 9 and synthesized with the received signal delayed by the delay circuit 66. The transmission signal of the master station 1 is removed and the slave station 2-1 as shown in FIG. ~ 2-n are obtained. The output of the synthesizing circuit 9 is input to the demodulation circuit 10, and the slave stations 2-1 to 2-
The transmission signal from n is demodulated.

[0010]

In such a conventional communication system, when a master station receives its own transmission signal and demodulates a baseband signal from the received signal, the interference caused by the transmission signal from the slave station occurs. An error occurs during demodulation due to noise or the like, and a replica of the transmission signal of the master station is generated with an erroneous baseband signal. For this reason, the effect of interference removal is reduced, and the transmission quality of signals from slave stations is degraded.

The present invention has been made in view of such a background, and it is an object of the present invention to provide a communication apparatus capable of generating an error-free replica of a transmission signal of a master station and performing efficient interference cancellation. Aim. An object of the present invention is to provide a communication device capable of performing interference removal without deteriorating the transmission quality of a signal from a slave station.

[0012]

SUMMARY OF THE INVENTION A communication apparatus according to the present invention focuses on the fact that an interference signal to be eliminated by a master station is a transmission signal from its own station, and does not need to demodulate a baseband signal from a reception signal. The most main feature is that the baseband signal used for transmission is branched and delayed, and the baseband signal is used to generate a perfect replica of the transmission signal of the master station without errors. . By combining the complete replica of the transmission signal of the master station with the reception signal in reverse phase, the interference removal effect is improved, and the transmission quality of the signal from the slave station is improved.

That is, the present invention provides a single master station, a plurality of slave stations transmitting and receiving radio signals using the same frequency band as a part of the frequency transmitted by the master station, the slave station and the master station. A relay station for bidirectionally relaying a radio signal between stations, wherein the master station receives both the transmission signal of the own station and the transmission signal of the slave station that are looped back from the relay station; Replica generating means for generating a replica of the transmission signal of the station, and combining the signal received by the receiving circuit with the replica of the transmission signal of the own station in reverse phase to eliminate the transmission signal of the own station, thereby And a means for extracting a transmission signal of the station.

Here, it is a feature of the present invention that the replica generation means delays a baseband signal arriving at a modulation input of the own station, and generates the replica from an output signal of the delay means. And a means for reading out the signal delayed by the delaying means in synchronization with the output of the receiving circuit.

This makes it possible to generate a replica of the transmission signal of the master station by compensating for the delay time from when the transmission signal of the master station is looped back at the relay station and received again.

In order to generate a replica of the transmission signal of the master station, an independent carrier generation circuit for generating a carrier to be supplied to the replica generation means may be provided, or a carrier to be supplied to the replica generation means may be provided. Means for reproducing from the received signal may be provided. In the latter case,
Since the carrier actually follows the transmission signal looped back from the relay station, the frequency and phase of the replica of the transmission signal can completely match the reception signal.

Alternatively, the carrier supplied to the replica generation means may be branched from the carrier supplied to the transmission circuit. As a result, the configuration for generating or reproducing carriers can be omitted,
The device configuration can be simplified.

Alternatively, the replica generating means may include a delay circuit for branching and delaying the transmission signal of the own station. As a result, since the actual transmission signal can be delayed as it is and this transmission signal can be used as a replica of the transmission signal, there is no need to newly generate a replica of the transmission signal, and the device configuration can be simplified.

[0019]

Embodiments of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of the first embodiment of the present invention and the master station 1.

The present invention is directed to a master station 1, slave stations 2-1 to 2-n transmitting and receiving radio signals using the same frequency band as a part of the frequency transmitted by the master station 1, and slave stations 2-1 to 2-n. 2-1 to 2-
n and a communication satellite 3 as a relay station for bidirectionally relaying a radio signal between the master station 1 and the master station 1.
Transmission signal of the own station and slave stations 2-1 and 2-2
-N, a receiving circuit 8 for receiving both the transmission signals, a replica generation circuit 6 for generating a replica of the transmission signal of the own station, and a replica of the transmission signal of the own station in the signal received by the reception circuit 8 in opposite phase. This is a communication device including a combining circuit 9 as means for extracting transmission signals of the slave stations 2-1 to 2-n by combining and erasing transmission signals of the own station.

Here, a feature of the present invention is that a replica circuit 6 includes a delay circuit 5 as a means for delaying a baseband signal arriving at a modulation input of the own station.
A replica of the transmission signal of the master station 1 is generated from the output signal of the delay circuit 5. Further, the delay circuit 5
And a synchronizing circuit 11 as means for reading out the signal delayed by the synchronizing with the output of the receiving circuit 8.

[0022]

【Example】

(First Embodiment) A first embodiment of the present invention will be described. The first embodiment of the present invention includes an independent carrier generation circuit 12 'for generating a carrier to be supplied to the replica generation circuit 6. As shown in FIG. 1, the master station 1 inputs a baseband signal as a modulation signal including information to be transmitted by the master station 1 to a modulation input of the modulation transmission circuit 4. The modulation transmission circuit 4 modulates the carrier using the baseband signal. The transmission signal of the master station 1, which is the output of the modulation transmission circuit 4, is transmitted to the communication satellite 3
Sent to.

The plurality of (n) slave stations 2-1 to 2-n transmit the transmission signals of the slave stations 2-1 to 2-n to the same communication satellite 3. Here, as shown in FIG. 6 and FIG.
２−2-n are transmitted by FDMA (Frequency Divisio
n Multiple Access).

The master station 1 receives a signal from the communication satellite 3 as shown in FIG.
The signal having the spectrum shown in FIG. The received signal includes the transmission signal of the master station 1 and the slave station 2-
1 to 2-n. The received signal received by the receiving circuit 8 is input to the synthesizing circuit 9. Here, a baseband signal as a modulation signal including information to be transmitted by the master station 1 is input to the delay circuit 5, and a delay time equal to the transmission delay of the transmission signal of the master station 1 is added. If the transmission delay is not known or fluctuates, the timing at which the reception signal is read from the reception circuit 8 is determined by the synchronization circuit 11.
Is recognized, and a delay time suitable for it is set in the delay circuit 5.

The baseband signal output from the delay circuit 5 is input to the replica generation circuit 6, and the carrier generated from the carrier generation circuit 12 'is modulated using this baseband signal. As a result, a replica (hereinafter simply referred to as a replica) of the transmission signal of the master station 1 is generated.

The generated replica is transmitted to the replica control circuit 7.
Controls the propagation path characteristics such as the amplitude, phase, and nonlinearity of the satellite link, and generates a replica in which only the carrier phase of the transmission signal of the master station 1 is opposite to that of the carrier and all other phases are equal. This replica is input to the synthesizing circuit 9 and the receiving circuit 8
7, the slave stations 2-1 to 2-2 from which the transmission signal of the master station 1 has been removed, as shown in FIG.
-N is obtained. The output of the synthesizing circuit 9 is input to the demodulation circuit 10, and the transmission signals from the slave stations 2-1 to 2-n are demodulated.

(Second Embodiment) The configuration of the second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram of the overall configuration of the second embodiment of the present invention and the master station 1. As shown in FIG. The second embodiment of the present invention includes a master station transmission signal extraction circuit 67 and a reproduction circuit 18 as means for reproducing a carrier supplied to the replica generation circuit 6 from a received signal.

In the replica generating circuit 6 of the first embodiment of the present invention, the carrier is generated autonomously by the carrier generating circuit 12 'of the replica generating circuit 6. In the second embodiment of the present invention, the carrier is extracted from the received signal. Since the carrier is reproduced from the transmitted signal of the master station 1, a replica whose frequency and phase match those of the actual transmission signal of the master station 1 can be generated as compared with the first embodiment of the present invention.

The operation of the second embodiment of the present invention will be described. FIG.
As shown in (1), the master station 1 inputs a baseband signal as a modulation signal including information to be transmitted by the master station 1 to a modulation input of the modulation transmission circuit 4. The transmission signal of the master station 1, which is the output of the modulation transmission circuit 4, is transmitted to the communication satellite 3.

The plurality of (n) slave stations 2-1 to 2-n transmit the transmission signals of the slave stations 2-1 to 2-n to the same communication satellite 3. Here, as shown in FIG. 6 and FIG.
Transmission signals from .about.2-n are FDMA.

The master station 1 transmits a signal from the communication satellite 3 as shown in FIG.
Is received by the receiving circuit 8. The received signal includes the transmission signal of the master station 1 and the slave station 2-1.
~ 2-n are included. The reception signal received by the reception circuit 8 is combined with the synthesis circuit 9 and the master station transmission signal extraction circuit 67.
Is input to The master station transmission signal extraction circuit 67 extracts only the transmission signal of the master station 1 by filtering. The output of the master station transmission signal extraction circuit 67 is input to the reproduction circuit 18 and the carrier and clock whose frequency and phase are synchronized with the transmission signal of the master station 1 are reproduced. Here, the clock is a clock in which a baseband signal which is a digital signal is synchronized.

The carrier and clock reproduced by the reproduction circuit 18 are input to the replica generation circuit 6. In addition, master station 1
The baseband signal as a modulation signal including the information to be transmitted is input to the delay circuit 5, and a delay time equal to the transmission delay of the transmission signal of the master station 1 is added. If the transmission delay is not known or fluctuates, the receiving circuit 8
The synchronous circuit 11 recognizes the timing at which the received signal is read out from the, and sets an appropriate delay time in the delay circuit 5. The baseband signal output from the delay circuit 5 is also input to the replica generation circuit 6, and the reproduced carrier is modulated using the baseband signal synchronized with the reproduced clock. As a result, a replica is generated.

The generated replica is stored in the replica control circuit 7.
The propagation path characteristics such as the amplitude, phase, and nonlinearity of the satellite circuit are controlled, and only the transmission signal of the master station 1 and the carrier phase in the reception signal input to the synthesis circuit 9 are opposite phases, and all other phases are the same. Equal replicas are generated. The output of the replica control circuit 7 is also input to the synthesizing circuit 9 and synthesized with the received signal received by the receiving circuit 8 to remove the transmission signals of the master station 1 as shown in FIG. n transmission signals are obtained. The output of the synthesis circuit 9 is input to the demodulation circuit 10,
Transmission signals from slave stations 2-1 to 2-n are demodulated.

(Third Embodiment) The configuration of a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing the overall configuration of the third embodiment of the present invention and the master station 1. As shown in FIG. In the third embodiment of the present invention, the carrier supplied to the replica generation circuit 6 uses the carrier supplied to the modulation transmission circuit 4.

The replica generation circuit 6 according to the second embodiment of the present invention
Generates a replica according to the carrier and the clock supplied from the reproducing circuit 18, but the replica generating circuit 6 according to the third embodiment of the present invention generates the replica according to the carrier and the clock supplied from the modulation transmitting circuit 4. I do. Compared with the case where the carrier and the clock are reproduced from the actual received signal as in the second embodiment of the present invention, the consistency between the frequency and the phase of the replica and the frequency and the phase of the actual modulated signal is slightly inferior. Carrier generation circuit 12 'of replica generation circuit 6 as in one embodiment
Has a higher consistency compared to the case where the carrier is autonomously generating carriers. Therefore, the third embodiment of the present invention is as simple as the first embodiment of the present invention,
As with the second embodiment of the present invention, a replica having high frequency and phase matching with the actual transmission signal can be generated.

The operation of the third embodiment of the present invention will be described. FIG.
As shown in (1), the master station 1 inputs a baseband signal as a modulation signal including information to be transmitted by the master station 1 to a modulation input of the modulation transmission circuit 4. The transmission signal of the master station 1, which is the output of the modulation transmission circuit 4, is transmitted to the communication satellite 3.

The plurality of (n) slave stations 2-1 to 2-n transmit the transmission signals of the slave stations 2-1 to 2-n to the same communication satellite 3. Here, as shown in FIG. 6 and FIG.
Transmission signals from .about.2-n are FDMA.

The master station 1 receives the signal from the communication satellite 3 in FIG.
The signal having the spectrum shown in FIG. The received signal includes the transmitted signal of the master station 1 and the transmitted signals of the slave stations 2-1 to 2-n. The received signal received by the receiving circuit 8 is input to the synthesizing circuit 9. Here, a baseband signal as a modulation signal including information to be transmitted by the master station 1 is input to the delay circuit 5, and a delay time equal to the transmission delay of the modulation signal of the master station 1 is added. If the transmission delay is not known or fluctuates, the timing at which the reception signal is read from the reception circuit 8 is determined by the synchronization circuit 11.
Is recognized, and a delay time suitable for it is set in the delay circuit 5. The output of the delay circuit 5 is input to the replica generation circuit 6.

At the same time, the same carrier and clock as in the modulation transmission circuit 4 are also input to the replica generation circuit 6. Here, the clock is a clock in which a baseband signal which is a digital signal is synchronized. The baseband signal input to the delay circuit 5 is also input to the replica generation circuit 6. The input carrier is modulated using the baseband signal synchronized with the input clock. As a result, a replica is generated.

The generated replica is transmitted to the replica control circuit 7.
The propagation path characteristics such as the amplitude, phase, and the nonlinearity of the satellite link are controlled, and only the transmission signal of the master station 1 and the carrier phase in the reception signal input to the synthesis circuit 9 are opposite phases, and all other phases are the same. Equal replicas are generated. The output of the replica control circuit 7 is also input to the synthesizing circuit 9 and synthesized with the signal received by the receiving circuit 8, and as shown in FIG. 7, the slave stations 2-1 to 2-n from which the transmission signal of the master station 1 has been removed. A transmission signal is obtained. The output of the synthesizing circuit 9 is input to the demodulation circuit 10, and the transmission signals from the slave stations 2-1 to 2-n are demodulated.

(Fourth Embodiment) The configuration of a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram of the overall configuration of the fourth embodiment of the present invention and the master station 1. As shown in FIG.

The fourth embodiment of the present invention is different from the first to third embodiments of the present invention in that the replica generation circuit 6 includes a delay circuit 15 for branching and delaying the transmission signal of its own station. ing.

In the fourth embodiment of the present invention, since no replica is generated from the baseband signal, it is not necessary to reproduce the carrier and re-modulate the carrier with the baseband signal.
The device configuration can be simplified.

The operation of the fourth embodiment of the present invention will be described. FIG.
As shown in (1), the master station 1 inputs a baseband signal as a modulation signal including information to be transmitted to the modulation transmission circuit 4. The transmission signal of the master station 1, which is the output of the modulation transmission circuit 4, is transmitted to the communication satellite 3.

The plurality of (n) slave stations 2-1 to 2-n transmit the transmission signals of the slave stations 2-1 to 2-n to the same communication satellite 3. Here, as shown in FIG. 6 and FIG.
Transmission signals from .about.2-n are FDMA.

The master station 1 receives from the communication satellite 3 in FIG.
The signal having the spectrum shown in FIG. The received signal includes a transmitted signal from the master station 1 and a transmitted signal from the slave station. The received signal received by the receiving circuit 8 is input to the synthesizing circuit 9. Here, the modulation transmission circuit 4
Is also input to the delay circuit 15, and a delay time equal to the transmission delay of the modulation signal of the master station 1 is added. If the transmission delay is not known or fluctuates, the synchronization circuit 11 recognizes the timing at which the reception signal is read from the reception circuit 8 and determines a delay time suitable for the timing.
Set to. The output of the delay circuit 15 has its propagation path characteristics such as amplitude, phase and satellite channel nonlinearity controlled by the replica control circuit 7. A replica is generated in which only the phase is reversed and all others are equal. The output of the replica control circuit 7 is also input to the synthesizing circuit 9 and synthesized with the received signal received by the receiving circuit 8, and the slave stations 2-1 to 2-n from which the transmission signal of the master station 1 is removed as shown in FIG. Is obtained. The output of the synthesizing circuit 9 is input to the demodulation circuit 10, and the transmission signals from the slave stations 2-1 to 2-n are demodulated.

The delay circuit 15 can be realized by using a delay line formed by an inductor or a delay line formed by a cable.

(Summary of Embodiment) In the first to fourth embodiments of the present invention, the transmission signals from the slave stations 2-1 to 2-n are FDM
Although described as A, the present invention is applied to a superimposed transmission system in which one master station and a plurality of slave stations communicate via the same frequency band using a satellite line, and the effect is great. Therefore,
TDMA (Time Division Multiple Access), CDMA
(Code Division Multiple Access) or other signal formats have the same effect.

In the first to fourth embodiments of the present invention, when the transmission delay set in the delay circuit 5 is not known or fluctuates, the timing at which a reception signal is read from the reception circuit 8 is determined by the synchronization circuit 11. Has been described, and an appropriate delay time is set in the delay circuit 5 or 15. However, the output of the synthesizing circuit 9 or the output of the demodulation circuit 10 is monitored and the interference of the transmission signal of the master station 1 is monitored. The delay time of the delay circuit 5 or 15 can be set to a position where the interference cancellation situation is the best according to the cancellation situation.

In the first to fourth embodiments of the present invention, the communication satellite 3 has been described as a relay station. However, the same description can be applied to a relay station such as a relay station located on a mountaintop. it can.

[0051]

As described above, according to the present invention,
An error-free modulated signal replica of the master station can be generated, and efficient interference cancellation can be performed. The present invention can perform interference cancellation without deteriorating the transmission quality of a signal from a slave station.

[Brief description of the drawings]

FIG. 1 is a block diagram of an overall configuration and a master station according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an overall configuration and a master station according to a second embodiment of the present invention.

FIG. 3 is a block diagram of an overall configuration and a master station according to a third embodiment of the present invention.

FIG. 4 is a block diagram of an overall configuration and a master station according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing the overall configuration of a conventional example and a master station.

FIG. 6 is a diagram showing a spectrum of a received signal in a master station.

FIG. 7 is a diagram illustrating a spectrum of a signal output from a synthesis circuit.

[Explanation of symbols]

 Reference Signs List 1 master station 2-1 to 2-n slave station 3 communication satellite 4 modulation transmission circuit 5, 15, 66 delay circuit 6 replica generation circuit 7 replica control circuit 8 reception circuit 9 synthesis circuit 10 demodulation circuit 11 synchronization circuit 12, 12 ' Carrier generation circuit 18 Regeneration circuit 67 Master station transmission signal extraction circuit 68 Demodulation circuit 69 Remodulation circuit

Claims (5)

[Claims] 1. A master station, a plurality of slave stations transmitting and receiving radio signals using the same frequency band as a part of a frequency transmitted by the master station, and a plurality of slave stations between the slave station and the master station. A relay station that relays a radio signal in both directions, wherein the master station receives a transmission signal of the own station and a transmission signal of the slave station that are both returned from the relay station, and a transmission signal of the own station. Replica generating means for generating a replica of the slave station, and synthesizing the replica of the transmission signal of the own station in reverse phase with the signal received by the receiving circuit to eliminate the transmission signal of the own station, thereby transmitting the transmission signal of the slave station. A replica generating means, a means for delaying a baseband signal arriving at a modulation input of its own station, and a means for generating the replica from an output signal of the delaying means. To delay this Communication apparatus characterized by comprising a reading means in synchronism with signal delayed by stages to the output of the receiver circuit. 2. An independent carrier generating circuit for generating a carrier to be supplied to said replica generating means.
The communication device as described. 3. The communication apparatus according to claim 1, further comprising: means for reproducing a carrier to be supplied to said replica generating means from a received signal. 4. The communication apparatus according to claim 1, wherein a carrier supplied to said replica generation means is branched from a carrier supplied to said transmission circuit. 5. A master station, a plurality of slave stations transmitting and receiving radio signals using the same frequency band as a part of a frequency transmitted by the master station, and a plurality of slave stations between the slave station and the master station. A relay station that relays a radio signal in both directions, wherein the master station receives a transmission signal of the own station and a transmission signal of the slave station that are both returned from the relay station, and a transmission signal of the own station. Replica generating means for generating a replica of the slave station, and combining the signal received by the receiving circuit with a replica of the own station's transmission signal in reverse phase to eliminate the own station's transmission signal, thereby transmitting the slave station's transmission signal. A replica generating means including a delay circuit for branching and delaying a transmission signal of its own station.