JPH0120813B2 - - Google Patents

Description

[Detailed Description of the Invention] Diversity systems using multiple antennas are generally used in mobile communications, but the present invention provides a method for mobile communications using leaky coaxial cables. This relates to a diversity system using leaky coaxial cables to prevent drops in received signals.

Wireless communication using radio waves as a medium is used for mobile communication between a base station and a mobile station mounted on a mobile body such as a vehicle. This utilizes the phenomenon that voltage is induced in the receiving antenna by radio waves radiated from the transmitting antenna. This method is suitable for locations with few radio wave interferences, but it cannot be used in closed spaces such as tunnels, where there is a lot of attenuation and the length of the tunnel is long. In mobile communication in such places, radio waves are not radiated from only one place like a base station antenna, but are radiated from the entire leaky coaxial cable laid along the direction of movement of the mobile object. Communication is carried out using signals. A leaky coaxial cable is a type of coaxial cable in which a center conductor and a sheath conductor are concentric, and utilizes the property that signals inside the coaxial cable leak through slits provided in the sheath.

FIG. 1 is a block diagram showing mobile communication using a conventionally used leaky coaxial cable. In the figure, reference numeral 1 denotes a base station, which includes a transmitter 2 for transmitting signals, a receiver 3 for receiving signals, and an output terminal 2a of the transmitter 2 and an input terminal 3a of the receiver 3 connected to each other. 1, and an antenna duplexer 4 connected to the input/output terminal 1a of 1. The operation of the antenna duplexer 4 is such that the signal supplied from the transmitter 2 is outputted only from the input/output terminal 1a of the base station 1, and the signal supplied to the input/output terminal 1a of the base station 1 is outputted only to the receiver 3. Ru. 5 to 7 are leaky coaxial cables connected in series to the input/output terminals 1a of the base station 1, and are laid along the movement trajectory of a moving body (not shown). The leaky coaxial cables 5 to 7 are provided with slits 5a to 5n, 6a to 6n, and 7a to 7n. The coupling degree of each adjacent leaky coaxial cable is
Grading processing is applied to raise the signal by about 10dB. Reference numeral 8 denotes a leaky coaxial cable laid along the moving trajectory of the moving object and connected to the end of the leaky coaxial cable 7 via a repeater 9, and has the same configuration as the leaky coaxial cables 5 to 7 described above. are doing. Here, the repeater 9 is the leaky coaxial cable 5~
If the amount of attenuation caused by 8 exceeds the compensation range by grading, the leaky coaxial cable 7, 8
This problem is solved by amplifying the signals between the two. 10 is a mobile station mounted on a mobile body, which, like the base station 1, has a transmitter 11 and a receiver 1.
2 and the output end 11a of the transmitter 11 and the receiver 12
and an antenna duplexer 13 which couples the input ends 12a of the antennas and connects them to the antenna 14. The leaky coaxial cables 5 to 8 and the repeater 9 are connected by cables 15a to 15d, and leaky coaxial cables are connected in series to the end of the leaky coaxial cable 8 as shown by dotted lines. has been done.

In mobile communication using a leaky coaxial cable configured in this way, first, when a mobile body carrying a mobile station 10 travels at point A in FIG. 1, a transmission output is sent from the transmitter 2 of the base station 1. Then, this transmission output signal is supplied to the antenna duplexer 4. The antenna duplexer 4 transmits the supplied output signal of the transmitter 2 to a leakage coaxial cable 5 via the input/output terminal 1a of the base station 1.
supply to. The signal supplied to the leaky coaxial cable 5 leaks from the slits 5a to 5n provided in the leaky coaxial cable 5 while passing through the leaky coaxial cable 5, and is radiated to the outside. The externally radiated signal is received by the antenna 14 of the mobile station 10 to induce a signal voltage, and this signal voltage is supplied to the antenna duplexer 13. Aerial duplexer 1
3 supplies the supplied signal voltage only to the receiver 12. Therefore, the receiver 12 can demodulate the signal supplied from the base station and extract information. Furthermore, communication from the mobile station 10 to the base station 1 is the opposite of how information is transmitted from the base station 1 to the mobile station 10, from the transmitter 11 to the antenna duplexer 13 to the antenna 14 of the mobile station 10. Information sent via the path of leaky coaxial cable 5 - antenna duplexer 4 - receiver 3, demodulated by receiver 3 and sent from mobile station 10 is extracted by base station 1. Next, when the mobile station 10 loaded on the mobile body moves to point B or point C, the distance of the leaky coaxial cable 5 between the base station 1 and the mobile station 10 becomes longer, and the amount of attenuation increases. As a result, as the mobile station 10 moves away from the base station 1, the received input level decreases. This state is shown in FIG. 2, where the horizontal axis d indicates the distance from the base station 1 to the mobile station 10,
A, B, C... on the horizontal axis are points A, B, B, etc. in Figure 1.
C...corresponds to... The vertical axis L represents the relative reception input level of the base station 1 or mobile station 10, and is based on the reception input level at point A.

Next, when the mobile station 10 reaches the connection point between the leaky coaxial cables 5 and 6, signals are transmitted and received between both the leaky coaxial cables 5 and 6 and the antenna 14 of the mobile station 10. . Therefore, the signals leaked from the leaky coaxial cables 5 and 6 are received by the mobile station 10 in a combined state. Further, the signals transmitted from the mobile station 10 are received by the leaky coaxial cables 5 and 6, and the combined output thereof is supplied to the base station 1. In this case, the leaky coaxial cables 5 and 6 are connected by a cable 15a, by means of which the signals passing therein undergo a phase lag. in this case,
If the transfer between the two signals becomes opposite in phase due to the phase delay of the connection cable 15a, the received input level of both the base station 1 and the mobile station 10 will drop because they cancel each other out, and if the amplitudes are equal, The line becomes disconnected and no communication is possible. In order to prevent this drop in the received input level, the length of the cable 15a can be determined by calculation so that the phase change at the connection point of the leaky coaxial cables 5 and 6 is small. This is the same for the cable 15b, and even when dealing with multiple frequencies, if the frequency difference is small, the difference in the amount of phase shift change is also small, so there is no problem.

However, when using the repeater 9, since the phase amount of the repeater 9 at the insertion point of the repeater 9 is unknown, the length of the cables 15c and 15d that does not cause a drop in the receiving input level is required. cannot be determined by calculation. Therefore, when the mobile station 10 reaches point E in FIG. 1, a large drop in the received input level occurs as shown at point E in FIG. 2. In order to prevent this drop in the reception input level, it is necessary to change the length of the connection cables 15c and 15d when the equipment is installed, and to perform phase adjustment to prevent the drop in the reception input level.
This phase adjustment had the drawback of requiring a large amount of manpower and time. Further, according to a general diversity method, the problem can be solved by performing space diversity using a plurality of antennas and receivers in reception by a mobile station. However, in base station reception, it is not possible to eliminate the drop in the reception input level for the same reason as mentioned above.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a diversity system using a leaky coaxial cable that does not cause a drop in the received input level.

In order to achieve this purpose, the diversity method using a leaky coaxial cable according to the present invention involves laying a sub-leaky coaxial cable in parallel to the connection point of the leaky coaxial cable to obtain a received signal without drop, and The signal passing through the cable is frequency-converted and sent to the receiving side, and the receiving side receives both the non-frequency-converted signal sent via the leaky coaxial cable and the frequency-converted signal supplied via the auxiliary leaky coaxial cable. Diversity reception is performed. The diversity system using a leaky coaxial cable according to the present invention will be explained in detail below with reference to the drawings.

Figure 3 is a block diagram of the diversity method using a leaky coaxial cable according to the present invention for preventing a drop in the received input level toward the base station, and the same parts as in Figure 1 are given the same symbols. . In the figure, 16 is a short auxiliary leaky coaxial cable, which is laid parallel to the connection point of the leaky coaxial cables 7 and 8 where the drop in the received signal is large.
Signals are received through the slits 16a-16n. Reference numeral 17 denotes a frequency converter which inputs a signal output from the sub-leakage coaxial cable 16, converts it into a signal of a frequency different from the input frequency, and outputs the signal. 18 is a coupler that couples the frequency converter 17, the repeater 9, and the leaky coaxial cable 8; the coupler 18 outputs the output of the frequency converter 17 to the repeater 9; is output to the leaky coaxial cable 8, and the output of the leaky coaxial cable 8 is output to the repeater 9, respectively. Reference numeral 19 denotes a distributor that divides the received signal output from the antenna duplexer 4 into two parts, supplies one signal to the receiver 3, and supplies the other signal to the receiver 20. In this case, the receiver 20 is configured to receive and demodulate only the frequency signal whose frequency has been converted by the frequency converter 17 described above. Reference numeral 21 denotes a combiner, which combines the output of the receiver 3 and the output of the receiver 20 at a ratio corresponding to each received input, and outputs the output from the output terminal 22.
supply to. These transmitter 2, receiver 3, antenna duplexer 4, distributor 19, receiver 20, and combiner 21 constitute a base station 23 to which a diversity communication system is applied. Note that 24 is a resistor connected to the terminal end of the sub-leakage coaxial cable 16.

In the diversity method using the leaky coaxial cable configured in this way, the leaky coaxial cable 5
The changes in the reception input level depending on the positions .about.7 are the same as in the conventional case. When the mobile station 10 transmits at point E, the signal from the mobile station 10 is transmitted through the leaky coaxial cables 7 and 8 and the auxiliary leaky coaxial cable 16.
received by. The signal received by the leaky coaxial cable 8 is passed through the coupler 18 to the repeater 9
The signal is amplified and combined with the signal received by the leaky coaxial cable 7. In this case, since phase adjustment is not performed between the leaky coaxial cables 7 and 8, the phase shift that occurs between them causes a drop in the transmission input level as described above, and in extreme cases The line will be disconnected. Therefore, a demodulated output cannot be obtained from the receiver that receives the transmission frequency signal of the mobile station 10. This state is the state of the depressed portion shown by the solid line at point E in FIG. On the other hand, the auxiliary leaky coaxial cable 16, which is placed along the connecting part between the leaky coaxial cables 7 and 8 so as to cover the part, moves without falling as shown by the dotted line at point E in FIG. A signal is being received from station 10. After the output of this sub-leaky coaxial cable is frequency-converted in the frequency converter 17,
The signal is supplied to the repeater 9 via the coupler 18 and amplified. As a result, even if a demodulated output is not obtained from the receiver 3 that receives the transmission frequency signal of the mobile station 10, the demodulated output is not obtained from the receiver 20 that receives the frequency at which the transmission frequency signal of the mobile station 10 is frequency-converted. The output will be obtained normally. The demodulated outputs of the receiver 3 and the receiver 20 are combined in a combiner 21 according to the proportion of the received input, and the output is sent to the output terminal 22 to connect the leaky coaxial cables 7 and 8. Even if the reception input level at the connection point drops, instantaneous interruption of the reception signal can be prevented. Note that the mobile station 10
An instantaneous interruption of about several microseconds occurs when switching between the demodulated output of the receiver 3 that receives the transmitted frequency signal of the mobile station 10 and the demodulated output of the receiver 20 that receives the frequency-converted transmitted frequency signal of the mobile station 10 If this can be tolerated, the synthesizer 21 may be replaced with a switch, and the demodulated output of the receiver with a better signal-to-noise ratio may be selected. For ease of understanding, only the direction from the mobile station 10 to the base station 23 has been described above. However, in this system, a similar phenomenon occurs in the opposite direction, so similar countermeasures are required.

FIG. 5 is a block diagram of a system that takes measures in both directions as described above, and corresponds to the structure of the claims. With this configuration, it is possible to prevent the reception input level from dropping in the direction from the base station 23 to the mobile station 10a. In other words, in the direction of the mobile station, the frequencies of the signals from the leaky coaxial cables 5, 6, 7, 8, ... are connected to the coupler 3.
3, 34, the frequency is converted by the frequency converter 35 so that it can be supplied to the sub-leaky coaxial cable 16, and the mobile station 10a divides the received input signal by the distributor 30, and converts the received frequency from the leaky coaxial cable and the sub-leaky coaxial cable. It is sufficient to be able to receive both frequencies from the leaky coaxial cable.

As explained above, the diversity method using a leaky coaxial cable according to the present invention involves laying a sub leaky coaxial cable along the connection point of the leaky coaxial cable, frequency converting the signal passing through this sub leaky coaxial cable, and transmitting the signal to the receiving side. By transmitting the signal, both the leaky coaxial cable and the sub-leaky coaxial cable are received using the diversity method.
This has an excellent effect of preventing a drop in the reception input level caused by the location of the mobile station.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a communication system using a conventionally used leaky coaxial cable, Fig. 2 is a waveform diagram showing changes in the receiving input level in the block diagram shown in Fig. 1, and Fig. 3 is a diagram of the present invention. FIG. 4 is a block diagram for explaining the operation of preventing drop from the mobile station toward the base station in the diversity system using the leaky coaxial cable according to the invention.
FIG. 5 is a waveform diagram showing changes in the received input level in the block diagram shown in the figure. FIG. . 1, 23... base station, 2, 11... transmitter,
3, 12...Receiver, 4, 13...Antenna duplexer, 5-8...Leaky coaxial cable, 9...Repeater, 10...Mobile station, 14...Antenna, 15a-
15d...Cable, 16...Sub-leakage coaxial cable, 17...Frequency converter, 18...Coupler, 1
9...Distributor, 21...Synthesizer, 22...Output terminal, 24...Resistor.

Claims (1)

[Claims] 1. A leakage system that includes a mobile station loaded on a moving object, a leaky coaxial cable in which multiple cables are connected in series along the moving trajectory of the moving object, and a base station connected to one end of the leaky coaxial cable. In mobile communication using a coaxial cable, a sub-leaky coaxial cable is installed along a portion of the leaky coaxial cable that includes the connection point, and a sub-leaky coaxial cable is supplied to or output from the sub-leaky coaxial cable. A first receiver for receiving the output frequency signal of the frequency converter and a first receiver for receiving the frequency signal output from the frequency converter at both the mobile station and the base station and receiving the frequency signal sent from the transmitter of the other station. By combining the demodulated outputs of the first and second receivers or extracting the selected output, the drop in the received signal can be prevented when the mobile station is located at the connection of the leaky coaxial cable. Diversity method using coaxial cable that prevents leakage.