JPH07118680B2 - Two-way communication device for underground facility - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device such as a wireless telephone used for two-way communication in an underground facility such as a mine, and a mode used for radio wave propagation is a mine particularly in long-distance communication. It is based on connecting electromagnetic waves to metal structures, pipes, and other conductors installed in horizontal shafts and vertical shafts.

BACKGROUND ART A problem when using a wireless telephone underground is that electromagnetic waves are greatly attenuated under the above conditions. In other words, a wireless telephone that works perfectly on the ground is not good enough at all without special measures underground. Other ambient environments may also require other conditions for the equipment used.

There are three ways to connect a wireless phone to a mine.

1. Use waveguide mode for propagation with frequencies above 200 MHz.

2. Use leaky feeder line with frequency of 2-200MHz.

3. Using direct propagation through bedrock and based on conductors installed in the mine. Frequency band from 0.1 to 2MHz is possible.

The waveguide mode is a propagation mode of electromagnetic waves in which the movement of the electromagnetic waves is as if traveling through a conduit. The mine shaft is considered to be a type of waveguide. However, the signal attenuation is remarkable, and the attenuation is further increased by obstacles such as vehicles placed on the side road. This method is not suitable for use in a complicated communication network of a horizontal shaft in an existing mine, which has a long transmission distance.

In the leaky feed line approach, a pair of long cables or loose braided coaxial transmission lines within the same shield are coupled to a radio transmitter. The electric field from the transmission line is at most a few
Received with a portable receiver up to a distance of 10 meters. An antenna cable is installed on the side tunnel of the mine, and a portable device can be used near this antenna.

At frequencies below 2MHz, such radiotelephone systems can be used when the signal goes directly into the bedrock, power cables, plumbing,
Or, it can be used when an existing conductor such as a hoist rope can be used. Direct propagation through a bedrock depends on the conductivity of the rock and the frequency used. With existing conductors, the communication distance is very long. The same result is obtained even if the base station is directly coupled to the cable as the antenna.

The purpose of the present invention is a device such as a radiotelephone for two-way communication in an underground facility, which functions in the frequency band of 0.1 to 2 MHz and is used for the propagation of a signal part of which propagates in the bedrock. It is to provide a device that uses an existing conductor in a mine. The essential novel features of the invention will be apparent from the appended claims.

DISCLOSURE OF THE INVENTION According to the present invention, a loop antenna is used by utilizing an existing conductor such as a power cable, a metal pipe for ventilation, a metal pipe for compressed air, a hoist rope and the like existing in a mine and a floor rock. By converting the analog signal into a digital signal and transmitting it in the frequency band of 2MHz or less that can propagate in the bedrock, the bidirectional communication in the underground facility is performed by compensating for the attenuation and the interference caused by the mining equipment. A loop antenna is advantageously coupled to a transceiver device for a two-way communication connection, for example a speech connection, said device using digital transmission techniques to digitally encode the speech in delta modulation.
Frequency shift keying (FS) is used when modulating signals to radio frequencies.
K) is used.

With digital modulation techniques, the sensitivity of the device to interference and noise in mines, for example due to the electric machines used, is substantially reduced for the following reasons. That is, in digital transmission, for example, sample values of analog signals obtained at sufficiently short intervals can be transmitted, and the original signal can be reproduced from these sample values. These sampled values are advantageously coded so that only two binary signals are transmitted at any given time. Such a signal which is distorted and noisy during transmission is interpreted as either of two binary signals upon reception. In this case, the distorted signal is reproduced by the intermediate image width device or repeater in the apparatus.

In digital communications, voice quality criteria are maintained as long as the received bits are correctly interpreted, even if the signal-to-noise (S / N) ratio changes during transmission. When S / N deteriorates to a certain point during digital modulation, the error probability of the received bit increases rapidly, and the original speech signal can no longer be accurately decoded. Thus, in the method according to the invention, the coding of the speech in digital form is carried out using delta modulation, in which case the transmitted sample values are decoded bit by bit. This differential encoding is based on the fact that consecutive sampled values taken from a signal are correlated with each other, and a sampled value taken earlier from the same signal can predict the next sampled value.
Therefore, the difference between the actual sample value and the predicted sample value becomes the sample value to be transmitted. This allows the call to be encoded with a relatively small number of bits.

With the digital modulation technique applied according to the invention, there is sufficient tolerance to interference and noise, so that the communication range achieved is also long. In the case of modulation methods that are not tolerant of interference and noise, this interference limits the connection much more than the attenuation of the signal on the channel. Therefore, even when the signal is modulated to radio frequency, the method of the present invention uses angle modulation, where the signal-to-noise ratio is adjustable with respect to bandwidth and good results have been obtained.

In addition, digital transmission allows complex processing of the signal, compensating for attenuation and interference related to propagation. In this case, in order to improve the mutual correlation of the consecutive sampled values extracted from the signal, the number of transmission bits becomes larger than the number of bits required for the information at the transmission end. When receiving,
Some of these redundant bits may be misinterpreted without error in decoding the required signal. Furthermore,
Since it is digital transmission, the device of the present invention can use highly integrated circuits such as a delta modulation circuit and a phase synchronization circuit during radio frequency modulation.

The communication method used in the device according to the invention may advantageously be, for example, the so-called half-duplex method. In this case, the two-way conversation connection operates without simultaneous listening during transmission. Such a communication method can be used, for example, when all the receivers can hear the transmission from the base station or a single radio telephone. Furthermore, the device of the present invention can be applied to the transmission of information other than a call. Considering the bandwidth limitation, the bandwidth for the speech channel also makes it possible, for example, to transmit measurement information, control information, production information and stationary monitor images, if desired.

Description of Embodiments Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram of the apparatus within the preferred embodiment of the apparatus of the present invention. The second is an antenna circuit diagram which is advantageously applied to the embodiment of FIG.

In FIG. 1, during the transmission operation of the device, the audio signal from the microphone is amplified by the amplifier 2, passes through the limiter 3 and the filter 4, and becomes a signal having an appropriate amplitude for the analog-digital converter 5. In the filter 4, frequency components other than those required for audibility are removed from the audio signal. The analog-to-digital converter 5 converts the signal thus processed into a digital form, i.e. a signal represented by sampled values taken from the signal. The sampling interval can be varied using the timing generator 6.

The analog-to-digital converter 5 operates on the principle of delta modulation and gives a theoretical value "1" when the speech signal value is increasing and specifies a logical "0" when the signal value is decreasing. The frequency shift keying FSK modulator 7 is controlled by these speech signal bits. When the bit is “0”, the modulator 7 generates a designated frequency and outputs the other designated frequency for the bit 1. The radio frequency signal thus modulated in the bedrock and modulated to 0.1 to 2 MHz is amplified by the control stage 8 and the power stage 9 of the power amplifier. The obtained signal is sent to the antenna 12 via the antenna matching circuit 10 and the antenna switch 11.
Sent out. The antenna 12 is aimed at existing conductors, such as power cables, ventilation metal pipes, and the like.

When the device of the present invention is used for signal reception, a weak signal received by the antenna 12 on the receiving side through floor rocks, power cables, metal pipes for ventilation, etc. is received by the receiving device 14 via the antenna switch 11 and the matching circuit 13. Sent to. This receiver 14 also includes a frequency tuning circuit 15, a display unit 16, and a signal strength meter 17. The intermediate frequency signal generated by the receiver 14 is supplied to the FSK detector 18. The FSK detector 18 advantageously operates on the principle of phase synchronization. The signal obtained from the detector 18 is amplified and filtered in a separate amplification and filter stage 19 so that the bit string corresponding to the transmitted bit string is regenerated. Based on the resulting bit sequence, the digital-to-analog converter 20 produces an analog signal, which is filtered through the filter 21 to remove the effects of sample processing. After that, the signal amplified by the amplifier 22 is sent to the speaker 23 or the headphones 24.
Can be heard as a voice corresponding to the voice transmitted from.

In order to make the device of the present invention function both for transmission and reception, the tangent circuit 25 is provided for the microphone 1 as shown in FIG. 1, and transmission / reception control is executed. This T / R control unit 25 is necessary because the device of the present invention includes elements shared for transmission and reception,
Therefore, these elements require information about which operating mode they are in at each point in time. Furthermore, the receiver must be attenuated during transmission and the voltage of the transmitter circuit must be off during reception.

The antenna 12 is a common element for transmitting and receiving in the apparatus of the present invention, and its operation will be described with reference to FIG. During transmission, the antenna 12 is tuned to obtain series resonance and maximum power is available to the antenna 12 from the power stage 9. Switch 26 for reception
Are set as in FIG. 2 and parallel resonance is used to obtain maximum power from the antenna 12. The operation of the switch 26 is controlled by the control unit 25. By tuning the antenna 12 shown in FIG. 2, not only maximum power transmission but also band control of an interference signal can be performed. The antenna 12 may be, for example, a substantially circular loop antenna, but the size of the antenna 12 may be reduced, for example, by advantageously using a ferrite core in the loop antenna.

In summary, the present invention uses existing metal conductors and floor rocks installed in underground facilities, operating in the frequency band of 0.1-2MHz, which can propagate floor rocks for underground use, to facilitate two-way communication. Then, the electromagnetic wave is propagated advantageously. According to the invention,
The transmitter / receiver includes an analog / digital converter 5 and a digital / analog converter 20, respectively, and transmits / receives a digital signal converted from an analog signal between the two devices and converts it again into an analog signal for attenuation and interference by the equipment. The two-way communication is performed by compensating for the above, and the existing metal conductor for other purposes and the bedrock are used as the conductor without newly installing a communication conductor, and the floor rock propagating from 0.1 to 2MHz. It is a communication device that enables effective two-way communication at low cost by using electromagnetic waves in the frequency band of (1) and digital transmission capable of compensating for attenuation and interference.

[Brief description of drawings]

FIG. 1 is a schematic view of a device in a preferred embodiment of the device of the present invention, and FIG. 2 is an antenna circuit diagram which is advantageously applied to the embodiment of FIG. Description of main part code 1 …… Microphone 2 …… Voice amplifier 5 …… A / D converter 7 …… FSK modulator 10 …… Antenna matching circuit (transmitting side) 11 …… Antenna switch 13 …… Antenna matching circuit (Reception side) 18 …… FSK detector 20 …… D / A converter 23 …… Speaker 24 …… Headphones

Claims (4)

[Claims] 1. In an underground facility, an electromagnetic wave in a frequency band of 0.1 to 2 MHz that can favorably propagate through a bedrock is used, and the floor rock and a metal structure such as an existing metal cable pipe buried underground are used as a conductor. In the two-way communication device for underground facility, which operates using as, and has a transmitting device, a receiving device, and an antenna, the transmitting device is an analog-digital converter that converts an analog signal to be transmitted into a corresponding digital signal. A transmitting circuit that modulates a radio frequency in a frequency band of 0.1 to 2 MHz with the digital signal and transmits the radio frequency from the antenna, the antenna transmitting the modulated radio frequency to the bedrock and the metal structure. The receiving device receives the radio frequency propagated through the bedrock and the metal structure, and the receiving device demodulates the radio frequency received by the antenna into a digital signal. If, underground facilities for two-way communication device which comprises a digital-to-analog converter for converting a digital signal the demodulated into corresponding analog signals. 2. The two-way communication device according to claim 1, wherein the analog-digital converter operates based on delta modulation. 3. The two-way communication device according to claim 1 or 2, wherein, when converting a received digital signal, a detection device that operates based on frequency shift keying is provided in the receiving device. A two-way communication device for an underground facility, which is provided and detects the received digital signal. 4. The two-way communication device according to claim 1, wherein the communication device includes a transmission / reception control device for controlling transmission and reception of signals. A two-way communication device for underground facilities.