JP2003078500A - Communication device and communication method in noise environment - Google Patents

Abstract

(57) [Summary] When noise generated by an artificial noise source 8 interferes with a signal transmitted and received by transceivers 4 and 5, the influence of the noise is removed to accurately perform position detection and the like. Also receiver 5
There is no need to respond to the transmitter 4 with information on the error status from the side, and the system is simplified accordingly. A signal transmitted / received by transmission / reception means (4, 5) includes:
It is applied in a noise environment where noise generated by the artificial noise source 8 interferes. On the transmission means 4 side, the sound intensity (ratio of signal to noise: S / N ratio) is determined for each channel ch1, ch.
2... Measured for each ch8. Then, based on the measurement result, the information amount is allocated to each channel such that the information amount of the signal increases as the channel has lower noise intensity. The signals of the channels ch1, ch2,..., Ch8 are transmitted in association with the data of the assigned information amount. On the receiving means 5 side, data indicating the information amount is detected for each of the channels ch1, ch2,. Then, the signal of each channel ch is extracted based on the detected information amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device and a communication method in a noisy environment, and more particularly to a device and method suitable for transmission and reception between a transmitter and a receiver affected by noise generated by the same noise source. Is.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of the Internet, the laying of optical fiber networks has been rapidly advanced. There are two methods of laying the end part of the optical fiber network: an open-cutting method of digging a groove from the surface of the earth and laying the fiber, and a non-cutting method of digging a hole in the ground to allow the fiber to pass therethrough.
There are types.

Conventionally, the open-cutting method has been widely used, but the introduction of the non-open-cutting method is being considered because the non-open-cutting method is advantageous in view of cost, construction period, influence on the ground and the like. The horizontal drilling method is a typical non-excavation method.

The horizontal drilling method will be described with reference to FIGS. 1 and 2.

In the horizontal drilling method, as shown in FIG. 1, a shaft called a drill rod 1 is equipped with a tip end called a drill head 2 to excavate the ground. The blade 2 at the tip of the drill head 2
Excavate the ground by a. When a force F is applied to the drill rod 1 in the direction indicated by the arrow F to rotate the drill rod 1, excavation is performed in a spiral shape, and the drill rod 1 goes straight on average. However, if a strong force is applied in synchronization with a specific rotation angle, the excavation direction can be changed. For example, when a force is applied in the direction of arrow F in the posture shown in FIG. 1, the posture of the drill head 2 changes to the direction indicated by arrow G, and the excavation direction changes.

By changing the timing of the force applied to the drill rod 1 in this way, the excavation path can be changed in any direction. This is a major feature of the horizontal drilling method.

In the horizontal drilling method, the posture of the drill head 2 is changed so as to excavate along a predetermined laying line.

However, the drill head 2 deviates from the planned excavation route due to, for example, uneven soil quality in the ground. Therefore, it is necessary to detect the current position of the drill head 2 and use the detected position as a feedback amount to correct the excavation route.

As a method of detecting the position of the buried object in the ground, there is a method using a radar. However, the radar method has a problem that the exploration depth and the accuracy are in conflict with each other. It is also difficult to detect the tilt of the drill head 2.

There is also a method of performing wired communication by using an electromagnetic wave having an extremely low frequency. But according to this method,
It is necessary to connect a signal line to the drill head 2, and there are problems that the excavation range is restricted by the length of the signal line and that the efficiency is lowered due to the signal line connecting work.

There is also a method of installing a radar at the tip of the drill head 2. However, according to this method, not only the cost is increased, but also the signal line connecting work is required.

[0012] Therefore, the walk-over type position detecting method has been adopted from the viewpoint that the excavation range is not restricted and the efficiency of the signal line connecting work is not reduced, the cost is low, and the position detecting accuracy is excellent. . An example of this position detection system by the walkover method will be described with reference to FIG.

A transmitter 4 is provided on the drill head 2. Further, a position detection sensor 6 is provided on the ground. This position detection sensor 6 has a receiver 5.

On the ground, the position detection sensor 6 moves on a dolly or the like. A signal is amplitude-modulated and transmitted from the transmitter 4. The receiver 5 of the position detection sensor 6 receives the transmitted signal, and detects the moving position of the position detection sensor 6 when the intensity of the signal becomes strongest as the position of the drill head 2 in the ground. That is, the three components of the magnetic field of the radio wave transmitted from the drill head 2 are measured on the ground, and
The arrival direction is determined from the ratio of the magnetic field strengths of the components. This is done at a plurality of points to detect the position of the drill head 2.

As described above, the position detection system of the walkover system has an advantage that signals are transmitted and received wirelessly, and it is not necessary to connect a signal line to the drill head 2.

However, if the noise source 8 exists near the transmitter 4 and the receiver 5, noise generated by the noise source 8 is superimposed on the signals transmitted and received by the transceivers 4 and 5. Therefore, there is a problem that the accuracy of the position detection deteriorates due to the influence of the noise. This noise is called artificial noise, and the influence of artificial noise is particularly remarkable in urban areas.

The present invention has been made in view of these circumstances, and when noise generated by a single or a plurality of artificial noise sources interferes with a signal transmitted and received by a transceiver,
The problem to be solved is to eliminate the influence of the noise and to perform position detection and the like with high accuracy.

Further, the characteristic of the frequency spectrum of the artificial noise changes with changes in the environment and the passage of time.
Then, even if the characteristic of artificial noise changes, this invention makes it a problem to be solved by catching the change and removing the influence of noise and enabling position detection etc. to be performed accurately.

Here, regarding the communication system, there are the following techniques as conventional general technical levels.

(1) OOK (On-Off-Keying) OOK is a modulation method for expressing information with a time waveform. O
FIG. 21 shows a block diagram of OK modulation / demodulation. The time required for 1-bit transmission is defined as T1 bit, and the center frequency of the signal spectrum (carrier frequency in the case of OOK) is defined as f0.

The modulation / demodulation procedure is as follows.

First, a Hanning window function h having a width of 2T1bit
Let Fourier transform of (t) be H (ω), and the band limiting filter be H ′ (ω) = √ (H (ω)). H '
Let the inverse Fourier transform of (ω) be h ′ (t). The transmission signal is given by s (t) = f (t) {h '(t) * i (t)}. Where f (t) is the carrier wave and i (t) is the period T1b.
It is a unit impulse sequence of it, and h ′ (t) * i (t) is a convolution integral of h ′ (t) and i (t). f0 = 3
0 kHz, transmission speed is 8 kbps (T1 bit = 1/8 m
FIG. 22 shows the spectrum of the transmission signal in the case of s). From FIG. 22, the transmission rate is 8 kbp centering on f0.
It can be seen that it has a band corresponding to s.

The received signal processing is performed as follows in order to perform processing matched with the band limiting filter H '(ω) at the time of transmission.

First, S (ω) = F (ω) * (H '(ω) I
(Ω)), and R (ω) = S (ω) × H ′ (ω−ω)
0) is calculated. After that, the Fourier inverse transform r ′ (t) of R (ω + ω0) is obtained, and by sampling the value of t = nT1bit (n: integer), demodulation can be performed without interference of the preceding and following bits. However, ω0 is 2πf0, and S
(Ω) and F (ω) are Fourier transforms of s (t) and f (t), respectively.

An example of signal processing is shown in FIGS. 23 and 24.
FIG. 23 shows an OOK signal before signal processing, and FIG. 24 shows an OOK signal after signal processing. T1 bit = 50. Figure 2
As shown in Fig. 3, it can be seen that the signal "0101" is transmitted first. Looking at FIG. 24, “010
1 ”signal is t = nT1bit (n = 1, 2, 3, 4)
You can confirm that it appears in.

(2) OFDM (Orthogonal Frequency Division Multiplexing; Or
thogonal Frequency Division Multiplexing) T1bit is the time for transmitting 1 bit. In contrast to the method of sending data bit by bit at T1 bit intervals, N sub-channels divided by frequency are used to express 1-bit information on each sub-channel, and even if data is sent for each NT1 bit, the transmission rate Does not change. This transmission method is FD
M (Frequency Division Multiplexing)
g). Among FDM, OFDM is a method in which a guard band is not provided between adjacent subchannels and the orthogonality of each carrier wave is used for separation. When the frequencies of the sub-channels are orthogonal to each other, the base band signal is demodulated when the received signal is subjected to the discrete Fourier transform. OF
Modulation and demodulation of DM can be realized by using discrete Fourier transform and inverse discrete Fourier transform. As an example, BPSK (Binary Phase Shift Keyin)
FIG. 3 shows the configuration of a modulator / demodulator that realizes OFDM in g).

As shown in FIG. 3, a serial / parallel conversion circuit 40 converts a serial signal into a parallel signal, and an inverse fast Fourier transform circuit 41 converts a signal having time as a variable into a signal having frequency as a variable. To be converted. Then, the orthogonal carrier waves generated by the carrier signal generator 42 are multiplied by the signals of the respective sub-channels by the multiplier 43, and the carrier waves are phase-shift modulated. Then, the modulated wave signal of each sub-channel is transmitted from the transmitting antenna 44. The transmission signal is received by the reception antenna 45, and is multiplied by the orthogonal carrier generated by the carrier signal generator 46 by the multiplier 47. Then, the fast Fourier transform circuit 49 converts the signal having the frequency as a variable into a signal having the time as a variable, and the parallel / serial conversion circuit 50 converts the parallel signal into a serial signal to reproduce the original signal.

The operation of FIG. 3 will be described with reference to FIGS. 9 and 10.

That is, as shown in FIG. 9A, bit stream data is input and converted into data for each channel. Then, as shown in FIGS. 9B and 9A, the digital signal of each channel is converted into an analog signal of each channel.

Next, the frequency-divided signal shown in FIG. 9C is modulated into a time-divided signal as shown in FIG. 10 and transmitted.

(3) DSL (Digital Subscriber Lin
e) -DMT (Discrete Multi-Tone) system (digital subscriber line-multi-frequency carrier modulation / demodulation system) BPSK
-In OFDM, each sub-channel transmits one bit of information. However, depending on the condition of the communication path, the S / N ratio may differ depending on the channel. In this case, in a channel in which the signal is sufficiently larger than noise, a large amount of information is transmitted by reducing the quantization width and making the amplitude multi-valued. If you increase the size and reduce the information to be transmitted,
It is advantageous in terms of S / N ratio. Therefore, in the DSL-DMT system, the number of allocated bits for each channel is determined in advance from the condition of the communication path, and a signal is transmitted by OFDM.

Communication using OFDM is used in DSL and power line communication. Regarding how many bits are allocated to which channel, a method is adopted in which error status information on the receiving station side is determined in response to the transmitting station.

However, the method of responding the error information from the receiving station side to the transmitting station side requires two-way communication, which complicates the system. Therefore, if this method is applied to the position detection system described with reference to FIG. 2, the number of parts and the cost are increased, and it is difficult to employ it as a system for small-scale construction.

Therefore, the present invention further enables the effect of noise to be eliminated without the need for bidirectional communication from the receiver side to respond to the error side information toward the transmitter side, Therefore, it is a problem to be solved to enable accurate position detection and the like.

[0035]

According to a first aspect of the present invention, a predetermined frequency band is divided into a plurality of channels and transmitting means for transmitting a signal for each channel, and each channel transmitted from the transmitting means. In a communication device having a receiving means for receiving each signal, the signal transmitted and received by the transmitting and receiving means is applied under a noise environment in which noise generated by a single or a plurality of artificial noise sources interferes, On the transmitting means side, the noise intensity is measured for each channel, and based on this measurement result, the channel with the smaller noise intensity is
The information amount is assigned to each channel so that the information amount of the signal becomes large, and the signal of each channel is transmitted in association with the data indicating the assigned information amount. It is characterized in that the data indicating the amount is detected for each channel and the signal of each channel is extracted by the detected information amount.

The second invention is characterized in that, in the first invention, the data indicating the information amount is given by the most significant bit of the binary data of each channel.

As shown in FIG. 2, the devices of the first and second inventions are applied in a noise environment where the noises generated by the artificial noise source 8 interfere with the signals transmitted and received by the transmitting and receiving means 4, 5. To be done. The artificial noise source 8 may be single or plural.

On the transmitting means 4 side, as shown in FIG. 11A, the intensity of noise (ratio of signal to noise: S / N
Ratio) is measured for each channel ch1, ch2 ... ch8. Then, based on this measurement result, FIG.
As shown in, the information amount is assigned to each channel such that the smaller the noise intensity is, the larger the signal information amount is. Specifically, 3 bits (“1 1”) for ch1, ch4, and ch8 with low noise intensity.
Information amount is assigned to ch3, which has a high noise intensity,
An information amount of 0 bits (“0 0”) is assigned to ch5 and ch6.

11 (c), (d), (e),
As shown in (f), each channel ch1, ch2 ... ch
8 signals are transmitted in association with the data of the allocated information amount. For example, the binary data “1 b1 b2 b3” of the transmission signal corresponding to the channel ch1,
The most significant bit of "1 b13 b14 b15" is data indicating the allocated information amount (3 bits; "11")
Is given.

On the receiving means 5 side, as shown in FIG.
As shown in (b), (c), (d), and (e), data indicating the amount of information is detected for each channel ch1, ch2 ... ch8. For example, channel c of information frame FL1
The amplitude of the signal of h1 is the maximum signal amplitude S1ch (voltage value Vma
Since x) exceeds 1/2 (voltage value Vmax / 2), it is determined that the most significant bit is "1", and the information frame FL
The amplitude of the signal of the second channel ch1 is the maximum signal amplitude S1c.
Since it exceeds 1/2 (voltage value Vmax / 2) of h (voltage value Vmax), it is determined that the most significant bit is "1".
From the determination result of these most significant bits, the amount of information assigned to channel ch1 is "11", and it is detected that it is 3 bits.

13 (a), (b), (c),
As shown in (d), the signal of each channel ch is extracted with the detected amount of information.

For example, the information amount of channel ch1 is 3 bits, and the total number of bits is 4 bits by adding the most significant bit to this. So channels ch1 information frames FL1 is divided into levels of ^{2 4} (16). The amplitude of the signal of channel ch1 is Sch × 15/16
And is determined to be at the 15th level. Therefore, the binary data corresponding to the channel ch1 is “11
10 ”(= 15), and this binary data“ 111
“110”, which is obtained by removing the most significant bit “1” from “0”, is extracted as the signal magnitude information. This "110" is
This corresponds to the information “b1 b2 b3” of the signal of the channel ch1 of the information frame FL1 transmitted from the transmitter 4.

Thus, according to the first and second inventions,
The intensity of noise is measured on the transmitting means 4 side, and based on the measurement result, the information amount of each channel is assigned such that the information amount of the signal becomes larger as the noise intensity of the channel becomes smaller. Therefore, when the noise generated by the artificial noise source 8 interferes with the signals transmitted and received by the transceivers 4 and 5, the influence of the noise can be removed. Therefore, position detection and the like can be performed accurately.

According to the first and second inventions, the data indicating the information amount can be detected for each channel on the receiver 5 side, and the signal of each channel can be taken out by the detected information amount. Therefore, it is not necessary for the receiver 5 side to respond to the transmitter 4 side with the information on the error condition, and the system can be simply configured accordingly.

In a third aspect based on the first aspect, the transmitting means is provided on the side of the excavator for excavating the ground, and the receiving means is provided on the ground to receive the signal transmitted from the transmitting means. Depending on the intensity when received by the means,
It is characterized by detecting the position of the excavator in the ground.

According to the third invention, as shown in FIG. 2, the transmitting means 4 is provided on the excavator 3 side for excavating the ground, and the receiving means 5 is provided on the ground. Then, the position of the excavator 3 in the ground is detected according to the intensity when the signal transmitted from the transmitting unit 4 is received by the receiving unit 5.

According to the third invention, the position of the excavator 3 can be accurately detected even when the excavator 3 is operated in a noisy environment.

The fourth invention is a communication method in which a predetermined frequency band is divided into a plurality of channels, a signal is transmitted for each channel, and the transmitted signal for each channel is received. It is applied under the noise environment where the noise generated by the artificial noise source interferes with the transmitted and received signals, and the noise intensity is small based on the process of measuring the noise intensity for each channel and the measurement result. Assigning an information amount to each channel so that the information amount of the signal becomes larger for each channel, and transmitting the signal of each channel in association with the data indicating the assigned information amount, Receiving the transmitted signal,
Detecting the data indicating the amount of information for each channel,
Extracting the signal of each channel with the detected amount of information.

The fifth invention is characterized in that, in the fourth invention, the data indicating the information amount is given by the most significant bit of the binary data of each channel.

The fourth and fifth inventions are obtained by replacing the device inventions of the first and second inventions with a method invention.

In a sixth aspect of the present invention, in the fourth aspect, when the frequency spectrum characteristic of the measured noise intensity changes, the step of changing the amount of information assigned to each channel according to the change. It is characterized by further including.

According to the sixth aspect of the present invention, when the characteristic of the frequency spectrum of the artificial noise changes due to the change of environment, the change of the artificial noise is captured and each channel ch.
1, the amount of information assigned to ch2 ... ch8 is changed, and the changed data is transmitted in real time.

Therefore, even in an environment in which the frequency characteristic of noise changes from moment to moment, position detection and the like can be performed accurately.

[0054]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of the apparatus of the embodiment. FIG. 5 is a block diagram showing the signal processing of the embodiment. In this embodiment, it is assumed that the position of the underground excavator 3 is detected as described with reference to FIG. In this embodiment, it is assumed that artificial noise is generated in the noise source 8 shown in FIG.

First, the characteristics of artificial noise will be described. Here, artificial noise is noise that has non-uniform frequency characteristics in a predetermined frequency band, and changes in the environment (changes in time)
It is used in the sense of noise whose frequency characteristic changes according to. It is distinguished from white noise, which has a substantially uniform frequency characteristic, in that it has a non-uniform frequency characteristic.

Artificial noise has several characteristics that distinguish it from white noise. This will be described with reference to actual noise measurement results shown in FIGS.

FIG. 14 shows 2000 in Minosato-cho, Gunma-gun, Gunma prefecture.
The frequency spectrum of the noise measured for 1.25 seconds from 9: 2: 18 on April 18, 2014 is shown. Within this measurement time, no anticorrosion current (current for corrosion prevention) is flowing through the gas pipe (steel pipe) buried about 1 m underground. 14
The horizontal axis indicates the frequency, and the vertical axis indicates the noise intensity (power). The measurement is done on the ground and the sampling rate is 4
It is 00 kHz. FFT was performed at 1600 points to obtain a power spectrum, and the results shown in FIG. 14 were obtained through signal processing for averaging five consecutive spectra.

As shown in FIG. 14, except for the line spectrum component around 50 kHz, the intensity is distributed almost uniformly in the entire frequency band and can be regarded as almost white noise.

FIG. 15 shows the same place as in FIG.
The frequency spectrum of the noise measured for 0.2 seconds from 10:54:29 on May 5 is shown. The measurement conditions and the signal processing method are the same as in FIG. However, in FIG.
Unlike 4, the anticorrosion current flows through the gas pipe within the measurement time.

As shown in FIG. 15, a line spectrum having a width of about 3 kHz, which is about 10 dB stronger than the surroundings, is seen near 50 kHz. Further, it can be seen that the spectral components having 10 to 15 dB stronger than the periphery and having almost no width are distributed at intervals of about 1.5 kHz. Comparing FIG. 14 and FIG. 15, it can be seen that the average power of noise increases by nearly 20 dB due to the flow of anticorrosion current.

FIG. 16 shows 2 in front of a private house in Isehara City, Kanagawa Prefecture.
From 11:51:33 on April 14, 000 to about 0.6
The frequency spectrum of noise measured for 2 seconds is shown.
In front of the private house is a residential alley. The measurement conditions and the signal processing method are the same as in FIG.

As shown in FIG. 16, it can be seen that there is a channel in which noise energy is concentrated near about 50 kHz.

Comparing FIG. 14 with FIGS. 15 and 16,
In FIG. 14, the noise is uniformly distributed over the entire frequency band and has a substantially flat spectrum, whereas in FIGS. 15 and 16, it can be seen that there is a channel in which noise energy is concentrated. . Further, it can be seen that there are two types of noise, one having a single wide and extremely strong peak, and the other having various intensities but almost no width. Depending on the measurement location, either one of these two types may be present, but in most cases these two types of noise are considered to occur simultaneously.

When a train runs, a current is induced in the rail, which causes noise. Next, the analysis result of the artificial noise measured on the rail side of the train will be described.

FIG. 17 shows the frequency spectrum of noise measured for about 10 minutes at the side of the railroad near Tokai University front station on the Odakyu line in Hadano, Kanagawa prefecture. The measurement is performed on the ground and the sampling rate is 352.8 kHz. Fifty
FFT is performed at 000 points to obtain the power spectrum, and 2
The result shown in FIG. 17 was obtained through signal processing for averaging 0 spectra. The vertical axis of FIG. 17 shows the value of the value of each channel normalized by the average value in dB.

As shown in FIG. 17, a very strong peak is seen around 63 kHz, and it can be seen that the peaks are distributed at equal intervals apart from this.

Next, the time change of the spectrum of FIG. 17 will be described. The frequency band 0 to 88.2 kHz in FIG. 17 is divided into five regions at equal intervals, and the regions 1 to
Name it 5. FIG. 18 shows the result of obtaining the maximum value (dB) of the regions 1 to 5 every about 2 seconds. The horizontal axis of FIG. 18 represents time and the vertical axis represents normalized noise intensity in dB.

As shown in FIG. 18, from the start of measurement to 3.7 minutes later, there is not much change in each region except that the value of region 4 fluctuates by about 10 dB in a cycle of about 10 seconds.
After that, the value of the noise intensity of the regions 4 and 5 suddenly decreases,
It can be seen that it gradually increases with the passage of time. Considering the measurement location, this is considered to be a change accompanying the passage of a train.

The frequency spectrum about 4 minutes after the start of measurement is shown in FIG.

Comparing FIG. 19 and FIG. 17, in FIG.
It can be seen in FIG. 19 that the very strong peak around 63 kHz and the peaks distributed at equal intervals disappear.

FIG. 20 shows the frequency spectrum about 8 minutes after the start of measurement.

Comparing FIG. 20 with FIG. 17 and FIG. 19, the very strong peak in the vicinity of 63 kHz in FIG.
Although it disappears in FIG. 20, it can be seen that the equally spaced peaks that disappeared in FIG. 19 reappear in FIG.

From these facts, it is considered that the very strong peak seen in the vicinity of 63 kHz in FIG. 17 is "noise generated by passing a train".

From the above, the frequency spectrum of the artificial noise may have strong peaks at specific frequencies or peaks distributed at substantially equal intervals, but the frequency spectrum characteristics are such as location and situation. It can be seen that the change in the environment changes rapidly in a short time.

Therefore, a structure capable of transmitting and receiving a signal by catching the change of the artificial noise which changes rapidly in such a short time will be described.

(Outline of Embodiment) The artificial noise is characterized in that the energy of the noise is different for each frequency region and that the frequency characteristic changes in a short time due to the change of the environment.

Of these, the fact that the noise energy differs depending on the frequency region is dealt with by selecting a channel by OFDM and transmitting information. Since the artificial noise has different noise intensities depending on the channel, in the channel with weak noise, the quantization width is reduced to multi-value the amplitude and increase the amount of information to be transmitted. On the contrary, in a noisy channel, the amount of information is reduced by increasing the quantization width. The DSL-DMT system is a modulation system suitable for this purpose, and this system is adopted in the embodiment.

In the general DSL-DMT system, after the number of allocated bits for each channel is decided, it is kept fixed and is not changed. This cannot deal with artificial noise whose frequency characteristics change dynamically.

Therefore, by adding a configuration for dynamically changing the number of allocated bits of each channel to the DSL-DMT system, it is possible to cope with artificial noise in which the frequency characteristic changes in a short time due to a change in environment.

FIG. 4 is a block diagram showing the configuration of the apparatus of the embodiment.

In the search coil 10 of the transmitter 4, the noise generated by the noise source 8 is measured. The noise source 8 is the artificial noise source described in FIG. 2, and may be a single source or multiple sources. The output signal of the search coil 10 is passed through the preamplifier 11 to A
It is input to the / D converter 12. The analog signal is converted into a digital signal in the A / D converter 12 and input to the data processing device 13.

The data processing device 13 determines the number of bits to be assigned to each channel in the frequency band of the transmission signal based on the noise measurement result, and performs processing such as constructing an information frame as described later with reference to FIG. This is executed, and the transmission signal of one cycle shown in FIG. 6 is generated.

The one-cycle transmission signal output from the data processing device 13 is converted into an analog signal by the D / A converter 14 and transmitted.

On the other hand, the search coil 15 of the receiver 5 receives the signal transmitted from the transmitter 4. The signal received by the search coil 15 contains noise generated by the noise source 8. The output signal of the search coil 15 is input to the A / D converter 17 via the preamplifier 16. A / D
The converter 17 converts the analog signal into a digital signal and inputs the digital signal to the data processing device 18.

The data processor 18 detects the allocated bit information of each channel from the received signal, and the transmitter 4
A process of analyzing the information frame transmitted from the device and detecting the position and tilt of the drill head 2 is executed. Further, the timing and amount for correcting the position and inclination of the drill head 2 are calculated, and the force F is applied to the drill rod 1 at a predetermined timing according to the calculation result. This corrects the position and tilt of the drill head 2. The correction of the drill head 2 is repeatedly performed at regular intervals.

FIG. 5 is a block diagram showing the processing contents of signal modulation / demodulation according to the embodiment.

The noise measuring section 20 of the transmitter 4 measures the noise of the noise source 8 and inputs the measurement result to the FFT (Fast Fourier Transform) section 21. The FFT unit 21 divides the noise frequency band into a plurality of channels.

The data of the maximum signal amplitude (strength) S1ch of each channel of the signal to be transmitted from the transmitter 4 is input to the synchronous frame composing unit 25, and the synchronous frame composing unit 25 constructs the synchronous frame FC shown in FIG. To be done. The synchronization frame Fc is input to the IFFT (Fast Inverse Fourier Transform) unit 26. The IFFT unit 26 time-divisionally outputs the synchronization frame FC.

The comparison / bit allocation unit 22 compares the maximum signal amplitude S1ch and the noise amplitude for each channel to determine the number of bits to be allocated for each channel.

The allocation bit number determined by the comparison / bit allocation unit 22 is input to the information frame construction unit 23. The information frame configuration unit 23 associates the information about the amplitude of the signal for each channel with the number of allocated bits to construct the information frame FL shown in FIG. The information frame FL is input to the IFFT unit 24. IFFT
In the section 24, the information frame FL is time-divided and output.

The synchronous frame FC output from the IFFT unit 26 and the information frame FL output from the IFFT unit 24 are input to the 1-cycle composing unit 27, and the 1-cycle transmission signal shown in FIG. 6 is constructed and transmitted. It is transmitted from the machine 4.

The noise generated by the noise source 8 is added to the transmitted signal by the adder 28 and received by the receiver 5.

The FFT section 32 divides the frequency band of the received signal into a plurality of channels. Further, the noise of the noise source 8 is measured by the noise measuring unit 30 and input to the FFT unit 31. The FFT unit 31 divides the noise frequency band into a plurality of channels.

The subtracting unit 33 executes a process of subtracting the noise signal output from the FFT unit 31 from the received signal output from the FFT unit 32 for each channel.

The signal output from the subtractor 33 is input to the most significant bit detector 34 and the information extractor 35. The most significant bit detection unit 34 detects the number of allocated bits for each channel, and the detected number of allocated bits is input to the information extracting unit 35. The information extraction unit 35 extracts information on the magnitude of the signal amplitude of each channel based on the information on the number of allocated bits for each channel.

Next, with respect to the contents of the bit allocation process and the information frame construction process executed by the data processing device 13 on the transmitter 4 side of FIG. 4, and the contents of the signal modulation process executed by the transmitter 4 shown in FIG. explain.

In this embodiment, a signal is transmitted from the transmitter 4 by the DSL-DMT method.

Therefore, the DSL-DMT system will be described first.

In the DSL-DMT system, the frequency band of the signal to be transmitted is divided into a plurality of frequency regions, that is, a plurality of channels. Then, an inverse Fourier transform of this by IFFT is defined as one frame.

It is assumed that the width of the frequency band is B and the channel is divided into Nch channels. The channel interval is Δf,
When the length of one frame is T1flame, T1flame is given by the following equation.

[0102] Also, the time required for 1-bit transmission by the OOK method is T1bit.
And At this time, the information rate transmission rate is 1 / T1 bit. In the OOK method, information is transmitted bit by bit for every T1 bit. However, in the DSL-DMT system, information is divided into blocks and transmitted. When the number of information bits in one block is N bits, T1flame = NT1bit. Further DS
In the L-DMT method, a plurality of bits are assigned to one channel.

If the maximum M bits are assigned to one channel, the maximum number of bits that can be sent in one frame is given by nmax = MNch.

However, the number of allocated bits is actually changed according to the S / N ratio of each channel. The average bit allocation rate is R (0 <R ≦ 1), and this is called a rate. When this rate R is used, the total number of transmission bits Nall is Nall = Rn
It can be expressed as max = MRNch.

Even if the frequency band is the same, the selectable channel changes depending on the center frequency. This center frequency is set to f0.

As described above, the parameter of the signal of the DSL-DMT system is the time T1bit required for 1-bit transmission,
Center frequency f0, number of quantization bits M, number of channels Nch,
There are five parameters of rate R.

One frame of a signal is formed by combining the frames defined as described above. A schematic configuration of one cycle is shown in FIG.

As shown in FIG. 6, one cycle is composed of three types of frames: a silent frame FS, a synchronization frame FC, and an information frame FL. One cycle includes one silent frame FC, one synchronization frame FC, and a plurality of information frames FL.
The functions of each of these three types of frames are as follows.

That is, in this embodiment, since a series of information is sent using a plurality of frames, it is necessary to synchronize these. Therefore, the synchronization frame FC is required. The maximum amplitude S1c of each channel is included in the synchronization frame FC.
Contains information for h.

The silent frame FS immediately before the sync frame FC is not transmitted. This silent frame FS
In between, the noise is measured. Also silent frame F
S makes it easy to detect the start of the synchronization frame FC.

In this embodiment, unlike the normal DSL-DMT system, the number of allocated bits for each channel dynamically changes. Therefore, it is necessary to transmit the current allocated bit number from the transmitter 4. The most significant bit of each information frame FL is used to transmit the allocated bit number information.

FIGS. 11A and 11B are views for explaining the process of assigning the number of bits to each channel.

That is, as shown in FIG. 5, the noise measuring unit 20 of the transmitter 4 measures the noise of the noise source 8 during the silent frame FS. The measurement result is input to the FFT unit 21. In the FFT unit 21, as shown in FIG. 11A, noise frequency bands are eight channels ch1 and ch.
It is divided into 2 ... ch8.

In the comparison / bit allocation unit 22, the maximum signal amplitude S1ch and the noise amplitude are compared for each channel to determine the number of bits to be allocated for each channel. In this case, the number of bits is assigned such that the information amount of the signal increases as the noise intensity of the channel decreases. Specifically, as shown in FIG. 11A, the ratio of signal power to noise power is calculated as the S / N ratio, and this S / N ratio is 4
Every time the number exceeds (= 6 dB), 1 bit is assigned to the channel. As a result, as shown in FIG. 11B, 3 bits (“11”) are allocated to the channel ch1, 1 bit (“01”) is allocated to the channel ch2, and 0 bit (“” is allocated to the channel ch3. 00 ") is assigned, and channel ch4 has 3 bits (" 11 ").
Is assigned to channel ch5 and 0 bit (“0
0 "), 0 bits (" 00 ") are assigned to channel ch6, 3 bits (" 11 ") are assigned to channel ch7, and 2 bits (" 10 ") are assigned to channel ch8. To be

FIG. 7 is a flow chart showing the procedure of processing for assigning the number of bits to each channel. However, b
Is the number of allocated bits.

That is, as shown in FIG. 7, the noise is subjected to fast Fourier transform (FFT) and frequency-divided into each channel, and the noise power PN of each channel is obtained (step 101). Next, the allocated bit number b is M-1.
One bit is allocated to the channel having the smallest noise power PN among the channels below (step 102). Next, the noise power PN of the assigned channel is multiplied by 4 (step 103). The above process is repeated until the total number of bits, which is the total number of allocated bits of all channels, becomes N (step 104). Finally, 1 bit is assigned to all channels to express the information of the number of assigned bits to be b + 1 bits.

However, in the worst case, the algorithm shown in FIG. 7 requires about Nch calculations for each loop, which takes a very long time.

Here, since the average number of allocated bits of each channel is given by n = (Nall-Nch) / Nch = MR-1, the bit number allocation processing can be speeded up by the algorithm shown in FIG. . Here, ni is the maximum number of allocated bits of channel i, Bi is the number of roughly allocated bits of channel i, and ri is a bit margin indicating how many bits are left after allocating Bi bits.
Q is the number of bits to be adjusted.

The flowchart of FIG. 8 will be described below.

That is, first, noise is subjected to fast Fourier transform (FFT) and frequency-divided into each channel, and the noise power PN of each channel is obtained (step 20).
1). Next, the average value PN of noise power is obtained (step 202).

Next, assuming that the noise power of channel i is PNi, the maximum number of allocated bits ni of channel i can be obtained by the following equation.

[0122] (Step 203) Next, the rough allocation bit number Bi of the channel i is Bi = [ni] (0≤Bi≤M-1)
Is asked for. Here, "[]" means that the fractional part is truncated (step 204).

Thereafter, the bit margin ri and the number of bits Q to be adjusted are ri = ni-Bi, (Steps 205 to 210).

Next, it is judged whether or not Q> 0 (step 211). If Q> 0, Bi <M-1.
Among the channels having the following, +1 is added to the channel having the maximum ri and −1 is added to the ri (step 21).
2). Next, Q is decremented by 1 (step 213). The processing of these steps 212 and 213 is repeated until Q = 0 (step 214). Similarly, in the case of Q <0, among the channels with Bi> 0, the channel with the minimum ri is incremented by -1 and ri is incremented by 1 (step 215). Next, Q is incremented by 1 (step 2
16). The processing of these steps 215 and 216 is Q = 0.
It is repeated until (step 217).

One bit is further allocated to the rough allocation bit number Bi of each channel i thus obtained. Let the total number of bits of the confirmed channel i be bi (number of allocated bits + 1 bit).

Next, a transmission signal is constructed based on the determined total number of bits bi.

When all the bits bi of each channel i are determined, the synchronization frame FC is first constructed.

The amplitude spectrum of the synchronization frame FC has a fixed pattern, and the maximum signal amplitude S1ch is assigned to the channel for transmitting the signal. Letting Eb be the energy per signal bit, the maximum signal amplitude S1ch is S1ch =
√ (Eb) × Δf

11 (c), (d), (e), and (f) are diagrams for explaining the process of forming the information frame FL.

That is, the information frame construction unit 2 shown in FIG.
3 constructs the information frame FL shown in FIG. 6 by associating the number of assigned bits with the information on the amplitude of the signal of each channel. At this time, the information of the bit allocation number of the channel i is added to the most significant bit of each channel of the information frame FL, and the lower bit of each channel of the information frame FL has the magnitude of the signal of the channel i. Information is given.

The process of adding information to each bit of the total number of bits bi of channel i will be described below with reference to FIG.
Description will be given with reference to (c), (d), (e), and (f).

FIG. 11C shows the first information frame FL1.
Shows the configuration of.

Since the number of allocated bits of the channel ch1 is 3 bits ("11") (FIG. 11 (b)), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Become. Information of the high-order bit “1” of the allocated bit number “11” is given to the highest-order bit of the channel ch1. Further, the lower three bits b1, b2, b3 of the channel ch1 are provided with the information "110" of the signal magnitude of the channel ch1.

Since the number of allocated bits of the channel ch2 is 1 bit ("01") (FIG. 11B), the total number of bits bi is 2 bits obtained by adding 1 bit to the number of allocated bits of 1 bit. Becomes Information of the high-order bit “0” of the allocated bit number “01” is given to the highest-order bit of the channel ch2. Further, information "1" of the signal magnitude of the channel ch2 is added to the lower 1 bit b4 of the channel ch2.

Since the number of allocated bits of the channel ch3 is 0 bit (“00”) (FIG. 11 (b)), the total number of bits bi is 1 bit obtained by adding 1 bit to the allocated number of 0 bits. Becomes Information of the high-order bit “0” of the allocated bit number “00” is given to the highest-order bit of the channel ch3.

Since the number of allocated bits of the channel ch4 is 3 bits (“11”) (FIG. 11 (b)), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Becomes Information of the high-order bit “1” of the allocated bit number “11” is given to the highest-order bit of the channel ch4. Further, the lower three bits b5, b6, b7 of the channel ch4 are provided with information "000" of the signal magnitude of the channel ch4.

Since the number of allocated bits of channel ch5 is 0 bit (“00”) (FIG. 11 (b)), the total number of bits bi is 1 bit obtained by adding 1 bit to the allocated number of 0 bits. Becomes Information of the high-order bit “0” of the allocated bit number “00” is given to the highest-order bit of the channel ch5.

Since the number of allocated bits of channel ch6 is 0 bit ("00") (FIG. 11 (b)), the total number of bits bi is 1 bit obtained by adding 1 bit to the allocated number of 0 bits. Becomes Information of the high-order bit “0” of the allocated bit number “00” is given to the highest-order bit of the channel ch6.

Since the number of allocated bits of channel ch7 is 3 bits ("11") (FIG. 11B), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Becomes The information of the high-order bit “1” of the allocated bit number “11” is given to the highest-order bit of the channel ch7. Further, the lower 3 bits b8, b9, b10 of the channel ch7 are provided with information "010" of the signal magnitude of the channel ch7.

Since the number of allocated bits of the channel ch8 is 2 bits ("10") (FIG. 11B), the total number of bits bi is 3 bits obtained by adding 1 bit to the number of allocated bits of 2 bits. Becomes Information of the high-order bit “1” of the allocated bit number “10” is given to the highest-order bit of the channel ch8. Further, information “11” of the signal magnitude of the channel ch8 is given to the lower two bits b11 and b12 of the channel ch8.

FIG. 11 (d) shows the amplitude of the signal of each channel of the information frame FL1 shown in FIG. 11 (c).

The maximum signal amplitude S1ch (voltage value Vmax) of each channel is divided into 2 ^bi levels, and the signal amplitude of each channel is obtained based on the data shown in FIG. 11 (c).

For example, channel ch1 is divided into 2 ⁴ (16) levels. This channel ch1
The data "1 b1 b2 b3" corresponding to
Since it is “0” (= 15), the amplitude of the signal of the channel ch1 is Sch × 15/16.

FIG. 11E shows the structure of the information frame FL2 following the information frame FL1.

Since the number of allocated bits of the channel ch1 is 3 bits (“11”) (FIG. 11B), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Become. Information of the lower bit “1” of the allocated bit number “11” is given to the most significant bit of the channel ch1. Furthermore, the lower 3 bits b13, b14, b15 of the channel ch1 are set to the channel ch1.
The signal magnitude information “101” is added.

Since the number of allocated bits of the channel ch2 is 1 bit (“01”) (FIG. 11 (b)), the total number of bits bi is 2 bits obtained by adding 1 bit to the number of allocated bits of 1 bit. Becomes Information of the lower bit “1” of the allocated bit number “01” is given to the most significant bit of the channel ch2. Further, information "1" on the signal magnitude of the channel ch2 is added to the lower 1 bit b16 of the channel ch2.

Since the number of allocated bits of channel ch3 is 0 bit ("00") (FIG. 11B), the total number of bits bi is 1 bit obtained by adding 1 bit to the number of allocated bits of 0 bit. Becomes Information of the lower bit “0” of the allocated bit number “00” is given to the most significant bit of the channel ch3.

Since the number of allocated bits of the channel ch4 is 3 bits (“11”) (FIG. 11B), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Becomes Information of the lower bit “1” of the allocated bit number “11” is given to the most significant bit of the channel ch4. Further, the lower three bits b17, b18, and b19 of the channel ch4 are set to the channel ch4.
The signal magnitude information “101” is added.

Since the number of allocated bits of channel ch5 is 0 bit ("00") (FIG. 11 (b)), the total number of bits bi is 1 bit obtained by adding 1 bit to the allocated number of 0 bits. Becomes Information of the lower bit “0” of the allocated bit number “00” is given to the most significant bit of the channel ch5.

Since the number of allocated bits of channel ch6 is 0 bit ("00") (FIG. 11 (b)), the total number of bits bi is 1 bit obtained by adding 1 bit to the allocated number of 0 bits. Becomes Information of the lower bit “0” of the allocated bit number “00” is given to the most significant bit of the channel ch6.

Since the number of allocated bits for channel ch7 is 3 bits ("11") (FIG. 11B), the total number of bits bi is 4 bits obtained by adding 1 bit to the number of allocated bits of 3 bits. Becomes The information of the lower bit "1" of the allocated bit number "11" is given to the most significant bit of the channel ch7. Further, the lower three bits b20, b21, b22 of the channel ch7 are set to the channel ch7.
The information “001” on the signal magnitude is added.

Since the number of allocated bits of the channel ch8 is 2 bits (“10”) (FIG. 11 (b)), the total number of bits bi is 3 bits obtained by adding 1 bit to the number of allocated bits of 2 bits. Becomes Information of the lower bit “0” of the allocated bit number “10” is given to the most significant bit of the channel ch8. Further, information "01" on the signal magnitude of the channel ch8 is given to the lower two bits b23 and b24 of the channel ch8.

FIG. 11 (f) shows the signal amplitude of each channel of the information frame FL2 shown in FIG. 11 (e).

The maximum signal amplitude S1ch (voltage value Vmax) of each channel is divided into 2 ^bi levels, and the signal amplitude of each channel is obtained based on the data shown in FIG. 11 (e).

For example, channel ch1 is divided into 2 ⁴ (16) levels. This channel ch1
The data corresponding to "1 b13 b14 b14" is "110
1 ”(= 14), the amplitude of the signal of channel ch1 is Sch × 14/16.

As described above, each information frame FL1, FL
Information on the number of allocated bits of each channel i is added to the most significant bit of each channel of No. 2. In this case, even for channels (channels ch3, ch5, and ch6) where the number of allocated bits is 0 due to strong noise, the most significant bit is used to express the number of allocated bits. However, since an error may occur when the signals are combined, the information frame FL3 and the information frame FL are further added.
4 is added to give a sufficient redundancy, and the error is corrected. Also, the information frame FL
Information about the magnitude of the signal is given to the lower bits of the channels 1 and FL2.

Next, the error correction of this embodiment will be described.

Consider a case where an m-fold error is corrected using, for example, a BCH code. Assuming that the BER (bit error rate) when the BCH code is not used is p, the error is not corrected after the error correction is performed when m + 1 or more errors occur. Therefore, the BER corrected by the BCH code is reduced to p ^{m + 1} .

First, the BER required to obtain information on the number of allocated bits from the most significant bit of each information frame will be described.

Transmission rate 8 kbps, number of bits N = 150
If the communication is carried out according to, the length of one frame of the signal (transmission time) is 18.75 ms. If the maximum bit number M of one channel is M = 3, the total bit number of each channel is 1
Since it is ~ 3, it can be expressed by 2 bits. If the information frame FL is composed of 4 frames in consideration of error correction, 1
The cycle is 6 frames long (transmission time) 112.5
ms. If you request an error rate such that an error will occur once in one hour of communication, the error rate will be 3.1 × 1 in one cycle.
0 becomes about ^-5.

If the number of channels Nch is Nch = 200,
The number of bits required to express the number of allocated bits for each channel is 400 bits. B required for this
If ER is p1, 1- (1-p1) ⁴⁰⁰ ≦ 3.6
From × ^{10 -5,} it is about p1 = 7.8 × ^{10 -8.}

Considering that a channel having a large noise intensity is included, the BER when the BCH code is not used is pr
= 0.01, quadruple error correction is required to satisfy the request. In order to correct the t-fold error using the BCH code, an error correction code can be created by using check bits of mt bits or less for a code length of 2 ^m -1. If m = 7 (1 block = 127 bits), 28 check bits are required at the maximum. Therefore, the number of information bits is 99 bits or more, and encoding can be performed with sufficient margin by performing encoding of 5 blocks. At this time, the total number of bits becomes 635, and the number of allocated bits can be expressed by the most significant bit of 4 frames.

BE when the BCH code is not used
When R is set to pr = 0.001, triple error correction is sufficient, and therefore, when calculated in the same manner, m = 7 can be encoded in 4 blocks, and the information frame FL can be 3 frames. However, when the number of frames is three, it is impossible to perform coding with a margin.

The error rate required when re-analyzing the information frame FL is about 10 ⁻⁶ . For this reason, if an attempt is made to correct a double error, triple error correction is required to realize an error rate of 10 ⁻² when the BCH code is not used. Also, double error correction is required to achieve an error rate of 10 ⁻³ . Similarly, when the BCH code is used, if one block of m = 8 is coded when N = 150, it is possible to code with a margin in either case.

Next, the contents of the allocated bit number detection process, the signal size information extraction process executed by the data processing device 18 on the receiver 5 side of FIG. 4, and the signal executed by the receiver 5 shown in FIG. The content of the demodulation process of will be described.

In the receiver 5, first, noise is measured during the silent frame FS shown in FIG. In the horizontal drilling method constructed in Japan, the distance between the drill head 2 (transmission side) and the position detection sensor 6 (reception side) is 1 m.
Very close to the degree. Therefore, the signal delay time is about 10 ns, where the relative permittivity in the ground is 10.

On the other hand, in the case of this embodiment, the transmission rate is 8 kbps, the number of bits is N = 150, and 1
The frame length (transmission time) is 18.75 ms. Therefore, the delay time is much smaller than the transmission time. Therefore, it may be considered that the transmitter 4 and the receiver 5 measure noise almost at the same time. Therefore, the noise measured by the receiver 5 can be regarded as substantially the same as the noise near the drill head 2 on the transmitter 4 side.

That is, the noise of the noise source 8 is measured by the noise measuring unit 30 shown in FIG. 5 and input to the FFT unit 31.
In the FFT unit 31, the noise frequency band is a plurality of channels c
h1, ch2 ... ch8 is divided into noise amplitude (strength)
Is calculated for each channel.

The receiver 5 is then synchronized. The silent frame FS is only noise, and the amplitude of the time-divided signal shows a very small value.

Therefore, when the amplitude of the received signal exceeds a certain threshold value, it can be determined that the synchronization frame FC has started.

When the synchronization frame FC is detected, the subtraction unit 33 shown in FIG. 5 subtracts the noise power spectrum output from the FFT unit 31 from the power spectrum of the synchronization frame FC output from the FFT unit 32. The processing is executed, and the maximum signal amplitude S1ch of each channel is obtained from the amplitude spectrum obtained by taking the square root. Here, it is assumed that the maximum signal amplitude S1ch has the same value in each channel.
In this embodiment, the maximum signal amplitude is S1ch for simplicity.
Is known.

Power spectrum of noise and synchronization frame FC
It is preferable that the power spectrum of the above is time-averaged using the filter described below, instead of directly relying on the value measured at that time.

A case of obtaining the noise power spectrum N0 will be described. Letting the power spectrum measured at that time be N0, i, the time average value N0, i regarded as the noise power spectrum at that time is defined as follows.

[0174] Here, β (0 <β ≦ 1) is a value indicating how reliable the value measured at that time is, and N0, i is the average value up to the immediately preceding cycle. At this time, And the coefficient decreases exponentially, so (1-
β) ^{l for which l−1} = 1 / e is defined as the effective width of the filter.

As an example, the length of one frame (transmission time)
Is 12.5 ms, and 8 frames = 100 ms is one cycle. As described with reference to FIG. 18, noise is 1
It is assumed that the cycle changes in a 0 second cycle. Consider a case where the effective width l of the filter is set to about 1 second. At this time, (1
−β) ^{1 / 0.1} = 1 / e, so β =
It may be about 0.105.

Particularly, as shown in FIGS. 14 and 15, when the data length of the noise data is short, the noise power spectrum N
0 can be obtained, for example, by averaging the noise power spectra of the first 5 frames. When the information frame FL is detected, the subtraction unit 33 shown in FIG.
The process of subtracting the power spectrum of the noise output from the FFT unit 31 is executed from the power spectrum of the information frame FL output from, and the square root is taken to obtain the amplitude spectrum of the signal to which the noise fluctuation is added. can get. As described with reference to FIG. 18, the noise power spectrum hardly changes in a short time unless there is a change in the situation such as passing a train. Therefore, the influence of noise can be suppressed by subtracting the noise power spectrum.

FIG. 12 is a diagram for explaining the process of extracting information on the number of allocated bits from the most significant bit of each channel.

That is, as shown in FIG. 5, the signal output from the subtractor 33 of the receiver 5 is the most significant bit detector 34.
, And the most significant bit detector 34 detects the number of allocated bits for each channel. This is shown in FIG.
Description will be given with reference to (a), (b), (c), (d), and (e).

FIG. 12A shows the signal amplitude of each channel of the information frame FL1.

First, only the most significant bit of each channel of the information frame FL1 is detected. That is, the synchronization frame FC
1 / of the maximum signal amplitude S1ch (voltage value Vmax) obtained from
Logic "1" depending on whether it exceeds 2 (voltage value Vmax / 2)
Or logical "0".

Since the signal amplitude of the channel ch1 exceeds 1/2 (voltage value Vmax / 2) of the maximum signal amplitude S1ch (voltage value Vmax), the most significant bit of the channel ch1 is detected as "1". To be done.

The signal amplitude of channel ch2 is 1/2 (voltage value Vmax / of the maximum signal amplitude S1ch (voltage value Vmax)).
Since it does not exceed 2), the most significant bit of channel ch2 is detected as "0".

Other channels ch3, ch4, ch5, c
Similarly, the most significant bit is detected for h6, ch7, and ch8, and as shown in FIG.
The most significant bit of each channel of 1 is obtained.

FIG. 12C shows the signal amplitude of each channel of the information frame FL2.

As for the information frame FL2, like the information frame FL1, only the most significant bit of each channel is detected. The detection result of the most significant bit of each channel of the information frame FL2 is shown in FIG.

The detection result of the most significant bit of each channel of the information frame FL1 shown in FIG. 12 (b) and FIG. 12 (d)
Based on the detection result of the most significant bit of each channel of the information frame FL2 shown in, information on the number of allocated bits of each channel is obtained as shown in FIG.

That is, the most significant bit of the channel ch1 is "1" for the information frame FL1 and "1" for the information frame FL2, so "11".
Therefore, the number of allocated bits is extracted as 3 bits (“11”).

Similarly, the number of allocated bits of channel ch2 is extracted as 1 bit (“01”), and channel c is extracted.
The allocated bit number of h3 is extracted as 0 bit (“00”), the allocated bit number of channel ch4 is extracted as 3 bit (“11”), and the allocated bit number of channel ch5 is 0 bit (“ 00 ”), the number of allocated bits of channel ch6 is extracted as 0 bit (“ 00 ”), and the number of allocated bits of channel ch7 is extracted as 3 bits (“ 11 ”). It is extracted that the number of allocated bits of ch8 is 2 bits (“10”).

Generally, assuming that the number of frames of the information frame FL is Ninfo, from the information amount of Ninfo · Nch bits,
Information on the number of allocated bits can be acquired.

FIG. 13 is a diagram for explaining the processing for re-analyzing the information frame FL to extract the signal magnitude information.

That is, as shown in FIG. 5, the information extracting section 35 of the receiver 5 extracts the information on the amplitude of the signal of each channel based on the information on the number of allocated bits for each channel. 13 (a), (b),
Description will be given with reference to (c) and (d) together.

By adding the most significant 1 bit to the number of allocated bits shown in FIG. 12E, the total number of bits bi of each channel i can be obtained. Channel ch1 has a total bit number bi of 4 bits, channel ch2 has a total bit number bi of 2 bits, channel ch3 has a total bit number bi of 1 bit, channel ch4 has a total bit number bi of 4 bits, and channel ch5 has a total bit number bi of 4 bits. The total bit number bi of 1 is 1 bit, and the total bit number bi of channel ch6
Is 1 bit, the total bit number bi of channel ch7 is 4 bits, and the total bit number bi of channel ch8 is 3
Become a bit.

Next, the maximum signal amplitude S1ch of each channel
The (voltage value Vmax) is divided into 2 ^bi levels based on the total number of bits bi. Then, it is determined what level the amplitude of the signal of each channel is, and binary data is obtained from the determination result. Since the information about the number of allocated bits is given to the most significant bit of this binary data, the signal magnitude information is extracted from the lower bits except the most significant bit.

FIG. 13A shows the divided signal amplitude of each channel of the information frame FL1 shown in FIG. 12A.

Since the total number of bits bi of the channel ch1 is 4 bits, it is divided into 2 ⁴ (16) levels. The amplitude of the signal of channel ch1 is Sch × 15/1
6 and is determined to be at the 15th level. Therefore, the binary data corresponding to the channel ch1 is "1.
110 ”(= 15), and this binary data“ 11
“110”, which is obtained by removing the most significant bit “1” from “10”, is extracted as the signal magnitude information. This "110" corresponds to "b1 b2 b3" shown in FIG.

Similarly, for channel ch2, "0
Binary data "1" is obtained, and "1" excluding the most significant bit "0" is extracted as signal magnitude information. This "1" corresponds to "b4" shown in FIG.

Similarly, for channel ch3, "0"
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch3 in FIG. 11 (c).

Similarly, for channel ch4, "10
Binary data "00" is obtained, and "000" excluding the most significant bit "1" is extracted as signal magnitude information. This “000” is “b” shown in FIG.
5 b6 b7 ".

Similarly, for channel ch5, it is "0".
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch5 in FIG. 11 (c).

Similarly, for channel ch6, "0" is set.
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch6 in FIG. 11 (c).

Similarly, for channel ch7, "10
Binary data "10" is obtained, and "010" excluding the most significant bit "1" is extracted as signal magnitude information. This “010” is “b” shown in FIG.
8 b9 b10 ".

Similarly, for channel ch8, "11
Binary data "1" is obtained, and "11" excluding the most significant bit "1" is extracted as the information of the signal magnitude. This “11” is “b11” shown in FIG.
b12 ".

In this way, the signal magnitude information of each channel of the information frame FL1 is extracted as shown in FIG. 13 (b).

Information on the signal magnitude of each channel is extracted from the information frame FL2 in the same manner as the information frame FL1.

FIG. 13C shows the signal amplitude of each channel of the information frame FL2 shown in FIG. 12C in a divided form.

Since the total number of bits bi of channel ch1 is 4 bits, it is divided into 2 ⁴ (16) levels. The amplitude of the signal of channel ch1 is Sch × 14/1
6 and is determined to be at the 14th level. Therefore, the binary data corresponding to the channel ch1 is "1.
101 ”(= 14), and this binary data“ 11
"101", which is obtained by removing the most significant bit "1" from "01", is extracted as the signal magnitude information. This "101" corresponds to "b13 b14 b15" shown in FIG.

Similarly, for channel ch2, "1"
Binary data "1" is obtained, and "1" excluding the most significant bit "1" is extracted as signal magnitude information. This "1" corresponds to "b16" shown in FIG.

Similarly, for channel ch3, "0"
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch3 in FIG. 11 (e).

Similarly, for channel ch4, "11
Binary data "01" is obtained, and "101" excluding the most significant bit "1" is extracted as signal magnitude information. This “101” is “b” shown in FIG.
17 b18 b19 ".

Similarly, for channel ch5, "0"
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch5 in FIG. 11 (e).

Similarly, for channel ch6, "0"
When the most significant bit "0" is removed, since there is no signal magnitude information, it is extracted as "no signal". This corresponds to the fact that there is no information on the signal magnitude of ch6 in FIG. 11 (e).

Similarly, for channel ch7, "10
Binary data "01" is obtained, and "001" excluding the most significant bit "1" is extracted as signal magnitude information. This "001" corresponds to "b" shown in FIG.
20 b21 b22 ".

Similarly, for channel ch8, "00"
Binary data "1" is obtained, and "01" excluding the most significant bit "0" is extracted as signal magnitude information. This "01" corresponds to "b23" shown in FIG.
It corresponds to "b24".

In this way, the signal magnitude information of each channel of the information frame FL2 is extracted as shown in FIG. 13 (d).

In this embodiment, since the noise is strong, the number of assigned bits is 0 (channel ch).
The highest bit is also used to represent the bit allocation number “0” for (3, ch5, ch6). However, since "0" may be mistaken when the signals are combined, it is desirable to add the information frames FL3, FL4, ... To give redundancy. If the number of allocated bits "0" is given to the same channel of the information frames FL3, FL4, ... To give a sufficient redundancy, it is possible to deal with the error correction described above.

Next, using the BER (Bit Error Rate) as an index, to what extent can the error rate characteristic be improved by using the DSL-DMT method with respect to the conventionally used communication method OOK. consider.

First, the error rate characteristic of OOK will be described.

FIG. 25 shows the error rate characteristics in the case of the noise shown in FIG. 16 when the transmission rate is 8 kbps and f0 = 30 kHz and 55 kHz. Where N0
Is the average value of the noise power included in the signal band. FIG. 26 shows the band of each signal superimposed on the noise spectrum. When f0 = 55kHz, the frequency band of the signal contains a very strong noise band, so 30kHz
It can be seen that N0 is larger than in the case of z.

In the case shown in FIG. 25, the error rate characteristic greatly differs depending on f0. This is because when f0 is 55 kHz, N0 becomes large due to the existence of a very strong peak, and the BER sharply decreases as Eb / N0 increases as compared with the case of 30 kHz.

On the other hand, in the case of noise shown in FIG. 15, error rate characteristics are shown in FIG. 27 when the transmission rate and carrier frequency are the same as those in FIG. It can be seen that the error rate characteristics do not change so much even when the carrier frequency is changed, because the gap between the channels with strong noise is narrow and the channels are evenly distributed over a wide range, and the situation is similar to the case of white noise.

However, even in the case of the noise shown in FIG. 15, about half of the channels have strong noise, and there are not a few channels with weak noise of about 15 dB. Therefore, it is expected that the error rate characteristic will be improved by selecting such a frequency for communication.

Next, it will be described how much error rate improvement can be obtained by selecting a channel and performing communication using the DSL-DMT method, as compared with the case of OOK.

As described above, in the DSL-DMT system, N
= MRNch can be changed. Therefore, the quantization bit number M is fixed to M = 3, and how the error rate characteristic changes depending on the combination of Nch and R will be examined. For comparison with OOK, the transmission rate is 8 kbps and f0 = 30 kHz. The noise of interest is “noise of gas pipe anticorrosion current in Minoh town” shown in FIG.

As described above, the mean value N0 of the noise intensity contained in the artificial noise differs depending on the signal band. In the DSL-DMT system, since the signal band changes depending on R, when the band is narrow compared to the case of OOK, it is set to N0 of OOK, and when the band is wide, it is set to N0 according to the band.

The case where N is fixed will be described. N = 1
50, and the combination of Nch and R is (Nch, R) = (8
0, 0.625), (100, 0.5), (200,
0.25), (400, 0.125), (800, 0.
FIG. 28 shows how the error rate characteristics change when the value is changed to 0625).

When Nch = 80 and Nch = 800, the Eb / N0g that realizes the same BER is generally high, but in the case of three types in between, only about 1 dB to 2 dB changes.

In the case of FIG. 28, Nch = 1
As a result of adding and adding the cases of 60, 250, and 320, f0 = 30 kHz under "Noise in Minoh Town", and 150
When transmitting bit by bit, the characteristics do not change much even if Nch changes, except in extreme cases where Nch = 80 or 800.

However, as a result of changing the combination of Nch and R in the same manner by changing the location and f0, the variation of the error rate varies depending on the location. Dynamically changing these parameters for each case makes it difficult to synchronize transmission and reception. Therefore, the following method is used to determine the combination of Nch and R in which the situation is as good as possible.

First, as described above, the required error rate is 1
It is about 0 ⁻² to 10 ⁻³ . Therefore, Eb / N0 when this value is taken is examined. "Noise in residential area of Isehara city"
(Fig. 16) and "Noise of gas pipe corrosion protection current in Minoh Town" (Fig. 1
For each of 5), f0 = 30 kHz, 55 kHz
And N = 150, Nch = 80, 100, 160,
When changed to 200, 250, 320, 400,
FIG. 30 shows a plot of Eb / N0 at which BER = 10 ⁻³ .

However, the OOK error rate, which serves as a comparison reference, cannot be compared as it is because the characteristics greatly change depending on the measurement point and f0. Therefore, in OOK, Eb / N0 that also gives BER = 10 ⁻² and 10 ⁻³ is obtained (uniquely determined by the location and f0), and an evaluation is made as to how much dB there is in Eb / N0. In FIGS. 29 and 30, the margins for OOK with respect to Eb / N0 are shown in FIGS. 31 and 32, respectively.

In each case, there is an Nch that maximizes the margin, and since it is not common in each case, the optimum combination is defined as follows. That is, BER = 10
^-2 , for each Nch of 10 ^-3 , the minimum value of the values of the four characteristic curves (the worst value of the margin of Eb / N0) is determined, and the maximum parameter is set as the optimum value. Then BER
= 10 ⁻³ and Nch = 200 is optimal. At this time, in order to realize BER = 10 ⁻³ , the worst case was f 0 = 30 kHz of “noise in residential area of Isehara city”. However, there was still a margin of 15.9 dB with respect to OOK. At this time, the best value of the margin was 22 dB when f0 = 55 kHz of "noise in residential area of Isehara city".

Next, R was changed while fixing Nch = 200. As an example, f0 of "noise in residential area of Isehara city"
= 30 kHz, Nch = 200, R =
FIG. 33 shows the state of the error rate characteristics when changed to 0.1, 0.25, 0.4, 0.6 and 0.8. In FIG. 33, the BER characteristic deteriorates as R becomes higher.
It seems that this is because when R becomes high, bits have to be assigned to a channel having a bad noise condition.

FIG. 35 and FIG. 36 are the same as FIG. 31 and FIG. 32 with R changed at Nch = 200.
The view of the figure is the same as that of FIG. 31 and FIG.
Is. Also in the cases of FIGS. 35 and 36, the worst value was highest at BER = 10 ⁻³ and R = 0.25 (N = 150).

Next, fix R = 0.25 and set Nch to 2
It was changed around 00. F of "Noise in residential area of Isehara city"
In the case of 0 = 30 kHz, R = 0.25 and Nch
FIG. 34 shows the state of the error characteristics when changed to 160, 180, 200, 220, 240. As shown in FIG. 34, there is almost no change, but when Nch is larger than 200, the BER seems to be slightly deteriorated. The reason for this is considered as follows. That is, the band B of the signal is B
= 1 / MRT1 bit, the constant band B is divided more finely when Nch is increased, and the channel interval Δf is narrowed. It is considered that the noise fluctuation per channel increases as the channel interval Δf decreases.

Similarly, the worst value of the degree of improvement was examined by changing Nch. At this time, the worst value is highest around Nch = 200, 180, and 160 when Nch = 160, and the degree of improvement in this case is 16.2 dB. However, in this range, the change in improvement was very small, and all had values around 16 dB.

From the above, R = 0.25 and Nch =
With a value of 180, an improvement of 16 dB at the worst and 20 dB at the best can be obtained with respect to OOK.

In the above embodiment, the maximum signal amplitude S1c
Although h is assumed to be constant in all channels, in reality, as it propagates through the ground, the higher the frequency of the signal, the more severe the attenuation. In fact, when Eb / N0 becomes small, an error may occur when the bit allocation situation is known, and there is a risk that a burst error may occur in the information extraction. further,
OFDM has a problem that the peak of the transmission signal becomes very large depending on the signal to be transmitted. Since the function of the transmission signal is determined by this peak value, it is necessary to suppress the peak value. Therefore, the above-described embodiment may be appropriately modified in consideration of these matters.

[Brief description of drawings]

FIG. 1 is a diagram showing an underground excavator of an embodiment.

FIG. 2 is a diagram showing a device configuration of an embodiment.

FIG. 3 is a configuration diagram of a BPSK-OFDM modulator / demodulator.

FIG. 4 is a block diagram of an apparatus of an embodiment.

FIG. 5 is a block diagram of an apparatus of an embodiment.

FIG. 6 is a configuration diagram of one cycle of a transmission signal according to the embodiment.

FIG. 7 is a flowchart showing a procedure of processing for obtaining the number of allocated bits according to the embodiment.

FIG. 8 is a flowchart showing a procedure of processing for obtaining the number of allocated bits according to the embodiment.

9 (a), (b), and (c) are diagrams for explaining the principle of OFDM.

FIG. 10 is a diagram for explaining the principle of OFDM.

FIG. 11 is a diagram illustrating a process of determining the number of allocated bits of each channel and a process of adding signal information other than the most significant bit.

FIG. 12 is a diagram illustrating a process of detecting the number of allocated bits from the most significant bit.

FIG. 13 is a diagram illustrating a process of re-analyzing an information frame and extracting signal information.

FIG. 14 is a diagram showing a state of noise in a quiet state near a gas pipe in Minoh town.

FIG. 15 is a diagram showing a noise state of a gas pipe anticorrosion current in Minoh town.

FIG. 16 is a diagram showing a state of noise in a residential area of Isehara city.

FIG. 17 is a diagram showing a state of noise on the side of a railroad near the front of the Tokai University station on the Odakyu line.

FIG. 18 is a diagram showing how the peak value in FIG. 17 changes.

FIG. 19 is a diagram showing a state of noise after about 4 minutes from FIG.

20 is a diagram showing a state of noise after about 8 minutes from FIG.

FIG. 21 is a block diagram of an OOK melody processing system.

FIG. 2 is a diagram showing a spectrum of an OOK signal.

FIG. 23 is a diagram showing an OOK signal before signal processing.

FIG. 24 is a diagram showing an OOK signal after signal processing.

FIG. 25 is a diagram showing error rate characteristics under noise in Isehara city.

FIG. 26 is a diagram showing a state of noise included in a band of a transmission signal.

FIG. 27 is a diagram showing error rate characteristics under noise in Minoo-cho.

FIG. 28 is a diagram showing error rate characteristics when the number of transmission bits N is fixed.

FIG. 29 shows Eb / that realizes BER = 10 ⁻² .
It is a figure which shows the value of N0.

FIG. 30 shows Eb / that realizes BER = 10 ⁻³ .
It is a figure which shows the value of N0.

FIG. 31 is a diagram showing the degree of improvement with respect to the value of Eb / N0 where BER = 10 ^{−2 at} OOK.

FIG. 32 is a diagram showing the degree of improvement with respect to the value of Eb / N0 at which BER = 10 ^{−3 at} OOK.

FIG. 33 is a diagram showing error rate characteristics when the number of channels Nch = 200 and the rate R is changed.

FIG. 34 is a diagram showing error rate characteristics when the number of channels Nch is changed at a rate R = 0.25.

FIG. 35 shows the number of channels Nch = 200 and BER =
It is a figure which shows the margin with respect to OOK at the time of 10 ^<-2 >.

FIG. 36 shows the number of channels Nch = 200 and BER =
It is a figure which shows the margin with respect to OOK at the time of 10 < ^-3 >.

[Explanation of symbols]

1 drill rod 2 drill head 3 underground excavator 4 transmitter 5 receiver 8 noise sources

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiyuki Saito             1-21-15 Yamate Higashi, Kyotana-shi, Kyoto (72) Inventor Shigeki Matsumoto             3-27-16 Wakamiya, Nakano-ku, Tokyo F term (reference) 5K022 DD01 DD22 DD32

Claims (6)

[Claims] 1. A communication comprising: a transmission means for dividing a predetermined frequency band into a plurality of channels and transmitting a signal for each channel; and a reception means for receiving a signal for each channel transmitted from the transmission means. In the device, the signal transmitted and received by the transmitting and receiving means is applied in a noise environment in which noise generated by a single or a plurality of artificial noise sources interferes, and at the transmitting means side, the intensity of noise is changed for each channel. Based on this measurement result, the information amount is assigned to each channel so that the information amount of the signal becomes larger as the noise intensity of the channel becomes smaller, and the signal of each channel is assigned as described above. The data indicating the amount of information is transmitted in association with the receiving means, the data indicating the amount of information is detected for each channel, and the signal of each channel is extracted with the detected amount of information. Communication device in a noisy environment, wherein the door. 2. The communication device in a noise environment according to claim 1, wherein the data indicating the information amount is given by the most significant bit of binary data of each channel. 3. The transmitting means is provided on the side of an excavator for excavating the ground, and the receiving means is provided on the ground so that the intensity of the signal transmitted from the transmitting means when the receiving means receives the signal. The communication device in a noisy environment according to claim 1, wherein the position of the excavator in the ground is detected accordingly. 4. A communication method in which a predetermined frequency band is divided into a plurality of channels, a signal is transmitted for each channel, and the transmitted signal for each channel is received. It is applied in a noise environment where the noise generated by the noise source interferes with the transmitted and received signals, and the process of measuring the noise intensity for each channel, and based on this measurement result, the channel with lower noise intensity is A step of allocating the information amount to each channel so that the information amount of the signal becomes large; a step of transmitting the signal of each channel in association with the data indicating the allocated information amount; A miscellaneous process characterized by including a step of receiving a signal, a step of detecting data indicating the amount of information for each channel, and a step of extracting a signal of each channel with the detected amount of information. Communication method in the environment. 5. The communication method in a noise environment according to claim 4, wherein the data indicating the information amount is given by the most significant bit of binary data of each channel. 6. When the frequency spectrum characteristic of the measured noise intensity changes, the method further comprises the step of changing the amount of information allocated to each channel according to the change. Item 4. A communication method in a noise environment according to Item 4.