JP2007028175A - Communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device capable of automatically observing frequency characteristics of noise on a telephone line.
First, a calculation control unit 4 turns off a switch circuit SW1. Next, the spectrum analyzer 6 measures the frequency spectrum of the noise N1 appearing at the input part of the receiving unit 3. Subsequently, the calculation control unit 4 turns on the switch circuit SW1. Next, the spectrum analyzer 6 measures the frequency spectrum of the noise N2 that appears at the input portion of the receiving unit 3. Then, the calculation control unit 4 calculates the frequency spectrum of the noise N3 by subtracting the frequency spectrum of the noise N1 from the frequency spectrum of the noise N2. Therefore, it becomes possible to automatically observe the frequency characteristics of noise on the telephone line, and the noise measurement effort is reduced.
[Selection] Figure 1

Description

  The present invention relates to a communication device, and more particularly to a communication device that performs digital data communication using a telephone line.

  In VDSL (Very High-Bit-rate Digital Subscriber Line) which performs high-speed data communication using an existing telephone line, it is about several tens of Mbps between the station side device and the terminal side device. High-speed communication can be realized.

  As shown in Non-Patent Document 1, the ITU-T (ITU-Telecommunication standardization sector), which is a telecommunications standardization department of the ITU (International Telecommunication Union), is “G.993.1” related to the VDSL standard. Is recommended.

  In addition, as shown in Non-Patent Documents 2 to 4, there is HomePNA (Home Phone line Networking Alliance) as a method for performing data communication using a telephone line at home, and this is converted to a telephone line in a building. Communication service is provided.

  Further, as shown in Non-Patent Documents 5 and 6, an ADSL (Asymmetric DSL) that connects a station-side device installed in a telephone base station and a terminal-side device in a building or apartment house using a telephone line. Communication services using asymmetric digital subscriber lines) are also provided.

As described above, communication services using a plurality of different systems such as VDSL, HomePNA, ADSL, and other unique systems are provided via telephone lines.
"Very high speed digital subscriber line (VDSL)", ITU-T recommendation G.993.1 "Telephone line network transceiver-Foundation", ITU-T recommendation G.989.1 "Telephone line network transceiver-Payload format and link layer requirements", ITU-T recommendation G.989.2 "Telephone line network transceiver-Isolation function", ITU-T recommendation G.989.3 "Asymmetric digital subscriber line (ADSL) transceiver", ITU-T recommendation G.992.1 "Splitterless asymmetric digital subscriber line (ADSL) transceiver", ITU-T recommendation G.992.2

  A general telephone line is accommodated in a telephone cable in which a plurality of lines are bundled. For this reason, a phenomenon called crosstalk (crosstalk) in which a signal leaks from one line to the other line becomes a problem between two adjacent telephone lines in the same cable. When mutual interference due to crosstalk occurs, communication speed and communication quality may be reduced.

  Therefore, when there is a problem that a sufficient communication speed cannot be obtained or a communication line cannot be connected, it is necessary to quantitatively grasp the frequency characteristics of noise on the telephone line. However, since the conventional communication apparatus did not have a function of measuring noise on the telephone line, the noise on the telephone line was artificially measured using measurement equipment.

  In addition, since the line environment may fluctuate with time, it is necessary to continuously observe the frequency characteristics of noise on the telephone line. However, it is laborious to continuously measure noise on a telephone line using measurement equipment as in the past.

  Therefore, a main object of the present invention is to provide a communication apparatus capable of automatically observing the frequency characteristics of noise on a telephone line.

  A communication apparatus according to the present invention is a communication apparatus that performs digital data communication with a communication apparatus on the other side using a telephone line, and is a hybrid circuit that is connected to the telephone line and separates a transmission signal and a reception signal. ON / OFF provided between the hybrid circuit and the telephone line, a transmitter that transmits a transmission signal to the telephone line via the hybrid circuit, a receiver that receives the received signal from the telephone line via the hybrid circuit The controllable switch circuit and the switch circuit are turned off to measure the frequency spectrum of the first noise generated in the communication device, and then the switch circuit is turned on to turn on the first noise and the noise on the telephone line. By measuring the frequency spectrum of the second noise synthesized with and subtracting the frequency spectrum of the first noise from the frequency spectrum of the second noise, Is obtained by a noise observation means for calculating a frequency spectrum of the noise on the telephone line.

  Preferably, the noise observation means subtracts the frequency spectrum of the first noise from the frequency spectrum of the spectrum analyzer that measures the frequency spectrum of the first and second noises appearing at the input portion of the receiving unit. To calculate a frequency spectrum of noise on the telephone line.

  Another communication apparatus according to the present invention is a communication apparatus that performs digital data communication with a communication apparatus on the other side using a telephone line, and is connected to the telephone line for separating a transmission signal and a reception signal. A hybrid circuit, a transmission unit that transmits a transmission signal to a communication device on the other side during data communication, a transmission unit that transmits a test signal having a predetermined frequency band and a constant signal strength during noise observation, and a transmission during data communication A bypass means for receiving a transmission signal sent from the transmission section and applying it to the telephone line via the hybrid circuit, and receiving a test signal sent from the transmission section when observing noise, and a hybrid circuit for data communication The received signal is demodulated by receiving the signal from the telephone line via the receiver, and when the noise is observed, the test signal bypassed by the bypass means is received, demodulated, and demodulated. A receiver that calculates the frequency spectrum of the signal-to-noise ratio of the signal, a switch circuit that is provided between the hybrid circuit and the telephone line, can be controlled on / off, and at the time of noise observation, the switch circuit is turned off, The first signal-to-noise ratio frequency spectrum generated in the communication device is received by receiving the first signal-to-noise frequency spectrum from the receiver and subtracting the first signal-to-noise frequency spectrum from the pre-stored frequency spectrum of the test signal. The frequency spectrum of noise is calculated, then the switch circuit is turned on, the frequency spectrum of the second signal-to-noise ratio is received from the receiver, and the second signal-to-noise ratio is calculated from the frequency spectrum of the test signal stored in advance. The frequency spectrum of the second noise obtained by combining the first noise and the noise on the telephone line is calculated by subtracting the frequency spectrum of the second noise. And, by the frequency spectrum of the second noise subtracting the frequency spectrum of the first noise, in which a noise observation means for calculating a frequency spectrum of the noise on the telephone line.

  Preferably, digital data communication is performed using a multicarrier modulation method.

  In the communication apparatus according to the present invention, a hybrid circuit that is connected to a telephone line and separates a transmission signal and a reception signal, a transmission unit that transmits the transmission signal to the telephone line via the hybrid circuit, and a hybrid circuit are provided. A receiving unit that receives a received signal from the telephone line, a switch circuit that is provided between the hybrid circuit and the telephone line and that can be controlled on / off, and a first that is generated in the communication device by turning off the switch circuit. The frequency spectrum of the noise is measured, then the switch circuit is turned on, the frequency spectrum of the second noise obtained by combining the first noise and the noise on the telephone line is measured, and the frequency spectrum of the second noise is measured. Noise observation means for calculating the frequency spectrum of the noise on the telephone line by subtracting the frequency spectrum of the first noise from. Therefore, the communication apparatus has a function of observing the frequency characteristic of noise on the telephone line, and can automatically observe the frequency characteristic of noise on the telephone line. This reduces the noise measurement effort.

  In another communication apparatus according to the present invention, a hybrid circuit connected to a telephone line for separating a transmission signal and a reception signal and a transmission signal to a communication apparatus on the other side during data communication are transmitted, and noise observation is performed. When transmitting a test signal having a predetermined frequency band and constant signal strength at the time, and at the time of data communication, receiving a transmission signal transmitted from the transmitter and applying it to the telephone line via the hybrid circuit, when observing noise Is a bypass unit that receives the test signal sent from the transmitter and bypasses the hybrid circuit, and during data communication, it receives and demodulates the received signal from the telephone line via the hybrid circuit, and is bypassed by the bypass unit when observing noise. Receiving the received test signal, demodulating, and calculating the frequency spectrum of the signal-to-noise ratio of the demodulated signal, the hybrid circuit and the power A switch circuit provided between the line and capable of on / off control, and at the time of noise observation, the switch circuit is turned off, and the frequency spectrum of the first signal-to-noise ratio is received from the receiving unit and stored in advance. The frequency spectrum of the first noise generated in the communication device is calculated by subtracting the frequency spectrum of the first signal-to-noise ratio from the frequency spectrum of the test signal, and then the switch circuit is turned on to By receiving the frequency spectrum of the second signal-to-noise ratio and subtracting the frequency spectrum of the second signal-to-noise ratio from the frequency spectrum of the test signal stored in advance, the first noise and the noise on the telephone line are reduced. The frequency spectrum of the synthesized second noise is calculated, and the frequency spectrum of the first noise is subtracted from the frequency spectrum of the second noise. By, it is provided a noise observation means for calculating a frequency spectrum of the noise on the telephone line. Also in this case, the communication device has a function of observing the frequency characteristic of noise on the telephone line, and can automatically observe the frequency characteristic of noise on the telephone line. This reduces the noise measurement effort. In addition, the cost can be reduced and the size of the apparatus can be reduced.

[Embodiment 1]
FIG. 1 is a block diagram showing a schematic configuration of an xDSL communication apparatus according to Embodiment 1 of the present invention. In FIG. 1, the xDSL communication apparatus includes a transmission unit 1, a hybrid circuit 2, a reception unit 3, a calculation control unit 4, a high impedance probe 5, a spectrum analyzer 6, a memory 7, a jack 8, And a switch circuit SW1. The transmission unit 1 includes an encoder 11, a modulator (IFFT) 12, a parallel / serial (P / S) converter 13, a digital / analog converter (DAC) 14, and a driver 15. The receiving unit 3 includes a low noise amplifier 16, an analog / digital converter (ADC) 17, a serial / parallel (S / P) converter 18, a demodulator (FFT) 19, and a decoder 20.

  One of multicarrier modulation schemes using a plurality of subcarriers (subcarriers) having different frequencies is a DMT (Discrete Multi-Tone) modulation scheme. Here, an xDSL communication apparatus using the DMT modulation method will be described.

  The encoder 11 encodes input data from the outside, assigns data for each subcarrier (subcarrier), and outputs the data to the modulator 12. The modulator 12 digitally modulates data of each subcarrier received from the encoder 10 by inverse fast Fourier transform (IFFT) and outputs the result to the parallel / serial converter 13. The parallel / serial converter 13 converts the parallel signal received from the modulator 12 into a serial signal and outputs the serial signal to the digital / analog converter 14. The digital / analog converter 14 converts the digital signal received from the parallel / serial converter 13 into an analog signal and supplies the analog signal to the driver 15. The driver 15 amplifies the analog signal received from the digital / analog converter 14 to a predetermined level and outputs it to the hybrid circuit 2.

  The hybrid circuit 2 gives the analog signal received from the driver 15 to the other party's xDSL communication device via the telephone line. In addition, the hybrid circuit 2 outputs an analog signal received from the counterpart xDSL communication apparatus via a telephone line to the low noise amplifier 16. The hybrid circuit 2 has a function of separating a transmission signal transmitted to the counterpart xDSL communication device and a reception signal received from the counterpart xDSL communication device.

  The low noise amplifier 16 adjusts the analog signal received from the hybrid circuit 2 to a predetermined level, and then outputs the analog signal to the analog / digital converter 17. The analog / digital converter 17 converts the analog signal received from the low noise amplifier 16 into a digital signal and outputs the digital signal to the serial / parallel converter 18. The serial / parallel converter 18 converts the serial signal received from the analog / digital converter 17 into a parallel signal and outputs the parallel signal to the demodulator 19. The demodulator 19 digitally demodulates the data received from the serial / parallel converter 18 by fast Fourier transform (FFT) and outputs the data for each subcarrier to the decoder 20. The decoder 20 restores the original data from the data for each subcarrier received from the demodulator 19 and outputs it to the outside.

  The high impedance probe 5 detects noise appearing at the input portion of the receiver 3 and outputs it to the spectrum analyzer 6. The spectrum analyzer 6 measures the frequency spectrum (frequency characteristics) of noise that appears at the input portion of the receiver 3 via the high impedance probe 5. The spectrum analyzer 6 is a spectrum analyzer having a simple configuration. The memory 7 temporarily stores the frequency spectrum of noise measured by the spectrum analyzer 6. The calculation control unit 4 controls the operations of the high impedance probe 5 and the spectrum analyzer 6. The calculation control unit 4 reads the noise frequency spectrum stored in the memory 7 and performs arithmetic processing to calculate the noise frequency spectrum on the telephone line. A switch circuit SW <b> 1 is provided between the hybrid circuit 2 and the jack 8. The switch circuit SW1 is on / off controlled by the calculation control unit 4. Next, the operation for calculating the frequency spectrum of noise on the telephone line will be described in detail.

  FIG. 2 is a flowchart showing the operation of calculating the frequency spectrum of noise on the telephone line. Referring to FIG. 2, first, in step S1, calculation control unit 4 turns off switch circuit SW1. Next, in step S <b> 2, the spectrum analyzer 6 measures the frequency spectrum of the noise N <b> 1 that appears at the input portion of the receiver 3. This noise N1 consists only of device noise (device-specific noise) generated in the xDSL communication apparatus. The frequency spectrum of the noise N1 is stored in the memory 7.

  Subsequently, in step S3, the calculation control unit 4 turns on the switch circuit SW1. Next, in step S <b> 4, the spectrum analyzer 6 measures the frequency spectrum of the noise N <b> 2 that appears at the input portion of the receiver 3. This noise N2 consists of noise on the telephone line and equipment noise. Noise on a telephone line is crosstalk noise mainly received from an adjacent line. The frequency spectrum of the noise N2 is stored in the memory 7.

  FIG. 3 is a diagram showing the frequency spectrum of the noises N1 and N2 measured by the spectrum analyzer 6. As shown in FIG. In FIG. 2, the unit of noise intensity is dBm / Hz.

  Returning to FIG. 2, in step S <b> 5, the calculation control unit 4 reads the frequency spectra of the noises N <b> 1 and N <b> 2 stored in the memory 7 and performs arithmetic processing. Specifically, the frequency spectrum of the noise N3 is calculated by subtracting the frequency spectrum of the noise N1 from the frequency spectrum of the noise N2.

  FIG. 4 is a diagram illustrating a frequency spectrum of the noise N3 (= N2−N1) calculated by the calculation control unit 4. In FIG. 4, this noise N3 consists only of noise on the telephone line. In this way, the frequency characteristics of noise on the telephone line are automatically observed. Thereafter, normal data communication can be performed while the switch circuit SW1 is kept on.

  The above-described measurement operation and arithmetic processing are programmed in advance, and an instruction is given to the calculation control unit 4 via the interface. The user can acquire the frequency spectrum of the noise N3 from the calculation control unit 4 via the interface. It is also possible to read the frequency spectrum of the noises N1 and N2 from the memory 7 via the interface. However, the frequency spectrum of the noise N3 calculated by the calculation control unit 4 may be stored in the memory 7, and the frequency spectrum of the noise N3 may be read from the memory 7.

  As described above, in the first embodiment, the xDSL communication apparatus has a function of automatically observing the frequency characteristics of noise on the telephone line. For this reason, it is not necessary to prepare measurement equipment individually as in the prior art, and it becomes possible to continuously observe the frequency characteristics of noise on the telephone line. Therefore, the noise measurement effort can be reduced.

[Embodiment 2]
FIG. 5 is a block diagram showing a schematic configuration of an xDSL communication apparatus according to Embodiment 2 of the present invention, which is compared with FIG. Referring to FIG. 5, the difference from FIG. 1 is that calculation control unit 4, high impedance probe 5, spectrum analyzer 6 and memory 7 are deleted, and control unit 21, calculation unit 22, memory 23 and switch circuit SW2 are added. It is a point that has been. 5, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The transmission unit 1 has a function of transmitting a transmission signal to the other party's xDSL communication apparatus during data communication, and a function of transmitting a test signal TS having a predetermined strength having a predetermined frequency band during noise observation. Preferably, the test signal TS has the entire frequency band to be used (for example, 1.1 to 12 MHz in the case of the VDSL system), and the signal strength is about the maximum strength of the transmission signal to be used (for example, in the case of the VDSL system). −60 dBm / Hz).

  The decoder 20 restores the original data from the data for each subcarrier received from the demodulator 19 and outputs it to the outside, and gives the frequency spectrum of the signal-to-noise ratio SNR for each subcarrier to the calculator 22. Here, the signal-to-noise ratio SNR for each subcarrier is calculated based on the magnitude of the phase and amplitude deviation from the ideal signal, but since it is already a well-known technique, detailed description thereof is omitted here.

  The calculator 22 calculates the frequency spectrum of noise on the telephone line based on the frequency spectrum of the signal-to-noise ratio SNR for each subcarrier received from the decoder 20 at the time of noise observation. The memory 23 temporarily stores the noise frequency spectrum calculated by the calculation unit 22. The control unit 21 controls operations of the calculation unit 22 and the switch circuits SW1 and SW2. A switch circuit SW <b> 1 is provided between the hybrid circuit 2 and the jack 8. A switch circuit SW2 is provided between the driver 15 and the hybrid circuit 2. When the switch circuit SW2 is connected to the A side, the driver 15 is connected to the hybrid circuit 2, and when the switch circuit SW2 is connected to the B side, the driver 15 is connected to the low noise amplifier 16 via the bypass path. Is done. Note that the bypass path is not limited to that shown in FIG. 5. For example, the hybrid circuit 2 may have a bypass function. Here, the operation for calculating the frequency spectrum of noise on the telephone line during noise observation will be described in detail.

  FIG. 6 is a flowchart showing the operation of calculating the frequency spectrum of noise on the telephone line. Referring to FIG. 6, first, in step S11, control unit 21 turns off switch circuit SW1 and connects switch circuit SW2 to the B side. That is, the driver 15 is connected to the low noise amplifier 16 through a bypass path.

  Next, in step S12, a constant strength test signal TS having a predetermined frequency band is output from the transmitter 1. Next, in step S13, the calculation unit 22 receives the frequency spectrum of the signal-to-noise ratio SNR1 for each subcarrier from the decoder 20, and the frequency spectrum of the signal-to-noise ratio SNR1 from the frequency spectrum of the test signal TS stored in advance. Is subtracted to calculate the frequency spectrum of the noise N11. The calculated frequency spectrum of the noise N11 is stored in the memory 23.

FIG. 7 is a diagram illustrating frequency spectra of the test signal TS and the signal-to-noise ratio SNR1. FIG. 8 is a diagram illustrating a frequency spectrum of the noise N11 (= TS−SNR1) calculated by the calculation unit 22. This noise N11 consists only of device noise. 7 and 8, the unit of signal intensity is dB. In addition, this calculation process is performed for each subcarrier. That is, the calculation formula when paying attention to the i-th subcarrier is N11 _i = TS _i −SNR1 _i .

  Returning to FIG. 6, in step S14, the control unit 21 turns on the switch circuit SW1. Subsequently, in step S15, the calculation unit 22 receives the frequency spectrum of the signal-to-noise ratio SNR2 for each subcarrier from the decoder 20, and the frequency spectrum of the signal-to-noise ratio SNR2 from the previously stored frequency spectrum of the test signal TS. Is subtracted to calculate the frequency spectrum of the noise N12. The calculated frequency spectrum of the noise N12 is stored in the memory 23.

FIG. 9 is a diagram illustrating frequency spectra of the test signal TS and the signal-to-noise ratio SNR2. FIG. 10 is a diagram illustrating a frequency spectrum of the noise N12 (= TS−SNR2) calculated by the calculation unit 22. This noise N12 consists of noise on the telephone line and equipment noise. 9 and 10, the unit of signal intensity is dB. In addition, this calculation process is performed for each subcarrier. That is, the calculation formula when attention is paid to the i-th subcarrier is N12 _i = TS _i −SNR2 _i .

  Returning again to FIG. 6, in step S <b> 16, the calculation unit 22 reads the frequency spectra of the noises N <b> 11 and N <b> 12 stored in the memory 23 and performs arithmetic processing. Specifically, the frequency spectrum of the noise N13 is calculated by subtracting the frequency spectrum of the noise N11 from the frequency spectrum of the noise N12. The calculated noise N13 consists only of noise on the telephone line. The calculated frequency spectrum of the noise N13 is stored in the memory 23. In this way, the frequency characteristics of noise on the telephone line are observed. Thereafter, when the switch circuit SW2 is connected to the A side, normal data communication can be performed.

  The arithmetic processing described above is programmed in advance, and an instruction is given to the control unit 21 via the interface. Further, the user can obtain the frequency spectrum of the noises N11 to N13 from the memory 23 via the interface.

  As described above, in the second embodiment, as in the first embodiment, the xDSL communication apparatus has a function of automatically observing the frequency characteristics of noise on the telephone line. For this reason, it is not necessary to prepare measurement equipment individually as in the prior art, and it becomes possible to continuously observe the frequency characteristics of noise on the telephone line. Therefore, the noise measurement effort can be reduced. Further, as shown in the first embodiment, the cost can be reduced and the apparatus can be downsized as compared with the case where the spectrum analyzer 6 is incorporated.

  In the embodiment illustrated here, the xDSL communication apparatus using the DMT modulation method has been described. However, the present invention can also be applied to an xDSL communication apparatus using a QAM (Quadrature Amplitude Modulation) method. The QAM method is a method of assigning frequency bands to upstream and downstream bands and performing data communication using a single carrier for each assigned band. For this reason, when the QAM method is applied to the second embodiment, the calculation unit 22 performs a calculation process of each carrier wave, that is, a frequency spectrum of each band.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram which shows schematic structure of the xDSL communication apparatus by Embodiment 1 of this invention. It is a flowchart which shows the operation | movement which calculates the frequency spectrum of the noise on a telephone line. It is a figure which shows the frequency spectrum of noise N1, N2 measured by the spectrum analyzer shown in FIG. It is a figure which shows the frequency spectrum of the noise N3 (= N2-N1) calculated by the control part shown in FIG. It is a block diagram which shows schematic structure of the xDSL communication apparatus by Embodiment 2 of this invention. It is a flowchart which shows the operation | movement which calculates the frequency spectrum of the noise on a telephone line. It is a figure which shows the frequency spectrum of test signal TS and signal-to-noise ratio SNR1. It is a figure which shows the frequency spectrum of noise N11 (= TS-SNR1) calculated by the calculation part shown in FIG. It is a figure which shows the frequency spectrum of test signal TS and signal-to-noise ratio SNR2. It is a figure which shows the frequency spectrum of noise N12 (= TS-SNR2) calculated by the calculation part shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Transmission part, 2 Hybrid circuit 2, 3 Reception part, 4 Calculation control part, 5 High impedance probe, 6 Spectrum analyzer, 7, 23 Memory, 8 Jack, 11 Encoder, 12 Modulator, 13 Parallel / serial converter, 14 Digital / analog converter, 15 driver, 16 low noise amplifier, 17 analog / digital converter, 18 serial / parallel converter, 19 demodulator, 20 decoder, 21 control unit, 22 calculation unit, SW1, SW2 switch circuit.

Claims (4)

A communication device that performs digital data communication with a communication device on the other side using a telephone line,
A hybrid circuit connected to the telephone line for separating a transmission signal and a reception signal;
A transmission unit for transmitting a transmission signal to the telephone line via the hybrid circuit;
A receiving unit for receiving a received signal from the telephone line via the hybrid circuit;
A switch circuit provided between the hybrid circuit and the telephone line and capable of on / off control; and turning off the switch circuit to measure a frequency spectrum of the first noise generated in the communication device; Next, the switch circuit is turned on, and a frequency spectrum of a second noise obtained by combining the first noise and the noise on the telephone line is measured, and the first noise frequency spectrum is measured from the second noise frequency spectrum. A communication apparatus comprising noise observation means for calculating a frequency spectrum of noise on the telephone line by subtracting a frequency spectrum of noise. The noise observation means includes
A spectrum analyzer for measuring a frequency spectrum of the first and second noises appearing at an input portion of the receiving unit; and subtracting the frequency spectrum of the first noise from the frequency spectrum of the second noise, The communication apparatus according to claim 1, further comprising a calculation control unit that calculates a frequency spectrum of noise on the line. A communication device that performs digital data communication with a communication device on the other side using a telephone line,
A hybrid circuit connected to the telephone line for separating a transmission signal and a reception signal;
A transmitter that transmits a transmission signal to the communication device on the other side during data communication, and a test signal that transmits a test signal having a predetermined frequency band and a constant signal strength during noise observation,
At the time of data communication, a transmission signal transmitted from the transmission unit is received and applied to the telephone line via the hybrid circuit. At the time of noise observation, the hybrid circuit is received by receiving a test signal transmitted from the transmission unit. Bypass means to bypass,
During the data communication, a received signal is received from the telephone line via the hybrid circuit and demodulated. When the noise is observed, a test signal bypassed by the bypass means is received and demodulated. A receiver for calculating the frequency spectrum of the ratio,
A switch circuit provided between the hybrid circuit and the telephone line and capable of on / off control; and at the time of the noise observation, the switch circuit is turned off and the first signal-to-noise ratio is Receiving the frequency spectrum and subtracting the frequency spectrum of the first signal-to-noise ratio from the frequency spectrum of the test signal stored in advance to calculate the frequency spectrum of the first noise generated in the communication device; To turn on the switch circuit, receive a frequency spectrum of the second signal-to-noise ratio from the receiver, and subtract the frequency spectrum of the second signal-to-noise ratio from the frequency spectrum of the test signal stored in advance. To calculate a frequency spectrum of a second noise obtained by combining the first noise and the noise on the telephone line, A communication apparatus comprising noise observing means for calculating a frequency spectrum of noise on the telephone line by subtracting the frequency spectrum of the first noise from the frequency spectrum of the second noise.   The communication apparatus according to any one of claims 1 to 3, wherein digital data communication is performed using a multicarrier modulation method.

Images