JP2007228405A - Communication device, communication system, and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication device, a communication system, and a communication method which can prevent a reduction of a communication rate and actualize a stabilization of communication. <P>SOLUTION: A communication device is provided with a receiving portion 62 receiving a plurality of communication signals whose frequencies are different from each other from the other end of the communication, a measurement portion 53 measuring line states of the communication signals received, a margin setting portion 55 separately setting a margin value corresponding to at least one communication signal within the communication signals and a margin value corresponding to another communication signal, a communication rate determining portion 51 determining communication rates of the communication signals respectively so that error rates of the communication signals become less than a predetermined value in line states which have deteriorated from the measured line states by margin value set, and a transmitter 61 notifying the determined communication rates to the other end of the communication. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication device, a communication system, and a communication method, and more particularly, to a communication device, a communication system, and a communication method that communicate using a plurality of signals having different frequencies.

XDSL (x Digital Subscriber) for high-speed data communication using existing telephone lines
Examples of the Line (digital subscriber line) method include ADSL (Asymmetric DSL) and VDSL (Very high-bit-rate DSL).

  As an xDSL modulation system, there is a DMT (Discrete Multi-Tone) modulation system that performs communication by dividing a transmission frequency band to be used into a plurality of fine bands. For example, in full-rate ADSL (8 Mbps / 12 Mbps), the transmission frequency band of about 1 MHz is divided into 256 subchannels (4 kHz bandwidth).

  In a multicarrier communication system using the DMT modulation method, training for checking a line state between communication apparatuses connected to each other is performed before starting data communication. In this training, the signal-to-noise ratio (hereinafter also referred to as SNR (Signal to Noise Ratio)) is observed for each divided subchannel, and bits assigned to subcarriers that are subchannel carriers according to the observation results. Set the number distribution. Thereby, the communication speed corresponding to the line state is automatically set (best effort method). When the link (connection) between the communication devices is established after the training is completed, data communication is started at the set communication speed. Normally, the communication speed is not dynamically changed during data communication.

  By the way, since a general telephone line is accommodated in a telephone cable in which a plurality of lines are bundled, crosstalk due to electromagnetic coupling occurs between two adjacent telephone lines.

  In recent years, demand for IP telephones, videophones, competitive games, video distribution, and the like using real-time transmission is increasing. In real-time transmission, there is a tendency that communication stability is more important than communication speed. Therefore, there is a need for a stable communication service that does not disconnect the link even if the line condition deteriorates.

  As an example of a communication apparatus that realizes such a stable communication service, for example, Patent Document 1 discloses the following communication apparatus. That is, the communication apparatus monitors an error in the xDSL connection for each line, and when the communication error in a specific line exceeds a predetermined threshold, an error monitoring unit that gives an instruction to change the communication setting in the line And a communication setting changing unit for changing the setting, for example, by increasing the noise margin amount so that the communication on the line is further stabilized based on an instruction to change the communication setting.

Further, as an example of a communication system that realizes a stable communication service, Patent Document 2 discloses the following xDSL communication system. In other words, an xDSL communication system that connects a user's xDSL modem and a communication service provider's DSL modem device via an xDSL line, and the connection via the xDSL line during communication is disconnected and reconnection is performed using the xDSL modem. The number of bits of each carrier at the time of establishment of synchronization is compared with the number of bits of each carrier at the time of establishment of re-synchronization. The number of bits with a larger margin against noise is used, and the number of bits of each carrier is assigned using the same number of bits for carriers that are equal to each other, and communication after establishment of resynchronization is performed.
JP 2003-274053 A JP-A-2005-124012

  By the way, in the xDSL communication system, basically a communication signal on the transmission side transmits a communication signal of the same level on each subcarrier. Since the transmission line loss has frequency characteristics, that is, the transmission line loss differs for each frequency, the reception level of the communication signal in the communication device on the receiving side is often different for each subcarrier.

  Here, the communication device described in Patent Document 1 is configured to increase the noise margin amount for each specific line, but the noise margin amount of each subcarrier is constant. For this reason, in order to ensure that the error rate of the communication signal is less than a predetermined value even when the reception level of the communication signal in the communication device on the receiving side is different for each subcarrier, it is necessary to match the subcarrier with the lowest reception level. It is necessary to set the noise margin amount of each subcarrier. Therefore, there has been a problem that the communication speed of the entire communication system is lowered more than necessary.

  The communication device described in Patent Document 2 is configured to assign the number of bits of each carrier based on the number of bits at the time of establishment of synchronization and the number of bits at the time of establishment of resynchronization. For this reason, if a new interference source occurs in the transmission line after training and the frequency characteristics of the transmission line loss fluctuate, the error rate of the communication signal corresponding to the subcarrier whose line condition has deteriorated compared to the time of training Will increase. Therefore, there has been a problem that communication is unstable because line disconnection, connection and retraining are repeated due to fluctuations in frequency characteristics of transmission line loss.

  Therefore, an object of the present invention is to provide a communication device, a communication system, and a communication method capable of preventing a decrease in communication speed and stabilizing communication.

  In order to solve the above problems, a communication apparatus according to an aspect of the present invention measures a line state of a plurality of communication signals received from a receiving unit that receives a plurality of communication signals having different frequencies from a communication partner. Set from a measurement unit, a margin setting unit that separately sets a margin value corresponding to at least one communication signal of a plurality of communication signals and a margin value corresponding to another communication signal, and a measured line state A communication speed determining unit that determines the communication speed of each of the plurality of communication signals so that the error rate of each of the plurality of communication signals is less than a predetermined value in a line state deteriorated by the margin value, and the determined communication speed is communicated. A transmission unit for notifying the other party.

  According to still another aspect of the present invention, there is provided a communication device for transmitting a plurality of communication signals having different frequencies to a communication partner, and acquiring the line states of the plurality of communication signals measured by the communication partner from the communication partner. A margin setting unit that separately sets a margin value corresponding to at least one communication signal of a plurality of communication signals and a margin value corresponding to another communication signal, and the acquired line state A communication speed determining unit that determines the communication speed of each of the plurality of communication signals so that an error rate of each of the plurality of communication signals received by the communication partner is less than a predetermined value in a line state degraded by a set margin value; The transmission unit transmits a plurality of communication signals to the communication partner at the determined communication speed.

Preferably, the margin setting unit sets a margin value for each communication signal.
Preferably, the margin setting unit sets a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal to different values.

  Preferably, the line state is a signal-to-noise ratio, and the communication speed determining unit has an error rate of a plurality of communication signals received by a communication partner at a signal-to-noise ratio that is smaller than the measured signal-to-noise ratio by a margin value. The communication speeds of the plurality of communication signals are respectively determined so as to be less than a predetermined value.

  Preferably, the communication device further stores a plurality of tables in which a margin value corresponding to at least one communication signal of a plurality of communication signals and a margin value corresponding to another communication signal are defined. The margin setting unit selects and sets one of a plurality of tables.

  In order to solve the above-described problem, a communication system according to an aspect of the present invention is a communication system including a first communication device and a second communication device, and the first communication device includes a plurality of different frequencies. A transmission unit for transmitting the communication signal to the second communication device, the second communication device receiving a plurality of communication signals from the first communication device, and a plurality of received communication signals A measurement unit for measuring a line state, a margin setting unit for separately setting a margin value corresponding to at least one communication signal of a plurality of communication signals and a margin value corresponding to another communication signal, and measurement A communication speed determining unit for determining the communication speed of each of the plurality of communication signals so that the error rate of each of the plurality of communication signals is less than a predetermined value in the line state deteriorated by the margin value set from the set line state; A transmission unit that notifies the first communication device of the determined communication speed, and the transmission unit in the first communication device transmits a plurality of communication signals to the second communication device at the notified communication speed. system.

  In order to solve the above problems, a communication method according to an aspect of the present invention is a communication method in a communication system including a first communication device and a second communication device, wherein the first communication device Transmitting a plurality of different communication signals to the second communication device; measuring a line state of the plurality of communication signals received from the first communication device by the second communication device; A communication device separately setting a margin value corresponding to at least one communication signal of a plurality of communication signals and a margin value corresponding to another communication signal; and a second communication device measuring Determining the communication speeds of the plurality of communication signals so that the error rate of the plurality of communication signals is less than a predetermined value in the line state deteriorated by the margin value set from the determined line state; The second communication device notifies the first communication device of the determined communication speed, and the first communication device transmits a plurality of communication signals to the second communication device at the notified communication speed. Steps.

  According to the present invention, it is possible to prevent a decrease in communication speed and stabilize communication.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
[Configuration and basic operation]
FIG. 1 is a functional block diagram showing a configuration of a communication system according to an embodiment of the present invention and a communication apparatus in the communication system.

  Referring to FIG. 1, a communication system 100 includes a station side device 1 that is a communication device and a terminal side device 2 that is also a communication device. The station side device 1 and the terminal side device 2 are connected via a telephone line. The station-side device 1 transmits a plurality of communication signals corresponding to a plurality of subcarriers to the terminal-side device 2 that is a communication partner. Further, the terminal-side device 2 transmits a plurality of communication signals corresponding to the plurality of subcarriers to the station-side device 1 that is a communication partner. The communication system may have a configuration including a plurality of station-side devices 1 and terminal-side devices 2, and a configuration in which one station-side device 1 communicates with a plurality of terminal-side devices 2. It may be. Further, at least one station apparatus 1 may have a function as a management apparatus that monitors and controls other station apparatuses 1 and terminal apparatuses 2 in this communication system.

  The station apparatus 1 includes a transmission unit 61, a reception unit 62, a storage unit 8, a control unit 17, an encoder 10, and a decoder 32. The transmission unit 61 includes a modulator (IFFT) 12, a parallel / serial (P / S) converter 14, a digital / analog converter (DAC) 16, a driver unit 20, and a hybrid circuit 22. The receiving unit 62 includes a hybrid circuit 22, a low noise amplifier 24, an analog / digital converter (ADC) 26, a serial / parallel (S / P) converter 28, and a demodulator (FFT) 30.

  The encoder 10 encodes input data to be transmitted, and assigns the encoded input data to a plurality of subcarriers. Then, the encoder 10 outputs the data of each subcarrier to the modulator 12.

  The modulator 12 digitally modulates the data of each subcarrier received from the encoder 10 by inverse fast Fourier transform (IFFT). Then, the modulator 12 outputs the digital modulation signal to the parallel / serial converter 14.

  The parallel / serial converter 14 converts the parallel signal received from the modulator 12 into a serial signal and outputs the serial signal to the digital / analog converter 16.

  The digital / analog converter 16 converts the digital signal received from the parallel / serial converter 14 into an analog signal and outputs the analog signal to the driver unit 20.

  The driver unit 20 amplifies the analog signal received from the digital / analog converter 16 to a predetermined level and outputs the amplified signal to the hybrid circuit 22.

  The hybrid circuit 22 transmits the analog signal received from the driver unit 20 as a communication signal to the terminal side device 2 via the telephone line. The hybrid circuit 22 outputs an analog signal, which is a communication signal received from the terminal-side device 2 via the telephone line, to the low noise amplifier 24.

  The low noise amplifier 24 adjusts the analog signal received from the hybrid circuit 22 to a predetermined level, and then outputs the analog signal to the analog / digital converter 26.

  The analog / digital converter 26 converts the analog signal received from the low noise amplifier 24 into a digital signal and outputs the digital signal to the serial / parallel converter 28.

  The serial / parallel converter 28 converts the serial signal received from the analog / digital converter 26 into a parallel signal and outputs the parallel signal to the demodulator 30.

  The demodulator 30 digitally demodulates the data received from the serial / parallel converter 28 by fast Fourier transform (FFT). Then, the demodulator 30 outputs the digital demodulated data of each subcarrier to the decoder 32.

  The decoder 32 restores the original data from the data of each subcarrier received from the demodulator 30 and outputs it to the outside. Further, the decoder 32 outputs a part or all of the restored data to the control unit 17 as received data information.

  The control unit 17 controls each block in the communication device such as the encoder 10, the modulator 12, the demodulator 30, and the decoder 32.

FIG. 2 is a functional block diagram illustrating the configuration of the control unit.
Referring to FIG. 2, control unit 17 includes a communication rate determination unit 51, a modulation / demodulation method determination unit 52, an SNR measurement unit 53, an error rate measurement unit 54, and a margin setting unit 55.

  The communication speed determination unit 51 acquires SNR measurement results of a plurality of communication signals from its own communication device or a communication device that is a communication partner. In addition, the margin setting unit 55 sets a margin value for each communication signal. Then, the communication speed determination unit 51 determines the communication speed of the communication signal based on the acquired SNR measurement result and the set margin value.

  Since the configuration and basic operation of the terminal-side device 2 are the same as those of the station-side device 1, detailed description will not be repeated here.

  Next, the operation when the communication apparatus according to the embodiment of the present invention determines the communication speed will be described.

[Operation]
FIG. 3 is a flowchart defining an operation procedure when the communication apparatus according to the embodiment of the present invention determines the communication speed.

  In a state where the station-side device 1 and the terminal-side device 2 are communicating, the station-side device 1 monitors the reception quality of communication signals between the station-side device 1 and the terminal-side device 2.

  More specifically, in the station-side device 1, the error rate measuring unit 54 in the control unit 17 is based on the received data information received from the decoder 32 and communicates from the terminal-side device 2 to the station-side device 1 (hereinafter, The error rate of the communication signal is also calculated.

  On the other hand, in the terminal side device 2, the error rate measuring unit 54 in the control unit 17 is based on the received data information received from the decoder 32 and communicates from the station side device 1 to the terminal side device 2 (hereinafter also referred to as the downlink direction). The error rate of the communication signal is calculated. And the control part 17 in the terminal side apparatus 2 controls the encoder 10, and includes the calculation result of an error rate in a communication signal, and transmits to the station side apparatus 1. FIG. In the station apparatus 1, the error rate measuring unit 54 extracts the error rate of the downlink communication signal from the received data information received from the decoder 32.

  When the error rate of the downlink communication signal or the error rate of the uplink communication signal is equal to or greater than a predetermined value (YES in S1), the station-side device 1 performs control to disconnect the uplink and downlink lines. (S2).

  When the uplink and downlink lines are disconnected, the station side device 1 and the terminal side device 2 perform initialization (S3 and S21). For example, the control unit 17 in the station-side device 1 and the terminal-side device 2 includes the driver unit 20 and the low-noise amplifier 24 by controlling the modulator 12 and the demodulator 30 to transmit / receive an unmodulated signal. AGC (Auto Gain Control) circuit gain setting is performed. When the station side apparatus 1 or the terminal side apparatus 2 is turned on, or when the user inputs an initialization command to the station side apparatus 1 or the terminal side apparatus 2, the station side apparatus 1 and the terminal side apparatus 2 It may be configured to perform initialization.

  When the initialization is completed, the station-side device 1 selects the uplink and downlink margin tables. More specifically, the storage unit 8 in the station side device 1 stores a plurality of uplink margin tables and a plurality of downlink margin tables. The control unit 17 in the station side apparatus 1 selects and acquires one each of the uplink and downlink margin tables from the storage unit 8 (S4).

  FIG. 4 is a diagram showing an example of a margin table in the communication apparatus according to the embodiment of the present invention.

  Referring to FIG. 4, for example, the SNR margin of subcarriers 1 and 2 is 6 dB. The margin table is a table representing a correspondence relationship between a plurality of subcarriers used for communication between the station side device 1 and the terminal side device 2 and, for example, a margin value of SNR. The uplink margin table represents the correspondence between the subcarriers used for uplink communication and the SNR margin, and the downlink margin table represents the correspondence between the subcarriers used for downlink communication and the SNR margin.

  Referring to FIG. 3 again, the station side device 1 transmits the selected downlink margin table to the terminal side device 2. More specifically, the control unit 17 in the station apparatus 1 outputs the selected downlink margin table to the encoder 10. The selected margin table in the downstream direction is encoded and assigned to subcarriers in the encoder 10, and the modulator 12, the P / S converter 14, the digital / analog converter 16, the buffer unit 20, and the hybrid circuit. 22 is transmitted to the terminal side device 2 via S22 (S5).

  Further, the station side device 1 transmits, for example, a PN (Pseudo Noise) series signal (hereinafter also referred to as a test signal) to the terminal side device 2 as a communication signal. Similarly to the margin table, the test signal is transmitted to the terminal-side device 2 via the encoder 10, the modulator 12, the P / S converter 14, the digital / analog converter 16, the buffer unit 20, and the hybrid circuit 22 ( S6).

  The terminal side device 2 measures the SNR of the test signal received from the station side device 1. More specifically, in the terminal-side device 2, the demodulator 30 receives data corresponding to the test signal from the serial / parallel converter 28, performs digital demodulation, and outputs the constellation to the control unit 17. The SNR measurement unit 53 in the control unit 17 measures the SNR of the test signal based on the constellation received from the demodulator 30 (S22). Here, the constellation is a symbol point arrangement on an IQ coordinate axis plane composed of an in-phase (I-phase) component and a quadrature (Q-phase) component of a modulation signal.

  The terminal-side device 2 determines the speeds of a plurality of communication signals transmitted from the station-side device 1 based on the SNR measurement result of the test signal and the downlink margin table received from the station-side device 1. For example, the terminal-side device 2 generates a downlink bit table indicating the correspondence between a plurality of subcarriers used by the station-side device 1 for transmission of communication signals and the number of bits allocated to each subcarrier. Send to 1. More specifically, the communication speed determination unit 51 of the control unit 17 in the terminal side device 2 extracts the downlink margin table transmitted by the station side device 1 from the received data information received from the decoder 32. Then, the communication speed determination unit 51 generates a downlink bit table based on the SNR measurement result of the test signal and the extracted downlink margin table, and outputs the bit table to the encoder 10 and the modulation / demodulation method determination unit 52. The downlink bit table is transmitted to the station apparatus 1 via the encoder 10, the modulator 12, the P / S converter 14, the digital / analog converter 16, the buffer unit 20, and the hybrid circuit 22 (S23).

  Further, the modulation / demodulation method determination unit 52 in the terminal-side device 2 recognizes the modulation method of the communication signal transmitted from the station-side device 1 based on the downlink bit table received from the communication speed determination unit 51, and demodulates the demodulator. 30 is notified. The demodulator 30 demodulates the communication signal of each subcarrier by the modulation method indicated by the notification content from the control unit 17.

  The station-side device 1 uses, for example, a plurality of communication signal modulation schemes based on communication speeds of a plurality of communication signals corresponding to a plurality of subcarriers represented by the downlink bit table received from the terminal-side device 2. Respectively. More specifically, the modulation / demodulation method determination unit 52 of the control unit 17 in the station-side device 1 extracts the downlink bit table transmitted by the terminal-side device 2 from the received data information received from the decoder 32. Then, the modulation / demodulation method determination unit 52 determines modulation methods for a plurality of communication signals corresponding to the plurality of subcarriers based on the extracted downlink bit table, and notifies the modulator 12 of the determined modulation methods. To do. Modulator 12 modulates the data of each subcarrier by the modulation method indicated by the notification content from control unit 17.

  Similarly to the station-side device 1, the terminal-side device 2 transmits, for example, a test signal, which is a PN series signal, to the station-side device 1 as a communication signal (S24).

  The station side apparatus 1 measures the signal-to-noise ratio of the test signal received from the terminal side apparatus 2 (S8).

  The station-side device 1 transmits a plurality of communication signals transmitted from the terminal-side device 2 based on the SNR measurement result of the test signal and the uplink margin table selected by the margin setting unit 55 of the control unit 17 in its own communication device. Determine the speed of each. For example, the station-side device 1 generates an uplink bit table indicating the correspondence between a plurality of subcarriers used by the terminal-side device 2 for transmission of communication signals and the number of bits allocated to each subcarrier, and the terminal-side device 2 (S9).

  Further, the modulation / demodulation method determination unit 52 in the station side device 1 recognizes the modulation method of the communication signal transmitted from the terminal side device 2 based on the uplink bit table received from the communication speed determination unit 51, and demodulates the demodulator. 30 is notified. The demodulator 30 demodulates the communication signal of each subcarrier by the modulation method indicated by the notification content from the control unit 17.

  The terminal-side device 2 uses, for example, a plurality of communication signal modulation schemes based on communication speeds of a plurality of communication signals corresponding to a plurality of subcarriers represented by the uplink bit table received from the station-side device 1. Are determined respectively (S25).

  Referring again to FIG. 4, for example, the communication speed determination unit 51 in the terminal-side device 2 receives a predetermined reception quality of the communication signal under the SNR measurement result of the test signal, that is, the SNR condition of the communication signal measured by the SNR measurement unit 53. The communication speed lower than the communication speed that can satisfy the above condition is determined as the communication speed of the communication signal from the communication partner. That is, the communication speed determining unit 51 determines the communication speed at which the error rate of the communication signal is less than a predetermined value under the SNR condition that is further deteriorated by the SNR margin from the measured SNR of the communication signal. Determine as communication speed.

Specifically, when the SNR of the communication signal in the subcarrier 1 is 50 dB, the communication speed determination unit 51 uses the SNR in the subcarrier 1 under the condition of 44 dB, which is further deteriorated by 6 dB of the SNR margin from 50 dB. 15 bits at which the communication signal has a predetermined reception quality, for example, an error rate of less than 10 ⁻⁷ is assigned to subcarrier 1.

  FIG. 5 is a diagram showing an example of a bit table in the communication apparatus according to the embodiment of the present invention.

  Referring to FIG. 5, the number of assigned bits for subcarriers 1 and 2 is 15 bits, and the number of assigned bits for subcarriers 39 and 40 is 3 bits.

  The modulation scheme determination unit 52 of the control unit 17 in the communication device that has received the bit table has 16QAM (Quadrature Amplitude Modulation) with a large symbol rate corresponding to 15 bits because the number of bits allocated to the subcarriers 1 and 2 is 15. The modulation method of the communication signal of subcarrier 1 is determined. Further, since the number of bits allocated to subcarriers 39 and 40 is 3, modulation scheme determining unit 52 uses QPSK (Quadrature Phase Shift Keying) with a small symbol rate corresponding to 3 bits for the communication signals of subcarriers 39 and 40. The modulation method is determined.

  FIG. 6 is a diagram illustrating an example of the relationship between the setting of the SNR margin and the number of transmittable bits. In FIG. 6, a graph A is an SNR margin, a graph B is a graph relatively showing a transmission path loss, that is, an SNR of a communication signal between the station side device 1 and the terminal side device 2, and a graph C is a station side device. 1 is an example of noise power assumed to be generated in the future after the end of training between the terminal device 2 and the terminal side device 2, and the graph D shows the bits allocated to each subcarrier in the communication between the station side device 1 and the terminal side device 2 Is a number. The horizontal axis represents the subcarrier number, and the higher the subcarrier number, the higher the frequency. The vertical axis represents the decibel value and the number of bits.

  FIG. 6 shows a case where the communication apparatus has a configuration in which only the same SNR margin can be set for all subcarriers. In FIG. 6, the noise power has a frequency characteristic that increases to the right, that is, a frequency characteristic that gradually increases as the frequency increases. Such frequency characteristics are considered to be caused by crosstalk in the telephone line.

  In the communication apparatus having such a configuration, the error rate of each communication signal is less than a predetermined value with respect to the noise expected to occur in the future shown in the graph C. Therefore, the SNR margin is the same for all subcarriers. 16 dB. At this time, the total number of transmittable bits is 146 bits for the communication signals in subcarriers 1 to 40.

  FIG. 7 is a diagram showing a relationship between setting of the SNR margin and the number of transmittable bits in the communication apparatus according to the embodiment of the present invention. The way of viewing the figure is the same as in FIG. Further, the frequency characteristics of the graph B and the graph C are the same as those in FIG.

  In the communication apparatus according to the embodiment of the present invention, it is possible to set the SNR margin separately for each subcarrier using the margin table, in other words, independently.

  A margin table corresponding to the graph A is stored in the storage unit 8. Then, the margin setting unit 55 in the control unit 17 selects and sets a margin table corresponding to the graph A.

  Referring to graph A, margin setting unit 55 sets the SNR margin of subcarriers 1 to 9 with low noise power to 6 dB, and gradually sets the SNR margin after subcarrier 10 to increase the subband with high noise power. The SNR margin of carriers 37 to 40 is set to 16 dB. Note that FIG. 4 described above shows a margin table corresponding to the graph A.

  Then, the communication speed determination unit 51 generates a bit table based on the SNR measurement result of the test signal and the margin table.

  Referring to graph D, communication speed determining unit 51 sets the number of bits allocated to subcarriers 1 to 3 having a large SNR measurement result of the test signal and a small SNR margin to 15 bits, and the SNR measurement result of the test signal is The number of bits allocated to subcarriers 31 to 40 having a small and large SNR margin is set to 3 bits. Note that FIG. 5 described above shows a bit table corresponding to the graph D.

  Therefore, the number of bits that can be transmitted is 289 bits in the range of subcarriers 1 to 40, which is significantly larger than the SNR margin setting shown in FIG. As described above, in the communication apparatus according to the embodiment of the present invention, by setting the SNR margin for each subcarrier separately, it is possible to appropriately cope with fluctuations in the frequency characteristics of the transmission line loss due to noise that will occur in the future. be able to.

  FIG. 8 is a diagram showing another example of the relationship between the SNR margin setting and the number of transmittable bits in the communication apparatus according to the embodiment of the present invention. The way of viewing the figure is the same as in FIG. Further, the frequency characteristics of the graph B are the same as those in FIG.

  In FIG. 8, the noise power has a frequency characteristic in which a peak appears in a predetermined frequency band. Referring to graph C, noise power is maximum in subcarriers 15 and 16.

  Referring to graph A, margin setting unit 55 sets the SNR margins of subcarriers 15 and 16 that are the peak of noise power to 22 dB, and subcarriers 1 to 9 and subcarriers at which noise power is at a constant low level. The 22-40 SNR margin is set to 6 dB.

  As described above, the communication device according to the embodiment of the present invention is not limited to the case where the noise power has a frequency characteristic that rises to the right, but can correspond to the case where the noise characteristic has a frequency characteristic in which a peak appears in a predetermined frequency band. it can. Therefore, by storing a plurality of margin tables corresponding to the frequency characteristics of various noise powers in the storage unit 8, the margin setting unit 55 selects a margin table that is assumed to be generated in the future. For example, it is possible to cope with various frequency characteristics of noise power generated in the future, such as frequency characteristics in which a plurality of peaks of noise power appear. A margin table in which the SNR margins of all subcarriers used for communication between the station side device 1 and the terminal side device 2 are the same as shown in the graph A of FIG. is there.

  By the way, in the communication device described in Patent Document 1, since it is necessary to set the noise margin amount of each subcarrier in accordance with the subcarrier having the lowest reception level, the communication speed of the entire communication system is reduced more than necessary. There was a problem. Further, the communication device described in Patent Document 2 is configured to allocate the number of bits of each carrier based on the number of bits at the time of establishment of synchronization and the number of bits at the time of establishment of resynchronization. There was a problem that communication was unstable due to repeated disconnection, connection and retraining due to fluctuations.

  However, in the communication apparatus according to the embodiment of the present invention, margin setting unit 55 sets the SNR margin separately for each subcarrier. Then, the communication speed determination unit 51 transmits, from its own communication apparatus, a communication speed at which the error rate of the communication signal is less than a predetermined value under the SNR condition that is further deteriorated by the SNR margin from the SNR measurement result of the communication signal. It is determined as a communication speed of a communication signal or a communication signal received from a communication partner.

  With such a configuration, it is not necessary to determine the margin value of another subcarrier in accordance with a subcarrier having a large transmission line loss, and it is possible to prevent the communication speed of the entire communication system from being lowered. In addition, since the margin value for each subcarrier in the margin table is a predetermined value and is determined regardless of the SNR of the communication signal measured at the time of training, that is, when determining the communication speed, It is possible to prevent the line disconnection and the connection and retraining from being repeated due to the fluctuation of the frequency characteristic of the transmission line loss. Therefore, in the communication apparatus according to the embodiment of the present invention, it is possible to prevent a decrease in communication speed and to stabilize communication.

[Modification]
The present invention is not limited to the above embodiment, and includes, for example, the following modifications.

(1) SNR margin setting unit In the communication apparatus according to the embodiment of the present invention, the SNR margin can be set separately for each subcarrier using the margin table. However, the present invention is not limited to this. Not what you want. If the margin setting unit 55 is configured to separately set an SNR margin corresponding to at least one subcarrier of a plurality of subcarriers, that is, communication signals, and an SNR margin corresponding to another subcarrier, the communication It is possible to achieve the object of the present invention to prevent a decrease in speed and stabilize communication.

(2) SNR Margin Setting Unit FIG. 9 is a diagram showing the relationship between the SNR margin setting and the number of transmittable bits in a modification of the communication apparatus according to the embodiment of the present invention. The way of viewing the figure is the same as in FIG. Further, the frequency characteristics of the graph B and the graph C are the same as those in FIG.

  In this modification of the communication apparatus, it is possible to set the SNR margin separately for each band using a margin table. A plurality of subcarriers used for communication between the station side device 1 and the terminal side device 2 are divided into at least two bands. A band includes one or more subcarriers.

  Referring to graph A, margin setting unit 55 groups subcarriers 1 to 40 into five bands 1 to 5. Margin setting section 55 sets the SNR margin of band 1 including subcarriers 1 to 9 to 6 dB, sets the SNR margin of band 2 including subcarriers 10 to 18 to 9 dB, and includes bands including subcarriers 19 to 27 3 is set to 12 dB, the SNR margin of band 4 including subcarriers 28 to 36 is set to 15 dB, and the SNR margin of band 5 including subcarriers 37 to 40 is set to 17 dB.

  Accordingly, a margin table corresponding to the graph A is stored in the storage unit 8 and the margin setting unit 55 selects this margin table, so that an SNR margin is set for each band separately. Therefore, it is possible to appropriately cope with fluctuations in the frequency characteristics of transmission line loss due to noise generated in the transmission line.

  Referring to graph D, the number of transmittable bits can be significantly increased in the range of subcarriers 1 to 40 compared to 266 bits and the SNR margin setting shown in FIG. Therefore, similarly to the communication apparatus according to the embodiment of the present invention, it is possible to prevent a decrease in communication speed and to stabilize communication.

  Further, for example, in VDSL, the total number of subcarriers in the uplink and downlink directions is about 3500, and the number of subcarriers is very large. However, the communication for setting the margin is configured by separately setting the SNR margin for each band. It is possible to prevent the processing and configuration of the apparatus from becoming complicated.

(3) SNR Margin Setting Unit FIG. 10 is a diagram showing the relationship between the SNR margin setting and the number of transmittable bits in a modification of the communication apparatus according to the embodiment of the present invention. The way of viewing the figure is the same as in FIG. The frequency characteristics of graph B and graph C are the same as those in FIG.

  The noise power has a frequency characteristic in which a peak appears in a predetermined frequency band. Referring to graph C, noise power is maximum in subcarriers 15 and 16.

  Referring to graph A, margin setting unit 55 groups subcarriers 1 to 40 into three bands 1 to 3. The margin setting unit 55 sets the SNR margin of the band 1 including the subcarriers 1 to 9 where the noise power is a constant low level to 6 dB, and the SNR of the band 2 including the subcarriers 10 to 21 that is the peak of the noise power. The margin is set to 16 dB, and the SNR margin of band 3 including subcarriers 22 to 40 where the noise power is constant and low is set to 6 dB.

  Therefore, a margin table corresponding to the graph A is stored in the storage unit 8 and the margin setting unit 55 selects this margin table, so that an SNR margin is set for each band separately. Therefore, it is possible to appropriately cope with fluctuations in the frequency characteristics of transmission line loss due to noise generated in the transmission line.

  Also, with such a configuration, it is possible to prevent the processing and configuration of the communication apparatus for setting margins from becoming complicated when the number of subcarriers is very large.

  Further, by expanding the subcarrier range in which the SNR margin is set to be larger than 6 dB as compared with the margin table shown in FIG. 8, it is possible to cope with the case where the noise power peak frequency band shown in the graph C varies.

(4) Generation and transmission of bit table In the communication apparatus according to the embodiment of the present invention, when determining the communication speed of the downlink communication signal, the terminal-side apparatus 2 uses the SNR measurement result of the downlink test signal and Although the configuration is such that the downlink bit table is generated based on the downlink margin table and transmitted to the station-side apparatus 1, the present invention is not limited to this. The terminal device 2 transmits the SNR measurement result of the downlink test signal to the station device 1. Then, the station-side device 1 generates a downlink bit table based on the SNR measurement result of the downlink test signal and the downlink margin table, and transmits it to the terminal-side device 2. The terminal device 2 may be configured to recognize the modulation method of the communication signal transmitted from the station device 1 based on the downlink bit table received from the station device 1. Further, when determining the communication speed of the uplink communication signal, the station apparatus 1 transmits the SNR measurement result of the uplink test signal and the uplink margin table to the terminal apparatus 2. Then, the terminal-side device 2 generates an uplink bit table based on the SNR measurement result of the uplink test signal and the uplink margin table, and transmits it to the station-side device 1. The station-side device 1 may be configured to recognize the modulation method of the communication signal transmitted from the terminal-side device 2 based on the downlink bit table received from the terminal-side device 2.

(5) SNR
In the communication apparatus according to the embodiment of the present invention, the communication speed determining unit 51 performs communication in which the error rate of the communication signal is less than a predetermined value under the SNR condition that is further deteriorated by the SNR margin from the SNR measurement result of the communication signal. The speed is determined as the communication speed of the communication signal transmitted from the own communication device or the communication signal received from the communication partner. However, the SNR is not limited to the SNR, and any SNR can be used if it is an index representing the line state of the communication signal. Can be used instead of

(6) Update rate of communication speed In the communication apparatus according to the embodiment of the present invention, in the state where the station side apparatus 1 and the terminal side apparatus 2 are communicating, the station side apparatus 1 When the error rate or the error rate of the uplink communication signal is greater than or equal to a predetermined value, control is performed to disconnect the uplink and downlink lines. The station side device 1 and the terminal side device 2 select the margin table and generate the bit table to update the communication speed of the uplink and downlink communication signals. However, the present invention is limited to this. It is not a thing.

  When the uplink and downlink lines are frequently disconnected, for example, when the station-side device 1 disconnects the uplink and downlink lines a predetermined number of times within a predetermined time due to a deterioration in the error rate of the communication signal, The margin table can be selected and the bit table can be generated to update the communication speed of the upstream and downstream communication signals.

  Further, a margin used for communication between the station-side device 1 and the terminal-side device 2 by the communication system manager controlling the communication device based on the result of monitoring the error rate of the communication signal in the communication device. It is also possible to adopt a configuration in which the table is changed manually. Alternatively, the communication system monitors the error rate of the communication signal, and issues a warning to the administrator when the monitoring result satisfies a predetermined condition. If the margin table is not updated manually within a specified period of time after warning the administrator, or if the error rate is not improved sufficiently even if the margin table is updated The margin table may be changed by a combination of manual and automatic, such as the system automatically updating the margin table.

(7) Selection of Margin Table The margin setting unit 55 includes, for example, a plurality of margin tables stored in the storage unit 8 each time the communication speed is updated or the communication speed is updated a predetermined number of times. The structure which selects any one of them sequentially may be sufficient. In addition, the margin setting unit 55 determines which of the plurality of margin tables stored in the storage unit 8 is the current one based on the error occurrence state before the communication speed is updated and the past communication speed update frequency. A configuration may be adopted in which the margin table is selected in the order in which it is estimated to be suitable by estimating whether it is most suitable for the situation. In addition, the margin setting unit 55 may be configured to select a margin table based on an operation of the communication system manager on the communication device. Further, the margin setting unit 55 may be configured to automatically generate a margin table using a predetermined algorithm based on an error occurrence state before the communication speed is updated and a past communication speed update frequency.

(8) Holding Margin Table In the communication apparatus according to the embodiment of the present invention, only the storage unit 18 in the station side apparatus 1 is configured to store the margin table. However, the present invention is not limited to this. The storage unit 18 in both the side device 1 and the terminal side device 2 may be configured to store a margin table. In this case, it is not necessary to transmit / receive the margin table itself between the station-side device 1 and the terminal-side device 2, and the margin table identification number can be transmitted / received. Further, the margin setting unit 55 can automatically generate a margin table using a predetermined algorithm based on the parameters, and only the parameters can be transmitted / received between the station side device 1 and the terminal side device 2.

  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 functional block diagram which shows the structure of the communication system which concerns on embodiment of this invention, and the communication apparatus in this communication system. It is a functional block diagram which shows the structure of a control part. It is the flowchart which defined the operation | movement procedure at the time of the communication apparatus which concerns on embodiment of this invention determines a communication speed. It is a figure which shows an example of the margin table in the communication apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the bit table in the communication apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the relationship between the setting of a SNR margin, and the number of transmittable bits. It is a figure which shows the relationship between the setting of the SNR margin in the communication apparatus which concerns on embodiment of this invention, and the number of bits which can be transmitted. It is a figure which shows the other example of the relationship between the setting of the SNR margin in the communication apparatus which concerns on embodiment of this invention, and the number of transmittable bits. It is a figure which shows the relationship between the setting of a SNR margin and the number of bits which can be transmitted in the modification of the communication apparatus which concerns on embodiment of this invention. It is a figure which shows the relationship between the setting of a SNR margin and the number of bits which can be transmitted in the modification of the communication apparatus which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Station side apparatus (communication apparatus), 2 Terminal side apparatus (communication apparatus), 8 Memory | storage part, 10 Encoder, 12 Modulator (IFFT), 14 Parallel serial (P / S) converter, 16 Digital-analog converter (DAC), 17 control unit, 20 driver unit, 22 hybrid circuit, 24 low noise amplifier, 26 analog-digital converter (ADC), 28 serial / parallel (S / P) converter, 30 demodulator (FFT), 32 Decoder, 51 Communication speed determining unit, 52 Modulation / demodulation method determining unit, 53 SNR measuring unit, 54 Error rate measuring unit, 55 Margin setting unit, 61 Transmitting unit, 62 Receiving unit, 100 Communication system.

Claims (8)

A receiving unit for receiving a plurality of communication signals having different frequencies from a communication partner;
A measuring unit for measuring a line state of the received plurality of communication signals;
A margin setting unit for separately setting a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal;
A communication speed for determining communication speeds of the plurality of communication signals such that an error rate of the plurality of communication signals is less than a predetermined value in a line state that is deteriorated by the set margin value from the measured line state. A decision unit;
A communication apparatus comprising: a transmission unit that notifies the determined communication speed to the communication partner. A transmission unit for transmitting a plurality of communication signals having different frequencies to a communication partner;
A receiving unit that obtains line states of the plurality of communication signals measured by the communication partner from the communication partner;
A margin setting unit for separately setting a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal;
Communication speeds of the plurality of communication signals so that an error rate of the plurality of communication signals received by the communication partner is less than a predetermined value in a line state degraded by the set margin value from the acquired line state. A communication speed determining unit for determining
The transmission unit is a communication device that transmits the plurality of communication signals to the communication partner at the determined communication speed.   The communication apparatus according to claim 1, wherein the margin setting unit sets the margin value for each communication signal.   The margin setting unit sets a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal to different values. Communication equipment. The line condition is a signal to noise ratio;
The communication speed determining unit is configured so that an error rate of each of the plurality of communication signals received by the communication partner is less than a predetermined value at a signal-to-noise ratio that is smaller than the measured signal-to-noise ratio by the margin value. The communication apparatus according to claim 1, wherein communication speeds of the plurality of communication signals are respectively determined. The communication device further stores a plurality of tables in which a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal are defined. With
The communication apparatus according to claim 1, wherein the margin setting unit selects and sets any one of the plurality of tables. A communication system comprising a first communication device and a second communication device,
The first communication device is:
A transmission unit for transmitting a plurality of communication signals having different frequencies to the second communication device;
The second communication device is:
A receiver that receives the plurality of communication signals from the first communication device;
A measuring unit for measuring a line state of the received plurality of communication signals;
A margin setting unit for separately setting a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal;
A communication speed for determining communication speeds of the plurality of communication signals such that an error rate of the plurality of communication signals is less than a predetermined value in a line state that is deteriorated by the set margin value from the measured line state. A decision unit;
A transmission unit for notifying the determined communication speed to the first communication device,
The transmission unit in the first communication device is a communication system that transmits the plurality of communication signals to the second communication device at the notified communication speed. A communication method in a communication system comprising a first communication device and a second communication device,
The first communication device transmitting a plurality of communication signals having different frequencies to the second communication device;
The second communication device measuring line states of the plurality of communication signals received from the first communication device;
The second communication device separately setting a margin value corresponding to at least one communication signal of the plurality of communication signals and a margin value corresponding to another communication signal;
The second communication device has the plurality of communication signals such that an error rate of each of the plurality of communication signals is less than a predetermined value in a line state in which the set margin value has deteriorated from the measured line state. Determining each communication speed;
The second communication device notifying the determined communication speed to the first communication device;
A communication method including the step of the first communication device transmitting the plurality of communication signals to the second communication device at the notified communication speed.

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