JP2006203455A - Adsl modem apparatus and method of controlling communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform certainly a data communication by reducing an influence which gives an impulse response on a line to a pilot tone. <P>SOLUTION: A method of controlling the communication includes the steps of computing the energy E1 of the part which exceeds the length of a cyclic prefix among the impulse responses on a communication line (ST705), based on the specific signal for which it is exchanged before the data communication; selecting the number of subcarrier which turns off the transmission power among the subcarriers which adjoin the subcarrier utilized as a pilot tone in response to the energy E1 of the part exceeding the length of this cyclic prefix (ST710, etc.); informing the number of the subcarrier which turns off this transmission power to mating ADLS modem apparatus (ST712, etc.); and performing the data communication between the mating ADSL modem apparatus using the subcarrier except the subcarrier of the number which turns off this transmission power (ST709). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ADSL modem apparatus and a communication control method.

  In recent years, an ADSL service that enables simultaneous use of a high-speed Internet connection service and a conventional telephone service using an existing telephone line has been rapidly spreading. In such an ADSL service, symbol synchronization is established in an initialization sequence according to the G.lite or G.dmt recommendation before actual data communication is started. After the symbol synchronization is established, a cyclic prefix (hereinafter referred to as “CP (cyclic prefix)”) is inserted between symbols constituting communication data to indicate symbol delimiters and on the line. The effect of impulse response is absorbed.

The above-mentioned G. In data communication using the DMT modulation method adopted in the dmt recommendation, an ADSL modem apparatus that appropriately performs gain control of signal energy that can be deteriorated due to factors such as line conditions has been proposed (for example, see Patent Document 1). .
JP 2003-8536 A

  However, in the conventional ADSL service, the length of the CP is fixed, and the influence of the impulse response on the line may not be absorbed appropriately. That is, in general, the CP is composed of the length of 32 sampling data (generally, one symbol is composed of the length of 512 sampling data). However, the length of the impulse response on the line varies depending on the line state. When the line state is good, the length of the impulse response is shortened, whereas when the line state is bad, the length of the impulse response is long.

  For example, the length of the impulse response may correspond to the length of 50 sampling data depending on the line state. In this case, the length of the CP is less than the length of the impulse response on the line, and the impulse response that could not be absorbed appears as noise of the following symbol. As a result, there arises a problem that the S / N ratio in data communication is lowered and the transmission efficiency is lowered. In particular, when the noise generated in this way affects the pilot tone, the ADSL modem apparatus on the transmission side and the ADSL modem apparatus on the reception side cannot be properly synchronized, and data communication itself is impossible. Problem arises.

  The present invention has been made in view of the above circumstances, and provides an ADSL modem apparatus and a communication control method capable of reducing the influence of an impulse response on a line on a pilot tone and reliably performing data communication. The purpose is to do.

  The present invention calculates the energy of the portion of the impulse response on the communication line that exceeds the length of the cyclic prefix based on a specific signal exchanged before data communication, and exceeds the length of this cyclic prefix. The number of subcarriers whose transmission power is turned off is selected from the subcarriers adjacent to the subcarriers used as pilot tones according to the energy of the part, and the number of subcarriers whose transmission power is turned off is selected as the partner ADSL modem apparatus And the data communication with the partner ADSL modem apparatus is performed using the subcarriers excluding the number of subcarriers that turn off the transmission power notified to the partner ADSL modem apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the influence which the impulse response on a line | wire has on a pilot tone can be reduced, and data communication can be performed reliably.

  The ADSL modem apparatus according to the first aspect of the present invention calculates an energy of a portion exceeding a cyclic prefix length in an impulse response on a communication line based on a specific signal exchanged before data communication. Selecting means for selecting the number of subcarriers whose transmission power is turned off among subcarriers adjacent to subcarriers used as pilot tones according to the energy of the portion exceeding the length of the cyclic prefix; A notifying means for notifying the partner ADSL modem apparatus of the number of subcarriers for turning off the transmission power, and a partner ADSL modem using subcarriers excluding the number of subcarriers for turning off the transmission power selected by the selecting means; And a communication means for performing data communication with the apparatus.

  According to this configuration, the number of subcarriers whose transmission power is turned off is determined according to the magnitude of the energy of the portion exceeding the cyclic prefix length of the impulse response on the communication line, and the partner ADSL modem apparatus Data communication between the two. For this reason, the transmission power of subcarriers adjacent to the pilot tone is turned off according to the length of the impulse response on the line, thereby reducing the influence of the impulse response on the line on the pilot tone and ensuring data communication. It can be carried out.

  According to a second aspect of the present invention, in the ADSL modem apparatus according to the first aspect, the calculation means calculates an energy amount from a time point of the rear end of the cyclic prefix in the impulse response to a time point after a certain time has elapsed. By obtaining this, a configuration is adopted in which the energy of the portion exceeding the length of the cyclic prefix is calculated.

  According to this configuration, the size of the portion of the impulse response that exceeds the length of the cyclic prefix is calculated by obtaining the amount of energy from the time point of the cyclic prefix to the time point after a certain time has elapsed. . Therefore, the size of the portion exceeding the length of the cyclic prefix can be calculated only by obtaining the energy amount in a certain range of the impulse response.

  According to a third aspect of the present invention, in the ADSL modem apparatus according to the first aspect, the selecting means includes energy of a portion exceeding the length of the cyclic prefix and subcarriers used as the pilot tone. A configuration is adopted in which the number of subcarriers for turning off the transmission power is determined based on a comparison result with energy.

  According to this configuration, the number of subcarriers whose transmission power is turned off is determined based on a comparison result between the energy of the portion exceeding the length of the cyclic prefix and the energy of the subcarrier used as the pilot tone. . Therefore, the number of subcarriers whose transmission power is turned off can be determined in accordance with the relationship between the energy of the portion exceeding the length of the cyclic prefix and the energy of the subcarriers used as pilot tones.

  According to a fourth aspect of the present invention, in the ADSL modem apparatus according to the third aspect, the selection means uses a portion of energy exceeding the length of the cyclic prefix for subcarriers used as the pilot tone. The number of subcarriers that turn off the transmission power when the energy is greater than a certain value is increased, while the number of subcarriers that turn off the transmission power when the energy is smaller than the certain value of the subcarrier energy used as the pilot tone. Use a configuration that reduces the number of carriers.

  According to this configuration, the number of subcarriers whose transmission power is turned off is increased when the energy of the portion exceeding the length of the cyclic prefix is larger than a certain value of the energy of the subcarrier used as the pilot tone. On the other hand, when the energy of subcarriers used as pilot tones is smaller than a certain value, the number of subcarriers whose transmission power is turned off is reduced. For this reason, it is possible to appropriately increase or decrease the number of subcarriers whose transmission power is turned off in correspondence with the energy of the portion exceeding the length of the cyclic prefix.

  According to a fifth aspect of the present invention, in the ADSL modem apparatus according to the first aspect, the specific signal is a REVERB signal.

  According to this configuration, by using the REVERB signal that is repeatedly exchanged in the initialization procedure, the number of subcarriers whose transmission power is turned off is determined according to the energy of the portion exceeding the length of the cyclic prefix of the impulse response. Can do.

  The ADSL modem apparatus according to the sixth aspect of the present invention uses the energy of a portion exceeding the length of the cyclic prefix in the impulse response on the communication line calculated based on the specific signal exchanged before the data communication. The receiving means for receiving the notification of the number of subcarriers to be turned off according to the transmission from the partner ADSL modem apparatus, and subcarriers excluding the number of subcarriers for turning off the transmission power notified by the receiving means. And a communication means for performing data communication with the counterpart ADSL modem apparatus.

  According to this configuration, the number of subcarriers whose transmission power is turned off is determined according to the magnitude of the energy of the CP length exceeding part of the impulse response on the communication line notified from the partner ADSL modem apparatus. Data communication is performed with the ADSL modem apparatus. For this reason, among the subcarriers adjacent to the pilot tone according to the length of the impulse response on the line, the subcarrier for turning off the transmission power is determined. Therefore, the impulse response on the communication line has an influence on the pilot tone. The data communication can be performed reliably.

  The communication control method according to the seventh aspect of the present invention calculates the energy of the portion exceeding the length of the cyclic prefix in the impulse response on the communication line based on the specific signal exchanged before data communication, Select the number of subcarriers whose transmission power is to be turned off among the subcarriers adjacent to the subcarriers used as pilot tones according to the energy of the portion exceeding the length of the cyclic prefix, and turn off the transmission power. The number of subcarriers is notified to the partner ADSL modem apparatus, and data communication with the partner ADSL modem apparatus is performed using subcarriers excluding the number of subcarriers that turn off the transmission power notified to the partner ADSL modem apparatus. Is what you do.

  According to an eighth aspect of the present invention, in the communication control method according to the seventh aspect, the amount of energy from the time point of the rear end of the cyclic prefix in the impulse response to the time point after a predetermined time has been obtained. The energy of the portion exceeding the length of the click prefix is calculated.

  According to a ninth aspect of the present invention, in the communication control method according to the seventh aspect, the comparison result between the energy of the portion exceeding the length of the cyclic prefix and the energy of the subcarrier used as the pilot tone The number of subcarriers for turning off the transmission power is determined based on the above.

  According to a tenth aspect of the present invention, in the communication control method according to the ninth aspect, the energy of the portion exceeding the length of the cyclic prefix is greater than a constant value of the energy of the subcarrier used as the pilot tone. Is increased, the number of subcarriers for turning off the transmission power is increased, while the number of subcarriers for turning off the transmission power is decreased when the subcarrier energy used as the pilot tone is smaller than a certain value. It is something to be made.

  An eleventh aspect of the present invention is the communication control method according to the seventh aspect, wherein the specific signal is composed of a REVERB signal.

  In the communication control method according to the twelfth aspect of the present invention, the energy of a portion exceeding the length of the cyclic prefix in the impulse response on the communication line calculated based on the specific signal exchanged before the data communication is obtained. In response to the notification of the number of subcarriers for turning off the transmission power selected in response, the partner ADSL modem device uses the subcarriers excluding the number of subcarriers for turning off the notified transmission power. Data communication is performed with the device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a communication system on a terminal device (ATU-R) side installed in a home or the like to which the present invention is applied. The communication system on the exchange station (ATU-C) side also has the same configuration.

  In the communication system shown in FIG. 1, a public line network or an equivalent line network (hereinafter referred to as “line”) is connected to an ADSL modem apparatus 2 via a splitter 1, and a user terminal 3 is connected to the ADSL modem apparatus 2. It is connected. In addition, when the user terminal 3 and the telephone 4 are used on one line, the splitter 1 is necessary. However, if the telephone 4 is not used, the splitter 1 is not necessary. It is also possible to configure the user terminal 3 to incorporate the ADSL modem apparatus 2.

  The ADSL modem apparatus 2 includes a transceiver 11 that executes ADSL communication and a host 12 that controls the overall operation including the transceiver 11. The line side end of the transceiver 11 is constituted by an analog circuit via an analog front end (hereinafter referred to as “AFE”). A driver 15 is connected to the DA converter of the AFE 13 via an analog filter 14, and an analog signal amplified by the driver 15 is sent to a line via a hybrid 16. An analog signal coming from the line is received by the receiver 17 via the hybrid 16 and input to the AD conversion unit of the AFE 13 via the analog filter 18. The AFE 13 outputs the sampling data output from the AD conversion unit to the transceiver 11.

  FIG. 2 is a functional block diagram of the transceiver 11 included in the ADSL modem apparatus 2. The processor 20 has a function of executing a handshake procedure and an initialization procedure and executing communication control during data communication (Showtime).

  The transmission side of the transceiver 11 includes a Reed-Solomon encoding unit 21 for adding redundant bits for error checking, an interleaving unit 22 for rearranging data to enable correction for burst errors during Reed-Solomon decoding, and a trellis code A trellis encoding unit 23 that performs convolution of data by conversion, a tone ordering unit 24 that allocates the number of bits for each carrier, a constellation encoding unit 25 that allocates the phase of transmission data on constellation coordinates, and constellation encoded. The IFFT unit 26 that performs inverse fast Fourier transform (hereinafter referred to as “IFFT”), and the CP addition unit 27 that adds a cyclic prefix (hereinafter referred to as “CP (cyclic prefix)”) to the IFFT transmission data. It is configured.

  The receiving side of the transceiver 11 includes a CP removing unit 28 that removes the CP added to the received signal, an FFT unit 29 that performs fast Fourier transform (hereinafter referred to as “FFT”) on sampling data of the received signal, and an constellation of the FFT output signal. A constellation decoding / FEQ unit 30 that decodes data from the constellation coordinates and corrects the phase on the constellation coordinates, and a tone deordering unit 31 that restores data assigned to each carrier that has been tone-ordered on the transmission side A Viterbi decoding unit 32 for Viterbi decoding received data, a deinterleaving unit 33 for returning the data rearranged on the transmission side, and a Reed-Solomon decoding unit 34 for deleting redundant bits added on the transmission side. Yes. The RAM 35 is a work area of the processor 20 and is used when executing a handshake procedure and an initialization procedure. The transceiver 11 is connected to the host 12 via a host interface (I / F) 36.

  Having such a configuration, the ADSL modem apparatus 2 according to the present embodiment calculates an impulse response on the line based on a known signal transmitted from the switching center apparatus (ATU-C), and the impulse response Of these, energy E1 (hereinafter referred to as "CP length transcending portion") included in a portion exceeding the predetermined CP length (hereinafter referred to as "CP length") (hereinafter referred to as "CP length transcendental portion"). The transmission power to be given to the subcarrier adjacent to the pilot tone is switched on / off according to the above. Specifically, the number of transmission powers to be turned off among the subcarriers adjacent to the pilot tone is increased or decreased according to the magnitude of the energy E1. As a result, the influence of the impulse response on the line on the pilot tone is reduced. In the ADSL modem apparatus 2 according to the present embodiment, the number of subcarriers whose transmission power is turned off is increased when the energy E1 of the CP length excess portion is relatively large, and the transmission power is turned off when the energy is small. Reduce the number of

  In the following, a case where the length of the impulse response on the line is calculated based on the REVERB signal transmitted as a known signal from the switching center apparatus (ATU-C) in the initialization procedure will be described. However, the known signal is not limited to this REVERB signal.

  The impulse response on the line is calculated using the REVERB signal received by the FFT unit 29 by the processor 20. At that time, as shown in FIG. 2, the processor 20 performs X (ω), which is a signal obtained by IFFT of a known REVERB signal, and Y (ω), which is a signal obtained by performing FFT on the REVERB signal actually received via the line. Is used to calculate the impulse response on the line.

More specifically, the processor 20 acquires X (ω) obtained by performing IFFT processing on the REVERB signal stored in the RAM 35, and receives Y (ω) from the FFT unit 29. Since the REVERB signal is a known signal described in the recommendation, the ADSL modem apparatus 2 according to the present embodiment stores X (ω) calculated from the REVERB signal in the RAM 35 in advance. . The processor 20 then
Z (ω) = Y (ω) / X (ω)
And the impulse response is Impulse (t),
Impulse (t) = invers FFT (Z (ω))
Calculate In this way, a so-called impulse response on the line (Impulse (t)) is calculated.

  After calculating the impulse response (Impulse (t)) on the line, the processor 20 calculates the energy E1 of the CP length transcending portion of the impulse response. Then, the number of subcarriers that are adjacent to the pilot tone and whose transmission power is turned off is determined in accordance with the magnitude of the energy E1 of the CP length transcending portion.

  Hereinafter, a process in which the processor 20 calculates the energy E1 of the part exceeding the CP length and determines the number of subcarriers whose transmission power is turned off according to the calculated magnitude of the energy E1 will be described using a specific example.

  FIG. 3 is a diagram illustrating an example of a waveform of an impulse response (Impulse (t)) calculated by the processor 20. In the figure, the horizontal axis represents time and the vertical axis represents amplitude.

  In the figure, waveforms of impulse responses (Impulse (t)) having three types of lengths are shown. The waveforms of the impulse response (Impulse (t)) in which the length of the impulse response (Impulse (t)) is shortened are shown in the order shown in FIGS. In addition, since the CP length is generally fixed to the length of 32 sampling data, the length of the CP length transcending portion is also shortened in the order shown in FIGS. 3 (a) to 3 (c).

The processor 20 calculates the energy E1 of the part exceeding the CP length by obtaining the energy amount at the time t2 when a certain time has elapsed from the time t1 that is the rear end of the CP length. Specifically, the processor 20 calculates the energy E1 of the CP length transcending portion by obtaining an integral value from the time point t1 to the time point t2 according to the following equation. It should be noted that a calculation formula other than the following formula may be used as a calculation formula for calculating the energy E1 of the CP length transcending portion.

  As described above, in the present embodiment, the energy E1 of the CP length transcending portion is calculated by obtaining the energy amount from the time t1 at the rear end of the CP length to the time t2 after a certain time has elapsed in the impulse response. Therefore, it is possible to calculate the energy E1 of the CP-length exceeding portion simply by obtaining the energy amount within a certain range of the impulse response.

  Then, the energy E1 of the part exceeding the CP length and the energy E2 of the main part of the pilot tone (hereinafter referred to as “pilot tone energy E2”) are compared, and the subcarrier that turns off the transmission power according to the comparison result Determine the number of Specifically, the number of subcarriers whose transmission power is turned off is determined according to how much energy E1 in the CP-long transcendent portion is smaller than energy E2 of pilot tone. The pilot tone energy E2 is integrated from the time point t1 shown in FIG. 3 to a time point t3 (not shown) according to the above-described equation (1) in the same manner as the energy E1 of the CP length transcending portion. Calculated by finding the value.

  In the present embodiment, a difference in energy amount between the energy E1 of the CP-long portion and the energy E2 of the pilot tone (hereinafter referred to as “energy difference”) is: If it is less than 35 dB, In the case of 35 dB or more and less than 40 dB, C.I. It corresponds to the case of 40 dB or more. The number of subcarriers whose transmission power is turned off is determined depending on whether or not the energy E1 of the CP length transcending portion exists. Specifically, the processor 20 determines the number of subcarriers whose transmission power is to be turned off when the difference in energy amount falls within the range A, and determines the transmission power when the difference falls within the range B. The number of subcarriers to be turned off is determined to be two, the number of subcarriers to be turned off is determined to be one when belonging to the range of C, and the number of subcarriers to be turned off in the case of D is determined. The number is determined to be zero.

  Note that the criteria for determining the number of subcarriers for turning off transmission power and the number of subcarriers for turning off transmission power are not limited to those described above, and any value can be set. Is possible.

  In FIG. 3, the difference in energy amount shown in FIG. 3 (a) belongs to the range A, the difference in energy amount shown in FIG. 3 (b) belongs to the range B, and is shown in FIG. 3 (c). It is assumed that the difference in energy amount belongs to the above range C. Therefore, when the impulse response (Impulse (t)) shown in FIG. 3A, FIG. 3B, and FIG. 3C is calculated, the processor 20 determines the number of subcarriers whose transmission power is turned off. Decided to be 10, 2, or 1.

  Here, the influence of the energy E1 of the part exceeding the CP length on the pilot tone will be described. The energy E1 of the portion exceeding the CP length in each subcarrier appears as a side lobe emitted by each subcarrier on the frequency axis. This side lobe constitutes noise for adjacent subcarriers. In particular, the side lobe generated by the subcarrier adjacent to the pilot tone is a factor that hinders detection of the pilot tone.

  FIG. 4 is a diagram for explaining side lobes generated by subcarriers adjacent to pilot tones. In the figure, the horizontal axis represents frequency and the vertical axis represents energy amount. Also, the horizontal axis indicates the subcarrier number, and the case where the 64th subcarrier (hereinafter abbreviated as “subcarrier # 64”) is used as the pilot tone is shown. Furthermore, only the side lobes output by subcarriers # 63 and # 65 adjacent to the pilot tone are shown. Further, a REVERB signal for calculating an impulse response on the line is shown, and in the REVERB signal, transmission power of 55 dB is given to each subcarrier. Therefore, the energy amount E2 of the pilot tone also indicates approximately 55 dB.

  In the figure, the side lobes produced by the subcarriers # 63 and # 65 when the difference in the energy amount falls within the range B according to the energy E1 of the CP-long portion is indicated by a solid line. That is, the case where the energy E1 of the portion exceeding the CP length is small in the range of 35 dB or more and less than 40 dB as compared with the pilot tone energy amount E2 (55 dB) is shown (approximately 20 dB in the figure). Also, the side lobes produced by the subcarriers # 63 and # 65 when the difference in the energy amount falls within the range C according to the energy E1 of the CP-long portion is indicated by a one-dot chain line. That is, the case is shown where the energy E1 of the portion exceeding the CP length is smaller in the range of 40 dB or more than the energy amount E2 (55 dB) of the pilot tone (in the figure, approximately 15 dB).

  As shown in the figure, the side lobe produced by the subcarrier gradually attenuates as the distance from the subcarrier increases. Adjacent subcarriers have the greatest influence on the pilot tone. For this reason, ADSL modem apparatus 2 according to the present embodiment reduces the influence exerted on the pilot tone by turning off the transmission power applied to the subcarrier adjacent to the pilot tone. When the influence on the pilot tone is large, the number of subcarriers whose transmission power is turned off is increased.

  FIG. 5 is a block diagram showing a configuration of the IFFT unit 26 and the FFT unit 29 included in the transceiver 11 according to the present embodiment.

  As shown in the figure, the IFFT unit 26 includes a subcarrier on / off selection unit 41. The subcarrier on / off selection unit 41 selects transmission power on / off for subcarriers adjacent to the pilot tone under the instruction of the processor 20. In the present embodiment, the subcarrier on / off selection unit 41 sets the number of subcarriers for selecting on / off of transmission power to 0, 1 (2 in total), 2 (4 in total), Select between 10 (20 in total).

  The IFFT unit 26 performs an IFFT process on the data constellation-encoded by the constellation encoding unit 25 according to the number of subcarriers selected by the subcarrier on / off selection unit 41. Then, the data subjected to IFFT processing is sent to the CP adding unit 27.

  On the other hand, the FFT unit 29 includes a subcarrier on / off selection unit 42. The subcarrier on / off selection unit 42 selects on / off of transmission power for the subcarrier adjacent to the pilot tone under the instruction of the processor 20. The instruction of the number of subcarriers for selecting on / off of transmission power to the FFT unit 29 from the processor 20 is made based on a notification from the partner ADSL modem apparatus. In the present embodiment, the subcarrier on / off selector 42 sets the number of subcarriers for selecting transmission power on / off to 0, 1 (total of 2), and 2 (total of 4). Select between 10 (20 in total).

  The FFT unit 29 performs an FFT process on the data from which the CP has been removed by the CP removal unit 28 according to the number of points selected by the subcarrier on / off selection unit 42. Then, the data subjected to the FFT processing is sent to the constellation decoding / FEQ unit 30.

  Hereinafter, in the ADSL modem apparatus 2 according to the present embodiment, the impulse response on the line is calculated, and the number of subcarriers whose transmission power is turned off according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response is calculated. The operation when determining and performing data communication will be described.

  FIG. 6 is a diagram showing a state in which the ADSL modem apparatus 2A on the exchange station (ATU-C) side and the ADSL modem apparatus 2B on the home terminal apparatus (ATU-R) side are connected via a line. ing. In the figure, the configuration of the analog filter 14 and the driver 15 shown in FIG. 1 is omitted. Further, in the ADSL modem apparatus 2A on the exchange station (ATU-C) side, the configuration on the reception side and part of the configuration on the transmission side (22 to 24) are simplified. Furthermore, in the ADSL modem apparatus 2B on the terminal device (ATU-R) side in the home, the configuration on the transmission side and part of the configuration on the reception side (31 to 33) are simplified.

  FIG. 7 shows the number of subcarriers whose transmission power is turned off according to the magnitude of the energy E1 of the CP length transcending portion of the impulse response on the line in the ADSL modem apparatus 2B on the terminal device (ATU-R) side in the home. It is a flowchart for demonstrating the operation | movement at the time of determining and performing data communication. FIG. 8 shows the number of subcarriers whose transmission power is turned off in accordance with the magnitude of the energy E1 of the CP-length transcending portion of the impulse response on the line in the ADSL modem apparatus 2A on the exchange station (ATU-C) side. It is a flowchart for demonstrating the operation | movement at the time of determining and performing data communication.

  When data communication is performed by determining the number of subcarriers whose transmission power is turned off according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line, first, the processor 20 of the ADSL modem apparatus 2B As shown in FIG. 7, reception of the REVERB signal from the partner ADSL modem apparatus 2A is monitored (ST701).

  If the reception of the REVERB signal is confirmed, the processor 20 acquires X (ω) obtained by performing IFFT processing on the known REVERB signal from the RAM 35 (ST702). Thereafter, Y (ω) obtained by performing FFT processing on the received REVERB signal is acquired from the FFT unit 29 (ST703).

Next, an impulse response (Impulse (t)) on the line is calculated using X (ω) and Y (ω) (ST704). In particular,
Z (ω) = Y (ω) / X (ω)
After calculating
Impulse (t) = invers FFT (Z (ω))
To calculate the impulse response (Ipulse (t)).

  After calculating the impulse response, the processor 20 calculates the energy E1 of the portion exceeding the CP length in the impulse response (ST705). Specifically, the processor 20 calculates the energy E1 of the CP length transcending portion by obtaining an integral value from the time point t1 to the time point t2 corresponding to the rear end of the CP length illustrated in FIG.

  If the energy E1 of the CP length transcending part is calculated, the processor 20 determines whether the energy E1 of the CP length transcending part actually exists (ST706). Here, when the energy E1 of the CP length transcending portion does not exist, it is notified that there is no subcarrier for turning off the transmission power (ST707), and the exchange with the ADSL modem apparatus 2A on the exchange station (ATU-C) side is notified. Initialize is received and Showtime is received (ST708, ST709). If all data is received from the ADSL modem apparatus 2A on the exchange station (ATU-C) side at the show time, the process is terminated.

  On the other hand, when the energy E1 of the CP length exceeding portion is actually present, the energy E1 of the CP length exceeding portion is compared with the energy E2 of the pilot tone. Specifically, it is first determined whether or not the energy E1 of the CP length transcending portion is 40 dB or more smaller than the pilot tone energy E2 (ST710). If it is not smaller than 40 dB, it is determined whether the energy E1 of the CP length transcending portion is 35 dB or more smaller than the pilot tone energy E2 (ST711).

  Here, when the energy E1 of the CP length transcending portion is 40 dB or more smaller than the pilot tone energy E2, the processor 20 sends the pilot tone to the ADSL modem apparatus 2A on the exchange station (ATU-C) side. Is notified that transmission power is to be turned off for one of the subcarriers adjacent to (total 2) (ST712). At the same time, the subcarrier on / off selection unit 42 of the FFT unit 29 is instructed to set one subcarrier to turn off transmission power.

  On the other hand, if the energy E1 of the CP length transcending portion is 35 dB or more smaller than the pilot tone energy E2, the processor 20 changes the pilot tone to the ADSL modem apparatus 2A on the exchange station (ATU-C) side. Notify that the transmission power is turned off for two adjacent subcarriers (four in total) (ST713). At the same time, the subcarrier on / off selector 42 of the FFT unit 29 is instructed to use two subcarriers for turning off the transmission power.

  On the other hand, if the energy E1 of the part exceeding the CP length is not 35 dB or less smaller than the energy E2 of the pilot tone, the processor 20 sends the ADSL modem apparatus 2A on the exchange station (ATU-C) side to the ADSL modem apparatus 2A. Then, it notifies that the transmission power is to be turned off for 10 subcarriers adjacent to the pilot tone (20 in total) (ST714). At the same time, the subcarrier on / off selection unit 42 of the FFT unit 29 is instructed to set ten subcarriers to turn off transmission power.

  After notifying the number of subcarriers whose transmission power is turned off in ST712 to ST714, the ADSL modem apparatus 2A on the exchange station (ATU-C) side transmits initialization (Initialize) and showtime (Showtime) accordingly. Therefore, these are received (ST708, ST709). If all data is received from the ADSL modem apparatus 2A on the exchange station (ATU-C) side at the show time, the process is terminated. In this way, in the ADSL modem apparatus 2B on the terminal device (ATU-R) side in the home, the number of subcarriers whose transmission power is turned off according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line And data communication is performed.

  As described above, according to the ADSL modem apparatus 2B according to the present embodiment, the number of subcarriers whose transmission power is turned off is determined according to the magnitude of the energy E1 of the CP-length exceeding part of the impulse response on the line. Data communication is performed with the side ADSL modem apparatus 2A. For this reason, the transmission power of subcarriers adjacent to the pilot tone is turned off according to the length of the impulse response on the line, thereby reducing the influence of the impulse response on the line on the pilot tone and ensuring data communication. It can be carried out.

  Further, in ADSL modem apparatus 2B according to the present embodiment, the number of subcarriers whose transmission power is turned off is determined based on a comparison result between energy E1 of the CP-long transcendence portion and pilot tone energy E2. For this reason, the number of subcarriers whose transmission power is turned off can be determined according to the relationship between the energy E1 of the part exceeding the CP length and the energy E2 of the pilot tone.

  In particular, ADSL modem apparatus 2B according to the present embodiment increases the number of subcarriers whose transmission power is turned off when the energy E1 of the CP length transcending portion is larger than a certain value of pilot tone energy E2. When the pilot tone energy E2 is smaller than a certain value, the number of subcarriers whose transmission power is turned off is reduced. For this reason, it is possible to appropriately increase or decrease the number of subcarriers whose transmission power is turned off in correspondence with the energy E1 of the part exceeding the CP length.

  Further, in ADSL modem apparatus 2B according to the present embodiment, since the REVERB signal used in the initialization procedure is used as a known signal, the RVERB signal repeatedly exchanged in the initialization procedure is used, and the CP length transcendent portion of the impulse response is used. The number of subcarriers whose transmission power is turned off can be determined according to the energy E1.

  On the other hand, when data communication is performed by determining the number of subcarriers whose transmission power is turned off in accordance with the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line, the processor 20 of the ADSL modem apparatus 2A As shown in FIG. 8, first, a REVERB signal is transmitted to the counterpart ADSL modem apparatus 2B (ST801).

  After transmitting the REVERB signal, the processor 20 monitors whether or not there is a subcarrier for turning off transmission power from the counterpart ADSL modem apparatus 2B, and if so, the number of notifications. Specifically, processor 20 first monitors whether it receives a notification from partner ADSL modem apparatus 2B that there is no subcarrier for turning off transmission power (ST802). Here, if it is confirmed from the partner ADSL modem apparatus 2B that there is no subcarrier for turning off the transmission power, the processor 20 instructs the subcarrier on / off selection unit 41 of the IFFT unit 26 to perform transmission. The number of subcarriers for which power is turned off is set to zero (ST803). After that, the processor 20 transmits initialization (Initialize) and showtime (Showtime) to the counterpart ADSL modem apparatus 2B using the set subcarriers (all subcarriers) (ST804, ST805).

  In addition, when the notification that there is no subcarrier for turning off the transmission power from the partner ADSL modem apparatus 2B is not received, the notification that there is one subcarrier for turning off the transmission power, that there are two subcarriers. Notification of 10 is monitored (ST806, ST807, ST808). If each notification is confirmed, the processor 20 instructs the subcarrier on / off selection unit 41 of the IFFT unit 26 to set the number of subcarriers whose transmission power is turned off in response to each notification by 1 and 2 respectively. This is set to 10 (ST809, ST810, ST811). After that, the processor 20 transmits initialization (Initialize) and showtime (Showtime) to the counterpart ADSL modem apparatus 2B using the set subcarrier (ST804, ST805). When all data is transmitted to the other party ADSL modem apparatus 2B at the show time, the process is terminated. In this way, in the ADSL modem apparatus 2A on the exchange station apparatus (ATU-C) side, the number of subcarriers whose transmission power is turned off is determined according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line Data communication is then performed.

  As described above, according to the ADSL modem apparatus 2A according to the present embodiment, the transmission power is set according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line notified from the partner ADSL modem apparatus 2B. The number of subcarriers to be turned off is determined, and data communication with the partner ADSL modem apparatus 2B is performed. For this reason, among the subcarriers adjacent to the pilot tone according to the length of the impulse response on the line, the subcarrier for turning off the transmission power is determined, so the influence of the impulse response on the line on the pilot tone is reduced. Data communication can be performed reliably.

  In the above description, when calculating the impulse response (Impulse (t)), X (ω) calculated from the known REVERB signal and Y calculated from the REVERB signal actually received via the line. (Ω) is used. However, the calculation of the impulse response (Impulse (t)) is not limited to this REVERB signal. That is, any signal may be used as long as it is a signal recognized together between the switching center apparatus (ATU-C) and the terminal apparatus (ATU-R) installed in the home.

  In the above description, the ADSL modem apparatus is described as an example. However, the present invention can be similarly applied to an xDSL modem applied to other types of DSL.

  According to the ADSL modem apparatus and the communication control method of the present invention, it is possible to reduce the influence of the impulse response on the line on the pilot tone, to reliably perform data communication, and to provide an ADSL service with higher usability. Useful in that it can.

The figure which shows schematic structure of the communication system by the side of the terminal device installed in the house etc. where the ADSL modem apparatus which concerns on one embodiment of this invention is applied Functional block diagram of transceiver of the communication system The figure which shows an example of the waveform of the impulse response calculated with the processor of the said transceiver The figure for demonstrating the side lobe which the subcarrier adjacent to a pilot tone emits The block diagram which shows the structure of the IFFT part and FFT part which the said transceiver has The figure which shows about the state in which the ADSL modem apparatus by the side of the switching center apparatus which concerns on the said embodiment, and the ADSL modem apparatus by the side of the terminal device in a home are connected via the line In the ADSL modem device on the terminal device side in the home according to the above-described embodiment, the number of subcarriers whose transmission power is turned off is determined according to the magnitude of the energy E1 of the CP length transcend portion of the impulse response on the line. Flow chart for explaining the operation when performing data communication In the ADSL modem apparatus on the exchange station side according to the above-described embodiment, data communication is performed by determining the number of subcarriers whose transmission power is turned off according to the magnitude of energy E1 of the CP-length exceeding part of the impulse response on the line Flow chart for explaining the operation when performing

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Splitter 2 ADSL modem apparatus 3 User terminal 4 Telephone 11 Transceiver 12 Host 13 AFE
DESCRIPTION OF SYMBOLS 14 Analog filter 15 Driver 16 Hybrid 17 Receiver 18 Analog filter 20 Processor 21 Reed-Solomon encoding part 22 Interleaving part 23 Trellis encoding part 24 Tone ordering part 25 Constellation encoding part 26 IFFT part 27 CP addition part 28 CP removal part 29 FFT unit 30 Constellation decoding / FEQ unit 31 Tone deordering unit 32 Viterbi decoding unit 33 Deinterleaving unit 34 Reed-Solomon decoding unit 35 RAM
36 Host I / F
41, 42 Subcarrier on / off selector

Claims (12)

  Calculation means for calculating energy of a portion exceeding the length of the cyclic prefix in the impulse response on the communication line based on a specific signal exchanged before data communication, and a portion exceeding the length of the cyclic prefix Selecting means for selecting the number of subcarriers whose transmission power is turned off among subcarriers adjacent to the subcarriers used as pilot tones according to the energy of the other party, and the number of subcarriers whose transmission power is turned off as the counterpart ADSL A notification means for notifying the modem device, and a communication means for performing data communication with the partner ADSL modem device using subcarriers excluding the number of subcarriers for turning off the transmission power selected by the selection means, An ADSL modem apparatus comprising:   The calculation means calculates the energy of the portion exceeding the length of the cyclic prefix by obtaining an energy amount from the time point of the rear end of the cyclic prefix to a time point after a lapse of a certain time in the impulse response. The ADSL modem apparatus according to claim 1.   The selection means determines the number of subcarriers whose transmission power is turned off based on a comparison result between the energy of the portion exceeding the length of the cyclic prefix and the energy of the subcarrier used as the pilot tone. The ADSL modem apparatus according to claim 1, wherein:   The selection means determines the number of subcarriers to turn off the transmission power when the energy of the portion exceeding the cyclic prefix length is larger than a certain value of the energy of the subcarrier used as the pilot tone. 4. The ADSL modem apparatus according to claim 3, wherein the number of subcarriers for turning off the transmission power is decreased when the energy is smaller than a constant value of energy of subcarriers used as the pilot tone.   2. The ADSL modem apparatus according to claim 1, wherein the specific signal is a REVERB signal.   The number of subcarriers that turn off the transmission power selected according to the energy of the portion of the impulse response on the communication line calculated based on the specific signal exchanged before data communication that exceeds the length of the cyclic prefix Communication between the receiving ADSL modem apparatus and the receiving ADSL modem apparatus using subcarriers excluding the number of subcarriers that turn off the transmission power notified by the receiving means. A communication means for performing ADSL modem apparatus.   Based on a specific signal exchanged before data communication, the energy of the portion of the impulse response on the communication line exceeding the length of the cyclic prefix is calculated, and the energy of the portion exceeding the length of the cyclic prefix is calculated. In response, select the number of subcarriers whose transmission power is turned off among the subcarriers adjacent to the subcarriers used as pilot tones, and notify the partner ADSL modem apparatus of the number of subcarriers whose transmission power is turned off. A communication control method comprising performing data communication with a partner ADSL modem apparatus using subcarriers excluding the number of subcarriers for turning off transmission power notified to the partner ADSL modem apparatus.   The energy of a portion exceeding the length of the cyclic prefix is calculated by obtaining an energy amount from a time point at the rear end of the cyclic prefix to a time point after a lapse of a predetermined time in the impulse response. Item 8. The communication control method according to Item 7.   The number of subcarriers for which the transmission power is turned off is determined based on a comparison result between the energy of the portion exceeding the length of the cyclic prefix and the energy of the subcarrier used as the pilot tone. The communication control method according to claim 7.   When the energy of the portion exceeding the length of the cyclic prefix is larger than a certain value of the energy of the subcarrier used as the pilot tone, the number of subcarriers for turning off the transmission power is increased, The communication control method according to claim 9, wherein the number of subcarriers for turning off the transmission power is decreased when the energy of subcarriers used as pilot tones is smaller than a certain value.   The communication control method according to claim 7, wherein the specific signal is a REVERB signal.   The number of subcarriers that turn off the transmission power selected according to the energy of the portion of the impulse response on the communication line calculated based on the specific signal exchanged before data communication that exceeds the length of the cyclic prefix Is received from the partner ADSL modem apparatus, and data communication with the partner ADSL modem apparatus is performed using subcarriers excluding the number of subcarriers that turn off the transmission power received. Communication control method.

Images