KR100316782B1 - Digital subscriber line system using discrete multi tone - Google Patents

Abstract

The present invention provides a digital subscriber line system using discontinuous multi-tones that can provide broadband service without a divider and without the influence of frequency nulls formed at the interference and bridged taps of the Home Phoneline Network Alliance (HPNA). Initiate. In the system according to the present invention, the maximum frequency for downlink transmission is set to less than 4.5MHz, and the maximum frequency for uplink transmission is set to a frequency corresponding to 1/2 of the total available frequency band for downlink and uplink transmission. First means for assigning frequency bands, respectively; And second means for dividing the allocated frequency band by using subcarrier intervals, and transmitting an uplink signal or a downlink signal on the divided subcarriers. Therefore, the present invention prevents the influence of frequency nulls formed in the interference and bridge taps of HPNA even if the digital subscriber line system is installed in each home without a divider, and implements the digital subscriber line system and uses the existing G.lite. Whether it's a home or an upgrade to a broadband system.

Description

Digital subscriber line system using discrete multi-tone method

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a system of digital subscriber lines (hereinafter referred to as DSLs) using discrete multi-tones (also called discrete multi-tones or discrete multi-carriers), and in particular, HPNA (Home without the use of splitters). Home networks such as the Phoneline Network Alliance (hereinafter abbreviated HPNA) and DSL systems that are not affected by bridged taps in the home.

DSL system (or DSL transceiver) is to provide high speed subscriber network using existing telephone network. It is called ADSL (Asymmetrical Digital Subscriber Line, ADSL), HDSL (High-Speed DSL, HDSL). Weak), SHDSL (Single pair HDSL, hereinafter referred to as SHDSL), VDSL (Very-high DSL, hereinafter referred to as VDSL), and the like. Among them, VDSL can provide 26Mbps downstream and 3.2Mbps upstream asymmetric service or 6.4Mbps symmetric service to subscribers 1km away using 20MHz frequency band, and short distance subscribers less than 300m. It also has a feature that can provide high-speed services of 52 Mbps down and 13 Mbps up. However, in order to provide such a high-speed service, VDSL has a disadvantage in that digital signal processing is more complicated than a conventional DSL, and a divider must be installed at a subscriber line.

Therefore, residential users prefer G.lite, which uses relatively simple signal processing rather than VDSL, without using a divider. This G.lite is a kind of ADSL standard approved by the International Telecommunications Union-Telecommunications sector (ITU-Study Group) 15, which can provide 1.5Mbps downlink service in multi-tone without a divider. This is because the frequency band environment can be sufficiently accommodated. However, the frequency band used by G.lite is low at 552 KHz and is expected to saturate in the near future due to the increasing frequency band of the network, which is required to upgrade to the broadband service such as VDSL.

Accordingly, a DSL system capable of providing a 26Mbps downlink 3.2Mbps uplink service in a line (or loop) of about 1km by allocating a frequency band as shown in FIG. 1 without separately installing a divider at each inlet line of each home has been proposed.

Meanwhile, when the home network equipment such as HPNA is gradually spread in each home due to the development of the information society, a network as shown in FIG. 2 may be formed. That is, FIG. 2 is a subscriber terminal 200 in which HPNA transceivers 201 and 202 are installed to form an HPNA home network in a home, and a DSL system in which frequency bands are allocated and operated as shown in FIG. 1. And a twisted pair 230, which is connected to a subscriber terminal 210, an optical network, and a voice network, which is a network established in the home, by establishing a network in the home. It is a network structure formed between an optical network unit (hereinafter, referred to as ONU) 220 for transmitting and receiving data to and from each subscriber's terminal (200, 210). Subscriber stages 200 and 210 are neighboring different homes.

However, in the case where the network is formed in this way, the transmission power density for the frequency band used by HPNA is in the frequency bands of 4.5 MHz (point C in FIG. 3) and 7.0 MHz (point D in FIG. 3) as shown in FIG. Since a large power corresponding to 73.5 dBm / Hz is generated between the inverse and 7.3 MHz (point E of FIG. 3) and 9.5 MHz (point F of FIG. 3), a twisted pair 230 is used in a frequency band of 4.5 MHz or more. Cross talk by HPNA may be introduced into the DSL system 211 to generate an error in data received from the optical network unit 220. For reference, in FIG. 3, A is -140 dBm / Hz at 2.7 MHz, B is -93.5 dBm / Hz at 3.3 MHz, C is -73.5 dBm / Hz at 4.5 MHz, and D is 7.0 MHz. At -83.5dBm / Hz, E is -83.5dBm / Hz at 7.3MHz, F is -73.5dBm / Hz at 9.5MHz, and G is -83.5dBm / Hz at 10.0MHz Where H is -108.5 dBm / Hz at 5 MHz, I is -123.5 dBm / Hz at 12 MHz, and J is -135 dBm / Hz at 12.5 MHz.

In addition, most bridge taps present in the house are less than 30 m long and most are less than 10 m long. In the case of bridge taps less than 10 m long, frequency nulls are formed at 5 MHz or more, so that a divider is not shown in FIG. 1. As shown in the drawing, when the DSL system 211 allocates a frequency band, the frequency null formed at the bridge tap at a downward frequency of 5 MHz is affected.

In the above-described DSL system, as shown in FIG. 1, the largest frequency used for upstream is 3.5 MHz and the highest frequency used for downstream is 5 MHz, so the subcarrier of 4.3125 KHz is used. In the case of implementing DMT, the required number of subcarriers is 1159 downlink (5MHz / 4.3125KHz) and 811 uplink (3.5MHz / 4.3125KHz), respectively. Transform) must be provided, and the resolution of the analog-to-digital converter used in the upstream has to be complicated.

The present invention provides a digital subscriber line system using discontinuous multi-tones that can provide broadband service without a divider and without the influence of frequency nulls formed at the interference and bridged taps of the Home Phoneline Network Alliance (HPNA). The purpose is to provide.

Another object of the present invention is to provide a digital subscriber line system using discrete multi-tones that simplifies hardware implementation.

1 is a diagram illustrating frequency band allocation in a conventionally proposed digital subscriber line system.

2 is an example of a network formed between a subscriber end adopting the proposed digital subscriber line system and a subscriber end and an optical network unit in which an HPNA network is formed.

3 is a frequency spectrum diagram of HPNA.

4 is a diagram showing frequency band allocation in a digital subscriber line system proposed in accordance with the present invention.

5 is a configuration diagram of an optical network unit stage having a digital subscriber line system implementing frequency allocation as shown in FIG. 4 by using a DMT scheme.

FIG. 6 is a block diagram of a subscriber station having a digital subscriber line system in which frequency allocation as shown in FIG. 4 is implemented using a DMT scheme.

Figure 7 is a comparison of the performance of the existing DSL and the DSL according to the present invention when HPNA is present.

8 is a view comparing the performance of the DSL according to the present invention when there is a bridge tap of 30 m or less.

In the digital subscriber line system according to the present invention for achieving the above objects, the maximum frequency for downlink transmission is set to less than 4.5MHz, the maximum frequency for uplink transmission is a frequency corresponding to 1/2 of the total available frequency band First means for assigning frequency bands for downlink and uplink transmission, respectively; And second means for dividing the allocated frequency band by using subcarrier intervals, and transmitting an uplink signal or a downlink signal on the divided subcarriers.

In addition, the digital subscriber line system according to the present invention for achieving the objects of the present invention, an optical network unit that can be connected to the optical network and the general telephone network, an optical network unit connected through the general telephone network and a subscriber set in the room In a network environment formed with subscriber stages capable of transmitting and receiving data between networks, a digital subscriber line system provided in an optical network unit for data transmission and reception includes: a subcarrier in which downlink signals received from the optical network are divided by subcarrier intervals; A first encoder mounted on the first encoder; First modulation means for modulating a downlink signal divided and transmitted in subcarrier units from a first encoder in subcarrier units; A first digital-to-analog converter for converting the signal modulated by the first modulating means into an analog signal; A first filter for low-pass filtering such that only signals transmitted through a frequency band of less than 4.5 MHz among the signals transmitted from the first digital-to-analog converter are transmitted to the subscriber end; A second filter for performing low pass filtering to transmit only an uplink signal having a frequency less than one-half of all available frequency bands when an uplink signal is received from a subscriber station through a general telephone network; A first analog / digital converter for converting an uplink signal transmitted through the second filter into a digital signal; First demodulation means for demodulating an uplink signal transmitted from a first analog / digital converter and transmitting an uplink signal divided in subcarrier units; A first decoder which decodes the uplink signal transmitted from the first demodulation means in subcarrier units to be restored to its original form and transmits the decoded signal to the optical network; The digital subscriber line system provided at the subscriber end includes: a third filter for performing low pass filtering so that only a signal transmitted over a frequency band of less than 4.5 MHz is transmitted when the downlink signal passing through the first filter is received from the optical network unit; A second analog / digital converter for converting a downlink signal transmitted through the third filter into a digital signal; Second demodulation means for demodulating a signal transmitted from an analog / digital converter and transmitting a downlink signal divided into subcarriers; A second decoder which decodes the downlink signal transmitted from the second demodulation unit on a subcarrier basis to be restored to its original form and transmits it to the subscriber network; A second encoder for dividing an uplink signal received from the subscriber network into subcarrier units and transmitting the divided signal; Second modulation means for modulating an uplink signal, which is divided and transmitted in subcarrier units from a second encoder, in subcarrier units; A second digital-to-analog converter for converting the signal modulated by the second modulating means into an analog signal; It is preferable to include a fourth filter for low-pass filtering such that only an uplink signal below a frequency corresponding to 1/2 of the entire available frequency band among the signals transmitted from the second digital / analog converter is transmitted to the optical network unit.

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

4 is a frequency band allocation diagram of the proposed digital subscriber line system according to the present invention. Up to 1.1 MHz is allocated from 30 KHz to 138 KHz as an uplink channel to maintain compatibility with the existing hypothetical ADSL, and 138 KHz. Up to xMHz is allocated as the downlink channel, the second uplink channel is allocated from xMHz to 2.208MHz, and the second downlink channel from 2.208MHz to 4.416MHz is allocated. In this case, x has a value between 1.104 MHz and 2.208 MHz. Since the HPNA transceiver proposed at this time uses 10 MHz from 4.5 MHz, broadband service using the digital subscriber line system according to the present invention operated by allocating uplink and downlink frequency bands as shown in FIG. The impact of HPNA can be completely avoided by providing

FIG. 5 is a configuration diagram of an optical network unit (hereinafter referred to as ONU) stage having a digital subscriber line system in which frequency allocation as shown in FIG. 4 is implemented using a discrete multi-tone (DMT) scheme. , Optical network 501, first transmission convergence layer (TC layer) processing unit 503, encoder 505, 2048 point inverse fast Fourier transform unit (IFFT) 507, cyclic prefix and suffix A data insertion unit 509, a first latitude processing unit 511, a digital-to-analog (D / A) converter 513, a low pass filter 515, a line driver 517, a transmission / reception medium 519, Analog filter 523, analog / digital (A / D) converter 525, second windowing processor 527, cyclic potential and back data strip 529, 1024 point fast Fourier transform 531 ), A frequency equalizer (FEQ) 533, a decoder 535, and a second transmission convergence layer processor 537. Among them, the low pass filter 515 serves to set the maximum frequency that can be used for downlink transmission, and the analog filter 523 sets the maximum frequency that can be used for uplink transmission to a frequency corresponding to 1/2 of the total available frequency band. The encoder 505 divides the maximum usable frequency band using the interval of subcarriers and allocates only the subcarriers included in the frequency band allocated downward to the downstream.

The ONU stage configured as described above applies the signal received through the optical network 501 to the first transmission convergence layer processing unit 503 during downlink transmission and reception. The first transmission convergence layer processor 503 corrects a channel error for a signal received through channel coding and interleaving and transmits the correction to the encoder 505.

The encoder 505 encodes an applied signal to be carried on the DMT subcarrier by using a Quadrature Amplitude Modulation (QAM) scheme. The size of the QAM is adjusted according to the signal to noise ratio (SNR) of the channel. In other words, when the SNR is high, more bits are allocated to the encoder 505, and when the SNR is low, the lower bit is allocated to the encoder 505. At this time, the number of subcarriers used is 1024. The number of subcarriers is determined by the operation of dividing the highest frequency (4.416 MHz) used downward by the subcarrier interval (4.3125 KHz).

The 1024 subcarriers are transmitted to the 2048 point inverse fast Fourier transform unit 507. All of the 1024 subcarriers are not allocated bits, but only the subcarriers used for the downward purpose. For example, when the frequency band is allocated as shown in FIG. 4, bits are allocated only to the x / 0.0043125th and 513th to 1024th subcarriers, and nothing is carried on the remaining subcarriers. As described above, the 2048 point inverse fast Fourier transform unit 507 modulates 1024 subcarriers to which bits are allocated and transmits the modulated 1024 subcarriers to the cyclic potential and the post data inserter 509. In this case, the point of the inverse fast Fourier transform unit 507 is 2048 because the fast Fourier transform (FFT) size is usually represented by a power of 2, and the required fast Fourier transform is twice the number of subcarriers.

The cyclic potential and trailing data inserter 509 is an inter symbol interference and inter carrier interference in which a signal modulated by the 2048 point inverse fast Fourier transform 507 is generated due to a channel transfer function. The cyclic prefix and suffix data are inserted in the unit of DMT symbols so as to be insensitive to). In this case, the sum of the cyclic potential and the trailing data is 128, and the length of one DMT symbol is 4 KHz. The length of the DMT symbol is the same as ADSL.

The DMT symbol in which the cyclic potential and the trailing data are inserted is transmitted to the first windowing processor 511. The first window wing processing unit 511 performs an operation for increasing orthogonality of each subcarrier. This creates a data stream of 8.832 Msps (sampling per sec). This data stream is transmitted to the D / A converter 513, converted into an analog signal, and transmitted to the low pass filter 515. The low pass filter 515 is set so that the cut-off frequency is set to 4.416MHz to filter only signals below 4.416MHz. The filtered signal is transmitted through a line driver 517 to a transmission / reception medium 519 such as the twisted pair wire 230 shown in FIG. 2.

On the other hand, during uplink transmission and reception, when the ONU end as shown in FIG. 5 receives a signal from the subscriber end (200 or 210 shown in FIG. 2) through the transmission / reception media 519, the divider 521 receives data and voice signals. Disconnect. Since the divider 521 uses different frequency bands from the data and the voice signal, the divider 521 performs the dividing operation. The divided voice signal is transmitted to the voice network (not shown), and the data has a cutoff frequency of 2.208 MHz. Transmission is made to the set analog filter 523.

The analog filter 523 low-passes the filter so that only signals below 2.208 MHz are transmitted. Accordingly, the uplink signal transmitted to the A / D converter 525 has a state in which the downlink signal transmitted through the second downstream D region of the frequency band shown in FIG. 4 is removed. Accordingly, the A / D converter 525 may convert the uplink signal applied to the structure having the reduced dynamic range and the required resolution into a digital signal of 4.416 Msps, rather than considering all of the 4.416 MHz.

The digitally converted signal is transmitted to the second windowing processing unit 527, and after the windowing for suppressing the RFI (Radio Frequency Interference) is performed, the signal is transmitted to the cyclic potential and the post data removing unit 529. . The cyclic potential and back data remover 529 performs a strip process for cutting the cyclic potential and the back which are carried in units of DMT symbols. The DMT symbol from which the cyclic prefix and trailing data are removed is transmitted to the 1024-point fast Fourier transform unit 531 for demodulation.

When the demodulated uplink signal is applied, the frequency equalizer 533 outputs 512 subcarriers with phase compensation in subcarrier units. The output subcarrier is restored to the original transmission symbol (transmitted data) through the decoder 535 and transmitted to the second transmission convergence layer processor 537. The second transmission convergence layer processor 537 performs channel decoding and deinterleaving of the reconstructed data and transmits the recovered data to the optical network 501.

FIG. 6 is a block diagram of a subscriber station (hereinafter referred to as RT) having a digital subscriber line system in which frequency allocation as shown in FIG. 4 is implemented using a Discrete Multi Tone (DMT) scheme. 601, analog filter 603, A / D converter 605, third windowing processor 607, cyclic potential and back data processor 609, 2048 point fast Fourier transform 611, frequency equalizer 613, decoder 615, third transmission convergence layer processor 617, subscriber network 619, fourth transmission convergence layer processor 621, encoder 623, 1024 points inverse fast Fourier transform unit 625 And a circulating potential and back data inserter 627, a fourth windowing processor 629, a D / A converter 631, a low pass filter 633, and a line driver 635. Among them, the analog filter 603 serves to set the maximum frequency that can be used for downlink transmission, and the low pass filter 633 is the maximum frequency that can be used for uplink transmission. The encoder 623 divides the maximum usable frequency band using the interval of subcarriers and allocates only the subcarriers included in the frequency band allocated upward.

The RT configured as described above performs low pass filtering through the analog filter 603 having the cutoff frequency set to 4.416 MHz when the downlink signal transmitted from the ONU stage as shown in FIG. 5 is received through the transmission / reception medium 601. The low-pass filtered downlink signal is converted into a digital signal through a sampling of 8.832 Msps in the A / D converter 605 and transmitted to the third windowing processor 607. The third windowing processor 607 performs windowing for suppressing the RFI (Radio Frequency Interference), and then transmits it to the cyclic potential and back data removing unit 609. The cyclic potential and trailing data removing unit 609 removes the cyclic potential and trailing data carried in units of DMT symbols as in the cyclic potential and trailing data removing unit 529 of FIG. 5.

The DMT symbols from which the cyclic potential and the trailing data are removed are transmitted to the 2048 point fast Fourier transform unit 611 and demodulated, and the phase equalizer is compensated for each of 1024 subcarriers by the frequency equalizer 613. The output 1024 subcarriers are transmitted to the decoder 615. The decoder 615 detects the QAM signals of the applied 1024 subcarriers and restores the original transmitted symbols (transmitted data). The recovered transmission symbol is transmitted to the subscriber network 619 formed in the home through the third transmission convergence layer processor 617. The subscriber network 619 is connected to various information devices in the home to distribute broadband network access in the home.

On the other hand, during uplink transmission and reception, when the uplink signal is received from the subscriber network 619, the RT is transmitted to the encoder 623 through the channel encoding and interleaving process by the fourth transmission convergence layer processing unit 621. The encoder 623 carries the channel encoded uplink signal on the DMT subcarrier in the same manner as in the encoder 505 of FIG. 5. The subcarriers used at this time are the 7th to 32nd of the 512 subcarriers, and the 512th subcarriers at x / 0.0043125, and 0 is allocated to the remaining subcarriers. These subcarriers are modulated by the 1024 point inverse fast Fourier transform 625 and transmitted to the cyclic potential and back data inserter 627.

The cyclic prefix and trailing data inserting unit 627 inserts cyclic prefix and trailing data having a sum of lengths of 64 in units of modulated DMT symbols. At this time, the DMT symbol is 4KHz like the ADSL. The DMT symbols in which the cyclic potential and trailing data are inserted are applied to the fourth windowing processor 629 to be windowed as in the first windowing processor 511 of FIG. 5 to generate a data stream of 4.416Msps. This data stream is transmitted to the D / A converter 631, converted into an analog signal, and transmitted to the low pass filter 633. The low pass filter 633 performs low pass filtering so that only signals having a frequency less than 2.208 MHz pass through the analog signal transmitted from the D / A converter 631. The low-pass filtered signal is transmitted to the transmission / reception media 601 through the line driver 635 and transmitted to the ONU stage.

7 is a comparison of the performance of the DSL and the existing DSL according to the present invention when 10 HPNA, (a) is a performance comparison of the downstream, (b) is a performance comparison of the upstream. As can be seen from this performance comparison diagram, when HPNA is present, when the length of the loop becomes more than 0.6 km, there is almost no performance difference between the DSL system according to the present invention and the existing VDSL system in the downstream. Can be. Even in the upstream, the performance degradation caused by HPNA is negligible for both systems.

8 is a comparison diagram of the performance of the DSL according to the present invention when there is a bridge tap of 0 m to 30 m or less. FIG. 8 illustrates the worst case observation. In particular, when the length is limited to 30 m, the performance is particularly upstream. It can be seen that this degradation (data transmission rate is lowered), but there is no performance degradation due to a short bridge tap of 10 m or less.

As described above, the present invention provides a digital subscriber line system using a discontinuous multi-tone operating by allocating up and down frequency bands of less than 4.5 MHz, thereby preventing interference from neighboring HPNAs without installing a divider, and providing an indoor bridge. The advantage is that it is not affected by the frequency nulls formed at the taps. In addition, the splitter-free installation facilitates upgrading to broadband systems in existing homes using G.lite.

In addition, when allocating a frequency band so that the uplink signal uses only half of the totally available frequency band and transmitting the uplink signal, transmission of signals other than the maximum frequency allocated to the upstream signal is blocked. Reduced dynamic range and required resolution of the A / D converter, and the number of points of the inverse fast Fourier and fast Fourier transforms can be reduced to 1024, which makes the hardware implementation simpler than the existing DSL system. There is this.

Claims (7)

In the digital subscriber line system, The maximum frequency for downlink transmission is set to less than 4.5 MHz, and the maximum frequency for uplink transmission is set to a frequency corresponding to 1/2 of the total available frequency bands so that the frequency bands for downlink and uplink transmission are allocated respectively. First means; And a second means for dividing the allocated frequency band by using subcarrier spacing, and transmitting the uplink signal or the downlink signal on the divided subcarrier. 2. The apparatus of claim 1, wherein the first means comprises: a first analog filter for filtering only signals present in the frequency band less than 4.5 MHz during the downlink transmission; and 1 / of the total usable frequency band during the uplink transmission; A digital subscriber line system using discrete multi-tones, comprising a second analog filter for filtering only signals that are present in a frequency band below frequency 2. In a network environment comprising an optical network unit that can be connected to an optical network and a general telephone network, the optical network unit connected through the general telephone network, and a subscriber end capable of transmitting and receiving data between the subscriber network set in the room, The digital subscriber line system provided in the optical network unit for transmitting and receiving the data, A first encoder configured to transmit a downlink signal received from the optical network on a subcarrier divided by subcarrier intervals; First modulation means for modulating a downlink signal transmitted by being divided into subcarrier units from the first encoder in subcarrier units; A first digital-to-analog converter for converting the signal modulated by the first modulating means into an analog signal; A first filter for low-pass filtering only signals transmitted through a frequency band of less than 4.5 MHz among the signals transmitted from the first digital to analog converter; A second filter for performing low pass filtering to transmit only an uplink signal having a frequency less than one-half of all available frequency bands when an uplink signal is received from the subscriber end through the general telephone network; A first analog / digital converter for converting an uplink signal transmitted through the second filter into a digital signal; First demodulation means for demodulating an uplink signal transmitted from the first analog / digital converter and transmitting an uplink signal divided by the subcarrier unit; A first decoder which decodes the uplink signal transmitted from the first demodulation unit on a subcarrier basis to be restored to its original form and transmits the decoded signal to the optical network; The digital subscriber line system provided at the subscriber end, A third filter for performing low pass filtering so that only a signal transmitted through the frequency band less than 4.5 MHz is transmitted when the downlink signal passing through the first filter is received from the optical network unit; A second analog / digital converter for converting a downlink signal transmitted through the third filter into a digital signal; Second demodulation means for demodulating a signal transmitted from the analog / digital converter and transmitting a downlink signal divided by the subcarrier unit; A second decoder which decodes the downlink signal transmitted from the second demodulation unit in the subcarrier unit to be restored to its original form and transmits the decoded signal to the subscriber network; A second encoder for dividing an uplink signal received from the subscriber network into subcarrier units and transmitting the divided signal; Second modulation means for modulating an uplink signal, which is divided into subcarrier units and transmitted from the second encoder, in subcarrier units; A second digital-to-analog converter for converting the signal modulated by the second modulating means into an analog signal; A discrete multi-tone including a fourth filter for low-pass filtering such that only an uplink signal having a frequency less than half of the available frequency band among the signals transmitted from the second digital / analog converter is transmitted to the optical network unit; Digital subscriber line system. 4. The apparatus of claim 3, wherein the first modulating means and the second modulating means comprise an inverse fast Fourier transform unit for modulating a signal applied in a subcarrier unit using an inverse fast Fourier transform method. 2. The demodulation means is a digital subscriber line system using a discontinuous multi-tone including a fast Fourier transform unit for demodulating an applied signal by a fast Fourier transform. 5. The filter of claim 4, wherein the first filter and the third filter comprise a low pass filter having a cutoff frequency of 4.416 MHz, and the second filter and the fourth filter comprise a low pass filter having a cutoff frequency of 2.208 MHz. Digital subscriber line system using a discrete multi-tone, characterized in that the. 6. The digital subscriber line system according to claim 5, wherein the digital subscriber line system is configured to divide a frequency band in which the downlink signal is usable and a frequency band in which the uplink signal is available at intervals of a subcarrier of 4.3125 KHz. An inverse fast Fourier transform provided in the first demodulation means and a fast Fourier transform provided in the first demodulation means are 2048 points, and an inverse fast Fourier transform provided in the second modulation means and a fast Fourier transform provided in the second demodulation means. Digital subscriber line system using discrete multi-tones, characterized in that the unit consists of 1024 points. The second encoder of claim 6, wherein the first encoder allocates the x / 0.0043125 MHz and the 513 th to 1024 th subcarriers in the 33rd subcarrier divided in the frequency band where the downlink signal is available, and the second encoder. Is configured to allocate the 7th to 32nd and the 512th to 512th subcarrier of the subcarriers divided in the frequency band where the uplink signal is available, wherein x is a frequency of one of 1.104 to 2.208 MHz. Digital subscriber line system using discrete multitones.