JP2004072786A - Digital subscriber line transmission system and xdsl apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and efficiently notify a subscriber side of timing information (e.g., ISDN 400Hz signal phase) specifying a term of an influence of crosstalk from an adjacent line from a station side. <P>SOLUTION: When notifying the subscriber side of a transmission timing (phase of ISDN 400Hz signal) of a TDD-xDSL burst signal on the station side, a time which changes its phase once or more within one transmission burst is transmitted in addition to a pilot tone, a phase change of the tone is detected on a receiving side to recognize the transmission timing of the TDD-xDSL burst signal. In such a case, the phase of the tone is changed at 90° or 180°. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a digital subscriber line transmission method and an xDSL apparatus using a subscriber line (hereinafter, also referred to as a metallic line) connecting a subscriber exchange and a subscriber terminal as a high-speed data communication line, In particular, the present invention relates to a digital subscriber line transmission method and an xDASL device under a periodic crosstalk noise environment by ISDN ping-pong transmission or TDD-xDSL transmission.

  2. Description of the Related Art In recent years, multimedia services such as the Internet have become widespread throughout society, including ordinary households, and an economical and highly reliable digital subscriber line transmission system and digital subscription for using such services. There is a strong demand for early provision of a user line transmission device.

XDSL technology xDSL (Digital Subscriber Line) is known as a technology for providing a digital subscriber line transmission system using an existing telephone line as a high-speed data communication line. xDSL is a transmission method using a telephone line and is one of the modulation and demodulation techniques. In xDSL, the upstream transmission speed from the subscriber's home (hereinafter, referred to as subscriber side) to the accommodation station (hereinafter, referred to as office side) and the downstream transmission speed from the office side to the subscriber side are symmetric. And asymmetric ones.
A typical example is ADSL (Asymmetric DSL) for asymmetric xDSL, and HDSL (High-bit-rate DSL) and SHDSL (Single-pair High-bit-rate DSL) for symmetric xDSL. There is. And xDSL which can be used as both asymmetric type and symmetric type includes VDSL (Very high-bit-rate DSL). DMT for each xDSL system
(Discrete Multitone) and CAP (Carrierless Amplitude Phase Modulation) are used. For example, as an ADSL ITU-T recommendation, there are G.dmt for downlink transmission of about 6 Mbit / s and G.lite for about 1.5 Mbit / s, and both employ a DMT modulation method as a modulation method.

・ DMT modulation method
The DMT modulation method will be described using G.dmt as an example. Here, only the modulation and demodulation in the down direction from the station side to the subscriber side will be described.
In the DMT modulation method, the frequency band of 1.104 MHz is frequency-divided into M (= 255) multicarriers # 1 to # 255 at Δf (= 4.3125 KHz) intervals as shown in FIG. Then, in the training performed prior to the communication, the S / N ratio of each carrier # 1 to # 255 is measured, and 4-QAM, 16-QAM, 64-QAM, 128-QAM ... Which of the modulation schemes to transmit data is determined. For example, 4-QAM is allocated to a carrier having a small SN ratio, and 16-QAM, 64-QAM, 128-QAM... Are sequentially allocated as the SN ratio increases. In addition, 4-QAM is a modulation method that transmits 2 bits at a time, 16-QAM is a modulation method that transmits 4 bits, 64-QAM is a modulation method that transmits 6 bits, and 128-QAM is a modulation method that transmits 7 bits. .. Of the systems for transmitting signals simultaneously in the uplink / downlink, in the frequency division transmission system, of the 255 carriers, carriers # 1 to # 32 are used for the uplink direction from the subscriber side to the station side, and the carriers # 33 to # 33 255 can easily be used for the down direction from the station side to the subscriber side. In a system in which signals are not simultaneously transmitted in uplink and downlink, carriers # 1 to # 255 are all used for uplink and downlink.

FIG. 30 is a functional block diagram of a subscriber line transmission system using the DMT modulation method. The input transmission data for one subscriber is stored in a serial-to-parallel conversion buffer (Serial to
One symbol time (= 1/4000 sec) is stored in the Parallel Buffer 10. The stored data is divided for each transmission bit number per carrier, which is determined in advance by training and stored in the transmission bitmap 60, and is input to the encoder 20. That is, since the QAM modulation scheme for each carrier is known by the training, the bit stream for one symbol is divided by the number of bits bk according to the QAM modulation scheme for each carrier and input to the encoder 20. Therefore, the total number of output bits per symbol is Σbk (k = 1 to M). The encoder 20 converts each carrier corresponding to each input bit string into signal point data (signal point data on a constellation diagram) for quadrature amplitude modulation (QAM), and performs an inverse fast Fourier transform (IFFT: Inverse Fast Fourier Transform) 30. The IFFT 30 performs quadrature amplitude modulation on each signal point by performing an IFFT operation, and inputs the result to a parallel-to-serial conversion buffer 40 at the next stage. Here, a total of 32 samples of 480 to 511 IFFT outputs are added as cyclic prefixes (Cyclic Prefix) to the head of the DMT symbol (details will be described later). The parallel / serial conversion buffer 40 sequentially inputs 512 + 32 sample data to the DA converter 50 in series. The DA converter converts the input digital data into an analog signal at a sampling frequency of 2.208 MHz and transmits the analog signal to the subscriber via the metallic line 70.

  On the subscriber side, the AD converter 80 converts the input analog signal into a 2.208 MHz digital signal and inputs the digital signal to a time domain equalizer (TEQ) 90. The TEQ 90 processes the input digital data so that the Inter Symbol Interference (ISI) falls within the Cyclic Prefix of 32 samples, and inputs the processing result data to the serial / parallel conversion buffer 100. The serial / parallel conversion buffer 100 stores data for one DMT symbol, then removes the cyclic prefix, and inputs the data for one DMT symbol to the fast Fourier transformer (FFT) 110 simultaneously in parallel. The FFT 110 performs a fast Fourier transform to generate (demodulate) 255 signal points. A frequency domain equalizer (Frequency domain EQualizer: FEQ) 120 performs compensation of inter-channel interference (Inter Channel Interference: ICI) on the demodulated 255 signal point data, and the decoder 130 holds the same value as the transmission bitmap 60. In accordance with the received bit map 150, 255 signal point data is decoded, and the data obtained by the decoding is stored in the parallel / serial conversion buffer 140. Thereafter, the data is output bit by bit from the buffer, one bit at a time, to become received data.

・ Crosstalk from ISDN ping-pong transmission
The ISDN ping-pong transmission method (TCM: time compression multiplex) separates the transmission section and reception section in a time-division manner (total of 2.5 msec for one transmission section and reception section), and sets the timing of transmission and reception to all adjacent devices. Is the same method. In this ISDN ping-pong transmission method, 2B + D transmission data of 144 kbps is divided every 2.5 msec, compressed to 320 kbps by speed conversion, and transmitted in a transmission section. Therefore, the frequency band of the ISDN ping-pong transmission method overlaps with the frequency band of ADSL (or G.dmt) as shown in FIG. In addition, existing telephone lines are designed to be optimized for the human voice frequency band from about 200 Hz to 3.4 kHz, but when high-frequency signals such as ADSL and ISDN are passed through this line, telephone Since the lines are bundled as shown in FIG. 32, the ISDN signal leaks into the ADSL telephone line of another telephone line, which becomes noise and disturbs the ADSL communication. This noise is cross talk noise. The ADSL transmission rate is limited to this level of crosstalk noise.

FIG. 33 is an explanatory diagram of interference (crosstalk) from an ISDN line to an ADSL line, (a) is an explanatory diagram of interference with a station side ADSL device (ATU-C: ADSL Transceiver Unit at the Central office end), and (b) is ADSL device (ATU-R: ADSL Transceiver Unit at the subscriber side)
FIG. 3 is an explanatory diagram of interference with Remote terminal end). In (a), when an OCU (office channel unit) of an ISDN line is transmitting, the ADSL device ATU-C on the station side is greatly affected by noise. This crosstalk noise is called near-end noise (NEXT). On the other hand, when a DSU (digital service unit) is transmitting, the signal leaks into the ATU-C and becomes noise. This crosstalk noise is called far end cross-talk (FEXT). FEXT is far from ATU-C, that is, noise from the far end, and has a considerably smaller level than NEXT.
Further, in (b), when the DSU of the ISDN line is transmitting, the ATU-R on the subscriber side has a large noise effect, and this noise becomes near-end noise (NEXT). On the other hand, when the OCU is transmitting, the signal leaks into the ATU-R and becomes far-end noise (FEXT). This FEXT has a considerably smaller level than NEXT. As described above, it is necessary to reduce the influence of NEXT in ADSL communication.

As described above, if there is an ISDN ping-pong transmission line near the ADSL line, the ADSL line is affected by the TCM cross-talk from the ISDN ping-pong transmission line as described below. In ISDN ping-pong transmission, the station transmits downlink data in the first half cycle of 400 Hz in synchronization with the ISDN 400 Hz signal TTR (TCM-ISDN Timing Reference) shown in FIG. Transmits the uplink data. For this reason, the ADSL unit ATU-C on the station side is affected by the near-end crosstalk (NEXT1) from the ISDN in the first half cycle of 400 Hz, and the far-end crosstalk (FEXT1) from the upstream data of the subscriber ISDN in the second half cycle. ).
The ADSL device ATU-R on the subscriber side is affected by FEXT2 in the first half of 400 Hz, and is affected by NEXT2 in the second half cycle, contrary to the station side. In the following, the time regions affected by NEXT and FEXT are called a NEXT section and a FEXT section, respectively. FIG. 34 shows a NEXT section and a FEXT section on the subscriber side.

・ Sliding window method Japanese Patent Application No. Hei 10-144913 aims to provide a digital subscriber line transmission system capable of transmitting ADSL signals satisfactorily under the crosstalk environment from ISDN ping-pong transmission as described above. Has proposed a "sliding window method". The sliding window is used to transmit the ADSL signal from the ADSL unit (ATU-C) on the station side to the ADSL unit (ATU-R) on the subscriber side. There are two methods for determining the state of the ADSL signal transmitted by the station-side ADSL device (ATU-C) as follows, and there are a Dual Bitmap method and a Fext Bitmap method.

That is, as shown in FIG. 34, if the transmitted ADSL symbol (DMT symbol) SB is completely included in the FEXT section on the subscriber side, the station side ADSL device (ATU-C ) Transmits the symbol at high density as an inside symbol ISB. If at least part of the transmission symbol SB is included in the NEXT section on the subscriber side, the station side ADSL device (ATU-C) transmits the symbol as an outside symbol OSB at a low density (Dual Bitmap method). In the uplink direction, the subscriber ADSL device (ATU-R) divides the ADSL symbol into an inside symbol ISB and an outside symbol OSB and transmits the ADSL symbol in the same manner as in the downlink.
In the Dual Bitmap method, symbols are transmitted at a low density even outside the sliding window SLW in the downstream direction, but the station side ADSL device (ATU-C) uses the pilot / tone which is a tone for timing synchronization outside the sliding window SLW. There is also a method of transmitting only the tone PLT (Fext Bitmap method). At this time, in the upstream direction, the subscriber ADSL device (ATU-R) does not transmit anything outside the sliding window SLW.
FIG. 35 is a diagram showing the relationship between the transmission and reception in the ISDN OCU and the ADSL symbol in the station side ADSL device ATU-C, and shows the ADSL symbol in each of the Dual Bitmap system and the Fext Bitmap system.

Creation of Bitmap In order to support the Dual Bitmap method described above, the transmission bitmap unit 60 and the reception bitmap unit 150 in FIG. 30 use the bitmap for the inside symbol and the bitmap for the outside symbol during training. It is necessary to prepare two types of bitmaps. In the Fext Bitmap method, of the two types of bitmaps, the bitmap for the outside symbol is unnecessary.
The number of bits (bitmap) assigned to each carrier is determined by the receiving side. That is, the number of allocated bits for an uplink signal is determined on the station side, and the number of allocated bits for a downlink signal is determined on the subscriber side. During training, the ADSL devices on the office side and the subscriber side determine a bitmap according to a protocol called B & G (bit & gain).

  FIG. 36 is an explanatory diagram of the upstream B & G protocol. (1) During training, after recognizing each other's ADSL devices, for example, the subscriber ADSL device ATU-R sends some frequency signals to the opposing office ADSL device ATU-C. (2) The ADSL unit ATU-C on the station side measures the noise level and the received signal level for each carrier and calculates the SN ratio. (3) Next, the ADSL device ATU-C on the station side creates a bitmap based on the calculated SN ratio, and notifies the ADSL device ATU-R on the subscriber side of the bitmap and the transmission level. (4) The subscriber ADSL device ATU-R performs DMT modulation based on the notified bitmap and transmission level information, and transmits data.

FIG. 37 is a configuration diagram for measuring the SN ratio by the subscriber-side ADSL device ATU-R. The received data enters the demodulator 210 and outputs signal point data for each carrier as demodulated data. The reference 220 outputs signal point data for each carrier to be originally received. The difference between the signal point data from the reference and the demodulated signal point data is set as ERROR, and ERROR for each carrier is input to the selector 260.
On the other hand, the internal clock 230 is frequency-divided to 400 Hz by the frequency divider 240 and input to the phase determiner 250. The 400 Hz signal is previously adjusted in phase with the station side 400 Hz (ISDN 400 Hz signal) based on the 400 Hz information transmitted from the station side via the demodulator 210. The phase determiner 250 determines whether the received DMT symbol is a FEXT section or a NEXT section or other based on the input 400 Hz signal, and inputs the DMT symbol to the selector 260. The selector 260 outputs the input ERROR to the NEXT section S / N measuring device 270 or the FEXT section S / N measuring device 280 based on the information input from the determining device 250. Each S / N measuring device calculates the S / N by integrating the ERROR, and outputs the S / N to the transmission bit number converter 290 for each carrier. The transmission bit number converter 290 calculates the number of bits (bit map) to be transmitted for each carrier from the input S / N for each carrier, and calculates a bit map b-NEXT for the NEXT section and a bit map b-NEXT for the FEXT section. Calculate b-FEXT of the bitmap.

・ Frame configuration “Hyper Frame” was introduced to provide a digital subscriber line transmission system that can transmit ADSL signals well under the crosstalk environment from ISDN ping-pong transmission as described above. ing. ISDN ping-pong transmission switches transmission and reception every half cycle of a 400 Hz clock, 2.5 msec. On the other hand, one symbol, which is a transmission unit of ADSL transmission, which is being standardized as a global standard, is about 0.246 msec. Therefore, since the period of 34 cycles of ISDN ping-pong transmission, which is the least common multiple of the two communications, and the time length of 345 DMT symbols of ADSL transmission almost match, this section is defined as "hyperframe".

  As shown in FIG. 38, in ADSL, one frame corresponds to one symbol, and during steady data communication, 68 data ADSL frames and one synchronization frame (S) are used for one frame. Super frame is configured. Instead of the synchronization symbol (S), there may be an inverse synchronization symbol (I). The inverse synchronization symbol (I) is a symbol realized by rotating the phase of each carrier of the synchronization symbol (S) by 180 °. As shown in the figure, five super frames (= 345 symbols) are collected to form one hyper frame. In the figure, the downstream case where the ADSL signal is transmitted from the station side ADSL device (ATU-C) to the subscriber side ADSL device (ATU-R) is shown. In this case, the inverse synchronization symbol (I) is It is determined to be located in the fourth super frame in one hyperframe. In the case of the uplink direction, the inverse synchronization symbol (I) is included in the first super frame in one hyper frame. As described above, one hyper frame is synchronized with 34 cycles of a 400 Hz signal in ISDN ping-pong transmission.

-Another frame configuration As described above, if there is an ISDN ping-pong transmission line near the ADSL line, the ADSL line is affected by both NEXT and FEXT TCM Cross-Talk from the ISDN ping-pong transmission line. Therefore, in order to provide a digital subscriber line transmission system that can transmit ADSL signals well under such a crosstalk environment from ISDN ping-pong transmission, unlike the hyper frame described above, There is a method of transmitting an ADSL symbol in synchronization with ISDN ping-pong transmission.

In the ISDN ping-pong transmission, as shown in FIG. 39, in synchronization with the ISDN 400 Hz signal TTR, the station side OCU transmits downstream data in the first half cycle of 400 Hz and receives upstream data in the second half cycle of 400 Hz. Also in ADSL transmission, in synchronization with the ISDN 400 Hz signal TTR, the station-side ADSL device transmits an ADSL symbol for a downstream FEXT section in the first half cycle of 400 Hz, and transmits an ADSL symbol for a downstream NEXT section in the second half cycle of 400 Hz. The same applies to the ADSL device on the subscriber side. That is, two bitmaps (DMT symbol A) for NEXT section reception and two bitmaps (DMT symbol B) for FEXT reception section are prepared. Then, as shown in FIG. 39, by transmitting DMT symbol A in the NEXT section, the number of transmission bits is reduced to improve SN tolerance, and in the FEXT section, DMT symbol B is transmitted to increase the number of transmission bits. And increase the transmission capacity. At this time, the number of ADSL symbols for the FEXT section and the number of ADSL symbols for the NEXT section are matched by setting the cyclic prefix length to an appropriate length. For example, originally 32 samples of Cyclic
While the prefix is 246 μs per DMT symbol, the cyclic prefix of 40 samples is 250 μs per DMT symbol, and one cycle of TCM cross-talk is synchronized with the time of 10 DMT symbols.

-Introduction of TDD-xDSL TDD-xDSL (TDD: time divisional duplex-xDSL) is considered as an xDSL that does not use a sliding window and a hyper frame as described above. The TDD-xDSL scheme is a scheme of transmitting a symbol in synchronization with the above-described ISDN ping-pong transmission. However, unlike the above-described scheme, the receiving side does not transmit a TDD-xDSL symbol in the NEXT section. That is, the TDD-xDSL system is a system in which the xDSL line is used in the uplink direction and the downlink direction in a time division manner, and all the 255 carriers # 1 to # 255 are used in the uplink and downlink data transmission.

  As shown in FIG. 40, when the TDD-xDSL symbol sequence 460 is transmitted in synchronization with the ISDN ping-pong transmission at the station side, the TDD-xDSL symbol sequence 480 received at the subscriber side is only affected by FEXT440 from ISDN. . Further, when the subscriber transmits the TDD-xDSL symbol sequence 490 in synchronization with the ISDN ping-pong transmission, the TDD? -The DSL symbol sequence 470 is only affected by FEXT430 from ISDN. So TDD? -The DSL symbol sequence can avoid the effects of NEXT from ISDN ping-pong transmission. According to this transmission system, two types of bitmaps required in the Dual Bitmap method are reduced to one type as in the Fext Bitmap method.

-ISI removal method The time domain equalizer (Time domain EQualizer: TEQ) shown in Fig. 30 operates as follows using a cyclic prefix.
The DMT symbol input to the parallel-to-serial conversion buffer 40 in FIG. 30 is in a signal state without waveform distortion as shown in FIG. The parallel / serial conversion buffer 40 performs processing of adding the 32 samples after the DMT symbol to the position before the DMT symbol by copying as shown in FIG. 41 (b). This added part is called Cyclic Prefix. The DMT symbol with the Cyclic Prefix added thereto is transmitted to the receiving side after the subsequent processing on the transmitting side as shown in FIG. 41 (c).

A received signal received via the metallic line 70 whose amplitude characteristic and delay characteristic with respect to frequency are not constant is distorted due to the influence of inter symbol interference (Inter Symbol Interference: ISI) as shown in FIG. It is in a state.
However, the constant of the TEQ 90 is set by training so that the ISI falls within the cyclic prefix of 32 samples (TEQ training). Accordingly, upon receiving the signal shown in FIG. 41 (d), the TEQ performs processing so that the ISI falls within the cyclic prefix of 32 samples as shown in FIG. 41 (e). Thereafter, the serial / parallel conversion buffer 100 removes the cyclic prefix from the TEQ output. As a result, as shown in FIG. 41 (f), a DMT symbol from which the influence of ISI has been removed can be obtained. As described above, the TEQ uses the cyclic prefix to remove the effect of ISI from the received signal.

-The effect of ISI on xDSL symbols
The effect of ISI on xDSL symbols will be described with reference to FIG. FIG. 42A shows an ADSL transmission symbol sequence when a continuous signal is transmitted during training. However, it is assumed that there is no continuity between the hatched ADSL transmission symbol and the immediately preceding ADSL transmission symbol shown in FIG. FIG. 42 (b) is an ADSL reception symbol sequence for the ADSL transmission symbol sequence of FIG. 42 (a) before performing the TEQ training, and FIG. 42 (c) is an ADSL transmission symbol sequence of FIG. 41 (a) after performing the TEQ training. This is the ADSL received symbol sequence for the sequence.
FIG. 42 (d) shows an ADSL transmission symbol sequence to which a Cyclic Prefix is added at the time of steady data communication, and FIG. 42 (e) shows an ADSL reception symbol sequence for the ADSL transmission symbol sequence of FIG. 42 (d). is there.

As described above, the TEQ works to remove the effect of ISI from the received signal using the cyclic prefix. At the time of steady data communication, if a Cyclic Prefix is added to each ADSL transmission symbol as shown in FIG. 42 (d), as shown in FIG. 42 (e), the TEQ falls within the Cyclic Prefix of 32 samples of ISI. Thus, the influence of ISI can be removed from the received signal.
However, during training for transmitting a continuous signal with the same pattern, as shown in FIG. 42 (a), no Cyclic Prefix is added to each ADSL transmission symbol. This is because the cyclic prefix is not required because continuous signals are not affected by ISI. Rather, adding a cyclic prefix lowers the symbol rate by that amount, so it is better not to add a cyclic prefix.

  However, when transmitting a burst symbol sequence as a transmission signal as in the above-described sliding window method (Fext Bitmap method) or a method of transmitting a symbol in synchronization with ISDN ping-pong transmission (TDD-xDSL), the transmission signal Continuity is lost. Thus, even when TEQ training is completed during training for transmitting a continuous signal, as shown in FIG. 42 (c), the first ADSL received symbol in the ADSL received symbol sequence is affected by the waveform distortion corresponding to ISI. And training cannot be performed using the first ADSL received symbol.

FIG. 42 (b) shows the ADSL reception symbol sequence for the ADSL transmission symbol sequence of FIG. 42 (a) before performing the TEQ training at the time of training. Distorted under the influence. In FIG. 42 (c), the influence of the waveform distortion corresponding to the ISI received by the first ADSL received symbol by TEQ is within 32 samples, whereas in FIG. 42 (b), the effect before the TEQ training is performed
Since the ADSL reception symbol sequence is used, the influence of ISI on the ADSL reception symbol generally does not fall within 32 samples. Before the TEQ training, the influence of the waveform distortion may affect the second and subsequent ADSL received symbols as shown in FIG. Although not shown in FIG. 42, the ADSL reception symbol at the end of the ADSL reception symbol sequence may be affected by ISI.

  As described above, at the time of training for transmitting a continuous signal with the same pattern, the cyclic prefix is not added to each transmission symbol. For this reason, in TDD-xDSL transmission in which a burst symbol sequence is transmitted as a training signal to be transmitted, the receiving side cannot quickly respond when the burst symbol sequence rises, and waveform distortion occurs in the first symbol of the burst symbol sequence. . Therefore, training is performed only with the remaining TDD-xDSL received symbols that are not affected by the waveform distortion. For example, when transmitting 4 DMT symbols within one burst of training, DMT symbols that can be used for training are 3 DMT symbols. There is a problem that the training time becomes long.

Also, in TDD-xDSL transmission, if the transmission training symbol sequence falls within the reception section (NEXT section) of ISDN ping-pong transmission, it is affected by NEXT from the ISDN line, and TDD-xDSL transmission cannot be performed with a good SN ratio. is there.
Further, in TDD-xDSL transmission, a technique for setting a frequency of a pilot tone used as a timing recovery signal so as to ensure continuity of sample data of adjacent transmission burst symbol strings has not been established. For this reason, there arises a problem that processing cannot be performed at an accurate timing.
In TDD-xDSL, the phase of the training symbol to which the cyclic prefix is not added at the time of training the transceiver and the phase of the symbol to which the cyclic prefix is added at the time of steady data communication except for the cyclic prefix are added. There is a phase difference between For this reason, when the sequence shifts from a training symbol without a Cyclic Prefix to a symbol with a Cyclic Prefix added (training → normal communication), the phase of the timing reproduction signal (pilot tone) is shifted. There is.

Furthermore, the TDD-xDSL transmission needs to be synchronized with the ISDN ping-pong transmission on the station side, and the same applies on the subscriber side. The station side can obtain a 400 Hz synchronization signal synchronized with the ISDN ping-pong transmission using an 8 kHz network clock, but the subscriber side cannot obtain the 400 Hz synchronization signal. Therefore, it is important that the subscriber side be notified of the accurate TDD-xDSL transmission phase from the station side and obtain the information. Therefore, means for efficiently notifying the transmission phase from the station side to the subscriber side is required.
The above is a case where crosstalk from an ISDN line to an xDSL line is considered. However, crosstalk is not always from ISDN lines, but also from other xDSL lines within the same cable. In particular, since TDD-xDSL transmission performs downlink transmission and uplink transmission alternately in a time-division manner in synchronization with the 400 Hz signal TTR of ISDN ping-pong transmission as described above, the xDSL line is transmitted via ISDN ping-pong transmission from another TDD-xDSL line. And the same crosstalk effect (NEXT, FEXT). Therefore, the above problem can be applied not only to crosstalk from an ISDN line but also to crosstalk from another TDD-xDSL line.

The present invention has been made based on new findings and considerations on the above points, and is an effective transmission technology of TDD-xDSL under a noise environment from ISDN ping-pong transmission or other TDD-xDSL transmission. It is an object of the present invention to provide a specific method for adopting the method, or a digital subscriber line transmission device provided with means for implementing such a method.
It is another object of the present invention to accurately and efficiently notify timing information specifying a period affected by crosstalk from an adjacent line to a subscriber side from a station side, for example, an ISDN 400 Hz signal phase.

The first aspect of the present invention is a digital subscriber line transmission method for receiving crosstalk from an ISDN ping-pong transmission line, and in a transmission section (FEXT section) of ISDN ping-pong transmission, a phase is shifted twice between any two adjacent symbols. It is characterized by changing.
A second aspect of the present invention is an xDSL apparatus which receives crosstalk from an ISDN ping-pong transmission line, and in which data whose phase is changed twice between any two adjacent symbols in a transmission section (FEXT section) of ISDN ping-pong transmission. Is provided.
A third aspect of the present invention is a digital subscriber line transmission method for receiving crosstalk from an ISDN ping-pong transmission line, wherein a symbol pattern of two arbitrary sets of adjacent symbols is set in a transmission section (FEXT section) of the ISDN ping-pong transmission. and wherein the changing so that the phase difference becomes 90 ° or 180 ⁰ from one another in the QAM constellation diagram.
A fourth aspect of the present invention is an xDSL apparatus which receives crosstalk from an ISDN ping-pong transmission line. In the xDSL apparatus, a QAM constellation diagram is used as a symbol pattern of any two adjacent symbols in a transmission section (FEXT section) of ISDN ping-pong transmission. characterized in that it has means for transmitting data is varied so that the phase difference becomes 90 ° or 180 ⁰ from each other in.

According to the present invention, when notifying the subscriber of the transmission timing (phase of the ISDN 400 Hz signal) of the TDD-xDSL burst signal on the station side in TDD-xDSL transmission, one transmission burst within one transmission burst is provided separately from the pilot tone signal. Since the tone signal whose phase changes more than once is transmitted and the subscriber detects the phase change of the tone signal and recognizes the transmission timing of the TDD-xDSL burst signal, the transmission timing during training of TDD-xDSL transmission is determined. (ISDN 400Hz signal phase) and correct TDD-xDSL transmission. In this case, by making the phase of the tone signal to change 90 ° or 180 ^0, it transmits the initial time timing (ISDN 400-Hz signal of phase) can be recognized reliably the transmission timing even unknown. Further, according to the present invention, since the subscriber side can recognize the section affected by the crosstalk from the adjacent line on the station side, the subscriber side can transmit the uplink data to the station side excluding the section.

  In TDD-xDSL transmission, when notifying the subscriber side of the transmission timing of a TDD-xDSL burst signal (phase of an ISDN 400 Hz signal) on the station side, a tone that changes its phase at least once in one transmission burst is used in addition to the pilot tone. After transmitting, the receiving side detects the phase change of the tone and recognizes the transmission timing of the TDD-xDSL burst signal. In this way, the correct TDD-xDSL transmission can be performed by detecting the transmission timing (the phase of the ISDN 400 Hz signal) during training of the TDD-xDSL transmission. In this case, the phase of the tone is changed to 90 ° or 180 °. In this way, even if the transmission timing (phase of the ISDN 400 Hz signal) is unknown at the initial stage, the transmission timing can be surely recognized.

(A) Outline of the present invention The present invention has the following features in TDD-xDSL transmission under a periodic noise environment from a line that performs ISDN ping-pong transmission or another TDD-xDSL transmission. In the following, TDD-xDSL transmission under a periodic noise environment from a line performing ISDN ping-pong transmission will be described.
(a) First feature The first feature is that a training symbol sequence 500 as shown in FIG. 1 is transmitted in training a TDD-xDSL ADSL device (transceiver). That is, (1) in the training of the TDD-xDSL transceiver, before the conventional transmission symbol sequence 502 configured by continuously arranging the training symbols 501 without Cyclic Prefix, the same pattern 503 as the end portion of the first training symbol is added to the redundant signal. By adding a predetermined number of samples as, a pattern in which the training symbols including the added portion are continuous can be formed. The length to be added is
This is a predetermined sample number n1 larger than the Cyclic Prefix. (2) Alternatively, after the transmission symbol sequence 502, the same pattern 504 as the head of the last training symbol 501 is similarly added by the number of samples n2 determined separately from the number of samples n1 added to the head. (3) Alternatively, redundant signals 503 and 504 are added before and after the transmission symbol sequence 502, respectively.

  In TDD-xDSL, since each symbol at the time of training has the same pattern, a continuous signal can be transmitted between each symbol via IFFT. Therefore, the end portion of the training symbol is added before the transmitted symbol sequence, or the beginning portion of the training symbol is added after the transmitted symbol sequence, or both of them are added to the transmission symbol sequence. A continuous signal can be formed. As described above, if the redundant signal is added before or after the transmission symbol sequence, distortion occurs only in the redundant signal portion (503, 504) due to ISI, but distortion occurs in the transmission symbol sequence other than the redundant signal portion (503, 504). All the symbols can be used as training symbols, and the training time can be reduced. The transmission time does not increase even if the redundant signal is added. This is because a redundant signal can be transmitted using a period in the TDD-xDSL transmission section where no signal is transmitted.

(b) Second feature In the second feature, the training symbol sequence to which the redundant sample sequence has been added by the first feature does not enter the receiving section (NEXT section) of ISDN ping-pong transmission. That is, the transmission timing and length of the training symbol sequence are set.
That is, the TDD-xDSL transmission training symbol sequence is included in the transmission frame section of the ISDN ping-pong transmission, or in the transmission frame section of the ISDN ping-pong transmission and the guard time section between the transmission and reception in the ISDN ping-pong transmission. Then, the transmission timing of TDD-xDSL transmission and the length of the transmission training symbol sequence are set.

  With reference to FIG. 2, a description will be given of conditions for putting a TDD-xDSL transmission training symbol sequence 500 in a transmission section 601 of ISDN ping-pong transmission. Here, the time of the ISDN ping-pong transmission section is D (3.125 μs × 377 = 1.178125 ms), the card time between transmission and reception of the ISDN ping-pong transmission is a (= 18.75 μs to 23.4375 μs), and redundant data of TDD-xDSL is added. The transmission time of the training symbol 502 before the training is S1, the transmission times of the redundant signals 503 and 504 before and after the training DMT symbol sequence are x1 and y1, respectively, the interval of the TDD-xDSL transmission training symbol sequence 500 and the ISDN ping-pong transmission. Assuming that the margins with respect to the transmission section 601 are α1 and β1, respectively, the respective relationships to be satisfied in the present invention are shown below.

S1 + α1 + β1 + x1 + y1 ≦ D + a (1)
(However, 0 ≦ α1, 0 ≦ β1)
Or
S1 + α1 + β1 + x1 + y1 ≦ D (2)
(However, 0 ≦ α1, 0 ≦ β1)
Here, assuming that the number of samples in the DMT symbol without Cyclic Prefix is m, the number of DMT symbols without Cyclic Prefix included in the training symbol sequence 500 is N, and the frequency interval of the DMT carrier is fd, S1, x1, y1 Can be expressed by the following equation.

S1 = N × m × {1 / (m × fd)} = N / fd (3a)
x1 = nx × {1 / (mxfd)} (3b)
y1 = ny × {1 / (mxfd)} (3c)
Where m = 2n (n is a natural number)
nx and ny are arbitrary positive integers indicating the number of samples of x1 and y1, respectively, and (nx + ny)> (m / 8)
Similarly, as shown in FIG. 3, at the time of normal communication as well, at the time of training, it is possible to obtain a relationship for the TDD-xDSL DMT transmission symbol sequence 700 to fit in the transmission section 601 of ISDN ping-pong transmission. That is, as in training, the length of the ISDN ping-pong transmission section is D, the card time between transmission and reception of ISDN ping-pong transmission is a, the length of the TDD-xDSL DMT transmission symbol sequence 700 is S2, and the TDD-xDSL transmission DMT symbol The margins between the sequence section and the transmission section of ISDN ping-pong transmission are α2 and β2, respectively, the number of carriers of the DMT transmission symbol is m, the number of symbols included in the symbol sequence during normal communication is N, and the frequency interval of the DMT carrier is fd. Then, the respective relationships to be satisfied in the present invention are as follows.

S2 + α2 + β2 ≦ D + a (4)
Or S2 + α2 + β2 ≦ D (4) '
S2 = N × (m + nc) × {1 / (m × fd)} (5)
Here, 0 ≦ α1, 0 ≦ β1, and nc are the number of cyclic prefix samples during normal communication.

According to the equations (4) to (5), the conventional G. Fixed to 16sample in 992.2 (G.lite)
The length of the Cyclic Prefix can also be changed as long as the expression (4) is satisfied.
In this way, the transmission timing of the TDD-xDSL training symbol sequence falls within the transmission section (FEXT section) of the ISDN ping-pong transmission, and when the TDD-xDSL training symbol is received, NEXT noise from the ISDN line is received. Can be avoided. In addition, during normal data communication, the transmission timing of the TDD-xDSL transmission symbol sequence falls within the transmission section (FEXT section) of ISDN ping-pong transmission, and when the TDD-xDSL transmission symbol is received, the NEXT from the ISDN line is received. Noise contamination can be avoided.

(c) Third feature In the third feature, in TDD-xDSL, the frequency of the timing recovery signal (pilot tone signal) is selected so that the continuity of DMT symbols is maintained between transmission burst sections. It is to be.
FIG. 4 is an explanatory diagram of a frame phase between transmission bursts at the time of training of TDD-xDSL. In the DMT modulation, each symbol is preferably a continuous DMT sample sequence. That is, in a section where no signal is transmitted between transmission bursts indicated by Ta in FIG. 4, the length of the section is an integer of the pilot tone period. It needs to be double. Therefore, the pilot symbol is set such that (1) the length of the transmission symbol sequence indicated by Tb is an integral multiple of the pilot tone period, and (2) the burst interval indicated by Tc is an integral multiple of the pilot tone period.・ Select the tone cycle. By doing so, the length of the section Ta can be made an integer multiple of the pilot tone period, and continuity of DMT samples of adjacent transmission bursts can be maintained.

  FIG. 5 is an explanatory diagram of the phase relationship of transmission symbols between bursts during both training and normal communication, and illustrates a frame in a downlink direction. As already described (second feature), the transmission symbol sequences 500 and 700 at the time of training and at the time of normal communication need to be included in the transmission section 601 of TCM-ISDN. Therefore, symbol transmission is performed using the transmission section 601 of TCM-ISDN as a reference timing, and the burst intervals Tc and Td at the time of training and at the time of normal communication, respectively, are determined from the burst intervals of ISDN ping-pong transmission. In the present invention, each of these burst intervals Tc and Td is selected so as to be an integral multiple of the period of the pilot tone signal PLT for TDD-xDSL timing setting.

(d) Fourth Feature In a fourth feature, a symbol 501 included in a transmission symbol sequence 500 at the time of training using a training symbol without a CP (Cyclic Prefix) and a DMT symbol with a CP (Cyclic Prefix) are used. The phase difference θd (FIG. 6) between the symbol and the symbol 701 included in the transmission symbol sequence 700 at the time of the normal communication is set to be an integral multiple of the pilot tone period previously selected.
FIG. 6 is an explanatory diagram of the phase relationship between the transmission burst frames at the time of training and at the time of normal communication. This is to explain the relationship between the phase differences θd of the positions.

The transmission symbol sequence 500 at the time of training and the transmission symbol sequence 700 at the time of normal communication are transmitted independently and in synchronization with the burst period of ISDN ping-pong transmission. Also, the arrangement of symbols excluding the cyclic prefix in each transmission symbol sequence is different. For this reason, the phases of the individual symbols 501 and 701 included in the transmission symbol sequence are different between during training and during normal communication. This phase difference θd is set to be an integral multiple of the cycle of the pilot tone PLT. This makes it possible to execute both the training process and the normal data communication process in synchronization with the pilot tone signal.
Means for making the phase difference an integral multiple of the period of the pilot tone PLT include a method of adjusting the period of the pilot tone and a method of adjusting the transmission symbol sequence 500 during training to the transmission symbol sequence 700 during normal communication. A method of shifting the transmission timing of the data may be considered.

(e) Fifth feature The fifth feature is that, during training, a tone signal is transmitted separately from the pilot tone PLT for timing reproduction, and the phase of the ISDN 400 Hz signal from the station side to the subscriber side (TDD- xDSL transmission phase). That is, the station notifies the subscriber of the timing for specifying the period affected by the crosstalk.
Since the tone signal added in addition to the pilot tone PLT always includes one or more phase change points in one burst, the subscriber xDSL apparatus finds the phase change point and sets the phase change point for a set time. The time before or after the set time is defined as the TDD-xDSL transmission timing of the station side xDSL device or the rising time of the 400 Hz signal. According to the fifth feature, the timing can be reproduced more easily and in a shorter time than the conventional method.

FIG. 7 is an explanatory diagram for performing timing reproduction of an ISDN 400 Hz signal with a newly added tone. When one training symbol sequence includes four training symbols, the phase changes once in one burst ( FIG. 7 (a)) and an example of changing twice (FIG. 7 (b)).
In FIG. 7A, the phase of the training symbol changes from pattern A to pattern B between the second symbol and the third symbol. In FIG. 7B, the phase of the training symbol changes from pattern B to pattern A between the first and second symbols, and changes from pattern A to pattern B between the third and fourth symbols. . Note that a transition from the pattern A to a newer pattern C may be performed between the third and fourth symbols.
In the example of FIG. 7A, the time before the set time T1 from the phase change detection time is the rising time of the ISDN 400 Hz signal TTR. In the example of FIG. 7B, the time before the set time T2 from the average time of the two phase change detection times T21 and T22 is the rising time of the ISDN 400 Hz signal TTR.

(f) Sixth feature A sixth feature is that patterns A and B in the above-mentioned tones other than the pilot tone PLT are selected such that the phase difference between them is 90 ° or 180 ° in the QAM constellation diagram. A → B or B → A within one burst, thereby transmitting a phase change.
FIG. 8 is an explanatory diagram of patterns A and B, and shows how to select patterns A and B when the simplest 4QAM is used as a DMT symbol. 8A shows an example of a constellation when the phase difference between the patterns A and B is 90 °, and FIG. 8B shows an example of a constellation when the phase difference between the patterns A and B is 180 °. It is.

(B) Example Configuration (a) Overall Configuration FIG. 9 is a block diagram of a TDD-xDSL subscriber transmission system according to the present invention, and the same parts as those in FIG. 30 are denoted by the same reference numerals. 30 is different from the configuration in FIG. 30 in that a sequencer 310, a selector 320, and a training signal generation circuit 330 are provided on the transmission side, and a signal detection circuit 340, a sequencer 350, a pilot phase detection circuit 360, and a training signal processing unit 370 are provided on the reception side. It is a point.
The transmission-side sequencer 310 generates (1) a training state signal TRN and a communication state signal CMN to distinguish between training and normal communication, and (2) controls the parallel-to-serial conversion buffer 40 to transmit training symbols for training. A sequence 500 (see FIG. 1) and a transmission symbol sequence 700 for normal communication (FIG. 3) are output.

The training signal generation circuit 330 outputs (1) various training signals during training, and (2) a pilot tone signal PLT for timing reproduction in a TDD-xDSL transmission section regardless of training or normal communication. Is output. This pilot tone signal PLT is transmitted to the receiving side on carrier # 64. The training signal generation circuit 330 transmits a tone signal on the carrier # 48 separately from the pilot tone signal PLT at the time of training, and transmits the phase of the ISDN 400 Hz signal from the station side to the subscriber side (the transmission phase of the station side TDD-XDSL). ) (See FIGS. 7 and 8).
In the TDD-xDSL transmission section, the selector 320 selects (1) a training signal output from the training signal generation circuit 330 during training and inputs the training signal to the IFFT circuit 30, and (2) outputs the signal from the encoder 20 during normal communication. The transmission data is selected and input to the IFFT circuit 30. Also, the selector 320 inputs the pilot tone signal PLT output from the training signal generation circuit 330 to the # 64 terminal of the IFFT circuit in the TDD-xDSL transmission section.

The signal detection circuit 340 on the reception side monitors the output signal level of the AD converter 80 to detect that a training signal has been sent from the transmission side, and the sequencer 350 controls the serial / parallel conversion buffer 100 to perform training. At the time of / normal communication, control is performed so that data for one symbol excluding the redundant signal / Cyclic Prefix is input to the FFT circuit 110. Pilot phase detection circuit 360 detects the phase of pilot tone signal PLT based on the signal output from the # 64 output terminal of the FFT circuit, and controls the AD conversion timing of AD converter 80.
The training signal processing circuit 370 analyzes the training signal, detects the ISDN 400 Hz signal timing, and detects the start of normal communication based on the sequence switching data sent from the transmitting side.

(B) Configuration for Generating Transmission Symbol Sequences During Training and Normal Communication FIG. 10 is a block diagram of a configuration for generating symbol sequences during training and normal communication, and the same parts as in FIG. ing. FIG. 11 is a time chart for explaining an output sequence operation at the time of training, in which a redundant signal 503 having a length of 128 samples is added to the front side and a redundant signal 504 of 8 samples is added to the rear side. FIG. 12 is a time chart for explaining the output sequence operation at the time of normal communication, in which the length of the cyclic prefix is 16 samples.

(b-1) Creation of Training Symbol Sequence Sequencer 310 generates various control signals so that transmission symbol sequence 500 for training is transmitted within the transmission period of ISDN ping-pong transmission. That is, the sequencer 310 performs switching control between training and normal communication by timer control when activated, inputs the training / normal communication switching signal DTSL to the selector 320, and outputs the training state signal TRN to the training signal generation circuit 330. To enter. The selector 320 selects a training signal output from the training signal generation circuit 330 during training and inputs the training signal to the IFFT circuit 30 according to the training / normal communication switching signal DTSL, and selects transmission data output from the encoder 20 during normal communication to perform IFFT. Input to the circuit 30. The training signal generation circuit 330 generates a predetermined training signal during training.

In training, as shown in FIG. 11, when a predetermined time t1 elapses from the rise of the ISDN 400 Hz signal TTR during training, (1) the P / S load timing signal PSLD, (2) the P / S output mask signal PSMK, (3) Generate the P / S output select signal PSSL (= {11}).
The P / S load timing signal PSLD is a signal for loading the IFFT operation result (256 signal point data) into the buffer unit 40a of the parallel / serial conversion buffer 40. The P / S output mask signal PSMK is a signal that permits data output from the buffer unit 40a when it is at a high level, and prohibits data output from the buffer unit 40a when it is at a low level. The P / S output select signal PSSL instructs to read out the 0th signal, the 128th signal, or the 240th signal in order from the 256 signals stored in the buffer unit 40a. That is, the P / S output select signal PSSL takes a value of {10}, {11}, {01}, and if (1) {10}, the selector 40b sequentially outputs the signal from the 0th of the buffer unit 40a. If (2) {11}, the signal is read out from the 128th position of the buffer unit 40a in order, and if (3) {01}, the signal is read out from the 240th position in the buffer unit 40a.

As described above, when the P / S load timing signal PSLD is generated, 256 signals output from the IFFT circuit 30 are stored in the buffer unit 40a of the parallel-to-serial conversion buffer 40. Next, the selector 40b sequentially reads the signals from the 128th of the buffer unit 40a in synchronization with the P / S operation clock PSCL according to the P / S output select signal PSSL = {11}, and outputs the signals through the mask circuit 40c. . As a result, 128 signals from the 128th to 255th are read out as the redundant signal 503, and then, 256 training signals (1st symbol data) from the 0th to 255th are read out.
When reading of the first training symbol is completed, sequencer 310 again generates P / S load timing signal PSLD and generates P / S output select signal PSSL (= {10}). As a result, the next 256 signals output from the IFFT circuit 30 are stored in the buffer section 40a of the parallel / serial conversion buffer 40. Next, the selector 40b sequentially reads signals from the 0th of the buffer unit 40a in synchronization with the P / S operation clock PSCL according to the P / S output select signal PSSL = {10}, and outputs the signals via the mask circuit 40c. . As a result, 256 training signals (second symbol data) from the 0th to the 255th are read.

  When the reading of the second training symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD and sends the next 256 signals output from the IFFT circuit 30 to the buffer unit 40a of the parallel / serial conversion buffer 40. Store. The selector 40b sequentially reads and outputs signals from the 0-th buffer unit 40a in synchronization with the P / S operation clock PSCL. As a result, 256 training signals (third symbol data) from the 0th to the 255th are read.

When the reading of the third training symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD and sends the next 256 signals output from the IFFT circuit 30 to the buffer unit 40a of the parallel-to-serial conversion buffer 40. Store. The selector 40b sequentially reads and outputs signals from the 0-th buffer unit 40a in synchronization with the P / S operation clock PSCL. As a result, 256 training signals (last symbol data) from the 0th to the 255th are read. Thereafter, eight signals from the 0th to the 7th are read out and output as the redundant signal 504.
When the output of the redundant signal 504 is completed, the sequencer 310 sets the P / S output mask signal PSMK to a low level, sets the P / S output select signal to {00}, and enters the non-select state.
Thereafter, at the time of training, the above-described operation is repeated at every rise of the ISDN 400 Hz signal TTR to create and transmit a transmission symbol sequence at the time of training.

(b-2) Generation of Transmission Symbol Sequence During Normal Communication The sequencer 310 generates various control signals so that the transmission symbol sequence 700 for normal communication is transmitted within the transmission period of ISDN ping-pong transmission. That is, the sequencer 310 performs switching control from the training state to the normal communication state after a predetermined time has elapsed after activation. Accordingly, the selector 320 selects the transmission data output from the encoder 20 and inputs the transmission data to the IFFT circuit 30. The selector 320 selects the pilot tone signal PLT from the training signal generation circuit 330 and inputs it to the # 64 terminal of the IFFT circuit.
In normal communication, as shown in FIG. 12, when a predetermined time t2 elapses from the rise of the ISDN 400 Hz signal TTR during normal communication, (1) the P / S load timing signal PSLD, and (2) the P / S output mask signal PSMK , (3) Generate a P / S output select signal PSSL (= {01}).

  When the P / S load timing signal PSLD is generated, 256 signals output from the IFFT circuit 30 are stored in the buffer unit 40a of the parallel / serial conversion buffer 40. Next, the selector 40b sequentially reads the signals from the 240th buffer unit 40a in synchronization with the P / S operation clock PSCL according to the P / S output select signal PSSL = {01}, and outputs the signals via the mask circuit 40c. . As a result, 16 signals from the 240th to 255th are read as Cyclic Prefix, and then, 256 transmission signals (1st symbol data) from the 0th to 255th are read.

When the reading of the first transmission symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD again. As a result, the next 256 signals output from the IFFT circuit 30 are stored in the buffer section 40a of the parallel / serial conversion buffer 40. Next, the selector 40b reads out the 16 signals from the 240th to 255th of the buffer unit 40a as a Cyclic Prefix in synchronization with the P / S operation clock PSCL by the P / S output select signal PSSL = {01}, Subsequently, 256 transmission signals (second symbol data) from the 0th to 255th are read and output. Thereafter, similarly, if the third and fourth symbol data with the cyclic prefix are read and output, the sequencer 310 sets the P / S output mask signal PSMK to low level and sets the P / S output select signal to {00}. To the non-select state.
Thereafter, in the communication state, the sequencer 310 repeats the above operation each time the ISDN 400 Hz signal TTR rises to create and transmit a transmission symbol sequence for normal communication.

(b-3) Configuration of Sequencer FIG. 13 is a configuration diagram of a sequencer in the station-side ADSL device. The sequence switching unit 311 generates a training state signal TRN and a normal communication state signal CMN by timer control at the time of startup, and the ISDN 400 Hz signal generation unit 312 outputs a 400 Hz signal TTR of ISDN ping-pong transmission. The P / S operation clock generator 313 outputs the P / S operation clock signal PSCL in synchronization with the ISDN 400 Hz signal TTR, and the pilot tone signal generator 314 divides the P / S operation clock signal PSCL by 1/4. And outputs a pilot tone signal PLT for timing reproduction. Here, an example is shown in which the 400 Hz signal TTR of ISDN ping-pong transmission is output from the ISDN 400 Hz signal generation unit 312, but it may be input from outside. This configuration will be described later.

  The reason for outputting the pilot tone signal PLT by dividing the P / S operation clock signal PSCL by 1 is as follows. If the carrier frequency interval is, for example, 4 kHz, the number of samples in a DMT symbol is 256, and # 64 is used as a pilot tone transmission carrier, the FFT sampling frequency on the receiving side is 1024 kHz (= 4 × 256 kHz) from the carrier frequency interval and the number of carriers. ). The frequency of the pilot tone is 4kHz x 64 = 256kHz. That is, the data per cycle of the pilot tone is four samples. On the other hand, the P / S operation clock signal PSCL sends out the signal serially from the parallel / serial conversion buffer 40 at 1024 kHz, and is equal to the FFT sample frequency. As described above, the pilot tone signal PLT can be generated by dividing the P / S operation clock signal PSCL by / 4. The pilot tone signal PLT has the same phase and frequency as the pilot tone signal generated by the training signal generation circuit 330.

During training, the first transmission symbol output timing generation section 315 synchronizes with the pilot tone PLT after a predetermined time t1 (FIG. 11) elapses after the rise of the ISDN 400 Hz signal TTR so as to satisfy the expression (1) or (2). To generate a symbol output timing signal TSOT.
During normal communication, the second transmission symbol output timing generator 316 transmits in synchronization with the pilot tone PLT after a predetermined time t2 (FIG. 12) elapses after the rise of the ISDN 400 Hz signal TTR so as to satisfy Expression (4). Generates a symbol output timing signal DSOT.
The various control signal generator 317 synchronizes with the P / S operation clock signal PSCL based on the training state signal TRN, the normal communication state signal CMN, the transmission symbol output timing signals TSOT and DSOT, and outputs various control signals (P / S load signal). PSLD, P / S output select signal PSSL, P / S mask signal PSMK, training / normal communication switching signal DTSL, etc.) are output in synchronization with the P / S operation clock PSCL.

Each of the transmission symbol output timing generators 315 and 316 generates the symbol output timing signals TSOT and DSOT in synchronization with the pilot tone PLT, so that the individual symbols included in the transmission symbol sequence can be used during training and during normal communication. The phase difference θd between 501 and 701 (see FIG. 6) can be adjusted to an integral multiple of the pilot tone period.
The transmission symbol output timing generating sections 315 and 316 generate the symbol output timing signals TSOT and DSOT in synchronization with the pilot tone PLT, so that (1) the transmission symbol sequence The length can be an integral multiple of the pilot tone period, and (2) the transmission burst interval can be an integral multiple of the pilot tone period. As a result, in TDD-xDSL transmission, in the interval between transmission bursts that are temporally adjacent, the interval in which no signal is transmitted can be made an integral multiple of the pilot tone period, and the continuity of DMT samples in adjacent transmission bursts is maintained. it can. Since the number of samples of the transmission symbol sequence during training is 1160 (= 128 + 256 × 4 + 8), it is 290 times the pilot tone period, and the number of samples of the transmission symbol sequence during normal communication is 1088 ( = (16 + 256) × 4), which is 272 times the pilot tone period, and satisfies the above (1).

Another Configuration for Generating ISDN 400 Hz Signal TTR FIG. 14 shows an embodiment in which the ISDN 400 Hz signal TTR is input from outside. In FIG. 14, a plurality of office-side TDD-xDSL devices 3011 to 3014 installed in a telephone office are connected to an ISDN 400 Hz signal generator 401. Each of the station-side TDD-xDSL devices 3011 to 3014 has each functional block as shown in FIG. 9, but FIG. 14 shows only the sequencer 310 among them. Although the sequencer 310 has a configuration as shown in FIG. 13, in this embodiment, since a 400 Hz signal TTR is input from the outside, the ISDN 400 Hz signal acquisition unit 312 a is used instead of the ISDN 400 Hz signal generation unit 312. Is provided. The blocks other than the ISDN 400 Hz signal generation unit 312 shown in FIG. 13 are collectively shown as a processing unit 312b in the sequencer in FIG.

Now, the ISDN 400 Hz signal generator 401 is installed in every central office that can provide ISDN, and generates an ISDN 400 Hz signal TTR using an 8 kHz network clock. Each station-side TDD-xDSL device 3011 to 3014 is connected to the ISDN 400 Hz signal generator 401, and the ISDN 400 Hz signal acquisition unit 312a acquires the ISDN 400 Hz signal TTR. Then, the ISDN 400 Hz signal acquisition section 312 a supplies the acquired ISDN 400 Hz signal TTR to each section of the in-sequencer processing section 312 b in the same manner as the method shown in FIG. With this configuration, all the TDD-xDSL devices 3011 to 3014 and the ISDN-OCU (not shown) can communicate in synchronization with the ISDN 400 Hz signal TTR.
By the way, the ISDN 400 Hz signal generator 401 may not be installed in a telephone station which does not provide the ISDN service. In such a case, a device that generates a 400 Hz signal is installed in the central office in the same manner as the ISDN 400 Hz signal generator 401, and a 400 Hz signal is provided to each office side TDD-xDSL device 3011 to 3014 in the mode of FIG. In this way, crosstalk noise from an adjacent TDD-xDSL line can be prevented.

(C) Configuration of Each Part on the Receiving Side FIG. 15 is a configuration diagram of a main part on the receiving side, and the same parts as those in FIG. The signal detection circuit 340 monitors the output signal level of the AD converter 80 that performs AD conversion of the input signal at the FFT sampling frequency, detects that the training signal has been sent from the transmission side, and sends the training start signal TRST to the sequencer 350. input. The training signal processing circuit 370 analyzes the training signal and performs various training processes. For example, the training signal processing circuit 370 detects the timing of the ISDN 400 Hz signal TTR and determines the start timing of the normal communication based on the sequence switching data sent from the transmission side. Then, the normal communication start signal CMST is input to the sequencer 350. The sequencer 350 includes an S / P operation clock generator 350a and a control signal generator 350b. The S / P operation clock generator 350a generates an S / P operation clock SPCL having the same frequency as the FFT sampling frequency in synchronization with the ISDN 400 Hz signal TTR. The control signal generating section 350b generates various timing signals shown in FIG. 16 in synchronization with the S / P operation clock SPCL during training after the timing detection of the ISDN 400 Hz signal TTR and the phase control of the pilot tone signal are completed, and performs the normal communication. At this time, various timing signals shown in FIG. 17 are generated in synchronization with the S / P operation clock SPCL.

(c-1) Receiving sequence operation during training (see Fig. 16)
When the training start signal TRST is generated from the signal detection circuit 340, the sequencer 350 generates the S / P load timing signal SPLD after the arrival of the redundant signal of 128 samples. Thereby, redundant signal 503 added to the head of transmission symbol sequence 500 can be removed. When the S / P load timing signal SPLD is generated, the serial / parallel conversion buffer 100 (FIG. 9) sequentially stores the sample data output from the TEQ 90 in synchronization with the S / P operation clock SPCL. After storing one symbol (= 256 samples) of data, the sequencer 350 generates an FFT load timing signal FFTLD, loads one symbol of sample data from the serial / parallel conversion buffer 100 to the FFT circuit 110, and the FFT circuit 110 FFT operation is performed at the timing of and the operation result is output.

On the other hand, the serial / parallel conversion buffer 100 continuously stores the sample data output by the TEQ 90 continuously even after the generation of the FFT load timing signal FFTLD, and generates the next one symbol (= 256 samples) of data from the sequencer 350 after storing the data. The sample data for one symbol is input to the FFT circuit 110 according to the FFT load timing signal FFTLD.
Thereafter, the same reception sequence operation is repeated, and after the last symbol is input to the FFT circuit 110, the sequencer 350 sets the S / P load timing signal SPLD to low level and removes the redundant signal 504 added to the rear of the transmission symbol sequence. I do.

(c-2) Reception sequence operation during normal communication (see Fig. 17)
When the normal communication start signal CMST is input from the training signal processing unit 370, the sequencer 350 immediately generates the S / P load timing signal SPLD. When the S / P load timing signal SPLD is generated, the serial / parallel conversion buffer 100 (FIG. 9) sequentially stores the sample data output from the TEQ 90 in synchronization with the S / P operation clock SPCL. The sequencer 350 generates the FFT load timing signal FFTLD at the timing when the cyclic prefix (CP) and 272 (= 16 + 256) sample data corresponding to one symbol are stored in the serial / parallel conversion buffer. As a result, the sample data for one symbol excluding the cyclic prefix of 16 samples is loaded from the serial / parallel conversion buffer 100 to the FFT circuit 110, and the FFT circuit 110 performs the FFT operation at a predetermined timing and outputs the operation result.

On the other hand, the serial / parallel conversion buffer 100 sequentially stores the sample data output by the TEQ 90 continuously even after the generation of the FFT load signal FFTLD, and the sequencer 350 stores new 272 (= 16 + 256) sample data in series. The FFT load signal FFTLD is generated at the timing stored in the parallel conversion buffer. As a result, the serial / parallel conversion buffer 100 loads the sample data of one symbol excluding the cyclic prefix of 16 samples into the FFT circuit 110, and the FFT circuit 110 performs the FFT operation at a predetermined timing and outputs the operation result.
Thereafter, the same processing is repeated, and after the last symbol is input to the FFT circuit 110, the sequencer 350 sets the S / P load timing signal SPLD to low level.

(D) Transmission control of pilot tone signal PLT The pilot generation section 330a (FIG. 10) of the training signal generation circuit 330 generates a pilot tone signal. The training signal generation circuit 330 transmits a pilot tone signal to the subscriber side in the transmission section of TDD-xDSL transmission regardless of training or normal communication. That is, sequencer 310 generates select signal DTSL, and selector 320 inputs the pilot tone signal to the # 64 carrier terminal of IFFT circuit 30 within the TDD-xDSL transmission section. The IFFT circuit 30 performs an IFFT process on the pilot tone signal, and transmits the pilot tone signal to the receiving side via the parallel / serial conversion buffer 40 and the DA converter 50.
Pilot phase detection circuit 360 detects the phase of pilot tone signal PLT based on the signal output from the # 64 carrier terminal of FFT circuit 110, and controls the AD conversion timing of AD converter 80. This allows the receiving side to perform AD conversion and other processing in synchronization with the pilot tone signal.

(E) Phase transmission / reception of ISDN 400 Hz signal The training signal generation circuit 330 transmits a tone signal on the carrier # 48 separately from the pilot tone signal PLT during training, and transmits the phase of the ISDN 400 Hz signal from the station side to the subscriber side (station side). TDD-xDSL transmission phase) (see FIGS. 7 and 8). That is, the station uses the training tone signal to notify the subscriber of the timing for specifying the period affected by the crosstalk.
When four training symbols are included in a transmission symbol sequence of one burst, a tone signal indicating the phase of an ISDN 400 Hz signal is transmitted by changing the phase of an adjacent training symbol at least once in one burst.

  FIG. 7A shows an example in which the phase of an adjacent symbol is changed once in one burst, and the patterns of the first and second symbols and the third and fourth symbols are changed from A to B. Note that the first and second symbol patterns can be changed, and the third and fourth symbol patterns can be changed. As the symbol patterns A and B, as shown in FIG. 8, the phase difference is 90 ° with respect to each other in the QAM constellation diagram (FIG. 8A), or the phase difference is 180 ° with each other (FIG. 8B )). That is, in the case of the pattern A, the 2-bit set 11, 11,..., 11 is input to the selector 320, and in the case of the pattern B of FIG. 1 -1, ..., 1 -1 are input to the selector 320, and in the case of the pattern B in FIG. 8B, a set of 2 bits -1, -1, -1, -1,. 1 -1 is input to the selector 320.

FIG. 7B shows an example in which the phase of an adjacent symbol is changed twice within one burst. The first and second symbol patterns are changed from B to A, and the third and fourth symbol patterns are changed. A → B is changed. The phase change point may be such that the pattern changes between any two sets of adjacent symbols.
In order to notify the phase of the ISDN 400 Hz signal (the transmission phase of the station side TDD-xDSL) by the pattern change in FIG. 7A, the training signal generation circuit 330 uses the symbol pattern based on the rising edge of the ISDN 400 Hz signal TTR input from the sequencer 310. Generates data such that A → A → B → B changes. This data is subjected to IFFT processing by the IFFT circuit 30 and transmitted as a training symbol sequence shown in FIG. Thereby, the receiving side detects the phase change time of A → B, and recognizes the time before time T1 from the phase change time as the rising phase of the ISDN 400 Hz signal TTR. In practice, the rising phase of the ISDN 400 Hz signal TTR is determined based on a plurality of average values.

In order to notify the phase of the ISDN 400 Hz signal (station-side transmission phase) by the pattern change of FIG. 7B, the training signal generation circuit 330 changes the symbol pattern to B → based on the rise of the ISDN 400 Hz signal TTR input from the sequencer 310. Data is generated so that A → A → B changes. This data is subjected to the IFFT processing in the IFFT circuit 30 and transmitted as a training symbol sequence shown in FIG. As a result, the receiving side detects two phase change times B → A and A → B, finds the average time Tavr, and recognizes the time before the set time T2 before the average time as the rise time of the ISDN 400 Hz signal TTR. . In practice, the rising phase of the ISDN 400 Hz signal TTR is determined based on a plurality of average values. In the example of FIG. 7B, since two phase change times can be detected by one training, the rising phase of the ISDN 400 Hz signal TTR can be determined with a smaller number of times as compared with FIG. 7A.
Incidentally, even in G.lite which is the same xDSL system, a method of transmitting a phase change by a tone signal other than a pilot tone is used, but unlike the case of G.lite in the present invention, transmission in a NEXT section is performed. Do not do. For this reason, there is no need to distinguish between the FEXT section and the NEXT section. Therefore, 180 ° or a combination thereof can be used as the phase change method in addition to 90 °.

(C) First Embodiment of Burst Frame During Training and Normal Communication There is a G992.2 (G.lite) system as a conventional xDSL system. G.lite uses 4.3125 kHz for the carrier frequency interval, 256 for the number of samples in one DMT symbol, and # 64 as a carrier for transmitting a pilot tone. The first embodiment uses 4 kHz, which is slower than the G.lite system, for the carrier frequency interval. Other items, like the G.lite system, use 256 samples in one DMT symbol, and use ## as the carrier for transmitting pilot tones. I chose 64.
In the first embodiment, the FFT sampling frequency of the transmission signal is 1024 kHz from the carrier frequency interval and the number of samples. The frequency of the pilot tone is 4kHz x 64 = 256kHz. That is, data per one cycle of the pilot tone is equivalent to four samples. In the first embodiment, the symbol length of one symbol is 256 samples, the period is 250 μs, and the upper limit of the number of symbols included in one burst is 4, due to the relationship with the burst period of 1250 μs in the ISDN ping-pong transmission method. If the number of symbols is 4, there is a margin of about 250 μs, and a redundant signal can be added or a margin can be set using this margin period. That is, even if redundant signals 503 and 504 are added before and after the training symbol sequence, the number of symbols per burst does not decrease and four symbols can be transmitted.

(a) Signal transmission section during normal communication A transmission section of a transmission frame during normal communication in the first embodiment will be described with reference to FIG. In TDD-xDSL transmission, during normal communication, a symbol 701 with a Cyclic Perfix (CP) 702 is used. The length of the Cyclic Prefix can be any length as long as the transmission symbol sequence falls within the transmission interval, but in this embodiment, the length of the Cyclic Prefix is one of the xDSL systems G992.2 (G.lite) system 16 samples (15.625 μs), which is the same number of samples as above, and a transmission symbol sequence 700 is formed by continuing four cyclic prefixed symbols. Therefore, the symbol length of the transmission symbol sequence 700 is 1088 samples (1.0625 ms).

FIG. 19 shows the timing relationship between the transmission symbol sequence 700 and the signal of the ISDN ping-pong transmission during the normal communication in the first embodiment.
First, consider a downlink signal transmission section. In order to ensure that the TDD-xDSL transmission section does not overlap with the ISDN ping-pong transmission reception section, the TDD-xDSL downstream signal transmission section is arranged so as to be approximately at the center of the ISDN ping-pong transmission transmission section. Here, as described according to FIG.
S2 + α2 + β2 ≦ D + a
Need to be satisfied.
here,
Transmission interval D in ISDN ping-pong transmission = 1.178125ms (1206.4sample),
TDD-xDSL transmission signal length S2 = 1.0625ms (1088 samples)
It is. Assuming that a '<a where a' = a = 9.375 µs (9.6 samples) in consideration of the margin, S2 + α2 + β2 = D + a '≤ D + a
Α2 and β2 that satisfy the above may be obtained. Here, since the TDD-xDSL downlink transmission section is brought to the center of the ISDN ping-pong downlink transmission section, α2 = β2 = 62.5 μs (64 samples) is obtained.

Similarly, consider an uplink signal section. The guard time b for receiving the downlink signal and transmitting the uplink signal in ISDN ping-pong transmission has a value ranging from 18.75 μs (19.2 samples) to 23,4378 μs (24 samples).
Since this guard time is a value determined independently of the TDD-xDSL system, the transmission interval of the TDD-xDSL uplink transmission symbol sequence must be exactly aligned with the center of the ISDN ping-pong uplink transmission interval. Can not. Here, it is assumed that the guard time of ISDN ping-pong transmission is 18.75 μs (19.2 samples) by adjusting to the center, and in that case, the guard time end time tge1 of TDD-xDSL and the card time end time of ISDN Select the card time c of TDD-xDSL so that teg2 almost matches.
In the first embodiment, as shown in FIG. 19, (uplink transmission section of ISDN ping-pong transmission + guard time b) is 1196.875 μs, and (TDD-xDSL uplink signal transmission section S2 + front and rear margin sections α2 + β2) = 1187.5 μs (1216 samples) ), The guard time c of TDD-xDSL transmission is selected to be 9.656625 to 14.64844 μs (10 to 15 samples), and the transmission timing is determined similarly to the downlink signal.

(b) Signal transmission section during training Next, a signal transmission section during training according to the first embodiment will be described with reference to FIGS. 18 and 20. FIG. 18 shows a transmission symbol sequence 500 for TDD-xDSL training. It is desirable that the redundant signal 503 added before the four consecutive training symbols 501 be a sufficiently long section for the cyclic prefix 702 during normal communication. Here, as an example, it is assumed that a redundant signal 503 of 125 μs (128 samples), which is a sufficiently long section, is used for a cyclic prefix length of 16 samples (15.625 μs). Further, as an example of the redundant signal 504 added to the rear side, a redundant signal of 8 samples (7.8125 μs) is added. The above constitutes the training symbol sequence 500. Thus, x1 = 125 μs (128 samples) and y1 = 7.8125 μs (8 samples). S1 = 1 ms (1024 sample = 256 sample × 4). From this,
S1 + x1 + y1 = 1.132813ms (1160sample)
Is found. Subsequently, as shown in FIG. 20, the data is stored in D + a 'as in the normal communication.
When (S1 + α1 + β1 + x1 + y1) is obtained,
1.132813ms (1160sample) + α1 + β1 ≦ 1.1875ms (1216sample)
Therefore, here, α1 = 0 μs (0 sample) and β1 = 54.6875 μs (56 sample) are selected.

(c) Examination of the worst conditions By the way, the transmission delay of the ISDN ping-pong system and the transmission delay of the TDD-xDSL system are determined separately and independently. Therefore, for example, when the ISDN line is close (no delay) and the TDD-xDSL line is farthest (maximum delay), the subscriber side of the ISDN line before training ends receiving the TDD-xDSL downstream signal during training The transmission of the uplink signal from the side is started, and the timing of transmission / reception may be shifted. Therefore, the worst condition of the TDD-xDSL transmission / reception section for the ISDN transmission / reception section is considered. In the first embodiment, the length of the symbol sequence of TDD-xDSL transmission is longer at the time of training (= 1160 samples) than at the time of normal communication (= 1088 samples).

(c-1) First Worst Condition The worst condition firstly taken is a case where the delay time of TDD-xDSL transmission is the minimum and the delay time of ISDN ping-pong transmission is the maximum. As shown in FIG. 21, the transmission of the upstream signal of TDD-xDSL transmission must not start before the downstream signal of ISDN ends. In the first embodiment, the latest timing at the end of the reception of the ISDN downlink signal is the sum of the length of the ISDN downlink transmission signal of 1.178125 ms (1206.4 samples) and the transmission delay of 50 μs (51.2 samples).

On the other hand, the earliest timing of the start of transmission of the TDD-xDSL uplink signal is the TDD-xDSL downlink signal section 1.132813 ms (1160 sample), the margin section α1 = 0 μs (0 sample) before and after transmitting the signal, β1 = 54.6875 μs (56 sample ), The guard time between the upstream and downstream, and the margin section α1 (= 0) before the signal is transmitted. Compare the above,
The guard time between uplink and downlink of TDD-xDSL is determined to be 44.92188 to 49.80469 μs (46 to 51 samples) so that the end of the ISDN downlink signal section is shorter than the beginning of the TDD-xDSL uplink signal section. As a result,
ISDN downstream signal section end 1.228125ms (1257.6sample)
<TDD-xDSL upstream signal section head 1.232422ms (1262sample)
Thus, the TDD-xDSL upstream signal is not transmitted earlier than the end of ISDN downstream signal reception. In other words, even under the worst conditions, the transmission section of TDD-xDSL transmission falls within the transmission section of the ISDN apparatus on the side closer to the ADSL apparatus to be transmitted.

(c-2) Second Worst Condition The worst condition described below will be described for the worst condition in which the delay time of TDD-xDSL is the largest and the delay time of the ISDN device is the smallest. In this case, as shown in FIG. 22, the end of the reception period of the TDD-xDSL downlink signal must end before the start of transmission of the ISDN uplink signal. In the first embodiment, the latest timing at the end of the reception of the TDD-xDSL downlink signal is the transmission signal length of the TDD-xDSL downlink signal at 1132.813 ms (1160 sample), the transmission delay time 57.8125 μs (59.2 sample), Is added to the margin section α1 (= 0) μs (0 sample) before sending the 4.88813 μs (5 samples) for the deviation of the reception timing.

On the other hand, the transmission timing of the earliest uplink signal of ISDN ping-pong transmission is the sum of the ISDN downlink signal section of 1.178125 ms and the minimum uplink / downlink guard time of 18.75 μs (19.2 samples) (= 1.196875 msec). Become. Compare the above,
TDD-xDSL downstream signal section end 1.195508ms (1224.2sample)
<ISDN upstream signal section head 1.96875ms (1225.6sample)
Thus, the downlink signal reception of TDD-xDSL is received earlier than the start of transmission of the ISDN uplink signal. As a result, even under the worst conditions, the ISDN uplink signal transmission section does not extend to the TDD-xDSL downlink signal reception section.

(c-3) Third worst condition Next, when the delay time of TDD-xDSL transmission is the maximum, (1) the reception period of the TDD-xDSL upstream signal is the downstream signal transmission period of the next burst of ISDN ping-pong transmission What does not matter will be described with reference to FIG.
The end of the TDD-xDSL upstream reception signal is (1) TDD-xDSL downstream signal transmission section 1.132813 ms (1160 sample), (2) margin section α1 = 0 μs (= 0 sample) before and after signal transmission, ( 3) β1 = 54.6875 μs (56 samples), (4) Transmission delay 57.8125 μs (59.2 samples) × 2 (because of two directions of up and down), (5) Maximum guard time of up and down 49.80469 μs (51 samples) (8) DMT symbol in (8) a margin for timing deviation of 4.82813 μs (5 samples), (6) an upstream signal transmission interval of 1.128 313 ms (1160 samples), (7) a margin interval α1 = 0 μs (0 sample) before signal transmission, and (8) a DMT symbol This is the sum of the rising delay at the start of transmission or the margin of the residual signal remaining when the transmission is stopped, 0.976567 μs (1 sample) × 2 (= 2.492578 msec). On the other hand, the burst period of ISDN ping-pong transmission is 2.5 ms. Compare the above,
2.492578ms (2552.4sample) at the end of the TDD-xDSL upstream signal section
<ISDN burst cycle 2.5 ms (2560 sample)
Thus, the reception of the TDD-xDSL uplink signal ends earlier than the start of the transmission of the next ISDN downlink signal, that is, even if the delay time of the TDD-xDSL transmission is the maximum, the reception interval of the TDD-xDSL uplink signal is It does not span the ISDN transmission section of the next burst.

The worst conditions have been discussed above. However, when the ISDN line and the TDD-xDSL metallic line are adjacent to each other, they are connected to the same station, so the worst-case condition cannot actually exist.
For example, if the ISDN line has no transmission delay time and the TDD-xDSL line has the longest transmission delay time, the subscriber-side ISDN device DSU is arranged near the station CN as shown in FIG. This is a case where a place where the TDD-xDSL device xTU-R on the subscriber side is far from the station is located. In this case, when the upstream signal from the ISDN device DSU leaks into the TDD-xDSL line, in order for the noise to be transmitted from the location where the ISDN device DSU is located to the location where the TDD-xDSL device xTU-R is located, Since a transmission delay occurs, the transmission of the downstream TDD-xDSL signal from the station side is not affected by the upstream signal of the ISDN line.

  On the other hand, when the transmission delay time of the ISDN line is the maximum and there is no transmission delay time of the TDD-xDSL line, as shown in FIG. The TDD-xDSL device xTU-R on the subscriber side is located near the station. Also in this case, if the upstream signal of TDD-xDSL transmission leaks as noise to the subscriber ISDN device DSU, a transmission delay occurs, so if the transmission of the ISDN downstream signal from the station is finished, the ISDN line is affected. Never.

(d) Phase Difference Between Transmission Symbol Sequence During Training and Normal Communication The phase difference between the transmission symbol sequence for training and the transmission symbol sequence during normal communication will be described with reference to FIG. The difference between the start position of the first symbol 501 at the time of training and the start position of the first symbol 701 excluding the cyclic prefix (CP) at the time of normal communication is θd1 = 46.875 in the case of downlink transmission, as is clear from FIG. μs (48 samples), and θd2 = 82.0312 μs (84 samples) for uplink transmission.
Since 3.90625 μs (4 samples) is one cycle of the pilot tone, the phase differences θd1 and θd2 are 12 times and 21 times the pilot tones, respectively, and the phase difference is an integer multiple of the pilot tone period. Meets.

(D) Second Embodiment of Burst Frame During Training and Normal Communication The second embodiment is similar to the G.lite system in that the carrier frequency interval is 4.3125 kHz, the number of samples is 256, and the carrier for transmitting pilot tones is This is when # 64 is selected.
In the second embodiment, the sampling frequency is 1104 kHz and the pilot tone frequency is 276 kHz. Therefore, as in the first embodiment, one cycle of the pilot tone is 3.623188 μs (4 samples). In the second embodiment, the length of the Cyclic Perfix is set to 28.98551 μs (32 samples) as an example longer than that of the G.lite system, and the length of the redundant signal 503 added before training is set to the length of the Cyclic of the G.lite system. The length of the redundant signal is 115.94203 μ (128 samples), which is sufficiently longer than the prefix, and the length of the redundant signal to be added is 18.11594 μs (20 samples). From the above, the configuration of the transmission symbol arrays 500 and 700 for normal communication and training, respectively, is as shown in FIG.

The signal transmission section during the normal communication in the second embodiment will be described with reference to FIG. As in the case of the first embodiment, if the TDD-xDSL signal transmission section is located substantially at the center of the transmission section of ISDN ping-pong transmission,
D + a '= 1.1875 ms (1311 samples),
S2 = 1.043478ms (1152sample)
Then, since α2 + β2 = 144.0217 μs (159 samples), α2 = 70.65217 μs (78 samples) and β2 = 73.36957 μs (81 samples) are selected.
Similarly, FIG. 28 shows a signal transmission section during training in the second embodiment.

D + a '= 1.1875 ms (1311 samples),
S1 + x1 + y1 = 1.061594ms (1172sample)
Therefore, α1 + β1 = 125.9058 μs (139 samples). Therefore, as in the case of the first embodiment, assuming that the transmission section of the TDD-xDSL signal is located substantially at the center of the transmission section of the ISDN ping-pong transmission, α1 = 63.4057 μs (70 samples), β1 = 62.5 Select μs (69sample).

In the second embodiment, considering the first worst condition, the second worst condition, and the third worst condition, the following (1), (2), and (3) are satisfied.
Here, the guard time between the downstream and upstream signals was set to 27.17391 to 31.7029 μs (30 to 35 samples).
(1) The end of the slowest ISDN downlink signal section 1.228125ms (1355.85sample)
<1.27808ms (1411sampl) at the beginning of the earliest TDD-xDSL uplink signal section
(2) The end of the slowest TDD-xDSL downlink signal section 1.19029 ms (1316 samples)
<The first 1.96875ms (1321.35sampl) of the earliest ISDN uplink signal section
(3) The end of TDD-xDSL upstream signal section 2.475543ms (2733sample)
<ISDN burst period 2.5 ms (2760 samples)
According to (1), even under the first worst condition, an uplink signal of TDD-xDSL transmission is not transmitted earlier than the end of ISDN downlink signal reception.
Also, according to (2), even under the second worst condition, the downlink signal reception of TDD-xDSL is received earlier than the start of transmission of the ISDN uplink signal.
According to (3), even under the third worst condition, the reception of the TDD-xDSL uplink signal ends earlier than the start of the transmission of the next burst ISDN downlink signal.

The relationship between the phase difference between the transmission symbol sequence 700 for normal communication and the transmission symbol sequence 500 during training will be described with reference to FIG. 26. The phase difference is 79.71014 μs (88 samples) = pilot tone period × 22. Is an integral multiple (= 22 times) of the pilot tone.
As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in claims, and the present invention does not exclude these.

FIG. 4 is an explanatory diagram of a transmission symbol string at the time of TDD-xDSL training. FIG. 3 is a configuration diagram of a transmission frame according to the TDD-xDSL scheme (during training). FIG. 3 is a configuration diagram of a transmission frame according to the TDD-xDSL system (at the time of normal communication). FIG. 7 is an explanatory diagram of a frame phase relationship between bursts (in the case of a downstream). FIG. 10 is another explanatory diagram of the frame phase relationship between bursts (in the case of downstream). FIG. 8 is a phase relationship diagram between burst frames during training and normal communication. FIG. 8 is an explanatory diagram of a method of notifying a TDD-xDSL transmission phase (ISDN 400 Hz phase) during training. FIG. 4 is an explanatory diagram of a phase change transmission pattern. FIG. 1 is a block diagram of a subscriber transmission system using a DMT modulation method according to the present invention. FIG. 3 is a configuration diagram for realizing the rearrangement of symbol arrays according to the present invention. 6 is a time chart (training) showing an output sequence operation. 6 is a time chart (normal communication) showing an output sequence operation. It is a block diagram of a transmission side sequencer. FIG. 3 is a configuration diagram showing an external input of an ISDN 400 Hz signal TTR. It is a block diagram of each part of a receiving side. 5 is a time chart (training) illustrating a reception sequence operation. 5 is a time chart (normal communication) illustrating a reception sequence operation. FIG. 4 is a diagram showing a phase relationship between burst frames during training and during normal communication in the first embodiment. FIG. 3 is a diagram illustrating a burst frame configuration (at the time of normal communication) in the first embodiment. FIG. 7 is a diagram illustrating a burst frame configuration (at the time of training) according to the first embodiment. FIG. 8 is a diagram illustrating a first worst condition (during training) according to the first embodiment. FIG. 8 is a diagram illustrating a second worst condition (during training) according to the first embodiment. FIG. 10 is a diagram for explaining a third worst condition (during training) according to the first embodiment. It is two worst condition explanatory drawing. FIG. 4 is a diagram illustrating a phase difference between a training transmission symbol sequence and a normal communication transmission symbol sequence. FIG. 9 is a phase relationship diagram between burst frames during training and during normal communication in the second embodiment. FIG. 10 is a diagram illustrating a burst frame configuration (at the time of normal communication) according to a second embodiment. FIG. 11 is a diagram illustrating a burst frame configuration (at the time of training) according to a second embodiment. FIG. 4 is an explanatory diagram of a DMT transmission spectrum. FIG. 2 is a functional block diagram of a subscriber transmission system using a DMT modulation method. FIG. 3 is an explanatory diagram of a band of an ISDN ping-pong transmission system and a band of ADSL transmission. It is a crosstalk noise explanatory drawing. FIG. 4 is an explanatory diagram of interference (crosstalk) from an ISDN line to an ADSL line. It is a sliding window explanatory view. It is an explanatory view of Dual Bitmap and Fext Bitmap. FIG. 4 is an explanatory diagram of a bitmap creation method using the B & G protocol. FIG. 7 is an explanatory diagram of a mode of measuring S / N for each NEXT / FEXT section. FIG. 3 is an explanatory diagram of a hyperframe method. FIG. 3 is an explanatory diagram of a transmission method for synchronizing an ADSL symbol with ISDN ping-pong transmission. FIG. 4 is an explanatory diagram of a transmission method of a TDD-xDSL symbol. FIG. 4 is an explanatory diagram of an ISI removal method. FIG. 4 is an explanatory diagram of an influence of ISI received by an xDSL symbol.

Explanation of reference numerals

500 training symbol sequence 501 training symbol 502 conventional transmission symbol sequence 503, 504 redundant data

Claims (4)

In a digital subscriber line transmission method receiving crosstalk from an ISDN ping-pong transmission line,
A digital subscriber line transmission method characterized in that a phase is changed twice between arbitrary two sets of adjacent symbols in a transmission section (FEXT section) of ISDN ping-pong transmission. In an xDSL device that receives crosstalk from an ISDN ping-pong transmission line,
An xDSL apparatus comprising means for transmitting data in which a phase is changed twice between any two adjacent symbols in a transmission section (FEXT section) of ISDN ping-pong transmission. In a digital subscriber line transmission method receiving crosstalk from an ISDN ping-pong transmission line,
In a transmission section (FEXT section) of ISDN ping-pong transmission, as a symbol pattern of any two adjacent symbols, a QAM constellation diagram changes the phase difference so as to be 90 ° or 180 ° with respect to each other. Digital subscriber line transmission method. In an xDSL device that receives crosstalk from an ISDN ping-pong transmission line,
In a transmission section (FEXT section) of ISDN ping-pong transmission, data in which a phase difference is changed to 90 ° or 180 ° in a QAM constellation diagram is transmitted as a symbol pattern of any two adjacent symbols. An xDSL apparatus, comprising:

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