JP3771555B2 - Digital subscriber line transmission method and transmission apparatus - Google Patents

Description

  The present invention relates to a digital subscriber line transmission method and transmission apparatus that use 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 transmission apparatus in a periodic crosstalk noise environment by ISDN ping-pong transmission or TDD-xDSL transmission.

  In recent years, multimedia services such as the Internet have spread widely throughout society, including ordinary homes, and an economical and reliable digital subscriber line transmission system and digital subscription for using such services. There is a strong demand for early provision of line transmission equipment.

XDSL Technology As a technology for providing a digital subscriber line transmission system that uses an existing telephone line as a high-speed data communication line, xDSL (Digital Subscriber Line) is known. xDSL is a transmission system using a telephone line and is one of modulation / demodulation technologies. This xDSL is roughly divided into the uplink transmission rate from the subscriber's home (hereinafter referred to as the subscriber side) to the accommodating station (hereinafter referred to as the station side) and the downlink transmission rate from the station side to the subscriber side. It is divided into asymmetric and asymmetric.
A typical example is ADSL (Asymmetric DSL) for asymmetric xDSL, HDSL (High-bit-rate DSL) for Symmetric xDSL, and Single-pair High-bit-rate DSL (SHDSL). There is. And there is VDSL (Very high-bit-rate DSL) as xDSL that can be used as asymmetric or symmetric. DMT for each xDSL system
Modulation methods such as (Discrete Multitone) and CAP (Carrierless Amplitude Phase modulation) are used. For example, the ADSL ITU-T recommendation includes G.dmt for downlink transmission of about 6 Mbit / sec and G.lite for about 1.5 Mbit / sec, both of which adopt the DMT modulation scheme as a modulation scheme.

・ DMT modulation system
The DMT modulation method will be described by taking G.dmt as an example. However, only the modulation / demodulation in the downlink direction from the station side to the subscriber side will be described here.
In the DMT modulation method, as shown in FIG. 29, the frequency band of 1.104 MHz is frequency-divided into M (= 255) multicarriers # 1 to # 255 with an interval of Δf (= 4.3125 KHz). Then, the SN ratio of each carrier # 1 to # 255 is measured in the training prior to communication, and 4-QAM, 16-QAM, 64-QAM, 128-QAM ... Which modulation method is used to transmit data is determined. For example, 4-QAM is assigned to a carrier having a small SN ratio, and 16-QAM, 64-QAM, 128-QAM,. 4-QAM is a modulation method that transmits every 2 bits, 16-QAM is a modulation method that transmits every 4 bits, 64-QAM is a modulation method that transmits every 6 bits, and 128-QAM is a modulation method that transmits every 7 bits. .. Of the methods for transmitting signals simultaneously in uplink and downlink, in the frequency division transmission method, out of 255 carriers, carriers # 1 to # 32 are used for the uplink direction from the subscriber side to the station side, and carriers # 33 to ## 255 is used for the downlink direction from the station side to the subscriber side. In addition, in a method in which signals are not transmitted simultaneously in uplink / downlink, all of the carriers # 1 to # 255 can be easily used for uplink and downlink.

FIG. 30 is a functional block diagram of a subscriber line transmission system based on the DMT modulation method. The input transmission data addressed to one subscriber is a serial to parallel conversion buffer (Serial to
Parallel buffer) 10 is stored for one symbol time (= 1/4000 sec). The stored data is divided by the number of transmission bits 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 method for each carrier is known by training, a bit string for one symbol is divided for each bit number bk according to the QAM modulation method 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 IFFT operation to perform quadrature amplitude modulation for each signal point, and inputs the signal to a parallel-to-serial conversion buffer 40 (Parallel to Serial Buffer) 40 in the next stage. Here, a total of 32 samples of IFFT outputs 480 to 511 samples are added to the head of the DMT symbol as a cyclic prefix (details will be described later). The parallel / serial conversion buffer 40 sequentially inputs 512 + 32 pieces of 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 it to the subscriber side 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) is within the 32-sample cyclic prefix, 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, and then removes the cyclic prefix and inputs the data for one DMT symbol to the fast Fourier transform (FFT) 110 simultaneously in parallel. The FFT 110 performs fast Fourier transform to generate (demodulate) 255 signal points. A frequency domain equalizer (FEQ) 120 performs compensation for inter-channel interference (ICI) on the demodulated 255 signal point data, and the decoder 130 maintains the same value as the transmission bitmap 60. The 255 signal point data are decoded according to the received bitmap 150, and the data obtained by the decoding is stored in the parallel-serial conversion buffer 140. Thereafter, the bit data is output bit by bit from the buffer to be received data.

-Crosstalk from ISDN ping-pong transmission
The ISDN ping-pong transmission method (TCM: time compression multiplex) separates the transmission and reception sections in a time-sharing manner (one transmission section and a reception section of 2.5 msec in total), and the transmission and reception timings of all adjacent devices This is the same method. In this ISDN ping-pong transmission method, 2B + D 144kbps transmission data is divided every 2.5msec, compressed to 320kbps by speed conversion, and transmitted in the 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, the existing telephone line is designed to be optimized for a human voice band of about 200Hz to 3.4kHz, but if a high frequency signal such as ADSL or ISDN is passed through this line, the telephone line 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 interferes with ADSL communication. This noise is cross talk noise. The ADSL transmission rate is limited to the level of this 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 an ADSL device (ATU-C: ADSL Transceiver Unit at the Central office end), and (b) is an explanatory diagram of interference. Subscriber side ADSL equipment (ATU-R: ADSL Transceiver Unit at the
It is interference explanatory drawing with respect to (Remote terminal end). In (a), when an OCU (office channel unit) of the ISDN line is transmitting, it greatly affects the ADSL device ATU-C on the station side. This crosstalk noise is called near end cross-talk (NEXT). On the other hand, when a DSU (digital service unit) is transmitting, the signal leaks into 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, which is considerably smaller than NEXT.
Also, in (b), when the DSU of the ISDN line is transmitting, the subscriber side ADSL apparatus ATU-R is greatly affected by noise, 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), but this FEXT is considerably smaller than NEXT. From the 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 crosstalk (TCM cross-talk) as described below from the ISDN ping-pong transmission line. In ISDN ping-pong transmission, the station side 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. 34, and the subscriber side receives the second half cycle after receiving downlink data. Transmit upstream data with. For this reason, the ADSL equipment ATU-C on the station side is affected by the near-end crosstalk from ISDN (NEXT1) in the first half cycle of 400Hz, and the far-end crosstalk (FEXT1) from the upstream data on the subscriber side ISDN in the second half cycle. ).
In the subscriber side ADSL equipment ATU-R, contrary to the station side, it is affected by FEXT2 in the first half of 400Hz and affected by NEXT2 in the second half cycle. In the following, time regions affected by NEXT and FEXT are referred to as NEXT section and FEXT section, respectively. FIG. 34 shows the NEXT section and FEXT section on the subscriber side.

・ Sliding window method Japanese Patent Application No. 10-144913 for the purpose of providing a digital subscriber line transmission system capable of satisfactorily transmitting ADSL signals under the above-described crosstalk environment from ISDN ping-pong transmission Proposes a "sliding window method". The sliding window is a crosstalk environment from ISDN ping-pong transmission in the downlink direction where ADSL signals are transmitted from the station side ADSL equipment (ATU-C) to the subscriber side ADSL equipment (ATU-R). The method of determining the state of the ADSL signal transmitted by the station-side ADSL device (ATU-C) is 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 as an inside symbol ISB at high density. If at least a part of the transmission symbol SB is included in the NEXT interval on the subscriber side, the station ADSL device (ATU-C) transmits the symbol as an outside symbol OSB at low density (Dual Bitmap method). Also in the upstream direction, the subscriber-side ADSL equipment (ATU-R) transmits ADSL symbols by dividing them into the inside symbol ISB and the outside symbol OSB in the same manner as in the downstream direction.
In the Dual Bitmap method, symbols are transmitted at low density even outside the sliding window SLW in the downlink direction, but the ADSL equipment (ATU-C) on the station side is a pilot synchronization tone that is a timing synchronization tone 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-side ADSL device (ATU-R) does not transmit anything outside the sliding window SLW.
FIG. 35 is a diagram showing the relationship between transmission / reception in the ISDN OCU and the ADSL symbol in the station-side ADSL apparatus ATU-C, and shows the ADSL symbol in each case of the Dual Bitmap method and the Fext Bitmap method.

Creation of Bitmap In order to correspond to the above-described Dual Bitmap method, the transmission bitmap unit 60 and the reception bitmap unit 150 in FIG. 30 perform the mapping of the bitmap for the inside symbol and the bitmap for the outside symbol during training. Two types of bitmaps need to be prepared. The Fext Bitmap method does not require an outside symbol bitmap out of two types of bitmaps.
The receiving side determines the number of bits (bitmap) assigned to each carrier. That is, the number of allocated bits for uplink signals is determined on the station side, and the number of allocated bits for downlink signals is determined on the subscriber side. During training, the ADSL devices on the station side and the subscriber side determine bitmaps according to a protocol called B & G (bit & gain).

  FIG. 36 is an explanatory diagram of the B & G protocol in the upstream direction. (1) During training, after recognizing each other's ADSL devices, for example, the subscriber-side ADSL device ATU-R sends several frequency signals to the opposite station-side ADSL device ATU-C. (2) The ADSL device ATU-C on the station side measures the noise level and 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-side ADSL apparatus ATU-R performs data transmission after DMT modulation based on the notified bitmap and transmission level information.

FIG. 37 is a configuration diagram for measuring the SN ratio with the subscriber-side ADSL apparatus ATU-R. Received data enters demodulator 210 and outputs signal point data for each carrier as demodulated data. The reference 220 outputs signal point data for each carrier that should be received. The difference between the signal point data from the reference and the demodulated signal point data is set as ERROR, and the ERROR for each carrier is input to the selector 260.
On the other hand, the in-device clock 230 is frequency-divided to 400 Hz by the frequency divider 240 and input to the phase determiner 250. The phase of this 400 Hz signal is previously matched with 400 Hz on the station side (ISDN 400 Hz signal) based on 400 Hz information transmitted from the station side via the demodulator 210. The phase determiner 250 determines whether the received DMT symbol is the FEXT interval, the NEXT interval, or other than that based on the input 400 Hz signal, and inputs it to the selector 260. The selector 260 outputs the above inputted ERROR to the NEXT interval S / N measuring device 270 or the FEXT interval S / N measuring device 280 according to the information inputted from the determination unit 250. Each S / N measuring device integrates ERROR to calculate S / N, and outputs it to the transmission bit number converter 290 for each carrier. The transmission bit number converter 290 calculates the number of bits (bitmap) to be transmitted for each carrier from the inputted S / N for each carrier, and the bitmap b-NEXT for the NEXT section and the FEXT section B-FEXT of the bitmap is calculated.

・ Frame configuration “Hyper Frame” was introduced for the purpose of providing a digital subscriber line transmission system capable of transmitting ADSL signals satisfactorily in a crosstalk environment from ISDN ping-pong transmission as described above. ing. In ISDN ping-pong transmission, transmission and reception are switched 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, the 34 periods of ISDN ping-pong transmission, which is the least common multiple of the two communications, matches the time length of 345 DMT symbols of ADSL transmission, so this section is defined as a “hyperframe”.

  As shown in FIG. 38, in ADSL, 1 frame corresponds to 1 symbol, and in normal data communication, 68 ADSL frames for data and 1 synchronization frame (S) are 1 A super frame is configured. There may be an inverse synchronization symbol (I) instead of the synchronization symbol (S). 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 gathered to form one hyper frame. In the figure, the case of the downlink direction in which 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 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 periods of a 400 Hz signal in ISDN ping-pong transmission.

-Another frame configuration As described above, when 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 satisfactorily in a crosstalk environment from ISDN ping-pong transmission, it differs from the above-described hyper frame. There is a method of transmitting ADSL symbols in synchronization with ISDN ping-pong transmission.

In ISDN ping-pong transmission, as shown in FIG. 39, in synchronization with the ISDN 400 Hz signal TTR, the station-side OCU transmits downlink 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 ADSL device transmits the ADSL symbol for the downlink FEXT section in the first half cycle of 400 Hz, and transmits the ADSL symbol for the downlink 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 for NEXT interval reception (DMT symbol A) and two bitmaps for FEXT reception interval (DMT symbol B) are prepared. 39, the DMT symbol A is transmitted in the NEXT interval to reduce the number of transmission bits to improve the SN tolerance, and the FEXT interval is transmitted to increase the transmission bit number by transmitting the DMT symbol B. Increase the transmission capacity. At this time, by setting the Cyclic Prefix length to an appropriate length, the number of FDSL ADSL symbols is matched with the number of NEXT ADSL symbols. For example, 32 samples of Cyclic
While the prefix is 246 μs per 1 DMT symbol, the cyclic prefix of 40 samples is 250 μs per 1 DMT symbol, and one TCM cross-talk period is combined with the time of 10 DMT symbols.

-Introduction of TDD-xDSL A TDD-xDSL system (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 for transmitting symbols in synchronization with the ISDN ping-pong transmission as described above. However, unlike the above-described scheme, the TDD-xDSL scheme does not transmit TDD-xDSL symbols in the NEXT interval. That is, the TDD-xDSL scheme is a scheme that uses an xDSL line in time division in the uplink and downlink directions and uses all 255 carriers # 1 to # 255 in uplink and downlink data transmission.

  As shown in FIG. 40, when the TDD-xDSL symbol sequence 460 is transmitted in synchronization with ISDN ping-pong transmission on the station side, the TDD-xDSL symbol sequence 480 received on the subscriber side is only affected by ISDN from FEXT440. . When the TDD-xDSL symbol sequence 490 is transmitted in synchronization with ISDN ping-pong transmission on the subscriber side, the TDD-xDSL symbol sequence 470 received on the station side is only affected by the FEXT 430 from ISDN. Therefore, the TDD-xDSL symbol sequence can avoid the influence of NEXT from ISDN ping-pong transmission. According to this transmission system, only two types of bitmaps were required in the Dual Bitmap method, just like the Fext Bitmap method.

ISI Removal Method The time domain equalizer (TEQ) shown in FIG. 30 operates as follows using a cyclic prefix.
The DMT symbol input to the parallel-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 for adding the 32 samples after the DMT symbol to the front of the DMT symbol by copying as shown in FIG. This added part is called a Cyclic Prefix. The DMT symbol to which this cyclic prefix is added is transmitted to the receiving side after the subsequent processing on the transmitting side as shown in FIG. 41 (c).

The received signal received via the metallic line 70 whose amplitude characteristics and delay characteristics with respect to the frequency are not constant is distorted by the influence of inter symbol interference (ISI) as shown in FIG. It is in a state.
However, TEQ 90 is set with constants so that ISI can be accommodated within the cyclic prefix of 32 samples by training (TEQ training). Therefore, when the TEQ receives the signal shown in FIG. 41 (d), the TEQ performs processing to fit the ISI within the 32-sample cyclic prefix as shown in FIG. 41 (e). Thereafter, the serial / parallel conversion buffer 100 removes the cyclic prefix from the TEQ output. Thereby, as shown in FIG. 41 (f), it is possible to obtain a DMT symbol from which the influence of ISI is removed. TEQ functions to remove the influence of ISI from the received signal using the cyclic prefix as described above.

・ ISI impact of xDSL symbols
The influence of ISI on the xDSL symbol will be described with reference to FIG. FIG. 42 (a) 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 shown in FIG. 42 (a) and the preceding ADSL transmission symbol. 42 (b) shows an ADSL reception symbol sequence for the ADSL transmission symbol sequence of FIG. 42 (a) before TEQ training, and FIG. 42 (c) shows an ADSL transmission symbol of FIG. 41 (a) after TEQ training. ADSL received symbol sequence for the sequence.
FIG. 42 (d) shows an ADSL transmission symbol sequence to which a cyclic prefix is added during normal 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 functions to remove the influence of ISI from the received signal using the cyclic prefix. During regular data communication, if a Cyclic Prefix is added to each ADSL transmission symbol as shown in FIG. 42 (d), the TEQ fits within 32 samples of Cyclic Prefix as shown in FIG. 42 (e). Thus, the effect of ISI can be removed from the received signal.
However, at the time of training for transmitting a continuous signal with the same pattern, no cyclic prefix is added to each ADSL transmission symbol as shown in FIG. This is because the cyclic prefix is not necessary because the continuous signal is not affected by ISI. Rather, adding a Cyclic Prefix reduces the symbol rate accordingly, so it is better not to add a Cyclic Prefix.

  However, when transmitting a burst symbol sequence as a transmission signal, such as the sliding window method (Fext Bitmap method) or the method of transmitting symbols in synchronization with ISDN ping-pong transmission (TDD-xDSL), the transmission signal Continuity is lost. As a result, even when TEQ training is completed during training for transmitting a continuous signal, as shown in FIG. 42 (c), the ADSL received symbol at the beginning of the ADSL received symbol string is affected by waveform distortion corresponding to ISI. I cannot receive training using the first ADSL received symbol.

FIG. 42 (b) shows an ADSL reception symbol sequence for the ADSL transmission symbol sequence of FIG. 42 (a) before TEQ training at the time of training. This is also because the ADSL reception symbol is ISI. It is affected and distorted. 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 TEQ training before the TEQ training is performed.
Since it is an ADSL reception symbol string, generally, the influence of ISI that an ADSL reception symbol receives does not fall within 32 samples. Before TEQ training, as shown in FIG. 42 (b), the influence of waveform distortion may also affect the second and subsequent ADSL reception symbols. Although not shown in FIG. 42, the ADSL reception symbol at the end of the ADSL reception symbol string may also be affected by ISI.

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

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

Further, it is necessary to synchronize the TDD-xDSL transmission with the ISDN ping-pong transmission on the station side, and this is the same on the subscriber side. The station side can obtain a synchronization signal of 400 Hz with which the ISDN ping-pong transmission is synchronized by using an 8 kHz network clock, but the subscriber side cannot obtain this synchronization signal of 400 Hz. Therefore, it is important that the subscriber side is notified of the accurate TDD-xDSL transmission phase from the station side and obtains the information. Therefore, a means for efficiently notifying the transmission phase from the station side to the subscriber side is required.
The above is a case where the crosstalk from the ISDN line to the xDSL line is taken into consideration. However, crosstalk is not always from an ISDN line, but there is also crosstalk from another xDSL line in the same cable. In particular, 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, so the xDSL line is ISDN ping-pong transmission from other TDD-xDSL lines. Similar to the effects of crosstalk (NEXT, FEXT). Therefore, the above problem is applicable not only to crosstalk from ISDN lines but also to crosstalk from other TDD-xDSL lines.

The present invention has been made on the basis of new knowledge and considerations on the above points, and is effective transmission technology of TDD-xDSL in a noise environment from ISDN ping-pong transmission or other TDD-xDSL transmission. It is an object of the present invention to provide a digital subscriber line transmission apparatus equipped with a specific method for adopting the above-mentioned method or means for implementing such a method.
Another object of the present invention is to ensure continuity of sample data of adjacent transmission burst symbol sequences.

  In TDD-xDSL transmission, a pilot tone frequency as a timing reproduction signal is set so as to ensure continuity of sample data of adjacent transmission burst symbol sequences. That is, the length of the interval between adjacent transmission burst symbol sequences where no signal is transmitted is set to an integral multiple of the pilot tone signal period, and processing is executed in synchronization with the pilot tone signal. In this way, the phase of the pilot tone is not shifted between adjacent transmission burst symbol sequences, and processing can be performed with accurate timing.

  According to the present invention, in TDD-xDSL transmission, the frequency of a pilot tone used as a timing recovery signal is set so as to ensure the continuity of sample data of adjacent transmission burst symbol sequences, or adjacent transmission bursts Since the length of the interval in which no signal is transmitted between the symbol sequences is an integral multiple of the pilot tone period, the phase of the pilot tone is not shifted between adjacent transmitted burst symbol sequences, and the receiving side has accurate timing. Can be processed.

(A) Outline of the Present Invention The present invention has the following characteristics in TDD-xDSL transmission in a periodic noise environment from a line for performing ISDN ping-pong transmission or other TDD-xDSL transmission. Hereinafter, TDD-xDSL transmission in a periodic noise environment from a line performing ISDN ping-pong transmission will be described.
(a) First Feature The first feature is to transmit a training symbol sequence 500 as shown in FIG. 1 in training of a TDD-xDSL ADSL device (transceiver).

  That is, (1) In the training of the TDD-xDSL transceiver, the same pattern 503 as the last part of the first training symbol is used as a redundant signal before the conventional transmission symbol string 502 configured by continuously training symbols 501 without a cyclic prefix. By adding a predetermined number of samples, a pattern in which training symbols including the added portion are continuous can be formed. The length to be added is a predetermined number of samples n1 which is larger than the cyclic prefix during normal communication.

  (2) Alternatively, after the transmission symbol string 502, the same pattern 504 as the head portion of the last training symbol 501 is added in the same manner for the sample number n2 determined separately from the sample number n1 attached to the head. (3) Alternatively, redundant signals 503 and 504 are added both before and after the transmission symbol string 502.

  In TDD-xDSL, each symbol during training has the same pattern, so a continuous signal can be sent between each symbol via IFFT. Therefore, including the part added by adding the tail part of the training symbol before the transmission symbol string, adding the head part of the training symbol after the transmitted symbol string, or both. A continuous signal can be formed. Thus, if a redundant signal is added before or after the transmission symbol sequence, only the redundant signal portion (503,504) is distorted by ISI, but distortion occurs in the transmission symbol sequence other than the redundant signal portion (503,504). Therefore, all symbols can be used as training symbols, and training time can be shortened. Note that even if a redundant signal is added, the transmission time does not increase. This is because a redundant signal can be transmitted using a period during which no signal is transmitted in the TDD-xDSL transmission section.

(b) Second feature In the second feature, the training symbol sequence after the redundant sample sequence added by the first feature is not included in the reception interval (NEXT interval) of ISDN ping-pong transmission. This is to set the transmission timing and length of the training symbol string.
In other words, the TDD-xDSL transmission training symbol string is within the transmission frame section of ISDN ping-pong transmission or within the section of the transmission frame section of ISDN ping-pong transmission and the guard time section between transmission and reception in ISDN ping-pong transmission. The transmission timing of the TDD-xDSL transmission and the length of the transmission training symbol sequence are set.

  With reference to FIG. 2, conditions for storing the TDD-xDSL transmission training symbol sequence 500 in the transmission section 601 of ISDN ping-pong transmission will be described. Here, the ISDN ping-pong transmission section time is D (3.125 μs x 377 = 1.178125 ms), the ISDN ping-pong transmission card time is a (= 18.75 μs to 23.4375 μs), and TDD-xDSL redundant data is added. The transmission time of the training symbol 502 before the transmission is S1, the transmission times of the redundant signals 503 and 504 attached before and after the training DMT symbol string are x1, y1, and the TDD-xDSL transmission training symbol string 500 section and ISDN ping-pong transmission, respectively. Assuming that the margins with respect to the transmission section 601 are α1 and β1, respectively, the respective relationships to be satisfied by 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, if the number of samples in the DMT symbol without the cyclic prefix is m, the number of DMT symbols without the 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 as:

S1 = N * m * {1 / (m * fd)} = N / fd (3a)
x1 = nx * {1 / (m * fd)} (3b)
y1 = ny * {1 / (m * fd)} (3c)
However, m = 2n (n is a natural number)
nx and ny are arbitrary positive integers meaning the number of samples of x1 and y1, respectively, and (nx + ny)> (m / 8)
Similarly, as shown in FIG. 3, even during normal communication, the relationship for the TDD-xDSL DMT transmission symbol sequence 700 to fit within the transmission interval 601 of ISDN ping-pong transmission can be obtained as in training. That is, as in training, the length of the ISDN ping-pong transmission section is D, the card time between sending and receiving ISDN ping-pong transmission is a, the length of the TDD-xDSL DMT transmission symbol string 700 is S2, and the TDD-xDSL transmission DMT symbol The margin between the column section and the transmission section of ISDN ping-pong transmission is α2 and β2, respectively, the number of carriers of the DMT transmission symbol is m, the number of symbols included in the symbol string during normal communication is N, and the frequency interval of the DMT carrier is fd Then, each relationship to be satisfied by the present invention is 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 samples of the cyclic prefix during normal communication.
According to the equations (4) to (5), the conventional G.P. It was fixed at 16sample in 992.2 (G.lite)
The length of the Cyclic Prefix can also be varied within a range that satisfies Equation (4).
As described above, the transmission timing of the TDD-xDSL training symbol sequence will be within the transmission interval (FEXT interval) of ISDN ping-pong transmission, and the NEXT noise from the ISDN line will be received when receiving the TDD-xDSL training symbol. Can be avoided. Also, during normal data communication, the transmission timing of the TDD-xDSL transmission symbol sequence will be within the transmission interval (FEXT interval) of ISDN ping-pong transmission, and when receiving the TDD-xDSL transmission symbol, the NEXT from the ISDN line Mixing of noise 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 the transmission burst sections. It is to be.
FIG. 4 is an explanatory diagram of the frame phase between transmission bursts during TDD-xDSL training. In DMT modulation, each symbol is preferably a continuous DMT sample sequence, that is, in a section in which 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 is necessary to be double. Therefore, (1) the length of the transmission symbol sequence indicated by Tb is an integer multiple of the pilot tone period, and (2) the pilot interval is indicated by an integer multiple of the pilot tone period. • Select the tone cycle. In this way, the length of the interval Ta can be made an integral multiple of the pilot tone period, and the continuity of DMT samples in adjacent transmission bursts can be maintained.

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

(d) Fourth feature In the fourth feature, a symbol 501 included in a transmission symbol sequence 500 at the time of training using a training symbol without CP (Cyclic Prefix) and a DMT symbol with CP (Cyclic Prefix) are used. In other words, the phase difference θd (FIG. 6) between the symbols 701 included in the transmission symbol string 700 during normal communication is an integral multiple of the previously selected pilot tone period.
FIG. 6 is an explanatory diagram of the phase relationship between transmission burst frames during training and normal communication. The start of symbols 501 and 701 located at the heads of the transmission symbol string 500 during training and the transmission symbol string 700 during normal communication, respectively. The relationship of the position phase difference θd will be described.

The transmission symbol sequence 500 at the time of training and the transmission symbol sequence 700 at the time of normal communication are independently transmitted 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 during training and normal communication. This phase difference θd is set to be an integral multiple of the period of the pilot tone PLT. In this way, both the training process and the normal data communication process can be executed in synchronization with the pilot tone signal.
The means for adjusting the phase difference to an integral multiple of the period of the pilot tone PLT includes a method for adjusting the period of the pilot tone, and a transmission symbol string 700 in normal communication with respect to a transmission symbol string 500 in training. A method of shifting the transmission timing of the message can be considered.

(e) Fifth feature The fifth feature is that a tone signal is transmitted separately from the pilot tone PLT for timing reproduction during training, and the phase of the ISDN 400 Hz signal from the station side to the subscriber side (the TDD- xDSL transmission phase). That is, the station side notifies the subscriber side 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-side xDSL device finds the phase change point and sets the time from the phase change point. The time before or after the set time is the TDD-xDSL transmission timing of the station side xDSL device or the rise time of the 400 Hz signal. This fifth feature makes it possible to perform timing reproduction more easily and in a shorter time than the conventional method.

FIG. 7 is an explanatory diagram for performing timing recovery of an ISDN 400 Hz signal with a newly added tone. When four training symbols are included in one burst transmission symbol sequence, an example in which the phase changes once in one burst ( FIG. 7 (a)) and an example (FIG. 7 (b)) that changes twice are shown.
In FIG. 7A, the phase of the training symbol is changed from the pattern A to the pattern B between the second symbol and the third symbol. In FIG. 7 (b), the phase of the training symbol changes from pattern B to pattern A between the first and second symbols, and from pattern A to pattern B between the third and fourth symbols. . Note that the pattern A may be shifted to a new pattern C between the third and fourth symbols.
In the example of FIG. 7 (a), the time before the set time T1 from the phase change detection time is the rise time of the ISDN 400Hz 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 400Hz signal TTR.

(f) Sixth feature The sixth feature is that the patterns A and B in the above tone different from the pilot tone PLT are selected so that the phase difference is 90 ° or 180 ° in the QAM constellation diagram. In one burst, A → B or B → A is changed, thereby transmitting a phase change.
FIG. 8 is an explanatory diagram of patterns A and B, and shows how patterns A and B are selected when the simplest 4QAM is used as a DMT symbol. FIG. 8A shows an example of constellation when the phase difference between patterns A and B is 90 °, and FIG. 8B shows an example of constellation when the phase difference between patterns A and B is 180 °. It is.

(B) Configuration of Embodiment (a) Overall Configuration FIG. 9 is a block diagram of a subscriber transmission system according to the TDD-xDSL system of the present invention, and the same components as those in FIG. 30 is provided with a sequencer 310, a selector 320, and a training signal generation circuit 330 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 on the reception side. It is a point.
The transmission-side sequencer 310 (1) generates a training state signal TRN and a communication state signal CMN by distinguishing between training time and normal communication time, and (2) controls the parallel-serial conversion buffer 40 to transmit a training transmission symbol. A column 500 (see FIG. 1) and a normal communication transmission symbol column 700 (FIG. 3) are output.

The training signal generation circuit 330 (1) outputs various training signals during training, and (2) pilot tone signal PLT for timing recovery in the TDD-xDSL transmission section regardless of whether training or normal communication. Is output. This pilot tone signal PLT is transmitted to the receiving side on carrier # 64. In addition, the training signal generation circuit 330 transmits a tone signal using carrier # 48 separately from the pilot tone signal PLT during training, and the phase of the ISDN 400 Hz signal from the station side to the subscriber side (the transmission phase of the station TDD-XDSL) ) (See FIGS. 7 and 8).
In the TDD-xDSL transmission section, the selector 320 selects (1) the training signal output from the training signal generation circuit 330 during training and inputs it to the IFFT circuit 30, and (2) outputs it from the encoder 20 during normal communication. The transmission data is selected and input to the IFFT circuit 30. 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 and detects that a training signal is sent from the transmission side, and the sequencer 350 controls the serial / parallel conversion buffer 100 to perform training. Control is performed so that data for one symbol excluding the redundant signal / Cyclic Prefix is input to the FFT circuit 110 at each time of normal communication. 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 to detect the ISDN 400 Hz signal timing, and detects the start of normal communication based on the sequence switching data sent from the transmission side.

(B) Transmission symbol sequence generation configuration during training and normal communication FIG. 10 is a block diagram of a configuration for generating a symbol sequence during training and normal communication. The same parts as those in FIG. ing. FIG. 11 is a time chart for explaining the output sequence operation at the time of training, in which a 128-sample redundant signal 503 is added to the front side and an 8-sample redundant signal 504 is added to the rear side. FIG. 12 is a time chart for explaining an 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 The sequencer 310 generates various control signals so that the training transmission symbol sequence 500 is transmitted within the transmission period of ISDN ping-pong transmission. That is, when activated, the sequencer 310 performs switching control between training and normal communication by timer control, inputs the training / normal communication switching signal DTSL to the selector 320, and also outputs the training state signal TRN to the training signal generation circuit 330. To enter. Based on the training / normal communication switching signal DTSL, the selector 320 selects a training signal output from the training signal generation circuit 330 during training and inputs it to the IFFT circuit 30, and selects transmission data output from the encoder 20 during normal communication and performs IFFT. Input to the circuit 30. The training signal generation circuit 330 generates a predetermined training signal during training.

During training, as shown in FIG. 11, the sequencer 310, when a predetermined time t1 has elapsed from the rise of the ISDN 400Hz signal TTR, (1) P / S load timing signal PSLD, (2) P / S output mask signal PSMK, (3) Generate a P / S output select signal PSSL (= ˜11).
The P / S load timing signal PSLD is a signal for loading IFFT calculation results (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 allows data output from the buffer unit 40a when it is at a high level and prohibits data output from the buffer unit 40a when at a low level. The P / S output select signal PSSL instructs to sequentially read from the 0th signal, the 128th signal, or the 240th signal among the 256 signals stored in the buffer unit 40a. That is, the P / S output select signal PSSL takes values of ¨10, ¨11, ¨01, and if (1) ¨10, the selector 40b outputs signals in order from the 0th of the buffer unit 40a. If (2) ¨11 part, the signal is read in order from the 128th in the buffer section 40a, and if (3) ¨01 part, the signal is read in order from the 240th part of the buffer part 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 40 a of the parallel-serial conversion buffer 40. Next, the selector 40b sequentially reads out signals from the 128th position 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 it via the mask circuit 40c. . Thereby, 128 signals from the 128th to the 255th are read out as the redundant signal 503, and then 256 training signals (the first symbol data) from the 0th to the 255th are read out.
When the reading of the first training symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD and also generates the 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 unit 40 a of the parallel-serial conversion buffer 40. Next, the selector 40b sequentially reads out signals from the 0th position 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 out.

  When the reading of the second training symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD and outputs 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 reads and outputs signals sequentially from the 0th buffer section 40a in synchronization with the P / S operation clock PSCL. Thereby, 256 training signals (third symbol data) from the 0th to the 255th are read out.

When the reading of the third training symbol is completed, the sequencer 310 generates the P / S load timing signal PSLD and outputs 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 reads and outputs signals sequentially from the 0th buffer section 40a in synchronization with the P / S operation clock PSCL. Thereby, 256 training signals (last symbol data) from the 0th to the 255th are read out. Thereafter, 8 signals from 0th to 7th are read and output as redundant signals 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 and sets the P / S output select signal to “00” to make it non-selected.
Thereafter, during training, the above operation is repeated every time the ISDN 400 Hz signal TTR rises to create and transmit a transmission symbol string during training.

(b-2) Creation 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 when a predetermined time elapses after activation. As a result, the selector 320 selects transmission data output from the encoder 20 and inputs it 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.
During normal communication, as shown in FIG. 12, the sequencer 310 (1) P / S load timing signal PSLD and (2) P / S output mask signal PSMK after a predetermined time t2 has elapsed from the rise of the ISDN 400Hz signal TTR. (3) A P / S output select signal PSSL (= (0101) is generated.

  When the P / S load timing signal PSLD is generated, 256 signals output from the IFFT circuit 30 are stored in the buffer unit 40 a of the parallel-serial conversion buffer 40. Next, the selector 40b sequentially reads out signals from the 240th position of the buffer unit 40a in synchronization with the P / S operation clock PSCL in accordance with the P / S output select signal PSSL = 0101, and outputs the signals via the mask circuit 40c. . As a result, the 16th signal from the 240th to the 255th is read as a Cyclic Prefix, and then 256 transmission signals (the first symbol data) from the 0th to the 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 unit 40 a of the parallel-serial conversion buffer 40. Next, the selector 40b reads 16 signals from the 240th to the 255th of the buffer unit 40a as a cyclic prefix in synchronization with the P / S operation clock PSCL according to the P / S output select signal PSSL == 0101. Subsequently, 256 transmission signals (second symbol data) from the 0th to the 255th are read and output. Thereafter, if the third and fourth symbol data with the cyclic prefix are similarly read and output, the sequencer 310 sets the P / S output mask signal PSMK to the low level and sets the P / S output select signal to 00. To select no state.
Thereafter, in the communication state, the sequencer 310 repeats the above operation every time the ISDN 400 Hz signal TTR rises to create and transmit a transmission symbol string for normal communication.

(b-3) Configuration of Sequencer FIG. 13 is a configuration diagram of the sequencer in the station ADSL apparatus. The sequence switching unit 311 generates a training state signal TRN and a normal communication state signal CMN by timer control when activated, and the ISDN 400 Hz signal generation unit 312 outputs a 400 Hz signal TTR for 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. Then, a pilot tone signal PLT for timing reproduction is output. Here, an example is shown in which the ISDN 400 Hz signal generator 312 outputs a 400 Hz signal TTR for ISDN ping-pong transmission, but it may also be input from the outside. This configuration will be described later.

  The reason why the pilot tone signal PLT is output by the 1/4 frequency division of the P / S operation clock signal PSCL is as follows. For example, if the carrier frequency interval is 4 kHz, the number of samples in a 1 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 pilot tone frequency is 4 kHz x 64 = 256 kHz. In other words, the data per cycle of the pilot tone is 4 samples. On the other hand, the P / S operation clock signal PSCL is a signal that is serially sent out from the parallel-serial conversion buffer 40 at 1024 kHz, and is equal to the sampling frequency of the FFT. As described above, the pilot tone signal PLT can be generated by dividing the P / S operation clock signal PSCL by 1/4. This pilot tone signal PLT has the same phase and frequency as the pilot tone signal generated by the training signal generation circuit 330.

The first transmission symbol output timing generation unit 315 synchronizes with the pilot tone PLT after a predetermined time t1 (FIG. 11) has elapsed after the rise of the ISDN 400 Hz signal TTR so as to satisfy the expression (1) or (2) during training. Then, a symbol output timing signal TSOT is generated.
The second transmission symbol output timing generation unit 316 transmits in synchronization with the pilot tone PLT after a predetermined time t2 (FIG. 12) after the rise of the ISDN 400Hz signal TTR so as to satisfy the expression (4) during normal communication. Generates symbol output timing signal DSOT.
The various control signal generator 317 is based on the training state signal TRN, the normal communication state signal CMN, and the transmission symbol output timing signals TSOT and DSOT, and controls various control signals (P / S load signal) in synchronization with the P / S operation clock signal PSCL. 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 transmission symbol output timing generation section 315, 316 generates symbol output timing signals TSOT, DSOT in synchronization with the pilot tone PLT, thereby enabling individual symbols included in the transmission symbol sequence during training and during normal communication. The phase difference θd (see FIG. 6) between 501 and 701 can be adjusted to an integral multiple of the pilot tone period.
Each of the transmission symbol output timing generation units 315 and 316 generates symbol output timing signals TSOT and DSOT in synchronization with the pilot tone PLT, so that (1) the transmission symbol string is transmitted during training and during normal communication. The length can be an integer multiple of the pilot tone period, and (2) the transmission burst interval can be an integer multiple of the pilot tone period. As a result, in TDD-xDSL transmission, the interval between transmission bursts that are temporally adjacent can be set to an integral multiple of the pilot tone period, and the continuity of DMT samples in adjacent transmission bursts can be maintained. it can. Since the number of samples of the transmission symbol sequence at the time of 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 at the time of normal communication is 1088 ( = (16 + 256) × 4), which is 272 times the pilot tone period, thus satisfying the above (1).

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

The ISDN 400 Hz signal generator 401 is installed in all telephone stations 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 312 a acquires the ISDN 400 Hz signal TTR. Then, the ISDN 400 Hz signal acquisition unit 312a supplies the acquired ISDN 400 Hz signal TTR to each unit of the in-sequencer processing unit 312b, similarly to the method shown in FIG. With this configuration, all TDD-xDSL apparatuses 3011 to 3014 and ISDN-OCU (not shown) can communicate in synchronization with the ISDN 400 Hz signal TTR.
By the way, it is possible that the ISDN 400 Hz signal generator 401 is not installed in a telephone station that does not provide an ISDN service. In such a case, similarly to the ISDN 400 Hz signal generator 401, a device that generates a 400 Hz signal is installed in the telephone station, and 400 Hz signals are provided to the TDD-xDSL devices 3011 to 3014 on the side of the station in the manner shown in FIG. In this way, crosstalk noise from adjacent TDD-xDSL lines can be prevented.

(C) Receiving-Side Unit Configuration FIG. 15 is a configuration diagram of the main part on the receiving side, and the same components as those in FIG. The signal detection circuit 340 monitors the output signal level of the AD converter 80 that AD converts 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 normal communication based on the sequence switching data sent from the transmission side. 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 400Hz signal TTR. The control signal generator 350b generates various timing signals shown in FIG. 16 in synchronization with the S / P operation clock SPCL during the training after the timing detection of the ISDN 400Hz signal TTR and the phase control of the pilot tone signal is completed. At this time, various timing signals shown in FIG. 17 are generated in synchronization with the S / P operation clock SPCL.

(c-1) Reception sequence operation during training (see Fig. 16)
If 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 128-sample redundant signal has arrived. 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 data of one symbol (= 256 samples), the sequencer 350 generates an FFT load timing signal FFTLD, loads sample data for one symbol from the serial / parallel conversion buffer 100 to the FFT circuit 110, and the FFT circuit 110 is predetermined. Perform the FFT operation at the timing and output the operation result.

On the other hand, the serial / parallel conversion buffer 100 sequentially stores the sample data output from the TEQ 90 after the FFT load timing signal FFTLD is generated, and is generated from the sequencer 350 after storing the next one symbol (= 256 samples). The one-symbol sample data is input to the FFT circuit 110 in accordance with 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 the low level and removes the redundant signal 504 added to the rear part of the transmission symbol string. To 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 16-sample cyclic prefix is loaded from the serial / parallel conversion buffer 100 to the FFT circuit 110, and the FFT circuit 110 performs an FFT operation at a predetermined timing and outputs an operation result.

On the other hand, the serial / parallel conversion buffer 100 sequentially stores the sample data output from the TEQ 90 after the FFT load signal FFTLD is generated, 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 for one symbol excluding the 16-sample cyclic prefix to the FFT circuit 110, and the FFT circuit 110 performs the FFT operation at a predetermined timing and outputs the operation result.
Thereafter, similar 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 the low level.

(D) Transmission control of pilot tone signal PLT The pilot generator 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 period of the TDD-xDSL transmission regardless of the normal communication during training. That is, the sequencer 310 generates the select signal DTSL, and the selector 320 inputs the pilot tone signal to the # 64 carrier terminal of the IFFT circuit 30 in the TDD-xDSL transmission section. The IFFT circuit 30 performs IFFT processing on the pilot tone signal and transmits it 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. As a result, AD conversion and other processes can be performed on the receiving side in synchronization with the pilot tone signal.

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

  FIG. 7A shows an example in which the phase of adjacent symbols is changed once in one burst. The pattern of the first to second symbols and the third to fourth symbols is 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 in the QAM constellation diagram is 90 ° relative to each other (FIG. 8A), or the phase difference is 180 ° relative to 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 in FIG. 1 -1,..., 1 -1 are input to the selector 320, and in the case of pattern B in FIG. 1 -1 is input to the selector 320.

FIG. 7 (b) is an example in which the phase of adjacent symbols is changed twice in 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 of 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. The data is generated such that A changes from A → A → B → B. This data is IFFT processed by the IFFT circuit 30 and transmitted as a training symbol string shown in FIG. As a result, the receiving side detects the phase change time of A → B, and recognizes the time before the time T1 from the phase change time as the rising phase of the ISDN 400 Hz signal TTR. Actually, the rising phase of the ISDN 400 Hz signal TTR is determined based on the average value of a plurality of times.

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 sets the symbol pattern B → based on the rising edge of the ISDN 400 Hz signal TTR input from the sequencer 310. Data is generated so that A → A → B. This data is IFFT processed by the IFFT circuit 30 and transmitted as a training symbol string shown in FIG. As a result, two phase change times B → A and A → B are detected on the receiving side, the average time Tavr is obtained, and the time before the set time T2 from the average time is recognized as the rise time of the ISDN 400 Hz signal TTR. . Actually, the rising phase of the ISDN 400 Hz signal TTR is determined based on the average value of a plurality of times. 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 than in FIG. 7A.
In G.lite, which is the same xDSL system, a method of transmitting a phase change by a tone signal other than the pilot tone is used. However, in the present invention, unlike the case of G.lite, transmission in the NEXT section is used. Do not do. For this reason, it is not necessary to distinguish between the FEXT section and the NEXT section. Therefore, the phase change method can use 180 ° or a combination thereof in addition to 90 °.

(C) First Embodiment of Burst Frame at Training and Normal Communication There is a G992.2 (G.lite) method as a conventional xDSL method. 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 pilot tones. In the first embodiment of the present invention, 4 kHz slower than the G.lite system is used for the carrier frequency interval, and the other items are set to 256 samples in one DMT symbol as in the G.lite system, and a pilot tone is transmitted. # 64 is chosen as a career.
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 pilot tone frequency is 4 kHz x 64 = 256 kHz. That is, the data per one pilot tone cycle is 4 samples. In the first embodiment, the symbol length of one symbol is 256 samples, the period is 250 μs, and the maximum number of symbols included in one burst is 4 from 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 is not reduced, and four symbols can be transmitted.

(a) Signal transmission period during normal communication A transmission frame transmission period during normal communication in the first embodiment will be described with reference to FIG. In TDD-xDSL transmission, a symbol 701 with a cyclic perfix (CP) 702 is used during normal communication. The length of the Cyclic Prefix can be any length as long as the transmission symbol string fits within the transmission interval, but in this embodiment, the Cyclic Prefix is set to the G992.2 (G.lite) method, which is one of the xDSL methods. The transmitted symbol string 700 is composed of 16 samples (15.625 μs) that are the same number of samples as in the above, and four consecutive symbols with a cyclic prefix. Therefore, the symbol length of the transmission symbol string 700 is 1088 samples (1.0625 ms).

FIG. 19 shows the timing relationship between the transmission symbol string 700 and the ISDN ping-pong transmission signal during normal communication in the first embodiment.
First, consider the downlink signal transmission interval. In order to ensure that the TDD-xDSL transmission section does not overlap with the ISDN ping-pong transmission reception section, the TDD-xDSL downlink signal transmission section is arranged so as to be approximately at the center of the ISDN ping-pong transmission transmission section. Here, as explained according to FIG.
S2 + α2 + β2 ≦ D + a
It is necessary to satisfy.
here,
Transmission section D = 1.178125ms (1206.4sample) in ISDN ping-pong transmission,
TDD-xDSL transmission signal length S2 = 1.0625ms (1088sample)
It is. Assuming a margin, if a ′ <a = 9.375 μs (9.6 samples) is taken, 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 the upstream signal interval. The guard time b for downstream signal reception and upstream signal transmission of ISDN ping-pong transmission is a value having a width of 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 string should be strictly aligned with the center of the uplink transmission interval of the ISDN ping-pong method. I can't. Here, it is assumed that the guard time for ISDN ping-pong transmission is 18.75μs (19.2 samples) by adjusting to the center, and in that case, the TDD-xDSL guard time end time tge1 and the ISDN card time end time The card time c of TDD-xDSL is selected so that teg2 substantially matches.
In the first embodiment, as shown in FIG. 19, (the uplink transmission period of ISDN ping-pong transmission + guard time b) is 1196.875 μs, and (TDD-xDSL upstream signal transmission period S 2 + front and rear margin period α 2 + β 2) = 1187.5 μs (1216 samples Therefore, the guard time c of TDD-xDSL transmission is selected from 9.656625 to 14.64844 μs (10 to 15 samples), and the transmission timing is determined in the same manner as 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 string 500 for TDD-xDSL training. The redundant signal 503 added before the four consecutive training symbols 501 is desirably a sufficiently long section with respect to the Cyclic Prefix 702 during normal communication. Here, as an example, 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 to be added to the rear side, a redundant signal of 8 samples (7.8125 μs) is added. As described above, the lane symbol row 500 for lanening is configured. As a result, x1 = 125 μs (128 samples) and y1 = 7.8125 μs (8 samples). S1 = 1 ms (1024 samples = 256 samples × 4). From this,
S1 + x1 + y1 = 1.132813ms (1160sample)
Is obtained. Subsequently, as shown in FIG. 20, it is stored in D + a ′ as in normal communication.
When (S1 + α1 + β1 + x1 + y1) is calculated,
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) Consideration of worst conditions By the way, the transmission delay of the ISDN ping-pong method and the transmission delay of the TDD-xDSL method are determined separately. Therefore, for example, when the ISDN line is close (no delay) and the TDD-xDSL line is the farthest (maximum delay), the ISDN subscriber before receiving the TDD-xDSL downstream signal at the subscriber side during training The transmission of the uplink signal from the side starts, and the transmission / reception timing may shift. Therefore, the worst condition of the TDD-xDSL transmission / reception section with respect to the ISDN transmission / reception section is considered. In the first embodiment, the length of the TDD-xDSL transmission symbol string is longer during training (= 1160 samples) than during normal communication (= 1088 samples).

(c-1) First Worst Condition The worst condition taken up first is when the delay time of TDD-xDSL transmission is minimum and the delay time of ISDN ping-pong transmission is maximum. As shown in FIG. 21, the transmission start of the uplink signal of TDD-xDSL transmission must not start before the ISDN downlink signal ends. In the first embodiment, the latest timing of the end of reception of an ISDN downlink signal is obtained by adding a transmission delay of 50 μs (51.2 samples) to the length of 1.178125 ms (1206.4 samples) of the ISDN downlink transmission signal.

On the other hand, the TDD-xDSL upstream signal transmission start timing is the TDD-xDSL downstream signal interval 1.132813ms (1160sample), margin interval α1 = 0μs (0sample) before and after signal transmission, β1 = 54.6875μs (56sample ) And a guard time between upstream and downstream and a margin interval α1 (= 0) before sending a signal. 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 <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 start 1.232422ms (1262sample)
Thus, the TDD-xDSL upstream signal is not transmitted earlier than the end of receiving the ISDN downstream signal. In other words, even under the worst conditions described above, the transmission section of TDD-xDSL transmission is in the transmission section of the ISDN device closer to the transmitting ADSL device.

(c-2) Second Worst Condition The worst condition given below will be explained, conversely, the worst condition in which the TDD-xDSL delay time is the maximum and the ISDN device delay time is the minimum. In this case, as shown in FIG. 22, the end of the reception section of the TDD-xDSL downlink signal must end before the transmission start of the ISDN uplink signal. In the first embodiment, the latest timing of the end of reception of the TDD-xDSL downlink signal is the length of the transmission signal of the TDD-xDSL downlink signal 1132.813 ms (1160 samples), the transmission delay time 57.8125 μs (59.2 samples), Is obtained by adding a margin of 4.882813 μs (5 samples) to the shift of the reception timing to the margin interval α1 (= 0) μs (0 sample) before transmitting.

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

(c-3) Third worst condition Next, when the delay time of TDD-xDSL transmission is the maximum, (1) the TDD-xDSL upstream signal reception section is the downstream signal transmission section of the next burst ISDN ping-pong transmission This will not be described with reference to FIG.
The end of the TDD-xDSL uplink reception signal is (1) TDD-xDSL downlink signal transmission interval 1.132813ms (1160sample), (2) margin interval α1 = 0μs (= 0sample) before and after signal transmission, ( 3) β1 = 54.6875μs (56sample), (4) Transmission delay 57.8125μs (59.2sample) x 2 (because it has two directions, uplink and downlink), (5) Received at the maximum guard time of 49.80469μs (51sample) (8) DMT symbol margin in timing margin of 4.82813 μs (5 samples), (6) Upward signal transmission section 1.132813 ms (1160 samples), (7) Margin section α1 = 0 μs (0sample) before signal transmission The delay is the rise delay when sending starts, or the addition of a margin of 0.976567 μs (1 sample) × 2 (= 2.492578 msec) with respect to the signal of the remnant remaining when the sending is stopped. On the other hand, the burst period of ISDN ping-pong transmission is 2.5 ms. Compare the above
End of TDD-xDSL upstream signal section 2.49278ms (2552.4sample)
<ISDN burst cycle 2.5ms (2560sample)
Thus, reception of the TDD-xDSL uplink signal ends earlier than the start of transmission of the next ISDN downlink signal, that is, even when the TDD-xDSL transmission delay time is maximum, the reception period of the TDD-xDSL uplink signal is , It does not span the ISDN transmission section of the next burst.

Thus, the worst conditions have been examined. However, when an ISDN line and a TDD-xDSL metallic line are adjacent to each other, they are connected to the same station, so the worst condition is not actually possible.
For example, if there is no transmission delay time on the ISDN line and the transmission delay time on the TDD-xDSL line is the maximum, as shown in FIG. 24 (a), the subscriber side ISDN device DSU is placed near the station CN and joined. This is a case where the remote side TDD-xDSL device xTU-R is located away from the station. In this case, if the upstream signal from the ISDN device DSU leaks into the TDD-xDSL line, noise is transmitted from the point where the ISDN device DSU is placed to the point where the TDD-xDSL device xTU-R is placed. Since transmission delay occurs, if transmission of the downlink TDD-xDSL signal from the station side is completed, it is not affected by the uplink 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, the subscriber side ISDN device DSU is located away from the station CN as shown in FIG. This is the case when the TDD-xDSL device xTU-R on the subscriber side is placed near the station. Also in this case, if the upstream signal of TDD-xDSL transmission leaks as noise into the ISDN device DSU on the subscriber side, transmission delay will occur, so if the transmission of the ISDN downstream signal from the station side ends, it will affect the ISDN line There is nothing.

(d) Phase difference of 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. As is clear from FIG. 25, the difference between the start position of the first symbol 501 during training and the start position of the first symbol 701 excluding the cyclic prefix (CP) during normal communication is θd1 = 46.875. μs (48 samples), and in the case of uplink transmission, θd2 = 82.0312 μs (84 samples).
3.90625μs (4sample) is 1 pilot tone period, so the phase difference is θd1 and θd2 are 12 times and 21 times the pilot tone respectively, and the phase difference is an integral multiple of the pilot tone period. Meet.

(D) Second Embodiment The second embodiment is a case where the carrier frequency interval is 4.3125 kHz, the number of samples is 256, and # 64 is selected as the carrier for transmitting pilot tones as in the G.lite system.
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 pilot tone period is 3.623188 μs (4 samples). In the second embodiment, the length of the Cyclic Perfix is 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 the Cyclic of the G.lite system. The length is 115.94203 μ (128 samples) which is sufficiently redundant than the prefix, and the length of the redundant signal to be added later is 18.11594 μs (20 samples). From the above, the configurations of the transmission symbol strings 500 and 700 during normal communication and during training are as shown in FIG.

A signal transmission section in normal communication in the second embodiment will be described with reference to FIG. As in the case of the first embodiment, when the TDD-xDSL signal transmission section is located approximately at the center of the transmission section of ISDN ping-pong transmission,
D + a ′ = 1.875 ms (1311 samples),
S2 = 1.043478ms (1152sample)
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 ′ = 1.875 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, if the TDD-xDSL signal transmission section is located approximately at the center of the ISDN ping-pong transmission transmission section, 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 established.
Here, the guard time between the upstream and downstream signals was set to 27.17391 to 31.7029 μs (30 to 34 samples).
(1) End of the slowest ISDN downlink signal section 1.228125ms (1355.85sample)
<Start of the earliest TDD-xDSL upstream signal section 1.278808ms (1411sampl)
(2) The end of the slowest TDD-xDSL downlink signal section 1. 192029ms (1316sample)
<The beginning of the earliest ISDN upstream signal section 1.196875ms (1321.35sampl)
(3) End of TDD-xDSL upstream signal section 2.475543ms (2733sample)
<ISDN burst cycle 2.5ms (2760sample)
According to (1), even under the first worst condition, the upstream signal of TDD-xDSL transmission is not transmitted earlier than the end of ISDN downstream signal reception.
Further, according to (2), the TDD-xDSL downlink signal reception is received earlier than the ISDN uplink signal transmission start even under the second worst condition.
Also, according to (3), reception of the TDD-xDSL uplink signal ends earlier than the start of transmission of the ISDN downlink signal of the next burst even under the third worst condition.

The relationship of the phase difference between the transmission symbol sequence 700 for normal communication and the transmission symbol sequence 500 for training will be described with reference to FIG. 26. The phase difference is 79.71014 μs (88 samples) = pilot tone period × 22. Is an integer multiple (= 22 times) of the pilot tone.
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 the claims, and the present invention does not exclude these.

It is transmission symbol sequence explanatory drawing at the time of TDD-xDSL training. It is a transmission frame configuration diagram by TDD-xDSL system (during training). It is a transmission frame configuration diagram (during normal communication) by the TDD-xDSL system. It is explanatory drawing (in the case of downstream) of the frame phase relationship between bursts. It is another explanatory drawing (in the case of a downstream) of the frame phase relationship between bursts. It is a phase relationship diagram between burst frames at the time of training and normal communication. It is a TDD-xDSL transmission phase (ISDN 400Hz phase) notification method explanatory diagram at the time of training. It is phase change transmission pattern explanatory drawing. 1 is a block diagram of a subscriber transmission system according to the DMT modulation method of the present invention. It is a block diagram which implement | achieves rearrangement of the symbol row | line | column of this invention. It is a time chart (training) which shows an output sequence operation | movement. It is a time chart (normal communication) showing an output sequence operation. It is a block diagram of a transmission side sequencer. It is a block diagram which shows the ISDN400Hz signal TTR input from the outside. It is a block diagram of each part by the side of reception. It is a time chart (training) which shows reception sequence operation | movement. 6 is a time chart (normal communication) showing a reception sequence operation. It is a phase relationship diagram between burst frames at the time of training and normal communication in the first embodiment. It is a burst frame block diagram (at the time of normal communication) in a 1st embodiment. It is a burst frame configuration diagram (during training) in the first embodiment. It is the 1st worst condition explanatory view in the 1st embodiment (at the time of training). It is the 2nd worst condition explanatory view in the 1st embodiment (at the time of training). It is 3rd worst condition explanatory drawing in the 1st embodiment (at the time of training). It is two worst condition explanatory views. It is phase difference explanatory drawing of the transmission symbol sequence for training, and the transmission symbol sequence at the time of normal communication. It is a phase relationship diagram between burst frames at the time of training and normal communication in the second embodiment. It is a burst frame block diagram in the second embodiment (during normal communication). It is a burst frame block diagram (during training) in the second embodiment. It is DMT transmission spectrum explanatory drawing. It is a functional block diagram of the subscriber transmission system by a DMT modulation system. It is a band explanatory diagram of ISDN ping-pong transmission system and ADSL transmission. It is a crosstalk noise explanatory drawing. It is an explanatory diagram of interference (crosstalk) from an ISDN line to an ADSL line. It is a sliding window explanatory drawing. It is Dual Bitmap and Fext Bitmap explanatory drawing. It is explanatory drawing of the bitmap preparation method by a B & G protocol. It is form explanatory drawing which measures S / N for every NEXT / FEXT area. It is hyperframe system explanatory drawing. It is transmission system explanatory drawing which synchronizes an ADSL symbol with ISDN ping-pong transmission. It is a transmission method explanatory drawing of a TDD-xDSL symbol. It is an explanatory view of an ISI removal method. It is explanatory drawing of the influence of ISI which a xDSL symbol receives.

Explanation of symbols

500 · Training symbol sequence 601 · · TCM-ISDN transmission section 700 · · Transmission symbol sequence PLT · · Pilot tone signal

Claims (2)

The downlink data transmission from the station side device to the subscriber side device and the uplink data transmission from the subscriber side device to the station side device are time-divisionally switched and transmitted on one line, and one symbol data is divided, In a digital subscriber line transmission method in which a carrier wave having a different frequency is modulated and frequency-multiplexed with each divided data and transmitted in bursts every several symbols,
The length of the interval in which no signal is transmitted between adjacent transmission burst symbol sequences is an integral multiple of the pilot tone signal period,
Ensuring the continuity of the sample data of adjacent transmission burst symbol sequences by executing processing in synchronization with the pilot tone signal;
A digital subscriber line transmission method. The downlink data transmission from the station side device to the subscriber side device and the uplink data transmission from the subscriber side device to the station side device are time-divisionally switched and transmitted on one line, and one symbol data is divided, In a digital subscriber line transmission apparatus that modulates a carrier wave having a different frequency with each divided data and frequency multiplexes and transmits in bursts every several symbols,
Means for making the length of a section not transmitting a signal between adjacent transmission burst symbol sequences an integral multiple of a pilot tone signal period;
Means for executing processing in synchronization with a pilot tone signal and ensuring continuity of sample data of adjacent transmission burst symbol sequences;
A digital subscriber line transmission apparatus comprising:

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