JP2005516531A - Zipper DMT system and timing advance determination method in this system - Google Patents

Abstract

The present invention relates to a method for determining timing advance in a zipper DMT system. According to this method, when the remote transmission / reception unit first receives a signal for starting training from the central office transmission / reception unit, the response signal is transmitted by the first timing advance from the end point of the sample period of the reception signal. . When the central office transceiver receives the response signal, it calculates the number of delay samples in the transmission signal section and the reception signal section in the central office transceiver, and takes the second timing add in consideration of the number of delay samples and the first timing advance. Determine the burns. Next, the second timing advance is transmitted to the remote transmission / reception unit, and the remote transmission / reception unit transmits the response signal prior to the end of the sample period of the received signal by the second timing advance.

Description

  The present invention relates to a method for determining timing advance in a Zipper discrete multi-tone (hereinafter referred to as “DMT”) system.

  Recently, the demand for multimedia service supply over communication networks has increased, and data transmission of several hundred kbps to several tens of Mbps using existing copper telephone lines without amplifiers or repeaters to satisfy such demands. An xDSL (digital subscriber line) scheme has been developed to provide speed.

  xDSL is available in various forms such as HDSL (high-data-rate DSL), SDSL (single-line HDSL), ADSL (asymmetry DSL), UADSL (universal ADSL), and VDSL (very-high-bit-rate DSL). Has developed. In particular, VDSL was developed to transmit data at high speed from a short distance of 300 to 1,500 m.

  The modulation / demodulation method used in such xDSL includes SCM (single-carrier modulation) CAP (carrierless AM / PM) method and QAM (quadrature amplitude modulation) method and MCM (multi-carrier modulation) DMT (multi-carrier modulation) method. discrete multi-tone).

  Among these, the DMT method is a simple single-tap equalizer that divides the entire transmission band into a number of narrow-band subchannels and increases the transmission period of each subchannel by the number of subchannels. Channel distortion compensation is possible. Further, by adding a cyclic prefix as a guard interval to the DMT symbol, it is possible to eliminate inter-symbol interference while maintaining orthogonality between the subchannels, so that the structure of the equalizer at the receiving end Becomes easier. The modulation / demodulation process can be realized at high speed using IFFT (inverse fast Fourier transform) and FFT (fast Fourier transform), respectively.

  Factors that reduce the maximum performance of such a DMT system include a near end cross-talk signal and an echo signal. The near-end crosstalk signal is noise generated when data is simultaneously transmitted from two different transmission ends, and is generated when data in the same frequency band is simultaneously transmitted in both directions within the same binder group. The echo signal is noise that affects a signal received when data is transmitted from the transmission side at the same end.

  The zipper DMT method is a method developed to prevent such near-end crosstalk signals and echo signals, and adds a cyclic suffix to the end portion of the signal in addition to the cyclic prefix. To use. In order to minimize the interference between the near-end crosstalk signal and the echo signal, the orthogonality between the frequencies must be maintained. Therefore, the zipper DMT system generates a cyclic suffix so that the near-end crosstalk signal and the echo signal are included in only one symbol within the symbol period of the received signal at the end of each network in order to ensure orthogonality between frequencies. Transmit in addition to the signal.

  Also, the zipper DMT uses the U2 interface as a reference so that the central transceiver unit and the remote transceiver unit transmit signals simultaneously from the start of the symbol interval of the received signal at the U2 interface of the remote transceiver unit. A signal is transmitted ahead of timing advance. In the conventional technique, the number of samples of the cyclic suffix is made longer than the number of samples of the timing advance to eliminate the effects of near-end crosstalk and echo.

  In the prior art, such timing advance is determined from the shock response or transfer function of the channel. In order to determine the timing advance in such a manner, a channel shock response and a transfer function estimation process are required.

It is a technical object of the present invention to simultaneously transmit and receive signals between a central office transceiver and a remote transceiver with the U2 interface as a reference.
Moreover, this invention makes it a technical subject to remove a near-end crosstalk signal and an echo signal using only the cyclic suffix of the minimum length.
Another object of the present invention is to determine a timing advance by measuring a channel group delay.

The above object is achieved by measuring the group delay and determining the timing advance.
According to one aspect of the present invention, a zipper DMT system is provided that includes a central office transceiver and a remote transceiver. The central office transceiver includes a first transmission buffer, a first transmission sample counter, a first reception buffer, and a first reception sample counter. The first transmission buffer temporarily stores samples to be transmitted, and the first transmission sample counter is a first transmission sample counter. A first transmission sample count value indicating the position in the symbol of the output sample of the transmission buffer is set, the first reception buffer temporarily stores the received sample, and the first reception sample counter is in the symbol of the input sample of the first reception buffer. A first received sample count value indicating the position is set. The remote transmission / reception unit includes a second transmission buffer, a second transmission sample counter, a second reception buffer, and a second reception sample counter. The second transmission buffer temporarily stores samples to be transmitted, and the second transmission sample counter is a second transmission. A second transmission sample count value indicating the position in the symbol of the output sample of the buffer is set, the second reception buffer temporarily stores the received sample, and the second reception sample counter is in the symbol position of the input sample in the second reception buffer Is set to the second received sample count value.

  At this time, the remote transmission / reception unit changes the second transmission sample count value and transmits the signal by the first timing advance from the end point of the sample period of the reception signal at the U2 interface of the remote transmission / reception unit. When the second timing advance is received from the transmitter / receiver, the signal is transmitted by the U2 interface of the remote transmitter / receiver prior to the end of the sample period of the received signal by the second timing advance. The central station transmission / reception unit calculates the number of delay samples in the transmission signal interval and reception signal interval in the U2 interface of the central station transmission / reception unit, and determines the second timing advance by considering the first timing advance and the delay sample. To do.

  At this time, it is preferable that the central office transmission / reception unit and the remote transmission / reception unit update the cyclic prefix and the cyclic suffix, and the updated cyclic prefix is (cyclic prefix + first timing advance−second timing add). The updated cyclic suffix becomes (cyclic suffix−first timing advance + second timing advance).

  According to another aspect of the invention, a method is provided for determining timing advance in such a system. According to this method, when the remote transmission / reception unit first receives a signal for starting training from the central office transmission / reception unit, the response signal is transmitted from the U2 interface of the remote transmission / reception unit to the first timing add from the end of the sample period of the received signal. Send ahead of Barns. When the central office transceiver receives the response signal, it calculates the number of delay samples in the transmission signal section and the reception signal section in the central office transceiver, and takes into account the number of delay samples and the first timing advance, Decide Next, the second timing advance is transmitted to the remote transmission / reception unit, and the remote transmission / reception unit transmits the response signal by the U2 interface of the remote transmission / reception unit prior to the end of the sample period of the received signal by the second timing advance. To do.

  At this time, the cyclic prefix is updated to (cyclic prefix + first timing advance−second timing advance), and the cyclic suffix is changed to (cyclic suffix−first timing advance + second timing add). It is preferable to update to (Berns).

  At this time, the number of delay samples is determined from the group delay from the transmission side of the central station transmission unit to the U2 interface of the central transmission / reception unit and the reception side of the central station transmission / reception unit based on the transmission sample count value indicating the position in the symbol of the transmission sample. The value is preferably determined by subtracting the group delay to the U2 interface of the central office transceiver.

  The second timing advance is preferably determined by the following equation.

Here, TA is the second timing advance, TA ₀ is the first timing advance, Δ is the number of delayed samples, _NT is the sample length, and mod is a modulo operation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily implement the embodiments. However, the present invention can be realized in various forms, and is not limited to the following examples.
First, a zipper DMT system for determining timing advance according to an embodiment of the present invention and a timing advance determination method in this system will be described in detail with reference to the drawings.

  For details on the O-SIGNATURE, R-MSG1, R-ACK, O-UPDATE, and R-IDLE messages described in the present invention, refer to the T1E1.4 VDSL Recommendation (VDSL Metallic Interface, Part 3: Technical Specification of a Multi-Carrier). Modulation Transceiver).

A zipper DMT transmission / reception system according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram showing a zipper DMT transmission / reception system according to an embodiment of the present invention. FIG. 2 is a diagram showing the number of samples of one symbol used in the zipper DMT transmission / reception system according to an embodiment of the present invention.

  As shown in FIG. 1, a zipper DMT transmission / reception system according to an embodiment of the present invention includes an optical network unit transmission / reception unit 100 and a remote site transmission / reception unit 200. Are connected to the respective U2 interfaces 400, 500 via channels 300. As such a channel, a UTP (unshielded twisted pair) cable is generally used.

  The transmission / reception units 100 and 200 convert digital signals into physical layer signals in the U2 interfaces 400 and 500, or conversely convert physical layer signals into digital signals, and transmit units 110 and 210, transmission buffers 120 and 220, respectively. Sample counters 130 and 230, receivers 140 and 240, reception buffers 150 and 250, reception sample counters 160 and 260, and analog front end (AFE) 170 and 270 are included.

  The transmission units 110 and 210 include transmission control units (Tx front-end controllers) 111 and 211. The transmission control units 111 and 211 temporarily store the data subjected to the inverse fast Fourier transform (IFFT) in the transmission units 110 and 210 in the transmission buffers 120 and 220, and according to the counts of the transmission sample counters 130 and 230. The data is extracted from the transmission buffers 120 and 220 and transmitted to the analog front ends 170 and 270. Further, the transmission control units 111 and 211 adjust the count values of the transmission sample counters 130 and 230.

  The reception units 140 and 240 include reception control units (Rx front-end controllers) 141 and 241. The reception control units 141 and 241 temporarily store the data from the analog front ends 170 and 270 in the reception buffers 150 and 250, and extract the data from the reception buffers 150 and 250 according to the counts of the reception sample counters 160 and 260, This is transmitted to a fast Fourier transform (FFT) unit (not shown) in the receiving units 140 and 240. The reception control units 141 and 241 adjust the count values of the reception sample counters 160 and 260.

  The analog front ends 170 and 270 convert digital signals from the transmission units 110 and 210 into physical layer signals (analog signals) and transmit them to the remote transmission / reception unit 200 and the central office transmission / reception unit 100 via the U2 interfaces 400 and 500, respectively. At the same time, the physical layer signals received from the remote transmission / reception unit 200 and the central office transmission / reception unit 100 via the U2 interfaces 400 and 500 are converted into digital signals and transmitted to the reception units 140 and 240.

Then, as shown in FIG. 2, if the number of single tone and N _SC, symbols zipper DMT consists of a sample and the L _CS number of cyclic suffix samples L _CP number of cyclic prefix samples and 2N _NC . That is, the number of samples of one symbol (N _T ) is expressed by the following equation (1).

The transmission sample count values (OTxSampleCnt, RTxSampleCnt), which are the count values of the transmission sample counters 130 and 230, indicate the positions in the symbols of the output samples of the transmission buffers 120 and 220, and have a value of 0 to N _T −1. The transmission sample count values (OTxSampleCntAtU2, RTxSampleCntAtU2) in the U2 interfaces 400, 500 indicate the positions in the symbols of the transmission samples of the U2 interface 400, 500, which are the output of the transmission buffers 120, 220 by the transmission sample count values (OTxSampleCnt, RTxSampleCnt). To the U2 interfaces 400 and 500, taking into account group delays (ΔO _TX , ΔR _TX ), which are expressed by the following equation (2).

Similarly, the reception sample count values (ORxSampleCnt, RRxSampleCnt), which are the count values of the reception sample counters 160 and 260, indicate the positions in the symbol of the input samples of the reception buffers 150 and 250, which are values from 0 to N _T -1. Have The received sample count values (ORxSampleCntAtU2, RRxSampleCntAtU2) in the U2 interface 400, 500 indicate the positions in the symbol of the received samples of the U2 interface 400, 500, which are the received sample count values (ORxSampleCnt, RRxSampleCnt) and input to the receiving buffers 120, 220 To the U2 interfaces 400 and 500, taking into account the group delay (ΔO _RX , ΔR _RX ), and is expressed by the following equation (3).

In general, in order to transmit data in such a zipper DMT system, an initialization step must first be performed. Such an initialization phase includes an activation (handshake) phase, a training phase, and a channel analysis & exchange phase. The start (handshake) stage is a stage for checking whether or not a signal is ready to be transmitted between the transmitting and receiving terminals, and the training stage is a stage for performing symbol synchronization and equalizer training (channels). The analysis and inter-school steps measure the signal-to-noise ratio (SNR) for each sub-channel and generate a bit table with bit loading information suitable for each, and the various parameters determined at this time are determined. This is the stage of exchange between the transmitting and receiving ends.
At this time, the timing advance is determined in the training stage.

Hereinafter, a timing advance determination method according to an embodiment of the present invention will be described with reference to FIGS. 3A to 3C.
3a to 3c are time diagrams illustrating a method for measuring timing advance according to an embodiment of the present invention.

  After initializing the training stage in the training stage, the central office transceiver unit 100 repeatedly transmits an O-SIGNATURE message to the remote transceiver unit 200 and repeatedly until an R-MSG1 message is received from the remote transceiver unit 200. (S301). Such an O-SIGNATURE message includes fields such as a band to be used, an RFI band, and a PSD, which are used for setting a basic value necessary for data transmission. The remote transmission / reception unit 200 completes symbol synchronization and starts convergence of the equalizer (S302).

When the remote transmission / reception unit 200 completes the convergence of the equalizer, the remote transmission / reception unit 200 receives the O-SIGNATURE message, and the transmission control unit 211 starts the reception of the O-SIGNATURE message. The transmission sample count (RTxSampleCnt ) Is set to N _T -TA ₀ + ΔR _TX + ΔR _RX (S303). At this time, the sample count (RTxSampleCntAtU2) in the U2-R interface is N _T -TA ₀ + ΔR _RX in consideration of the channel delay.

Next, the remote transmission / reception unit 200 repeatedly transmits a confirmation message R-MSG1 indicating that the O-SIGNATURE message has been received to the central station transmission / reception unit 100, but starts transmission when the transmission sample count (RTxSampleCnt) becomes zero. (S304). Then, when the transmission sample count (RTxSampleCnt) reaches ΔR _TX , the sample count in the U2-R interface becomes 0, that is, transmission of R-MSG1 from the U2-R interface starts. Then, on the U2-R interface, the transmission message is transmitted by TA ₀ before the reception message.

と設定する（Ｓ３０５）。中央局送受信部１００は、等化器の収斂が完了すると、Ｒ−ＭＳＧ１メッセージを受信し（Ｓ３０６）、Ｒ−ＭＳＧ１のサンプル区間が完了する前にＯ−ＵＰＤＡＴＥメッセージを送信する（Ｓ３０７）。この際、Ｏ−ＵＰＤＡＴＥメッセージは、Ｒ−ＭＳＧ１メッセージを受信し、伝送サンプルカウント(OTxSampleCnt)が０になるときに送信する。このようなＯ−ＵＰＤＡＴＥメッセージは、タイミングアドバーンスの補正値が記録されるフィールドを含み、このフィールドに補正されたタイミングアドバーンスを記録して送信する。このような補正されたタイミングアドバーンスは次式（４）で与えられる。 Next, when the symbol synchronization is completed in the central office transceiver 100, the equalizer starts to converge, and the difference (Δ) in the number of samples between the transmission signal and the reception signal in the U2-O interface

Is set (S305). When the convergence of the equalizer is completed, the central office transceiver unit 100 receives the R-MSG1 message (S306), and transmits the O-UPDATE message before the R-MSG1 sample period is completed (S307). At this time, the O-UPDATE message is transmitted when the R-MSG1 message is received and the transmission sample count (OTxSampleCnt) becomes zero. Such an O-UPDATE message includes a field in which a correction value of timing advance is recorded, and the corrected timing advance is recorded and transmitted in this field. Such corrected timing advance is given by the following equation (4).

Here, TA is the corrected timing advance, TA ₀ is the previous timing advance, _NT is the length of the sample, and mod is the modulo operation.

  When receiving the O-UPDATE message, the remote transmission / reception unit 200 stores the TA included in the message (308). Thereafter, when the transmission sample count value (RTxSampleCnt) becomes 0, a confirmation message R-ACK message indicating that it has been received is transmitted to the central office transceiver unit 100 (S309). After transmitting the R-ACK message, the R-IDLE message, which is a meaningless signal, is repeatedly transmitted (S310).

Receiving the R-IDLE message, the control unit of the central office transceiver 100 transmits sample count (OTxSampleCnt) is N _T - time (TA-delta), sending samples counted (OTxSampleCnt) is set to 0, a new site The click prefix and the cyclic suffix are set to L _CP + TA ₀ + TA and L _CS − (TA ₀ −TA), respectively, and a new message is transmitted (S311). At this time, when the transmission sample count (RTxSampleCnt) is 0, the control unit of the remote transmission / reception unit 200 sets the new cyclic prefix and cyclic suffix to L _CP + TA ₀ -TA and L _CS- (TA ₀ -TA), respectively. Set and send a new message.

  The central office transmitting / receiving unit 100 calculates the number of delay samples and the new timing advance in the same manner as in the previous process, and repeats the above process if the new timing advance is different from the previous timing advance.

  In this way, the timing advance can be determined simply by measuring the channel group delay, and the length of the cyclic suffix can be reduced by the difference between the existing timing advance and the new timing advance. . In addition, by setting the timing advance in this way, when the U2 interface is used as a reference, signals can be simultaneously transmitted and received between the central office transmission / reception unit and the remote transmission / reception unit.

  As mentioned above, although the suitable Example of this invention was described in detail, this invention is not limited to these Examples. Various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the claims also belong to the scope of the present invention.

1 is a block diagram illustrating a zipper DMT transmission / reception system according to an embodiment of the present invention. It is a figure which shows the sample number of 1 symbol used with the zipper DMT transmission / reception system based on one Example of this invention. It is a time chart which shows the timing advance measurement method which concerns on one Example of this invention. It is a time chart which shows the timing advance measurement method which concerns on one Example of this invention. It is a time chart which shows the timing advance measurement method which concerns on one Example of this invention.

Explanation of symbols

100, 200 Transmission / reception unit 300 Channel 400, 500 U2 interface N Number of _SC symbol tones

Claims (7)

A first transmission buffer for temporarily storing samples to be transmitted; a first transmission sample counter for setting a first transmission sample count value indicating a position in a symbol of an output sample of the first transmission buffer; and temporarily storing the received samples. A first reception buffer, and a first reception sample counter that sets a first reception sample count value indicating a position in a symbol of an input sample of the first reception buffer, and the first reception sample counter sets the first reception sample count value according to the first transmission sample count value. A central station transceiver for extracting and transmitting samples from one transmission buffer, and extracting and receiving samples from the first reception buffer according to the first reception sample count value;
A second transmission buffer for temporarily storing samples to be transmitted; a second transmission sample counter for setting a second transmission sample count value indicating a position in a symbol of an output sample of the second transmission buffer; and temporarily storing the received samples. A second reception buffer, and a second reception sample counter that sets a second reception sample count value indicating a position in a symbol of an input sample of the second reception buffer, and the second reception sample counter sets the second reception sample count value according to the second transmission sample count value. A remote transmission / reception unit that extracts and transmits samples from the transmission buffer, and extracts and receives samples from the second reception buffer according to the second reception sample count value;
The remote transmission / reception unit changes the second transmission sample count value and transmits a signal by a first timing advance from the end point of the sample period of the reception signal at the U2 interface of the remote transmission / reception unit, Upon receiving the second timing advance from the central transceiver unit, the U2 interface of the remote transceiver unit transmits a signal by the second timing advance from the end of the sample period of the received signal,
The central station transmission / reception unit calculates the number of delay samples of the transmission signal interval and the reception signal interval in the U2 interface of the central station transmission / reception unit, and considers the first timing advance and the delay sample, Zipper DMT system that determines timing advance. The central office transceiver and the remote transceiver are
Update the cyclic prefix to (the cyclic prefix + the first timing advance−the second timing advance),
The zipper DMT system according to claim 1, wherein the cyclic suffix is updated to (the cyclic suffix-the first timing advance + the second timing advance). The remote transmission / reception unit performs the second timing ad burn.

(Where TA is the second timing advance, TA ₀ is the first timing advance, Δ is the number of delayed samples, _NT is the sample length, and mod is the modulo operation) And
The central office transceiver unit determines the number of delay samples.

(Where OTxSampleCnt is the first transmission sample count value, ΔO _TX is the group delay from the transmission side of the central station transmission / reception unit to the U2 interface of the central station transmission / reception unit, and ΔO _RX is from the reception side of the central station transmission / reception unit. The zipper DMT system according to claim 1 or 2, wherein a group delay to the U2 interface of the central office transceiver unit is determined. In the zipper DMT system where the central office transceiver and remote transceiver exchange data,
When the remote transmission / reception unit receives a signal for starting training from the central office transmission / reception unit, a response signal is transmitted from the U2 interface of the remote transmission / reception unit by a first timing advance from the end of the sample period of the reception signal. A first stage to transmit in advance;
When the central station transceiver receives the response signal, the second step of calculating the number of delay samples in the transmission signal interval and the reception signal interval in the central station transceiver,
A third stage in which the central office transceiver unit determines a second timing advance in consideration of the number of delay samples and the first timing advance;
And a fifth step in which the remote transmission / reception unit transmits a response signal by the U2 interface of the remote transmission / reception unit prior to the end of the sample period of the received signal by the second timing advance. How to determine the burns. The fifth stage includes
Update the cyclic prefix to (the cyclic prefix + the first timing advance−the second timing advance),
5. The timing advance determination method according to claim 4, further comprising: updating a cyclic suffix to (the cyclic suffix−the first timing advance + the second timing advance). The second stage includes
The number of delay samples is determined from the transmission sample count value indicating the position in the symbol of the transmission sample, the group delay from the transmission side of the central station transmission unit to the U2 interface of the central transmission / reception unit, and the central point from the reception side of the central station transmission / reception unit 6. The timing advance determination method according to claim 4, wherein a value obtained by subtracting the group delay to the U2 interface of the station transmission / reception unit is determined. The third stage includes
Second timing advance

(Where TA is the second timing advance, TA ₀ is the first timing advance, Δ is the number of delayed samples, _NT is the sample length, and mod is the modulo operation) The timing advance determination method according to claim 4 or 5.

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