JP2001298499A - Digital subscriber line transmission method, transmission apparatus and transmission / reception apparatus under periodic noise environment - Google Patents

Abstract

(57) [Problem] To provide a digital subscriber line transmission method and apparatus capable of performing high-speed data communication using an existing telephone line, and a method for suppressing periodic noise from an adjacent ISDN ping-pong transmission line or the like. High-speed and high-reliability digital subscriber line transmission is realized by a simple configuration. SOLUTION: Received data is demodulated by a demodulator 1-1, the demodulated data is compared with a reference signal 1-2, and a signal-to-noise ratio is measured from an error signal by an S / N measuring device 1-7. Also, the received data is input to the frequency divider 1-4, and the frequency dividers 1-4 and 1-5 divide the frequency of the internal clock 1-3 and match the phase of the received data with the hyperframe interval (DMT). The timing signal of the symbol length and the common multiple of the ping-pong transmission frame length) is output to the section determiner 1-6,
The section determiner 1-6 determines a high-noise section and a low-noise section in the hyperframe based on the measurement result of the S / N measuring apparatus 1-7, and transmits the entire section based on the signal-to-noise ratio of the high-noise section. Set the capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an xDSL (xDSL: x Digital Subscr) using an existing telephone line using a metallic line and coexisting with a call using an analog signal.
More particularly, the present invention relates to a digital subscriber line transmission method and apparatus that improves communication reliability under a periodic noise environment.

[0002] xDSL (x Digital Subscriber Line)
) Technology xDSL technology that enables high-speed data communication using existing telephone lines includes ADSL, HDSL, VDSL, etc.
Although there are various types having different transmission speeds and the like, they are collectively referred to as “xDSL”. Among them, the uplink transmission speed from the subscriber's house to the accommodation station is 16 to 640 Kb.
ps, the downlink transmission speed from the accommodation station to the subscriber's house is 1.5 ~
An outline of a digital subscriber line transmission system to which ADSL (Asymmetric DSL) technology of 6.784 Mbps is applied will be described below.

FIG. 6 shows a model of an accommodation station and a subscriber house connected by an ADSL transmission system. Containment Bureau 6
-1 and the subscriber's home 6-2 are connected to the existing metallic line 6-
3 and a narrow band network 6-12 such as a telephone exchange and an office side ADSL modem (ATU-C: ADSL Transceiver Unit) via a splitter 6-11 which separates a signal according to a frequency in the accommodation station 6-1. -Central Offi
ce) 6-13 are connected.

[0004] By the splitter 6-11, a signal in a low frequency band of about 4 KHz used for telephone voice and A
A signal in a high frequency band used as a modulated wave by the DSL modem 6-13 is separated. ADSL modem 6
Reference numeral 13 performs high-speed data communication via the broadband network 6-14.

On the other hand, a splitter 6-
21 is connected to a metallic line 6-3, and a general analog telephone 6-22 and an ADSL modem (ATU-A) for performing ADSL transmission via the splitter 6-21.
R: ADSL Transceiver Unit-Remote Terminal) 6-2
3, and an information communication device such as a personal computer 6-33 is connected to the ADSL modem 6-23. It should be noted that a splitter 6- 6 for frequency separation is provided on the subscriber home 6-2 side.
There is also known a splitterless ADSL transmission system that does not use C.21.

The above-mentioned ADSL transmission system makes it possible to transmit a high-speed digital signal of up to about 7 Mbit / sec without newly laying out a line for a high-speed digital signal. It can be suitably used for multimedia communication services such as demand.

As described above, in the ADSL transmission system, a conventional telephone voice signal and a high-speed data signal coexist on the same line, and a high-speed digital transmission service is provided by utilizing the conventional metallic telephone line as it is. To provide.

[0008]

2. Description of the Related Art ADSL transmission methods are ANSI and ITU.
-T is a technology that is being standardized by international organizations such as ITU-T. 99
It is recommended as 2.2. G. FIG. The 992.2 recommendation employs a DMT (discrete multitone) modulation method.

DMT (discrete multitone) modulation method In the DMT modulation method in the 992.2 recommendation, as shown in FIG. 7A, frequencies at 4.3125 KHz intervals are used as carrier waves. Each carrier is called a subcarrier. G. FIG. In the 992.2 recommendation, the number of subcarriers is 256, and the bandwidth of the ADSL transmission system is 0 to 0.
The frequency band is 1.104 MHz.

FIG. 7B shows an ADS by DMT modulation.
The L transmission system frequency band, the analog telephone frequency band, and the ISDN ping-pong transmission frequency band are shown. As shown, the frequency band of the analog telephone is up to about 4 KHz,
The upstream band of the DSL transmission system is 4.25 to 138 KHz,
The downstream band of the ADSL transmission system is 138 to 1104KH
z, the frequency band of ISDN ping-pong transmission has a number of side lobes as shown by the dotted line in FIG.
Hz, and the frequency band of the ADSL transmission system and the frequency band of the ping-pong transmission mostly overlap.

In the DMT modulation method, a modulated signal (symbol sequence) is transmitted in a signal unit called “DMT symbol”. The DMT symbol is a signal on which a sine wave of each subcarrier is superimposed. G. FIG. In the Annex A specification for North America of the 992.2 recommendation, this DMT symbol is continuously transmitted. The length of the DMT symbol is about 246 microseconds including the buffer section for reducing the influence of intersymbol interference between consecutive symbols.

Crosstalk from ISDN ping-pong transmission line The periodic noise environment will be described with reference to FIG. Office-side ISDN line termination unit (OCU: Office Channel
Unit) 8-1 is a subscriber ISDN line termination unit (DSU: Digital Service Unit) 8-2 at the subscriber's house.
Is connected by a metallic telephone line 8-3, and
Perform SDN ping-pong transmission.

On the other hand, the station side ADSL modem (AT) is located adjacent to the ISDN line termination unit (OCU) 8-1.
UC) 8-4 are accommodated, and the station-side ADSL modem (A
TU-C) 8-4 is the subscriber-side ADSL of another subscriber's house.
A modem (ATU-R) 8-5 has a metallic telephone line 8
-6, and ADSL transmission is performed between them. Here, a metallic telephone line 8 that performs ISDN ping-pong transmission
-3 is called “ISDN ping-pong transmission line” and ADSL
The metallic telephone line 8-6 that performs the transmission is called "ADSL transmission line".

On the ISDN ping-pong transmission line 8-3,
Between the office-side ISDN line termination unit (OCU) 8-1 and the subscriber-side ISDN line termination unit (DSU) 8-2, the timing of one 2.5 ms frame period is time-divided, and the upstream (subscriber) The timing is divided into data transmission timing in the direction from the station to the station and data transmission timing in the downlink direction (from the station to the subscriber), so-called ping-pong transmission is performed.

As described above with reference to FIG. 7, the frequency band used for ADSL transmission by DMT modulation and the ISDN
The frequency bands used in ping-pong transmission overlap. Therefore, the ADSL transmission line 8-6 laid adjacent to the ISDN ping-pong transmission line 8-3 is affected by the crosstalk noise from the ISDN ping-pong transmission line 8-3.

ISDN viewed from ADSL transmission line 8-6
Crosstalk noise from the ping-pong transmission line 8-3 is a certain ADS
An ISDN transmission device (for example, a subscriber ADS) installed on a side closer to the ADSL transmission device when viewed from the L transmission device.
When viewed from the L modem 8-5, it is strongly affected by crosstalk noise generated at the transmission timing of the subscriber side ISDN line termination unit 8-2). This crosstalk noise is referred to as “Near End Cross Talk (NEXT)”.

The effect of crosstalk noise on the transmission timing of an ISDN transmission device (for example, the station-side ISDN line termination unit 8-1 when viewed from the subscriber-side ADSL modem 8-5) installed on the far side is as follows. Relatively weak. This crosstalk noise is referred to as “far end crosstalk noise (FEXT: FAR END Cros).
s Talk) ".

That is, a timing section affected by near-end crosstalk noise (NEXT) (hereinafter referred to as a “high noise section”) is a signal-to-noise ratio (S / S / D) of a DMT-modulated symbol sequence on an ADSL transmission line. N) is likely to deteriorate, and the signal-to-noise ratio (S / N) is relatively good in a timing section (hereinafter referred to as a “low noise section”) affected by far-end crosstalk noise (FEXT).

Therefore, the ADSL transmission line 8-6 has the IS
From the DN ping-pong transmission line 8-3, as shown in the lower part of FIG. 8, a high-noise section caused by near-end crosstalk noise (NEXT) and a low-noise section caused by far-end crosstalk noise (FEXT) are periodically repeated. Affected by Such a noise environment is called a “periodic noise environment”.

FIG. 9 shows a telephone line cable susceptible to crosstalk. Telephone lines are often "quad cables"
A cable 9-1 is used, which is a bundle of a plurality of line pairs called a pair of lines. The bundle of line pairs in this cable 9-1 has AD
When the line pair 9-2 of the SL transmission line and the line pair 9-3 of the ISDN ping-pong transmission line coexist, the two lines are physically juxtaposed and adjacent to each other. Become.

When a large number of ISDN ping-pong transmission lines are adjacent to a pair of ADSL transmission lines, the large number of ISDN ping-pong transmission lines are usually
Each ISDN accommodated in the same station and accommodated in the same station
The ping-pong transmission line transmits and receives uplink and downlink data at the same timing.
The transmission line has a high-noise section due to near-end crosstalk noise (NEXT) and a low-noise section due to far-end crosstalk noise (FEXT),
It is the same for each ISDN ping-pong transmission line.

ADS for data transmission by DMT modulation
The L transceiver has a bitmap that determines the number of bits allocated to each subcarrier for both transmission and reception.
In the transmission bitmap, the number of bits allocated to each subcarrier is set according to the signal-to-noise ratio (S / N) for each subcarrier so that optimum communication conditions (transmission capacity) are obtained.

FIG. 10 shows an example of the number of bits allocated to each subcarrier using a bit map. As shown in the figure, the signal-to-noise ratio (S /
N) and measure the signal-to-noise ratio (S /
The number of transmission bits for each subcarrier is set in the bitmap such that the number of transmission bits according to N) is allocated.

[0024] In the i-th subcarrier, the relationship between the maximum allocated bit number b _i signal-to-noise ratio (S / N) is generally expressed by the following equation. b _i = log ₂ [1 + SNR _i / {2 × 10 ^{(SNRgap + SNRmargin-CodingGain)} }] (1)

Here, SNR _i is the signal-to-noise ratio (S / N) of the i-th subcarrier, SNRgap is the level gap of the signal-to-noise ratio (S / N) between symbols, and SNRm
argin is the symbol-level signal-to-noise ratio (S / N)
And CodingGain are data corrections by error correction coding.

FIG. 11 shows a configuration of a main part of an ADSL transmission apparatus using the DMT modulation method. Here, the opposing transmitting unit and receiving unit of the transceiver (transceiver) in the ADSL modem device opposing via the metallic line 11-10 are functionally shown. Their functions are usually
This is realized by software processing on an SP (Digital Signal Processor) chip.

On the transmitting side, the transmission data is stored in the serial / parallel conversion buffer 11-1 for one symbol time (1 / 4.3125).
KHz). The stored data is divided into the number of transmission bits for each subcarrier set in the transmission bitmap 11-6, and is input to the encoder 11-2.

The encoder 11-2 converts the input bit strings into signal points for DMT modulation, and outputs the signal points to the inverse fast Fourier transformer 11-3. The inverse fast Fourier transformer 11-3 performs an inverse fast Fourier transform based on the input signal points and outputs the result to the parallel-serial conversion buffer 11-4.

Here, 16 points of the output of the inverse fast Fourier transformer 11-3 are added as a cyclic prefix to the head of the DMT symbol for protection against intersymbol interference. An output signal from the parallel-to-serial conversion buffer 11-4 is output to the digital / analog (D / A) converter 1
The signal is converted to an analog signal in 1-5, and is converted to a metallic line 11.
It is transmitted to the subscriber side via -10.

On the receiving side, an analog reception signal received from the metallic line 11-10 is converted into a digital signal by an analog-to-digital (A / D) converter 11-11, and a 1-DMT signal is output by a serial-parallel conversion buffer 11-12.
Stored for symbols.

In the serial-parallel conversion buffer 11-12, the cyclic prefix is removed, and the output is input to the fast Fourier transformer 11-13. The fast Fourier transformer 11-13 converts the input signal into a component for each subcarrier and demodulates it by performing a fast Fourier transform.

The demodulated signal points are transmitted bitmap 1
Received bitmap 11 holding the same value as 1-6
According to -16, it is decoded by the decoder 11-14. The decoded data is sent to the parallel / serial conversion buffer 11-.
15 and the received data is output as a bit string from the parallel / serial conversion buffer 11-15.

FIG. 12 shows a configuration for measuring a signal-to-noise ratio (S / N) in a transceiver conforming to the Annex A recommendation specification. Here, all the symbols transmitted from the transmitting side during the period of the signal-to-noise ratio (S / N) measurement are used as demodulators 12-1.
And compares the demodulated data with the reference signal 12-2 stored in advance.

The error signal obtained as a result of the comparison is input to the S / N measuring device 12-3, and the S / N measuring device 1
Based on the signal-to-noise ratio (S / N) measured in 2-3, the transmission bit number converter 12-4 calculates the number of bits bi allocated to each subcarrier.

Since the ADSL transceiver of the Annex A recommendation specification does not consider the influence of the periodic noise from the ISDN ping-pong transmission line, it averages the signal-to-noise ratio (S / N) between the high noise section and the low noise section. The above-described bitmap is set based on the averaged signal-to-noise ratio (S / N).

Therefore, the averaged signal-to-noise ratio (S /
When a bitmap based on (N) is used, noise interference larger than an assumed signal-to-noise ratio (S / N) is received in a high noise section, and transmission errors frequently occur.

[0037] This means that the quality and reliability of the ADSL transmission line are reduced. The problem is that Ann
Since the exA recommendation specification assumes that the magnitude of the noise is almost constant, the noise amount in the low noise section and the high noise section due to crosstalk noise from the ISDN ping-pong transmission line cannot be distinguished and transmitted. This is generated to determine the transmission condition based on the noise amount obtained.

In order to address this problem, ITU-T recommendation G. In 992.2, the recommended specification AnnexC is:
For ADSL transmission under periodic crosstalk noise environment,
The following sliding window system and network timing reference technology are recommended.

Sliding window method In an environment where an ADSL transmission line is affected by periodic noise from an adjacent ISDN ping-pong transmission line, the ADSL transmission line
In order to transmit signals well, a method to transmit and receive bitmaps that determine the bits to be allocated to each subcarrier using two types, one for the high noise section and the other for the low noise section, is being studied. Have been.

Such a form is referred to as a “Dual Bit Map (DBM) method”. Further, data is transmitted only in a low noise section having a good signal-to-noise ratio (S / N), and data is not transmitted in a high noise section. A “FEXT Bit Map (FBM) method,” in which a bitmap is omitted, is also being studied.

In order to perform ADSL transmission using the dual bitmap (DBM) system, the present applicant has proposed an effective system for associating a bitmap with a transmission symbol (Japanese Patent Application Laid-Open No. H11-341153). ) Proposes a digital subscriber line transmission system using a sliding window system.

FIG. 13 is an explanatory diagram of ADSL transmission by the sliding window method. This system has a length of 34 frames of 2.5 ms per frame in ISDN ping-pong transmission shown in (i) of the figure and a DMT modulation method used in the ADSL transmission DMT modulation system shown in (iii) of the figure.
Utilizing the fact that the length of 345 symbols (approximately 246 μs) corresponds to 345 DMT symbol strings (# 0 to # 344), far-end crosstalk noise (FEX)
This is a method for associating a T) section with a near-end crosstalk noise (NEXT) section.

The section for 345 DMT symbols is the IS
Since the length matches 34 frame periods of the DN ping-pong transmission, this section is called a hyperframe. In the sliding window method, the start position of the hyperframe is matched with the start position of the ISDN ping-pong transmission, and each DMT symbol in the hyperframe is divided into a far-end crosstalk noise (FEXT) section and a near-end crosstalk noise (NEXT) section. And a far-end crosstalk noise (FEXT) section and a near-end crosstalk noise (N
(EXT) sections are assigned, and transmission bits are assigned using different bitmaps A and B for each noise section as shown in FIG.

In the ADSL transceiver according to the Annex C recommendation specification, the subscriber unit (ATU-R) measures a signal-to-noise ratio (S / N) at the time of starting communication to determine the maximum transmission capacity of the own unit. Dual bitmap (DBM) or far-end crosstalk noise bitmap (FB)
In the M) scheme, since the measurement of the signal-to-noise ratio (S / N) of each DMT symbol needs to be performed for each of the high-noise section and the low-noise section, a correct signal-to-noise ratio for each noise section is required. (S / N) It is necessary to define a measurement section.

The determination as to whether each DMT symbol belongs to a high noise section or a low noise section is performed as follows. FIG. 14 is an explanatory diagram of a method of determining a noise section to which each DMT symbol belongs.

(I) of the figure shows ISDN on the subscriber side.
The reception timing of the 400 Hz frame of the ping-pong transmission is shown. The frame period of the ISDN ping-pong transmission is 2.5 ms, and the number of DMT modulation signal samples in the frame is 1104 KHz × 2.5 ms = 2760.
Included.

FIG. 2 (ii) shows the crosstalk noise on the subscriber side. The first half is affected by far-end crosstalk noise (FEXT), and the second half is affected by near-end crosstalk noise (NEXT). (Iii) in the figure
Indicates a definite position of a noise section on the subscriber side, and (iv) in the figure indicates D in the far-end crosstalk noise (FEXT) section.
MT symbol, (v) in the figure is near-end crosstalk noise (NEX)
T) shows a DMT symbol in the section.

In one DMT symbol, 272 (≒
1104 KHz × about 246 μs). Now, the first symbol of the DMT symbol is I
It is assumed that it is synchronized with the head position of the reception timing in the 400 Hz frame of the SDN ping-pong transmission. In this case, which noise section is the n-th symbol in the hyperframe is calculated as follows.

S = (272 * (n-1)) mod 2
760, if {(S <(a-271)) or (S> (a + d + e + f)} then FEXT section (S / N measurement for section B) if {(a + d) <S <(a + d + e-271)} then NEXT section (S / N measurement for section A)

In the above calculation, the first sample of the n-th DMT symbol in the hyperframe is the 272 * (n-1) -th sample counted from the first synchronization position. Therefore, the sample is
272 counting from the start position of the N ping-pong transmission frame
The remainder obtained by dividing * (n-1) by 2760, that is, the S-th sample described above.

Therefore, when the value of S is equal to or less than (a-272), that is, when S <(a-271), or when the value of S exceeds the near-end crosstalk noise (NEXT) section. When the value of the position at the end position is greater than the value obtained by adding the far-end crosstalk noise (FEXT) section length a, the near-end crosstalk noise (NEXT) section length e, and their margin sections d and f, It is determined to be a far-end crosstalk noise (FEXT) section.

Further, the value of S is the near-end crosstalk noise (NE
(XT) section, that is, a value exceeding a value obtained by subtracting the symbol length 272 from the last position a + d + e of the near-end crosstalk noise (NEXT) section, which exceeds a + d, and is determined as a near-end crosstalk noise (NEXT) section. .

A received symbol that does not satisfy any of the above conditions, that is, a received symbol straddling the far-end crosstalk noise (FEXT) section and the near-end crosstalk noise (NEXT) section has a signal-to-noise ratio (S / N). ) Not to be measured. By defining a noise section for each DMT symbol in this way, the signal-to-noise ratio (S / N) for each noise section can be accurately measured.

FIG. 15 shows a configuration for independently setting the transmission capacity for each periodic noise section. The DMT symbol input as received data is demodulated by the demodulator 15-1 and compared with the reference signal 15-2. Further, the received data is applied to a frequency divider 15-3.
Is generated and output to the phase determination unit 15-4. The phase determination unit 15-4 determines the phase of the periodic noise section based on the clock signal, and distinguishes between the far-end crosstalk noise (FEXT) section and the near-end crosstalk noise (NEXT) section according to the determination. Output the signal shown.

An error signal obtained by comparison with the reference signal 15-2 is input to a selector 15-5, and the selector 15-5 receives the error signal according to the signal indicating the distinction of the noise section from the phase determination section 15-4. The error signal is distributed and output to the near-end crosstalk noise section S / N measuring unit 15-6 or the far-end crosstalk noise section S / N measuring unit 15-7.

Then, each S / N measuring device 15-6, 15-
7, based on the signal-to-noise ratio (S / N) measured by
The transmission bit number converter 15-8 outputs the number of allocated bits b _NEXT or b _FEXT in the near-end crosstalk noise section or the far-end crosstalk noise section for each subcarrier. The signal-to-noise ratio (S / N) margin for each periodic noise section is set in the transmission bit number converter 15-8.

With this configuration, the signal-to-noise ratio (S / N) is measured independently in the near-end crosstalk noise section and the far-end crosstalk noise section, and the signal-to-noise ratio (S / N) for each periodic noise section is measured. N) Margin can be set.

Network Timing Reference In the ADSL transmission under a periodic crosstalk noise environment, another approach for estimating a noise period other than the sliding window method described above will be described. In the transmission system on the accommodation station side, an 8 KHz timing reference signal is used to synchronize the transmission systems.

This timing reference signal may be used when the ADSL transmission apparatus (ATU-C) on the accommodation station synchronizes with the broadband network on the accommodation station. In this case, when a transmission device causing periodic noise such as an ISDN ping-pong transmission device is accommodated in the same accommodation station, the same timing reference signal may be used for the transmission device. Accordingly, in such an environment, the period of the periodic noise is synchronized with the transmission timing of the network on the accommodation station side.

On the other hand, Recommendation G. 992.2 specifies a timing signal called “network timing reference”. This signal is transmitted from the ADSL transmission apparatus (ATU-C) on the accommodation station side to the ADS on the subscriber side.
A method of transmitting a phase difference in transmission timing between the L transmission apparatus (ATU-R) and the accommodation station side network is defined.

Burst transmission at the time of power management When a digital subscriber line transmission system employing DMT modulation is incorporated in a personal computer or the like and used, a power management process for suppressing battery consumption of the personal computer is performed. For this reason, a method has been proposed in which transmission is stopped for some DMT symbols among continuous DMT symbols, and a group of DMT symbols is transmitted in a burst manner.

A transmission device built in a personal computer or the like having such a power management function is:
When connected to adjacent telephone lines, it is conceivable that those devices are affected by periodic noise in the burst data transmission cycle.

[0063]

Problems to be Solved by Sliding Window As described above, the sliding window system is
400 which is the transmission timing cycle of the SDN ping-pong transmission
With the start position of the Hz frame and the start position of the transmission timing of the hyperframe matched, a method is set in which each DMT symbol in the hyperframe belongs to a high noise section or a low noise section. is there. Therefore,
It is necessary to perform synchronization by aligning the start position of the hyperframe with the start position of the transmission timing of the ISDN ping-pong transmission.

For this purpose, each ADS on the office side and the subscriber side
The L modem (ATU-C, R) needs to receive a 400 Hz timing signal indicating the frame period of ISDN ping-pong transmission. The optical line terminal performs timing synchronization by supplying a 400 Hz timing signal supplied to an ISDN line termination unit (OCU) to an ADSL modem (ATU-C).

In order to extract the station-side 400 Hz timing on the subscriber side, the station-side ADSL modem (ATU-C) sends the four-point timing to the subscriber-side ADSL modem (ATU-R).
A signal for transmitting the 00 Hz timing is transmitted. This signal is transmitted using the forty-eighth subcarrier.

Further, since each successive DMT symbol has a different transmittable bit rate depending on whether the symbol is in a high noise section or a low noise section, the sliding window type ADSL transceiver has:
In order to absorb the difference in bit rate between successively transmitted DMT symbols, it is necessary to provide a buffer buffer as shown in FIG.

In FIG. 16, the ADSL transceiver encodes user data by the encoding processing section 16-1 and stores the encoded data in the buffer 16-2. The buffer 16-2 has a storage area for the high noise section and a storage area for the low noise section, and the DMT modulator 16-3 stores the code data from the buffer for the high noise section for the DMT symbol in the high noise section. To perform DMT modulation,
For DMT symbols in the low noise section, code data is read from the buffer buffer for the low noise section and DMT modulation is performed.

As described above, the sliding window type ADSL transceiver operates under a periodic noise environment.
In order to perform high-speed and high-reliability digital subscriber line transmission, significant additions and changes in functions and circuit configurations are required. For this reason, it is difficult to convert an existing North American version of Annex A standard ADSL transmission equipment under a periodic noise environment such as Japan where ping-pong transmission is performed, and it is required to provide an economical ADSL transmission service. It is incompatible with the demands of the market.

Problems with Power Management As described above, when a power management function is employed in a personal computer or the like connected to an adjacent telephone line, DMT symbols transmitted in bursts by the power management function are adjacent to each other. Crosstalk to other telephone lines becomes a source of periodic noise, but this cycle is
If it does not match the ping-pong transmission cycle, the existing sliding window type noise section setting method cannot be applied.

In order to apply the sliding window method, there is a method in which the burst transmission timing for transmitting a DMT symbol by power management is made to coincide with the ISDN ping-pong transmission cycle. , ADSL modem (AT
The configuration of U) becomes technically complicated and sophisticated, and it becomes difficult to convert the existing ADSL transmission device of the North American version Annex A recommendation specification, and it does not meet the demand of the market for providing an economical ADSL transmission service.

The present invention realizes high-speed and high-reliability digital subscriber line transmission in a digital subscriber line transmission under a periodic noise environment with a simple configuration having a smaller number of additional circuits and function processing units. With the goal.

[0072]

In order to achieve the above object, a digital subscriber line transmission method according to the present invention comprises the steps of (1) using a telephone line as a transmission line and adapting to a signal-to-noise ratio of the telephone line. In the digital subscriber line transmission method of setting the transmission capacity adaptively, the received data is compared with a reference signal, the signal-to-noise ratio of the telephone line is measured, and the measurement result of the signal-to-noise ratio is used for the telephone line. The phases of the high noise section and the low noise section of the periodic noise are determined, and a section for setting the transmission capacity is selected from the high noise sections based on the determined phase of the noise section, and the signal pair of the selected high noise section is selected. The transmission capacity for all sections is set based on the noise ratio.

Further, the digital subscriber line transmission apparatus of the present invention (2) uses a telephone line as a transmission line and adaptively sets the transmission capacity according to the signal-to-noise ratio of the telephone line. In the transmission device, signal-to-noise ratio measuring means for comparing received data with a reference signal and measuring a signal-to-noise ratio of the telephone line, and measuring a high level of periodic noise in the telephone line based on the measurement result of the signal-to-noise ratio. Phase determining means for determining the phase of the noise section and the low noise section; section selecting means for selecting a section for setting the transmission capacity from the high noise section based on the determined phase of the noise section; and the selected high noise section Transmission capacity setting means for setting the transmission capacity of all sections based on the signal-to-noise ratio.

(3) The digital subscriber line transmission device uses a plurality of subcarriers and a DMT (discrete
A device for transmitting data by multitone modulation, which measures the signal-to-noise ratio of DMT symbols transmitted and received for synchronization in order to estimate the high and low noise periods of periodic noise. Ratio measuring means, signal-to-noise ratio storing means for storing the measurement result measured by the signal-to-noise ratio measuring means over one noise period including at least one high noise section and low noise section; From the signal-to-noise ratio of the DMT symbol stored in the signal-to-noise-ratio storage means, the signal of the noise section used for setting the transmission capacity is obtained based on the phase determination result of the periodic noise based on the noise ratio measurement result. A section selecting means for selecting a noise-to-noise ratio; and a transmission capacity setting means for setting a transmission capacity using only the signal-to-noise ratio of the selected DMT symbol. Set the appropriate bit allocation amount,
It has a configuration in which a signal-to-noise ratio of the DMT symbol transmitted and received for synchronization during communication is measured, and a bit allocation amount for each subcarrier is adaptively changed according to the selected signal-to-noise ratio. .

(4) The signal-to-noise ratio storage means stores the sum of the signal-to-noise ratios for each subcarrier measured by the signal-to-noise ratio measurement means as a signal-to-noise ratio measurement result. It is provided with means for performing.

(5) The signal-to-noise ratio storage means individually stores the signal-to-noise ratio measurement results for each subcarrier measured by the signal-to-noise ratio measurement means, and the transmission capacity setting means Is to set the transmission capacity for each subcarrier based on the measurement result of the signal-to-noise ratio for each subcarrier.

(6) The signal-to-noise ratio storage means includes: a transmission period of burst data transmitted periodically;
The signal-to-noise ratio measurement result is held over a period of the least common multiple of the transmission / reception period of the ping-pong transmission in the ISDN line.

Further, the transmitting and receiving apparatus of the present invention is characterized in that: (7) a second line provided at least in part with the first line for transmitting and receiving signals by switching transmission and reception timing with periodicity. A transmitting / receiving device connected to a line, receiving means for receiving a signal via the second line, calculating a signal-to-noise ratio of the received signal, and setting the signal-to-noise ratio in accordance with the magnitude thereof; A first section having a large noise-to-noise ratio and a second section having a small signal-to-noise ratio, and based on the signal-to-noise ratio belonging to the second section,
And transmission capacity determining means for determining the transmission capacity of the line.

(8) In a transmitting / receiving apparatus connected to a line on which noise having periodic characteristics can be superimposed from outside, a receiving means for receiving a signal via the line, a signal-to-noise ratio of the received signal, Is calculated, and the signal-to-noise ratio is divided into a first section having a large signal-to-noise ratio and a second section having a small signal-to-noise ratio according to the magnitude thereof, and belongs to the second section. Transmission capacity determining means for determining the transmission capacity of the second line based on a signal-to-noise ratio.

[0080]

FIG. 1 shows a configuration for setting a noise section of periodic noise in a digital subscriber line transmission apparatus (ADSL transceiver) according to the present invention. In the figure, a DMT symbol input as received data is demodulated by a demodulator 1-1, and a known DMT symbol transmitted and received for synchronization is compared with a reference signal 1-2.

On the other hand, the received data is also input to the frequency divider 1-4, which divides the frequency of the internal clock 1-3.
A timing signal having a DMT symbol interval adjusted to the phase of the received data is output. Further, the frequency divider 1-5 divides the timing signal and outputs a timing signal indicating the hyperframe interval to the section determiner 1-6. .

The error signal obtained by comparison with the reference signal 1-2 is input to a signal-to-noise ratio (S / N) measuring device 1-7, and is input to a signal-to-noise ratio (S / N) measuring device 1-7.
7 converts the error signal into a signal-to-noise ratio (S / N).
The signal-to-noise ratio (S / N) is stored in the section determiner 1-6, which calculates the signal-to-noise ratio (S / N) of each DMT symbol over the hyperframe interval. Based on this, the high noise section and the low noise section are assigned.

The result of the noise section allocation by the section determiner 1-6 is stored in the phase determiner 1-8. With such a configuration, it is possible to set to which noise section of the periodic noise each DMT symbol in the subsequent hyperframe belongs.

Next, FIG. 2 shows a first embodiment for setting the number of transmission bits to be allocated to each subcarrier based on the determination result of the noise section in the subscriber line transmission apparatus of the present invention. In FIG. 1, a DMT symbol input as received data (for example, synchronization symbol data or predetermined test pattern data is preferably used) is demodulated by a demodulator 1-1 and a reference signal 1-
Compared to 2.

On the other hand, the received data is also input to the frequency divider 1-4, which divides the frequency of the internal clock 1-3.
A timing signal at a DMT symbol interval adjusted to the phase of the received data is output.
The phase determination unit 1-8 in which the noise section is set and stored by the configuration shown in (1) determines the noise section of the received data DMT symbol.

The error signal obtained by comparing the demodulated data from the demodulator 1-1 with the reference signal 1-2 is input to the selector 2-1. According to the noise section judgment result by
A noise section of the DMT symbol error signal used for calculating the number of transmission bits is divided into a noise section not used for calculating the number of transmission bits, and only the DMT symbol error signal of the noise section used for calculating the number of transmission bits is used as a signal pair. Noise ratio (S /
N) Output to the measuring device 2-2.

Then, a signal-to-noise ratio (S / N) measuring device 2
-2 is the D of the noise section selected by the selector 2-1.
The signal-to-noise ratio (S / N) is measured based on the MT symbol error signal, and the transmission bit number converter 2-3 assigns a signal to each subcarrier based on the measured signal-to-noise ratio (S / N). The number of allocated bits bi is calculated.

That is, the transmission bit number converter 2-3 has:
If the signal-to-noise ratio (S / N) is small, the number bi of bits allocated to each subcarrier is reduced, and the signal-to-noise ratio (S / N) is reduced.
If N) is large, the number bi of bits allocated to each subcarrier is increased.

The selector 2-1 selects the DMT symbol error signal in the high noise section and outputs it to the signal-to-noise ratio (S / N) measuring device 2-2. By doing so, the signal-to-noise ratio (S / N) of the high noise section is measured,
The number of allocated bits bi based on the measurement result is set in the bit map on the receiving side, and the signal-to-noise ratio (S
/ N) is set for the DMT symbols in all sections.

The number of transmission bits allocated to each subcarrier of the DMT symbol is reported to the digital subscriber line transmission device on the transmission side, and the digital subscriber line transmission device on the transmission side transmits the number of transmission bits reported from the reception side. The transmission data is set in a bitmap, and transmission data is transmitted by allocating the number of transmission bits to each subcarrier of the DMT symbol according to the bitmap. Therefore, communication quality and reliability in the digital subscriber line transmission device can be improved with a simple configuration.

FIG. 3 shows a second embodiment for setting the number of transmission bits based on the determination result of the noise section in the digital subscriber line transmission apparatus of the present invention. In the figure, the same components as those shown in FIG. 1 or FIG. 2 are denoted by the same reference numerals, and duplicate description will be omitted.

The selector 3-1 is similar to the configuration shown in FIG.
, The result of noise section determination by the phase determination section 1-8 is input, and the signal-to-noise ratio (S /
N) A signal-to-noise ratio (S / N) measurement value from the measuring device 1-7 is input.

The selector 3-1 determines the signal-to-noise ratio (S / S / D) of the DMT symbol in the noise section used for calculating the number of transmission bits according to the result of the noise section determination by the phase determination section 1-8.
N) The measured value is divided into those of the unused noise section, and only the measured value of the signal-to-noise ratio (S / N) of the DMT symbol in the noise section used for calculating the number of transmission bits is converted to the transmission bit number converter 2- Output to 3. Transmission bit number converter 2-3
Is the number of bits bi assigned to each subcarrier based on the signal-to-noise ratio (S / N) measurement value, as in the configuration shown in FIG.
Are calculated respectively.

FIG. 4 shows a first embodiment of a signal-to-noise ratio (S / N) measurement for determining a noise section in the present invention.
As shown in the figure, received data of 256 (# 0 to # 255) subcarriers is input to demodulator 1-1, and demodulator 1-1 outputs demodulated data for each subcarrier.

Each demodulated data from the demodulator 1-1 is compared with a reference signal 1-2 and converted into an error signal, and each error signal is converted into a signal-to-noise ratio (S / N) measuring instrument 1-7. Is input to The signal-to-noise ratio (S / N) measuring device 1-7 converts the error signal into a signal-to-noise ratio (S / N) for each subcarrier.

Signal-to-noise ratio (S / N) Signal-to-noise ratio (S / N) for each subcarrier output from measuring device 1-7
Are added by the adder 4-1 and the sum is stored in the section determiner 4-2. The section determiner 4-2 sorts the signal-to-noise ratio (S / N) of the DMT symbol into a high-noise section and a low-noise section based on the sum of the signal-to-noise ratio (S / N) of each subcarrier. I do.

As described above, the signal-to-noise ratio (S / N) of each subcarrier is used as the signal-to-noise ratio (S / N) of each DMT symbol, so that the signal-to-noise ratio (S / N) is obtained. In the calculation process of the noise section determination based on N), the number of calculation target elements can be significantly reduced.

FIG. 5 shows a second embodiment of the signal-to-noise ratio (S / N) measurement for determining a noise section in the present invention.
The difference from the first embodiment shown in FIG. 4 is that the output data of the signal-to-noise ratio (S / N) measuring unit 1-7 is sent to the section determining unit 5-1 for each subcarrier. It was done.

Here, the demodulated data compared with the reference signal 1-2 is converted into an error signal for each subcarrier, and a signal-to-noise ratio (S / N) measuring unit 1-7 converts the demodulated data for each subcarrier. Until the signal is converted to a signal-to-noise ratio (S / N), it is the same as in the first embodiment.

Thereafter, the converted signal-to-noise ratio (S / N) for each subcarrier is stored in the section determiner 5-1 for each subcarrier. , The signal-to-noise ratio (S / N) is individually determined for each subcarrier, and a high-noise section and a low-noise section are assigned to each subcarrier.

In this embodiment, an extremely large number of storage means such as registers are required for setting the noise section. However, as shown in FIG.
The bandwidth used for SL transmission does not completely overlap, and by setting the section for setting the transmission capacity for each subcarrier, it is possible to set a larger transmission capacity while maintaining reliability. Become.

In particular, the digital subscriber line transmission device has a D
Often configured as functional means by software processing on SP (Digital Signal Processor) chip,
This embodiment is very effective when the device is configured by mounting a large capacity memory.

The signal-to-noise ratio (S / N) of the low-noise section (first section) and the signal-to-noise ratio (S / N) of the high-noise section (second section) are calculated as follows. The number of known symbols belonging to a high noise section that may exist in a hyperframe may be divided as a threshold, an average value for a plurality of frames or a predetermined symbol, or a predetermined value may be divided as a threshold. Based on the information of N, the signal-to-noise ratios (S / N) stored once in a memory or the like may be separated by the determination that those corresponding to N in the ascending order belong to the high noise section.

On the other hand, based on the information on the number M of known symbols belonging to the low noise section (M + N = 1 the number of symbols in one hyperframe), M symbols in order from the one with the largest signal-to-noise ratio (S / N) are obtained. The removed remainder may be determined as a signal-to-noise ratio (S / N) belonging to a high noise section and separated.

A digital subscriber line transmission device connected to an adjacent telephone line is used by being built in or connected to an information communication device such as a personal computer. When a DMT symbol is transmitted periodically to an adjacent telephone line in a burst manner, it is affected by periodic noise having a period of the least common multiple of a transmission period of the burst data and a noise period of ping-pong transmission of another subscriber line. .

For such periodic noise, the measurement result of the signal-to-noise ratio (S / N) over the period of the least common multiple of the transmission period of the burst data and the transmission / reception timing period of the ping-pong transmission of the telephone line is shown. , And a signal to noise ratio (S / N) for a cycle of the least common multiple.
By setting the noise interval based on the above, the optimal number of transmission bits is allocated to the periodic noise caused by burst data transmission, as in the case of the periodic noise caused by ping-pong transmission, and high-quality data transmission is performed. It is possible to do.

The transmission cycle of the burst data in the other telephone line is considered to be substantially the same as the burst data transmission cycle of the information communication device having the power management function in the own device. The period of the least common multiple of the transmission period of burst data in the own device and the transmission / reception period of ping-pong transmission in the ISDN line, and the signal-to-noise ratio measurement result over the period is stored in storage means such as a register. Can be.

With such a configuration, when the communication line of the digital subscriber line transmission device having the same power management function as that of the own device is adjacent to the digital subscriber line transmission device, the mode is shifted to the power management mode on the adjacent communication line on the way. In the above, each noise section corresponding to the signal-to-noise ratio (S / N) is set for periodic noise in which periodic noise of ping-pong transmission on the ISDN line and burst periodic noise of the digital subscriber line are mixed. Becomes possible.

Further, in the digital subscriber line transmission device not synchronized with the timing of the station side network, by notifying the network timing reference information from the station side device to the subscriber side device, the subscriber side device becomes:
Recognize the phase difference between the communication timing of digital subscriber line transmission data and the timing of the office network,
It is also possible to adopt a configuration in which the period of periodic noise synchronized with the timing of the station network is estimated.

[0110]

As described above, according to the present invention,
In a digital subscriber line transmission under a periodic crosstalk noise environment, unlike the conventional transceiver of the Annex C recommendation specification, the transmission capacity of the entire section is determined based on the signal-to-noise ratio (S / N) measurement result in the high noise section. By setting, high-speed data transmission with high reliability can be realized with a simple configuration.

Further, since the transmission capacity is set according to the periodic noise environment, even if the signal-to-noise ratio (S / N) is deteriorated due to the fluctuation of the periodic noise, the signal-to-noise ratio (S / N) is reduced.
Since the transmission capacity is adaptively set according to N), the quality and reliability of communication by ADSL transmission can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration for setting a noise section of periodic noise according to the present invention.

FIG. 2 is a diagram illustrating a first embodiment of setting the number of transmission bits to be allocated based on a determination result of a noise section according to the present invention.

FIG. 3 is a diagram illustrating a second embodiment of setting the number of transmission bits to be allocated based on the determination result of a noise section according to the present invention.

FIG. 4 is a diagram illustrating a first embodiment of a signal-to-noise ratio (S / N) measurement for determining a noise section according to the present invention;

FIG. 5 is a diagram illustrating a second embodiment of a signal-to-noise ratio (S / N) measurement for determining a noise section according to the present invention.

FIG. 6 is a diagram showing a model of an accommodation station and a subscriber house connected by an ADSL transmission system.

FIG. 7 is a diagram illustrating frequency bands of a DMT modulation method and a ping-pong transmission method.

FIG. 8 is an explanatory diagram of periodic noise from a ping-pong transmission line.

FIG. 9 is a diagram showing a quad cable in which a plurality of telephone lines are bundled.

FIG. 10 is a diagram illustrating an example of the number of bits allocated to each subcarrier according to S / N according to a bitmap.

FIG. 11 is a diagram illustrating a configuration of a main part of an ADSL transmission device using a DMT modulation method.

FIG. 12 is a diagram showing a configuration for measuring a signal-to-noise ratio (S / N) in a conventional ADSL transceiver.

FIG. 13: ADS by sliding window method
FIG. 3 is an explanatory diagram of L transmission.

FIG. 14 is an explanatory diagram of a method of determining a noise section to which each DMT symbol belongs.

FIG. 15 is a diagram showing a conventional configuration for independently setting a transmission capacity for each noise section.

FIG. 16 is a diagram illustrating a configuration of a transmission unit including a conventional buffer.

[Explanation of symbols]

 1-1 Decoder 1-2 Reference signal 1-3 Internal clock 1-4 Divider 1-5 Divider 1-6 Section determiner 1-7 Signal-to-noise ratio (S / N) measuring instrument 1 8 Phase Determination Unit 2-1 Selector 2-2 Signal-to-Noise Ratio (S / N) Measuring Device 2-3 Transmission Bit Number Converter 3-1 Selector 4-1 Adder 4-2 Interval Judgment Unit 5-1 Interval Judgment vessel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04Q 3/42 104 H04L 11/02 E 5K101 (72) Inventor Yutaka Awata 2-chome Shin-Yokohama, Kohoku-ku, Yokohama, Kanagawa Prefecture No. 3-9 Fujitsu Digital Technology Co., Ltd. In-house (72) Inventor Koji Tokiwa 2-3-9 Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa Fujitsu Digital Technology Co., Ltd. In-house (72) Inventor Atsushi Manabe, Kohoku, Yokohama-shi, Kanagawa 2-3-9 Shin-Yokohama-ku Fujitsu Digital Technology Co., Ltd. In-house (72) Inventor Nobukazu Koizumi 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa F-term within Fujitsu Limited 5K004 AA08 JD04 JG00 5K022 AA21 AA42 5K030 HC02 HC04 JL08 MB04 5K050 AA01 BB01 BB02 BB03 BB06 B B15 DD21 GG10 5K051 AA02 BB02 CC01 CC02 CC04 DD07 GG15 HH01 JJ10 5K101 LL01 LL02 LL03 MM05 SS03

Claims (8)

[Claims] 1. A digital subscriber line transmission method in which a telephone line is used as a transmission line and a transmission capacity is adaptively set in accordance with a signal-to-noise ratio of the telephone line. The signal-to-noise ratio of the telephone line is measured, the phases of the high noise section and the low noise section of the periodic noise in the telephone line are determined from the measurement result of the signal-to-noise ratio, and based on the determined phase of the noise section. Selecting a section for setting the transmission capacity from the high noise section, and setting the transmission capacity for the entire section based on the signal-to-noise ratio of the selected high noise section. Line transmission method. 2. A digital subscriber line transmission apparatus which uses a telephone line as a transmission line and adaptively sets a transmission capacity in accordance with a signal-to-noise ratio of the telephone line. Signal-to-noise ratio measuring means for measuring a signal-to-noise ratio of a telephone line; and phase determining means for determining a phase of a high-noise section and a low-noise section of periodic noise in the telephone line from the measurement result of the signal-to-noise ratio. Section selecting means for selecting a section for setting the transmission capacity from the high noise sections based on the determined phase of the noise section; and selecting the transmission capacity of the entire section based on the signal-to-noise ratio of the selected high noise section. A digital subscriber line transmission device comprising: a transmission capacity setting means for setting. 3. The digital subscriber line transmission device uses a plurality of subcarriers and a DMT (discrete multiton).
e) A device for transmitting data by modulation, which measures the signal-to-noise ratio of DMT symbols transmitted and received for synchronization in order to estimate the interval between high and low noise periods of periodic noise. Ratio measuring means; signal-to-noise ratio storing means for storing a measurement result measured by the signal-to-noise ratio measuring means over one noise period including at least one high noise section and low noise section; According to the phase determination result of the periodic noise based on the measurement result of the noise ratio, the D stored in the signal-to-noise ratio storage unit is determined.
A section selecting means for selecting a signal-to-noise ratio of a noise section used for setting a transmission capacity from a signal-to-noise ratio of an MT symbol; and a transmission capacity using only the signal-to-noise ratio of the selected DMT symbol. Transmission capacity setting means for setting, before starting communication, setting a bit allocation amount for each subcarrier, measuring a signal-to-noise ratio of the DMT symbol transmitted and received for synchronization during communication, and 3. The digital subscriber line transmission device according to claim 2, further comprising a configuration for adaptively changing a bit allocation amount for each subcarrier according to the signal-to-noise ratio. 4. The signal-to-noise ratio storage means includes means for storing a sum of signal-to-noise ratios for each subcarrier measured by the signal-to-noise ratio measurement means as a signal-to-noise ratio measurement result. 4. The digital subscriber line transmission device according to claim 3, further comprising: 5. The signal-to-noise ratio storage means individually stores the signal-to-noise ratio measurement results for each subcarrier measured by the signal-to-noise ratio measurement means, and the transmission capacity setting means 4. The subscriber line transmission device according to claim 3, wherein a transmission capacity is set for each subcarrier based on a measurement result of a signal-to-noise ratio for each subcarrier. 6. The signal-to-noise ratio storage means measures a signal-to-noise ratio over a period of a least common multiple of a transmission period of burst data transmitted periodically and a transmission / reception period of ping-pong transmission in an ISDN line. 6. The digital subscriber line transmission device according to claim 3, wherein the result is retained. 7. A transmission / reception device connected to a second line provided at least in part with a first line for transmitting and receiving signals by switching transmission / reception timing with periodicity, Receiving means for receiving a signal via a second line; calculating a signal-to-noise ratio of the received signal; and calculating the signal-to-noise ratio according to the magnitude thereof in a first section having a large signal-to-noise ratio. And a second section having a small signal-to-noise ratio.
And a transmission capacity determining means for determining a transmission capacity of the second line based on a signal-to-noise ratio belonging to the category. 8. A transmitting / receiving apparatus connected to a line on which noise having periodic characteristics can be superimposed from outside, a receiving means for receiving a signal via the line, and calculating a signal-to-noise ratio of the received signal. , The signal-to-noise ratio is divided into a first section having a large signal-to-noise ratio and a second section having a small signal-to-noise ratio according to the magnitude thereof.
And a transmission capacity determining means for determining a transmission capacity of the second line based on a signal-to-noise ratio belonging to the category.