JP2001177495A - Multi-carrier transmission system and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain bit distribution of a DMT system where a performance margin is a maximum at a given transmission speed in the case that transmission power is revised between e.g. a NEXT state and a FEXT state under a noise environment having the NEXT state and the FEXT state where a noise amount is periodically changed. SOLUTION: Sets 11, 12 of SNR values of a transmission channel that are periodically changed due to a leaked noise are regarded as a set 13 of the SNR values without temporal change in a single transmission channel, and bits of each carrier in a multi-carrier consisting bit distributions of the carriers are distributed depending on the set 13 of the single signal to noise ratio and a preset maximum transmission power corresponding to the noise environment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicarrier transmission system and method, and more particularly to a DMT (Discrete M
The present invention relates to a multicarrier transmission system known as a multi-tone modulation system and a method thereof.

[0002]

2. Description of the Related Art An example of a conventional multi-carrier transmission system of the DMT system is disclosed in U.S. Pat.
There is a technique disclosed in Japanese Patent Application No. 79,447.

ADSL used in such a DMT system
As an (Asymmetric Digital Subscriber Line) device, QAM (Quadrature Amplitude M
odulation), and the modulated carrier is multiplexed using IFFT (Inverse Fast Fourier Transform) and transmitted. On the receiving side,
Each carrier is extracted from the multiplexed signal using FFT and demodulated into a QAM-modulated signal.

In this case, an SNR (Signal to Noise) of each carrier is used to allocate bits to each of a plurality of carriers.
Ratio: signal-to-noise ratio), and the measured SN
The bit allocation is determined according to R. For example, as shown at 15 in FIG. 13, the frequency on the horizontal axis is each carrier used for transmission, and the frequency width of each carrier is 4.3125 KHz and the total number is 256. Is not limited. At the time of data transmission, these carriers are respectively modulated. At this time, the SNR value is evaluated, and the bit allocation is obtained according to the evaluated SNR. In the evaluation of the SNR in this case, each SNR value is obtained in the frequency band of each carrier.

[0005] Each carrier transmits the number of bits according to each bit distribution thus determined. The number of bits satisfies a given transmission rate and a performance margin based on the evaluated SNR value.
Is calculated such that is maximized.

In the conventional DMT ADSL technology,
As an example of a method of calculating the bit allocation so that a given transmission rate becomes the bit allocation having the maximum performance margin, the above-mentioned US Pat.
No. 9,447. FIG. 13 shows an example of this bit allocation method. Given a transmission rate (bit rate) to be transmitted, the number of bits is allocated to each carrier based on the measured SNR value (15) of the transmission line so that each carrier has a maximum performance margin (16). It is.

[0007]

SUMMARY OF THE INVENTION This DMT type AD
In SL technology, in Japan, T
CM (Time Compression Multiplexing) method ISDN
, And the resulting periodic crosstalk is a significant noise in the signal to ADSL. AD using FIG.
Crosstalk that occurs when the SL line and the TCM-ISDN line coexist on the same cable will be described. FIG. 14 shows a case where an ADSL line is used for the downlink (ATU-C (ADSL
Termination Unit-Center side to ATU-R (AD
The crosstalk generated by the ATU-R due to the data transmission through the TCM-ISDN line during the data transmission in the direction of the SL Termination Unit-Remote side) is shown.

[0008] As shown in FIG. 14, when data is transmitted in the down direction on the ADSL line, the TCM-I
If the SDN line is also transmitting data in the down direction, far-end cross-talk (FEXT) occurs. Also, when the TCM-ISDN line is transmitting data in the reverse direction while transmitting data in the downstream direction on the ADSL line, near-end cross-talk (NEXT) occurs. . TC
In the M system ISDN line, data transmission is performed alternately in the upstream and downstream directions.
Affected by the ping-pong data transmission of the SDN line,
Near-end crosstalk and far-end crosstalk occur periodically.

When communication is performed using the conventional ADSL technology,
Due to this periodic crosstalk noise, a lot of errors occur at the time of near-end crosstalk (NEXT) where the noise state is poor. Further, when the transmission speed is set in accordance with the communication under the NEXT noise, the transmission speed is greatly reduced. Under the situation of crosstalk noise from the ISDN, a so-called dual bitmap method is considered to improve the communication performance of the ADSL device. In this method, the ADSL device has two types of bitmaps (bit allocation), and switches the bitmap in synchronization with the cycle of crosstalk noise to change the communication speed. In far end crosstalk (FEXT), the communication speed is increased because the noise is small, and in NEXT, the communication speed is reduced because it is large.

However, in this dual bit map system, since there are a plurality of SNR values of the transmission line, it is not possible to perform bit allocation by a conventional method from a bit rate (transmission speed) given from an upper layer. That is, the measured S
It is necessary to distribute a given bit rate to two types of transmission rates and further distribute the number of bits to each carrier so that each carrier has the maximum performance margin based on the NR value.

Due to the above problems, when the amount of noise in the line changes periodically and a plurality of transmission speeds are switched in synchronization with the change in the noise, the conventional bit allocation method obtains the maximum performance margin. Can not do.

[0012] For this purpose, a technique related to a bit allocation method that solves the above-mentioned problem by realizing a given transmission rate and maximizing a performance margin in accordance with a plurality of SNR values evaluated at different times. Has been proposed by the present inventor in Japanese Patent Application No. 10-366982. In this technology, the signal at the time of NEXT is IS
In order to cause near-end crosstalk to the DN, it is required to reduce the near-end crosstalk by reducing the maximum transmission power only at the time of NEXT. That is, in the above technique, FEXT
And the maximum transmission power at the time of NEXT is fixed, so that there is a problem that an ADSL signal at the time of NEXT becomes noise to ISDN. Therefore, in order to eliminate the influence on ISDN, it is necessary to be able to change the transmission power between NEXT and FEXT so as to be different.

An object of the present invention is to provide a multicarrier transmission system having a bit allocation method for maximizing a performance margin when the transmission power between NEXT and FEXT can be changed so as to be different, and a multicarrier transmission system therefor. Is to provide a way.

[0014]

According to the present invention, data transmission by the multi-carrier transmission method is performed between the first and second communication stations under a plurality of kinds of periodically changing noise environments. A multi-carrier transmission system, comprising: evaluating a signal-to-noise ratio of each carrier of a multi-carrier at different times respectively corresponding to the plurality of types of noise environments to obtain a plurality of types of signal-to-noise ratio pairs. The noise ratio evaluation means and the plurality of sets of signal-to-noise ratios are set to one set of signal-to-noise ratios evaluated at different frequencies at the same time that do not change periodically. Multi-carrier transmission, comprising: bit allocation means for allocating bits for each carrier according to a set of noise ratios and a maximum transmission power value set in advance corresponding to each of the noise environments. The stem can be obtained.

When the noise environment is of two types and changes at a predetermined period, the signal-to-noise ratio evaluation means calculates a corresponding signal-to-noise ratio set in each of the two types of noise environment. Wherein the bit allocation means is configured to perform the bit allocation using the two sets of signal-to-noise ratios as the one set of signal-to-noise ratios. . Further, the bit allocation means is configured to perform the bit allocation according to each value of the one set of signal-to-noise ratios and the maximum transmission power value of each carrier.

According to the present invention, there is provided a multi-carrier transmission system for performing data transmission by a multi-carrier transmission method between first and second communication stations under a plurality of periodically changing noise environments. Signal-to-noise ratio evaluation means for evaluating the signal-to-noise ratio of each carrier of the multi-carrier at different times respectively corresponding to the plurality of types of noise environments to obtain a plurality of types of signal-to-noise ratio sets, According to each value of the plurality of types of signal-to-noise ratio sets and the maximum transmission power value set in advance corresponding to the noise environment,
Bit allocation means for allocating bits to each carrier so as to realize a given transmission rate and maximize a performance margin.

If the noise environment is of two types and changes at a predetermined interval, the signal-to-noise ratio evaluation means sets a corresponding signal-to-noise ratio set in each of the two types of noise environment. The bit allocation means is configured to perform the bit allocation according to each value of the two sets of the signal-to-noise ratios. Further, the bit allocation means is configured to perform the bit allocation according to each value of the two types of signal-to-noise ratio sets, the total transmission power limit value, and the maximum transmission power value.

In the case of data transmission from the first communication station to the second communication station, the first communication station transmits a plurality of predetermined transmission rates to the second communication station. Means, the second communication station has the signal-to-noise ratio evaluation means and the bit allocation means, and the bit allocation means comprises the plurality of transmission rates transmitted from the first communication station. Means for calculating a margin in data transmission based on the set of the signal-to-noise ratio, means for selecting an optimum transmission rate from the plurality of transmission rates based on the calculated margin, and the selected Means for calculating a bit allocation of each carrier according to a transmission rate. Further, the second communication station further includes means for transmitting the bit allocation to the first communication station, and the first communication station performs data transmission to the second communication station according to the bit allocation. It is characterized by the following. Further, the above 2
The noise source of the kind of noise is present on the same cable as a communication line between the first and second communication stations, and the two kinds of noise environment are a first noise environment and a noise environment. The second noise environment is characterized in that the noise state is worse than the first noise environment. The two kinds of noise are caused by far-end crosstalk and near-end crosstalk, and data transmission between the first and second communication stations is performed by a digital subscriber line. And

According to the present invention, there is provided a multi-carrier transmission method for performing data transmission by a multi-carrier transmission method between first and second communication stations under a plurality of periodically changing noise environments. A signal-to-noise ratio evaluation step of evaluating the signal-to-noise ratio of each carrier of the multicarrier at different times respectively corresponding to the plurality of types of noise environments to obtain a plurality of types of signal-to-noise ratio sets; The plurality of types of signal-to-noise ratio sets are one set of signal-to-noise ratios evaluated at different frequencies at the same time that do not change periodically. A bit allocation step of allocating bits for each carrier according to a maximum transmission power value set in advance corresponding to a noise environment.

When the noise environment is of two types and changes at a predetermined cycle, the signal-to-noise ratio evaluation step calculates a corresponding signal-to-noise ratio set in each of the two types of noise environment. The bit allocation step is characterized in that the bit allocation is performed by using these two sets of signal-to-noise ratios as the one set of signal-to-noise ratios. In the bit allocation step, the bit allocation is performed in accordance with each value of the one set of signal-to-noise ratios and the maximum power value of each carrier.

According to the present invention, there is provided a multi-carrier transmission method for performing data transmission by a multi-carrier transmission method between first and second communication stations in a plurality of periodically changing noise environments. A signal-to-noise ratio evaluation step of evaluating the signal-to-noise ratio of each carrier of the multicarrier at different times respectively corresponding to the plurality of types of noise environments to obtain a plurality of types of signal-to-noise ratio sets; According to each value of the plurality of types of signal-to-noise ratio sets and the maximum transmission power value set in advance corresponding to the noise environment, a given transmission rate is realized and a performance margin is maximized. And a bit allocation step of allocating bits to each carrier as described above.

If the noise environment is of two types and changes at a predetermined period, the signal-to-noise ratio evaluation step calculates a corresponding signal-to-noise ratio set in each of the two types of noise environment. The bit allocation step is characterized in that the bit allocation is performed in accordance with each value of the two sets of signal-to-noise ratios. In the bit allocation step, the bit allocation is performed in accordance with each value of the two types of signal-to-noise ratio sets, the total transmission power limit value, and the maximum power value.

Further, the method further includes a step of transmitting a plurality of predetermined transmission rates from the first communication station to the second communication station, and the bit allocation step executed in the second communication station includes Calculating a margin in data transmission based on the set of the plurality of transmission rates and the signal-to-noise ratio transmitted from the first communication station; and Selecting the optimum transmission rate from the above transmission rates, and calculating the bit allocation of each carrier according to the selected transmission rate. And
Sending the bit allocation from the second communication station to the first communication station, and performing data transmission to the second communication station according to the bit allocation in the first communication station. It is characterized by including. Also,
The noise sources of the two types of noise are characterized in that they are present on the same cable as a communication line between the first and second communication stations, and the environment of the two types of noises is the first type. The noise environment and the second noise environment having a worse noise state than the first noise environment. The two types of noise are caused by far-end crosstalk and near-end crosstalk, and data transmission between the first and second communication stations is performed by a digital subscriber line. And

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. Referring to FIG. 1, an ATU-C100 as a central office and an ATU-R200 as a terminal.
, Respectively, and transmission between them is performed by a digital subscriber line. In this example, ATC
The determination of the transmission rate in the downlink direction from the C-C to the ATU-R will be described. The downstream transmission rate transmitting section 1 transmits downstream transmission rates r1 to r4 specified by an upper layer (not shown).
(In this example, four types of speeds) are transmitted to the ATU-R.

The selected transmission speed storage unit 9 is an ATU-R200
The bit and power distribution table 10 stores the bit and power distribution table transmitted from the ATU-R 200. In accordance with the bit and power distribution table 10, data transmission in the downlink direction is performed while bit distribution and power distribution (mapping) of each carrier are performed.

The above is the function of the ATU-C100.
The functions of the ATU-R200 are as follows. Downward direction S
The NR evaluation unit 2 evaluates the SNR of the transmission line at the time of downlink transmission, and here, as an example, the TCM-I
A case will be described in which the SDN exists in the same cable as the ADSL and the crosstalk noise changes periodically. FIG. 2 is a diagram for explaining crosstalk noise from TCM-ISDN to ADSL. Figure (A) shows the transmission direction of TCM-ISDN data, and (B) shows the ADSL (A
4 shows crosstalk noise generated for TU-R).

At the time of upstream transmission of ISDN, ATU-
Near-end crosstalk NEXT occurs in R, and at the time of downlink transmission,
Far end crosstalk FEXT occurs. Therefore, the down direction SN
The R evaluation unit 2 evaluates (calculates) each set of SNR values at each carrier frequency when two types of noise, NEXT and FEXT, are present, and determines the corresponding set of SNRs as NEX.
The T SNR and the FEXT SNR are respectively held in the holding units 3. FIG. 2B shows a case where the time intervals of crosstalk noise generated by TCM-ISDN are equal.
(C) shows an example in the case of unequal. FIG. 2 (C)
, F and n indicate the time ratio of the period during which noise occurs, and in this case, the period f during which FEXT occurs is shorter than the period n during which NEXT occurs.

The rate adaptation algorithm section 8 has a performance margin calculation section 4, a transmission rate selection section 5, and a bit and power distribution table transmission section 6. The performance margin calculator 4 calculates the ATU-C 100 based on the SNR value 3 of the line evaluated by the downlink SNR evaluator 2.
When each of the four transmitted transmission speeds is realized, the maximum performance margin value is calculated for each of the four types. The transmission speed selection unit 5 selects a value that allows transmission and has the highest transmission speed from these four types of performance margin values. Bit and power distribution table transmitter 6
Transmits a bit for transmitting at the selected transmission rate rn, and a power distribution table to the ATU-C 100. The bit and the power distribution table 7 have an SNR value that periodically changes during NEXT and FEXT. This is calculated for each set.

FIG. 3 is a flowchart showing the operation of the block shown in FIG. The four transmission rates provided by the upper layer are transmitted from ATU-C to ATU-R (step A1). For example, four types of transmission rates from r1 to r4 bit / s are used together with other parameters to make ATU-
Sent from C to ATU-R. The ATU-R side is used when the amount of noise changes periodically, especially in this case, the TCM-IS.
If DN is in the same cable, ISDN to A
NEXT and FEXT are generated for DSL. The downlink SNR evaluator 2 evaluates the SNR value of each frequency in both cases, and calculates the NEXT SNR, F
It is held in EXT SNR3. In FIG. 4, 11 and 12 indicate the SNR values of the respective evaluated frequencies, 11 indicates the SNR value when FEXT occurs, and 12 indicates the SNR value when NEXT occurs.

The performance margin calculator 4 calculates the SN
When four transmitted transmission speeds are realized based on the SNR value 3 of the line evaluated by the R evaluation unit 2, four types of bit allocation for setting the performance margin to the maximum value are calculated (step A2). FIG. 4 shows the calculation method.
The SNR values at the time of NEXT and FEXT shown in 11 and 12 are used as SNR values evaluated up to a double frequency without periodically changing, as shown at 13 in FIG.

Thus, when calculating the performance margin of the line, the frequency used is doubled and the SNR
For a line that does not change with time such that the value is 13, the transmission rate is doubled and the transmission rate is doubled.
The bit allocation method is used assuming that two carriers are used. In this example, the power of each carrier is limited, and the upper limit of the power of each carrier is set to Emask.
Here, the upper limit E of the total transmission power usable for data transmission.
The target is (the total number of carriers) × (the power upper limit Emask of each carrier), and the transmission power usable for each carrier is not limited by the upper limit of the total transmission power.

The transmission rate selector 5 calculates the four types of performance margin values calculated, for example, step A in FIG.
As shown in FIG. 2, a transmittable transmission speed having the highest transmission speed and a non-negative margin is selected from the four types of margin values m1 to m4 (step A3). If all margins are negative for all transmission rates, it indicates that all four transmission rates cannot be transmitted, and the ATU-R transmits a full transmission rate failure output to ATU-C (step A).
6). If any one of the transmission rates can be selected, the selected transmission rate and its performance margin are transmitted to the ATU-C (step A4).

The bit and power distribution table transmitting section 6 transmits a bit and power distribution table for performing transmission at the selected transmission rate (step A5). This table shows an SN that periodically changes between NEXT and FEXT.
It is necessary to calculate for each R value. From the bits and power distribution table 7 calculated when 512 carriers are used, a portion corresponding to the first 256 carriers is a FEXT table, and a portion corresponding to the second 256 carriers is NEXT.
Use as a table for Each calculated table is transmitted from the ATU-R to the ATU-C.

Further, in the case of FIG. 2C, since the change period of the noise in the transmission line is not equal, when a plurality of SNR values are converted into a single SNR value, only the ratios f and n of the time intervals are used. Increase the frequency of the SNR value. FIG. 5 shows a method of calculating the bit allocation. As shown in FIG. 5A, the SNR at the time of NEXT and FEXT shown in FIGS.
The SNR value at the time of FEXT is f-fold, and the SNR value at the time of NEXT is expanded to n-times frequency. The transmission speed is given by multiplying the value of the transmission speed by f + n, and (f + n)
Assuming that the line uses × 256 carriers, FIG.
A bit allocation method as shown in (B) is used.

The bit and power distribution table used for data transmission is the table used at the time of FEXT,
A bit and power distribution table allocated to any one set of carriers using the SNR value at the time of FEXT is used.
Similarly, the table at the time of NEXT also has the SN at the time of NEXT.
A table allocated to any one set of carriers using the R value is used. For example, (3 + 2) × 256 = 128
In the case of FIG. 5 which is calculated assuming that the carrier of 0 is used, 0 to 25 are obtained from the bit and power distribution table (FIG. 5B).
The part corresponding to the carrier of No. 5 is a FEXT table,
A portion corresponding to carriers 68 to 1023 is used as a NEXT table.

Each of the calculated tables is transmitted from the ATU-R to the ATU-C, held in the bit and power distribution table 10, and used for the bit and power distribution (mapping) at the time of downlink transmission. .

FIG. 6 is a flowchart showing a method of calculating a performance margin in step A2 of FIG. First, let the maximum value of the transmission power of each carrier i at the time of FEXT be Emaxi, F (a value preset for each system),
Further, the maximum value of the transmission power of each carrier i at the time of NEXT is set as Emaxi, N (a value preset for each system), and SNR ′ (i) obtained by multiplying these by SNR (i) is obtained (step A7). . And this calculated SNR
'(I) are rearranged in descending order (step A8), and the numbers are rearranged so that SNR' (i) ≧ SNR '(i + 1). The total number of carriers N
The above inequality applies to all numbers up to the smaller i.

Next, k = 1, γmax = −∞, count
= 0 (step A9). k is a counter, γmax is the current maximum possible system performance margin, co
unt is the number of carriers used to achieve γmax. Then, γ (k) is calculated (step A1).
0).

The equation for calculating γ (k) is:

(Equation 1) Given by

Γ (k) is the maximum system performance margin achievable in one carrier symbol. At this time, the target achievement speed is Btarget, the total effective coding gain is γeff, the desired bit error rate is 10 ^-7 , k best carriers are used, and the current geometric average SNR is

(Equation 2) Given by

The current transmission power Ei used by the i-th carrier is given by Ei = Emaxi, F (i∈F) Ei = Emaxi, N (i∈N) Here, the total input power Etarget limited by the transmitter is Etarget, F = kF · Emaxi, F (i∈F) Etarget, N = kN · Emaxi, N (i∈N), where kF and kN are This is the number of carriers used in FEXT and NEXT.

Emaxi is the maximum power that the i-th carrier can transmit, which is determined by the transmission power mask.
In this case, the maximum transmittable power of each carrier is not limited by the total input power Etarget.

When γ (k)> γmax, γ
max = γ (k) and count = k (step A1)
1, A12). If k is not N, k = k + 1 (step A14), and the process returns to step A10. here,
γmax represents the maximum possible system performance margin for a given system parameter, co
unt is the best number of carriers used to achieve γmax.

FIG. 7 is a flowchart showing a method of calculating the bit allocation table in step A5 of FIG. Using the above-mentioned γmax and count, the initial bit distribution table {b′i} is calculated as follows: bi = floor [log2 ＋ 1 + Emaxi, F · SNR (i) / Γmax｝] (i∈F) bi = floor [log2 ｛ 1 + Emaxi, N · SNR (i) / {max}] (i∈N). floor indicates truncation,
The truncated value after the decimal point is diffi: diffi = bi−log2 ｛1 + Emaxi, F · SNR (i) / Γmax｝ (i∈F) diffi = bi−log2 ｛1 + Emaxi, N · SNR (i) / Γmax｝ (I∈N) is calculated (step A15).

Where Γmax is

(Equation 3) Given by Pe is the bit error rate, Ne
Is the number of nearest points of the input signal constellation, and the Q function is

(Equation 4) Is defined by

Then, Btotal is calculated (step A).
16). This Btotal is the total number of bits that the current bit allocation table supports in one multicarrier symbol, and Btotal = Σb′i. Here, Σ is the sum of i = 0 to N−1.

Then, when Btotal <Btarget,
1 bit from current bit allocation table, minimum diffi
The bit distribution table {b'i} of the carrier having the value is set to 1
Increase the bits, diffi = diffi + 1, Btotal = Bto
tal + 1 is set (steps A17 and A18). This is B
Repeat until total = Btarget.

FIG. 8 is a flowchart showing a method of calculating the power distribution table in step A5 of FIG. First, based on a given bit distribution table {b'i}, Pe
(I) = input power ´E′i such that Pe, i, target
Is assigned (step A19). Where Pe
(I) is the error probability of the i-th carrier, Pe, i, target
Is the target error probability of the i-th carrier. In addition, ｛E
'I' is the total transmission power used by the i-th carrier. The current total transmission power Etotal is calculated as Etotal, F = ΣEi (i∈F) Etotal, N = ΣEi (i∈N) (step A20). Where Σ is i =
0 to N−1.

Then, the final power distribution {E'i} is readjusted (step A21). This readjustment is (Etarget, F
/ Etotal, F) · Ei and Emaxi, F (i∈F), or a small value between (Etarget, N / Etotal, N) · Ei and Emaxi, N (i∈N) To E
i. The initial bit and power allocation table in this system will be given by {b'i} and {E'i}.

Next, another embodiment of the present invention will be described. In the above embodiment, the transmission power of each carrier is limited, but in this example, the case where the total transmission power is limited will be described. Also in the present embodiment, the block diagram in FIG. 1 and the flowchart showing the operation in FIG. 3 are the same. The four transmission rates provided by the upper layer are transmitted from ATU-C to ATU-R (step A1). For example, from r1 to r
Four transmission rates of 4 bit / s are transmitted from the ATU-C to the ATU-R together with other parameters.

On the ATU-R side, when the amount of noise changes periodically, especially when the TCM-ISDN is present in the same cable, the ATU-R transmits NE to the ADSL from the NE.
XT and FEXT occur. Downstream SNR evaluation unit 2
Then, the SNR value of each frequency in both cases is evaluated, and each is held in NEXT SNR and FEXT SNR3. In FIG. 9, 11 and 12 show the SNR values of the respective evaluated frequencies, 11 is when FEXT occurs, and 12 is NE.
Each SNR value when XT occurs is shown.

The performance margin calculator 4 calculates the SN
When four transmitted transmission speeds are realized based on the SNR value 3 of the line evaluated by the R evaluation unit 2, four types of bit allocation for setting the performance margin to the maximum value are calculated (step A2). FIG. 9 shows the calculation method.
A given transmission rate is realized in consideration of a plurality of SNR values evaluated at different times and the total transmission power, and multi-carrier bit allocation that maximizes a performance margin is calculated. At that time, as shown in FIG. 9, S at the time of NEXT and FEXT evaluated at different times.
Considering the NR value and the total power during data transmission, ATU-
The transmission rate given from C100 is realized, and the bit allocation of each carrier of the multicarrier is calculated so as to maximize the performance margin.

The transmission rate selector 5 calculates the four types of performance margin values calculated, for example, step A in FIG.
As shown in FIG. 2, a transmittable transmission speed having the highest transmission speed and a non-negative margin is selected from the four types of margin values m1 to m4 (step A3). If all margins are negative for all transmission rates, it indicates that all four transmission rates cannot be transmitted, and the ATU-R transmits a full transmission rate failure output to ATU-C (step A).
6). If any one of the transmission rates can be selected, the selected transmission rate and its performance margin are transmitted to the ATU-C (step A4). The bit and power distribution table transmitting section 6 transmits a bit and power distribution table for performing transmission at the selected transmission rate (step A5). This table needs to be calculated for each of the SNR values that change periodically at the time of NEXT and FEXT. Each calculated table is AT
Sent from the U-R to the ATU-C.

In the case of FIG. 2C, since the change period of the noise in the transmission line is not equal, when a plurality of SNR values are converted into a single SNR value, only the ratios f and n of the time intervals are used. Increase the frequency of the SNR value. FIG. 5 shows a method of calculating the bit allocation. As shown in FIG. 5A, the SNR at the time of NEXT and FEXT shown in FIGS.
The SNR value at the time of FEXT is f-fold, and the SNR value at the time of NEXT is expanded to n-times frequency. The transmission speed is given by multiplying the value of the transmission speed by f + n, and (f + n)
Assuming that the line uses × 256 carriers, FIG.
A bit allocation method as shown in (B) is used.

The bit and power distribution table used for data transmission is the table used at the time of FEXT.
A bit and power distribution table allocated to any one set of carriers using the SNR value at the time of FEXT is used.
Similarly, the table at the time of NEXT also has the SN at the time of NEXT.
A table allocated to any one set of carriers using the R value is used. For example, (3 + 2) × 256 = 128
In the case of FIG. 5 which is calculated assuming that the carrier of 0 is used, 0 to 25 are obtained from the bit and power distribution table (FIG. 5B).
The part corresponding to the carrier of No. 5 is a FEXT table,
A portion corresponding to carriers 68 to 1023 is used as a NEXT table. Each calculated table is A
The bits are transmitted from the TU-R to the ATU-C, held in the bit and power distribution table 10, and used for bit and power distribution (mapping) at the time of downlink transmission.

FIG. 10 is a flowchart showing a method of calculating the performance margin in step A2 of FIG. First, SNR (i) is obtained by normalizing the transmission power of each carrier i as E (i) (step S10). And
The calculated SNR (i) is rearranged in descending order (step S11), and the numbers are rearranged so that SNR (i) ≧ SNR (i + 1). The above inequality applies to all numbers up to i which is smaller than the total number N of carriers.

Next, k = 1, KF = KN = 0, count
It is assumed that tF = countN = 0 and γmax = −∞ (step S12). k is a counter, γmax is the current maximum possible system performance margin, countF, cou
ntN is the number of carriers used to achieve γmax, and the subscript F is the first character F of the FEXT table,
N indicates the first character N of the NEXT table. Then, γF (k) and γN (k) are calculated (step S13). The calculation formulas for γF (k) and γN (k) are the same as those in the above “Equation 1”.

Γ (k) is the maximum system performance margin achievable in one carrier symbol. At this time, the target achievement speed is Btarget, the total effective coding gain is γeff, the desired bit error rate is 10 ⁻⁷ , k best carriers are used, and the current geometric average SNR is the above “Equation 2”. Is the same as

The current transmission power Ei used by the i-th carrier is

(Equation 5) Given by Here, Etarget, F and Etarget, N are the total input power limited by the transmitter.

Emaxi, F and Emaxi, N are equal to those in FEXT and NE.
The i-th carrier at each XT is the maximum transmittable power, which is determined by the transmission power mask. And γF (k)> γmax or γN (k)> γ
If it is max (step S14 / YES), count
tF = KF, countN = KN, γmax = γF (k) when γF (k)> γmax, and γmax = γN (k) when γN (k)> γmax (step S15).

If γF (k)> γN (k) (step S16 / YES), KF ++ (step S16)
17) If not (step S16 / NO), KN ++ is set (step S18). And KF = KN
= N (Step S19 / NO), Step S19
Return to 13. Here, γmax indicates the maximum possible system performance margin for a given system parameter, and countF and countN are γmax
Is the best number of carriers to achieve.

FIG. 11 is a flowchart showing a method of calculating the bit allocation table in step A5 of FIG. Using the above γmax, countF, and countN, the initial bit distribution table {b′i} is

(Equation 6) Calculate using

Floor indicates the truncation of the decimal point, and the value of the truncated decimal point is represented by diffi as:

(Equation 7) (Step S20).

Here, Γmax is the same as the above “Equation 3”. Also, Pe is the bit error rate, Ne is the number of the nearest points of the input signal constellation, and the Q function is the same as the above “Equation 4”. And
Btotal is calculated (step S21). This Btotal
Is the total number of bits supported by the current bit allocation table in one multicarrier symbol, and Btotal = Σb′i. Here, Σ is the sum of i = 0 to N−1.

If Btotal <Btarget (step S23 / YES), the bit allocation table {b'i} of the carrier having the maximum diffi value by one bit from the current bit allocation table is reduced by one bit,
= Diffi-1 and Btotal = Btotal-1 (step S24). When Btotal <Btarget (step S23 / NO), the bit allocation table {b'i} of the carrier having the minimum diffi value by one bit from the current bit allocation table is increased by one bit, and diffi = diffi.
+1 and Btatal = Btotal + 1 (step S2
5). This is expressed as Btotal = Btarget (step S22 /
Repeat until (YES).

FIG. 12 is a flowchart showing a method of calculating the power distribution table in step A5 of FIG. First,
Based on the given bit distribution table {b'i}, Pe
(I) = input power ´E′i such that Pe, i, target
Is assigned (step S30). Where Pe
(I) is the error probability of the i-th carrier, Pe, i, target
Is the target error probability of the i-th carrier. In addition, ｛E
'I' is the total transmission power used by the i-th carrier.

The current total transmission powers Etotal, F and Etotal,
N

(Equation 8) (Step S31). Here, Σ is the sum of i = 0 to N−1.

Then, the final power distribution {E'i} is readjusted (step S32). This readjustment is (Etarget, F
/ Etotal, F). The smaller value E 'of Ei and Emaxi, F
i, F or (Etarget, N / Etotal, N) Ei and E
maxi, N and the smaller value E'i, N

(Equation 9) Is performed. The initial bit and power allocation table in this system will be given by {b'i} and {E'i}.

In each of the above embodiments, the case of data transmission in the down direction has been described.
In the case of upstream data transmission to the TU-C100,
The configuration is exactly the same, and the configuration of the ATU-C100 shown in FIG.
Each is provided in the U-C100.

The present invention is not limited to the above embodiment. For example, a device using a DMT communication system other than ADSL exists on the same cable as ISDN, or two or more devices other than ISDN are used. The same applies to the case where the periodic noise source exists on the same cable.

[0071]

As described above, according to the present invention, when the amount of noise in the transmission line changes periodically, noise environments different from each other, such as FEXT and NEX, are used.
At time T, even if the maximum transmission power value is set differently so as to eliminate the influence of ADSL to ISDN at NEXT, a plurality of SNR values due to the noise of this periodic change are By regarding the SNR value of one line whose frequency band has increased without changing over time, it is possible to obtain a bit distribution having a maximum performance margin value with respect to a periodically changing noise amount. There is.

Further, according to the present invention, when the noise amount of the transmission line changes periodically, similarly, the maximum transmission power values are different from each other in different noise environments, for example, in FEXT and NEXT. Even if it is set to eliminate the influence of ADSL to ISDN at the time of NEXT, a given transmission rate is given according to a plurality of SNR values evaluated at different times due to the noise of this periodic change. And the bit distribution of each carrier that maximizes the performance margin can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between TCM-ISDN data and a noise state on ADSL.

FIG. 3 is a flowchart showing the operation of the block in FIG. 1;

FIG. 4 is a diagram illustrating an example of bit allocation when noise periods are at equal intervals.

FIG. 5 is a diagram illustrating an example of bit allocation when noise periods are not equally spaced;

FIG. 6 is a flowchart showing details of step A2 in FIG. 3;

FIG. 7 is a flowchart showing a method of calculating bit allocation in step A5 of FIG. 3;

FIG. 8 is a flowchart showing a method for calculating power distribution in step A5 of FIG. 3;

FIG. 9 is a diagram showing another example of bit allocation when the noise periods are at equal intervals.

FIG. 10 is a flowchart showing another example of the details of step A2 in FIG. 3;

FIG. 11 is a flowchart showing another example of the method of calculating the bit allocation in step A5 of FIG. 3;

FIG. 12 is a flowchart showing another example of the power distribution calculation method in step A5 of FIG. 3;

FIG. 13 is a diagram illustrating an example of conventional bit allocation.

FIG. 14 is a diagram illustrating an example of occurrence of far-end crosstalk and near-end crosstalk.

[Explanation of symbols]

 Reference Signs List 1 downlink transmission rate transmission section 2 downlink SNR evaluation section 3 SNR value 4 performance margin calculation section 5 transmission rate selection section 6 bits, power distribution table transmission section 7, 10 bits, power distribution table 8 speed adaptation algorithm 9 selected transmission rate Storage unit 100 ATU-C (central office) 200 ATU-R (terminal)

Claims (24)

[Claims] 1. A multi-carrier transmission system for performing data transmission by a multi-carrier transmission method between first and second communication stations under a plurality of types of periodically changing noise environments. Signal-to-noise ratio evaluation means for evaluating the signal-to-noise ratio of each carrier of the multi-carrier at different times corresponding to each type of noise environment to obtain a plurality of types of signal-to-noise ratio sets; and The signal-to-noise ratio set is one signal-to-noise ratio set evaluated at different frequencies at the same time that does not change periodically, and the one signal-to-noise ratio set and the noise environment A multi-carrier transmission system comprising: bit allocation means for allocating bits for each carrier according to a preset maximum transmission power value corresponding to each of the transmission power values. 2. When the number of noise environments is two and changes at a predetermined period, the signal-to-noise ratio evaluation means calculates a corresponding signal-to-noise ratio set in each of the two types of noise environments. Wherein the bit allocation means is configured to perform the bit allocation using the two sets of signal-to-noise ratios as the one set of signal-to-noise ratios. The multicarrier transmission system according to claim 1. 3. The bit allocation means according to claim 1, wherein the bit allocation is performed in accordance with each value of the one signal-to-noise ratio set and the maximum transmission power value of each carrier. 3. The multicarrier transmission system according to 1 or 2. 4. A multicarrier transmission system configured to perform data transmission by a multicarrier transmission method between first and second communication stations under a plurality of types of periodically changing noise environments. Signal-to-noise ratio evaluation means for evaluating the signal-to-noise ratio of each carrier of the multi-carrier at different times corresponding to each type of noise environment to obtain a plurality of types of signal-to-noise ratio sets; and According to each value of the signal-to-noise ratio set and the maximum transmission power value set in advance corresponding to the noise environment, a given transmission speed is realized and the performance margin is maximized. A bit allocation means for allocating bits for each carrier. 5. When the number of noise environments is two and changes at a predetermined interval, the signal-to-noise ratio evaluation means sets a corresponding set of signal-to-noise ratios in each of the two types of noise environments. 5. The apparatus according to claim 4, wherein the bit allocation means is configured to perform the bit allocation according to each value of the two types of signal-to-noise ratio sets. Multi-carrier transmission system. 6. The bit allocation means, wherein the bit allocation is performed according to each value of the two sets of signal-to-noise ratios, the total transmission power limit value, and the maximum transmission power value. The multicarrier transmission system according to claim 4 or 5, wherein 7. In the case of data transmission from the first communication station to the second communication station, the first communication station transmits a plurality of predetermined transmission rates to the second communication station. Means, the second communication station has the signal-to-noise ratio evaluation means and the bit allocation means, wherein the bit allocation means comprises the plurality of transmission rates transmitted from the first communication station. Means for calculating a margin in data transmission based on the set of the signal-to-noise ratio and
The apparatus according to claim 1, further comprising means for selecting an optimum transmission rate from the plurality of transmission rates based on the calculated margin, and means for calculating a bit allocation of each carrier according to the selected transmission rate. 7. The multicarrier transmission system according to any one of 1 to 6. 8. The second communication station further includes means for sending the bit allocation to the first communication station, wherein the first communication station transmits data to the second communication station according to the bit allocation. The multicarrier transmission system according to claim 7, wherein transmission is performed. 9. The apparatus according to claim 1, wherein the two noise sources are on the same cable as a communication line between the first and second communication stations. Multi-carrier transmission system. 10. The system according to claim 1, wherein the two types of noise environments are a first noise environment and a second noise environment having a noise state worse than that of the first noise environment. Or a multi-carrier transmission system according to the above. 11. The method according to claim 1, wherein the two types of noise are caused by far-end crosstalk and near-end crosstalk.
10. The multi-carrier transmission system according to any one of 10 above. 12. The multicarrier transmission system according to claim 1, wherein data transmission between the first and second communication stations is performed by a digital subscriber line. 13. A multi-carrier transmission method for performing data transmission by a multi-carrier transmission method between first and second communication stations under a plurality of types of periodically changing noise environments. A signal-to-noise ratio evaluation step of evaluating a signal-to-noise ratio of each carrier of a multi-carrier at different times corresponding to each kind of noise environment to obtain a plurality of sets of signal-to-noise ratios; The set of signal-to-noise ratios is one set of signal-to-noise ratios evaluated at different frequencies at the same time that do not change periodically,
A bit allocation step of allocating bits for each carrier according to the one set of signal-to-noise ratios and a maximum transmission power value set in advance corresponding to the noise environment. Carrier transmission method. 14. When the noise environment is of two types and changes at a predetermined period, the signal-to-noise ratio evaluation step calculates a corresponding signal-to-noise ratio set in each of the two types of noise environment. And the bit allocation step comprises:
14. The multicarrier transmission method according to claim 13, wherein the bit allocation is performed by using a set of kinds of signal-to-noise ratios as the one set of signal-to-noise ratios. 15. The bit allocation step according to claim 13, wherein the bit allocation is performed in accordance with each value of the one set of signal-to-noise ratios and the maximum power value of each carrier. Or the multicarrier transmission method according to 14. 16. A multi-carrier transmission method for performing data transmission by a multi-carrier transmission method between first and second communication stations under a plurality of types of periodically changing noise environments. A signal-to-noise ratio evaluation step of evaluating a signal-to-noise ratio of each carrier of a multi-carrier at different times corresponding to each kind of noise environment to obtain a plurality of sets of signal-to-noise ratios; According to each value of the set of signal-to-noise ratios and the maximum transmission power value set in advance corresponding to the noise environment, each of the above-described ones to realize a given transmission rate and maximize the performance margin. A bit allocation step of allocating bits of carriers. 17. When the number of the noise environments is two and changes at a predetermined period, the signal-to-noise ratio evaluation step calculates a corresponding signal-to-noise ratio set in each of the two types of noise environments. And the bit allocation step comprises:
17. The multicarrier transmission method according to claim 16, wherein the bit allocation is performed according to each value of a set of kinds of signal-to-noise ratios. 18. The bit allocation step, wherein the bit allocation is performed in accordance with each value of the two sets of signal-to-noise ratios, a total transmission power limit value, and the maximum power value. The multicarrier transmission method according to claim 16 or 17, wherein: 19. The method according to claim 19, further comprising: transmitting a plurality of predetermined transmission rates from the first communication station to the second communication station. Calculating a margin in data transmission based on the set of the plurality of transmission rates and the signal-to-noise ratio transmitted from the first communication station; and 19. The multi-carrier transmission according to claim 16, further comprising the steps of: selecting an optimum transmission speed from the transmission speeds of the two carriers; and calculating a bit allocation of each carrier according to the selected transmission speed. Method. 20. Transmitting the bit allocation from the second communication station to the first communication station, and transmitting data to the second communication station in the first communication station according to the bit allocation. 20. The method of claim 19, further comprising the step of: 21. The noise source of the two kinds of noises is present on the same cable as a communication line between the first and second communication stations. The multi-carrier transmission method as described. 22. The two noise environments are a first noise environment and a second noise environment whose noise state is worse than that of the first noise environment. Or the multi-carrier transmission method described in the above. 23. The method of claim 16, wherein the two types of noise are caused by far-end crosstalk and near-end crosstalk.
23. The multicarrier transmission method according to any one of claims 22. 24. The multicarrier transmission method according to claim 16, wherein data transmission between the first and second communication stations is performed by a digital subscriber line.