EP1797664A1 - Method for modifying power spectral density of a telecommunication line and adjusting method using same - Google Patents

Abstract

The invention concerns in particular a method for modifying power spectral density of a telecommunication line transmitting data from a transmitter terminal to a receiver terminal, the power spectral density being distributed between a number of data transmitting frequency sub-bands of the line. Said method comprises the following steps: transmitting (52) an activation message from the transmitter terminal to the receiver terminal; and the reception of said activation message causes retransmission (54) of a message requesting modification of the power spectral density transmitted in a selected sub-band, from the receiver terminal to the transmitter terminal.

Description

Method for modifying the power spectral density of a telecommunication line and adjustment method implementing this method

The present invention relates to a method for modifying the power spectral density of a telecommunication line transmitting data from a transmitting terminal to a receiving terminal, the power spectral density being allocated to frequency subbands for transmitting data. of the line.

The invention also relates to a method for adjusting spectral power densities of several telecommunication lines, implementing this modification method. It is known to transmit data, via a telecommunication line, from a transmitting terminal to a receiving terminal, the transmitting terminal assigning a power spectral density to frequency sub-bands for transmitting data from the line.

A power spectral density modification method is already known, in which the data receiver terminal itself initiates changes in the assigned power spectral density, automatically according to the received power and / or the estimated noise on the receiver. the line by the receiving terminal.

During this process, the receiving terminal transmits, to the transmitting terminal, a request message for modification of the power spectral density assigned to at least one selected subband.

Since the receiving terminal initiates the modification, it can at any time decode the data transmitted in each frequency subband. Thus, the change in spectral density does not generate a transmission error.

Nevertheless, the previously described method does not allow the transmitting terminal arbitrarily to modify the power spectral density, independently of the power received and the noise estimated on the line by the receiving terminal.

The aim of the invention is to remedy this drawback by providing a method in which the transmitter terminal initiates the modification of the power spectral density, without this modification leading to transmission errors. For this purpose, the subject of the invention is a method for modifying the power spectral density of a telecommunication line transmitting data from a transmitting terminal to a receiving terminal, the power spectral density being allocated to sub-bands. frequency of transmission of the data of the line, comprising a step of transmitting a modification request message of the power spectral density transmitted in a selected subband, from the receiving terminal to the transmitting terminal, characterized in that:

an activation message is transmitted from the transmitting terminal to the receiving terminal; and the reception of this activation message by the receiving terminal causes the transmission of the request message for modification of the power spectral density transmitted in the selected subband.

Thanks to the invention, it is possible arbitrarily to modify, as required, the power spectral density attributed. In addition, as for the method of the state of the art, the receiving terminal can at any time error-free decode the data transmitted in each frequency sub-band.

A method of modifying the power spectral density of a line according to the invention may further comprise one or more of the following characteristics: the activation message is sent in the form of a message of the type

"vendor specific" flowing through an overhead control channel in accordance with at least one of the xDSL standards;

- the power spectral density change request message transmitted in the selected subband is transmitted as a fast swap request through an overhead control channel in accordance with at least one of the xDSL standards ;

the fast swap request comprises a data field containing an indicator of a predefined minimum level of modification of the power spectral density; the data field comprises a data bit, a value of this bit indicating the predefined minimum level, the other value of this bit indicating a reference level; and

the activation message is issued as a fast swap request through an overhead control channel in accordance with at least one of the xDSL standards, includes a data field containing an indicator of a minimum level predefined power spectral density modification method, and further includes a "vendor-specific" type message header. The invention also relates to a use of a method for modifying the power spectral density of a line according to the invention, in order to restore an initial level of power spectral density. The invention also relates to a method for adjusting power spectral densities of a plurality of data transmission telecommunication lines, a power spectral density being assigned to frequency subbands of each data transmission line, characterized in that: selects at least one line, called "donor line", whose ability to transmit data is greater than a predetermined reference capacity, called "donor capacity";

at least one sub-band of this donor line is selected; and

the power spectral density assigned to the selected subband is reduced to a predefined minimum power level in this sub-band by the application of a modification method as described above.

An adjustment method according to the invention takes advantage of the property that by reducing the power spectral density assigned to a sub-band of a line, a stationary noise of crosstalk induced by this subband is reduced on the other lines. from the whole. This noise reduction has the effect of automatically increasing the capacity of these other lines to transmit data.

Thus, by selecting at least one line whose capacity to transmit data is greater than a predetermined reference capacity, and reducing the spectral power density of the selected line by the extinction of at least one of its sub bands (ie, the reduction of the power spectral density assigned to this subband to a predefined minimum power level in this sub-band), the capacities of the other lines of the set are increased without increasing the density spectral total power allocated on all lines. The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings, in which:

FIG. 1 schematically represents the general structure of an adjustment device for implementing a modification method according to the invention; FIG. 2 represents the successive steps of a power spectral density adjustment method according to a possible embodiment of the invention; and

FIG. 3 represents the successive steps of a power spectral density modification method according to a possible embodiment of the invention. The adjustment device 10 shown in FIG. 1 makes it possible to adjust the power spectral densities of a plurality of telecommunication lines 12a, 12b,..., 12c suitable for transmitting data. These are, for example, lines of the xDSL type, for the transmission of high-speed signals. Each line 12a, 12b, ..., 12c is associated with a transmission modem 16a, 16b,

..., 16c. The transmission modems 16a, 16b, ..., 16c are hosted by the same central office 14 and are all connected to the adjustment device 10.

Each line 12a, 12b 12c is further connected to a receiving terminal

18a, 18b, ..., 18c. The adjustment device 10 comprises means 20a, 20b, ..., 20c of connection to the lines 12a, 12b, ..., 12c. These connection means 20a, 20b 20c are themselves connected to a data transmission bus 22 of the adjustment device 10.

The adjustment device 10 further comprises means 24 for extracting parameters specific to the lines 12a, 12b, ..., 12c to which it is connected. These parameters specific to the lines 12a, 12b, ..., 12c are, for example, the desired bit rate, the minimum noise margin required, the bit rate actually transmitted, the power spectral density or parameters relating to error correction techniques. .

These means 24 for extracting parameters are connected to the transmission bus 22. They can be activated at any time, even during communication on one or more lines 12a, 12b, ..., 12c.

The adjustment device 10 also comprises means 26 for selecting at least one line, called "donor line" whose ability to transmit data is greater than a predetermined reference capacity. These selection means 26 are also suitable for selecting at least one sub-band of this donor line. In the example described, the capacity to transmit data is a maximum data rate that a line 12a, 12b 12c can emit with the power spectral density assigned to it, and the predetermined reference capacity is a bit rate equal to maximum of the sum of a minimum flow required to carry out at least one service to which a line 12a, 12b, ..., 12c is subscribed with a predetermined flow margin, and a minimum rate guaranteed by the operator

The adjustment device 10 finally comprises means 28 for reducing the power spectral density assigned to the selected sub-band of the selected donor line to a predefined minimum power spectral density level in this sub-band. This reduction is called "subband extinction". Note that the number of selected subbands of the donor line, to be extinguished, should be such that the actual rate in that line remains greater than the minimum required rate, even after the power spectral density has been reduced by the device. adjustment 10. The addition of the predetermined flow margin to the minimum required flow rate guarantees this requirement.

The function of the adjustment device 10 is in particular to optimize the power spectral densities allocated to each of the lines 12a, 12b,..., 12c as a function of the services to which each of these lines subscribes and of the resources available for the set. lines. The adjusting device 10 operates according to a method which will now be described with reference to FIG. 2.

During a first initialization step, for each line 12a, 12b,..., 12c, a minimum bit rate required to carry out the service or services at which this line 12a, 12b,... 12c is subscribed is subscribed. and that a customer wants to get. During this initialization step, for each line 12a, 12b,... 12c, two reference capacities are also determined, referred to as "donor capacity" and "recipient capacity", the recipient capacity being equal to the minimum required flow rate. , and the donor capacity being equal to the maximum of the sum of the minimum flow required with the predetermined flow margin, and a minimum flow guaranteed by the operator. During the initialization step 30, one finally reaches for each line 12a,

12b, ..., 12c at a maximum data rate that it can transmit with the power spectral density assigned to it. This maximum rate constitutes an ability to transmit data from line 12a, 12b, ..., 12c.

Then we go to a step 32 of selection of donor lines and donated lines. During this selection step 32, a first group of lines, called "donor lines", whose capacity to transmit data is smaller than the recipient capacity, is selected. A second group of lines is also selected, called "donor lines", whose capacity to transmit data is greater than the donor capacity. Then, during a step 33, for each donor line of the first group, the following two conditions are verified:

- if it was part of the second group of donor lines during a previous execution of the process; and

- if it is the case, if at least one of its subbands has been extinguished on this occasion by the means of reduction 28. If these two conditions are satisfied, the initial power spectral density level of the subbands extinguished of this donor line is restored before they are extinguished. To achieve this restoration, two methods are possible: use a modification method which will be described with reference to FIG. 3; or

- Restore the power spectral density level at the initiative of the transmitter associated with this line recipient, without necessarily notify the corresponding receiving terminal.

If at least one of these two conditions is not satisfied or if, after restoration of the initial power spectral density level of the subbands extinguished, this line still has a capacity to transmit data that is less than the recipient capacity, it is maintained this line in the first group. Otherwise, this line is removed from the first group of donated lines.

If one of the groups is empty, then the selection step 32 is repeated until each group has at least one line. Indeed, the setting method implemented by the device 10 requires that at least one donor line be able to reduce its ability to transmit data to allow at least one recipient line to increase its ability to transmit data. .

Then we go to a step 34 of classification of the donated lines. During this ranking step 34, the donor lines of the first group are classified according to two criteria, the first of which has priority over the second:

a predetermined privilege level associated with each line; a value Δ associated with each line, equal to the difference between the capacity to transmit data and the recipient capacity. Thus, the donor lines of the first group are first ranked in descending order of their level of privilege. Then, when several lines have the same level of privilege, they are ranked in increasing order of their Δ value. These lines are ordered in the first group.

This ranking makes it possible to define the order in which the lines of the first group will be treated in the rest of the process. In a step 35, the first recipient line of the first group is selected.

In a step 36, it is verified that the second group of lines, called "donor lines", is not empty. If it is empty, return to the selection step 32 previously described. Next, there is a step 37 of selecting at least one sub-band of the recipient line previously selected. For example, the sub-band is selected according to a crosstalk coupling level criterion between the lines, in each sub-band of the selected recipient line. In fact, the sub-bands of the recipient line that have a high level of coupling with the other lines are favored. One can also choose a standard signal to noise ratio criterion.

In the example described, several sub-bands are selected, for example the twenty-five sub-bands of the selected recipient line whose coupling level is the highest or their normalized signal-to-noise ratio. Depending on the chosen criterion, the selected sub-bands can themselves be classified. In the following process, to treat the selected recipient line more efficiently:

grouping the sub-bands selected in batches, which speeds up the processing, while still making it possible to accurately respond to the needs of the donor lines (a number Nsb of sub-bands per batch is defined); a number of donor lines are assigned to each batch of sub-bands, which number must not exceed a maximum number NId;

this batch assignment of sub-bands is carried out by batch of sub-bands and in several iterations during each of which one can not assign the same donor line to a single batch; the assignment of the donor lines to each batch of selected sub-bands of the recipient line can be repeated a maximum number N times.

We then go to a step 38 during which we group the subbands selected batches of Nsb subbands. In the case where Nsb is four, the twenty-five subbands are grouped into six batches containing four sub-bands each and one batch containing a sub-band.

A first assignment cycle of the donor lines is then started for each batch of sub-bands.

For this purpose, a first iteration is started during which each donor line is assigned to a batch of sub-bands, proceeding batch by batch. During an iteration, the maximum number of donor lines can be assigned to the same lot and the same donor line can not be assigned to more than one lot.

Thus, during a step 39, a batch is selected, to which the following steps 40 and 42 are applied. In step 40, it is first checked whether the selected batch is saturated, i.e. if a maximum number of bits per subband of the batch is reached. If so, we did not assign any donor line to this lot and select another batch from the donee line for which step 40 is taken at its beginning. Otherwise, we keep this selected batch. Then, the donor lines are scanned to determine at most one of the donor lines that can be assigned to the selected lot. A donor line is assigned to this batch of subbands if the corresponding subbands in the donor line are not already all extinguished and if this donor line has not already been assigned to another batch in the current iteration . Then all the corresponding sub-bands of the donor line are turned off.

Next, we go to step 42 during which we measure the new capacity to transmit data from the selected recipient line. If this capacity is greater than the recipient capacity, it is considered that the donee line is processed, it is removed from the first group of lines donee and we go to a test stage.

During this step 43, it is checked whether there is at least one recipient line in the first group. If this is the case, selecting a new recipient line and returning to step 36. Otherwise, proceeding to a step 44 of end of the process.

If in step 42 the measured capacity to transmit data is less than the recipient capacity, another batch of the recipient line is selected and step 40 is returned.

Steps 40 and 42 are repeated until no more donor lines can be assigned, for example because they have all been affected, or until there are no more lots to select.

If we can no longer assign donor lines, for example because they have all already been assigned once in the current iteration, we return to step 39 to perform a new iteration of assigning donor lines, to complete the assignments of previous iterations.

If there is no longer a lot to select, we go to a step 45 during which we verify that at least one donor line has been assigned to a batch of sub-bands of the donor line selected during the last iteration.

If at least one donor line has been assigned to a batch of sub-bands of the selected recipient line, and the maximum number of donor lines affected per subband lot has not been reached, from step 39, to perform a new iteration of assigning donor lines.

Otherwise, this means that no donor line has a non-extinguished sub-band corresponding to the selected sub-bands of the recipient line, or that the NId number has been reached for all subband batches before the donee line has reached its required minimum capacity. In the case where the number NId has been reached for all the batches of sub-bands, it is possible to return to the step 39, to carry out a new cycle of assignment of the donor lines to each batch of selected sub-bands of the line donee. Preferably, N assignment cycles are carried out at most, N being a predetermined number beyond which it is judged that new assignments of donor lines do not make it possible to increase the capacity of the recipient line significantly.

If the number N is reached, or if no donor line has an undelayed sub-band corresponding to the selected sub-bands of the recipient line, the donee line is extracted from the first group of the donee lines and integrated into a group line of donee lines can not be satisfied, then the process is resumed at step 43.

Optionally, the adjustment method described above is interrupted as soon as a new line becomes a donor. In this case, this new line is integrated in the second group of donor lines, the lines of the subsidiary group are reintegrated in the first group of the lines of the donees and the process resumes at the stage

34 classification of the donee lines.

It will be noted that if, at a given moment, there are no more donor lines or donor lines, then the process is interrupted and we return to step 32 of selection of the donor and donee lines. FIG. 3 shows a method for modifying the power spectral density according to the invention, which can notably be used to perform the power spectral density level recovery in subbands provided for in step 33 or in FIG. extinction of subbands provided in step 40 of the method of Figure 2. But the application of this method is not limited to the implementation of a power spectral density adjustment method such as that described above . It can be implemented independently, as soon as the extinction or restoration of at least one sub-band of a telecommunication line is to be considered. By line of communication is meant any wired system that uses multicarrier modulations, for example telecommunication systems on power line, called PLT systems ("Power One Telecommunication").

The power spectral density modification method shown in FIG. 3 comprises the following steps:

an activation message is transmitted from the transmitting terminal (ie the sending modem) to the receiving terminal; and the reception of this activation message by the receiving terminal causes the transmission of a spectral density modification request message. of power transmitted in the selected subband, from the receiving terminal to the transmitting terminal.

This modification method assumes that, if one wishes to change the transmit power spectral density without generating a transmission error, it is preferable that this change be initiated by the receiving terminal.

More specifically, during a first step 50, one of the lines 12a, 12b, ..., 12c is selected which it is desired to extinguish at least one sub-band.

Then, a step 52 for transmitting an activation message is carried out, so that the receiver terminal associated with this line returns a transmission power spectral density reduction request message allocated to the subbands to be switched off. The activation message is sent from the transmission modem 16a, 16b, ..., 16c associated with the selected line 12a, 12b 12c to the receiving terminal 18a, 18b, ..., 18c of this line 12a, 12b , ..., 12c.

The xDSL standards define an overhead control channel, through which messages may flow between the transmitting modem 16a, 16b, ..., 16c and the receiving terminal 18a, 18b 18c. These standards also define the structure of these messages, including the structure of a "vendor-specific" message, the size and content of which can be chosen freely. Thus, preferably, the activation message is a "vendor-specific" message flowing through the overhead control channel from the transmitting modem 16a, 16b, ..., 16c to the receiving terminal 18a, 18b. , ..., 18c.

Next, a step 54 for transmitting the request message for reducing the transmission power spectral density assigned to the subbands to be turned off is carried out. This reduction request message is sent from the receiving terminal 18a, 18b, ..., 18c to the transmission modem 16a, 16b, ..., 16c.

The xDSL standards define several types of messages intended to flow over the overhead control channel and may contain instructions for setting the transmission modem 16a, 16b, ..., 16c. One of these messages, called "fast swap request", makes it possible to adjust the power spectral densities allocated to each sub-band by the transmission modem 16a, 16b, ..., 16c and is transmitted by the terminal receiver 18a, 18b, ..., 18c.

Preferably, the transmit power spectral density reduction request message consists of a fast swap request.

We finally go to a step 56 during which the transmission modem 16a, 16b,..., 16c effectively reduces the power spectral density of the subbands switching off, in accordance with the instructions contained in the message sent by the receiving terminal 18a, 18b, ..., 18c.

In the current state of the xDSL standards, a fast swap message may contain instructions for reducing the power spectral density assigned to a subband by up to 4 dB, which may be insufficient to reach the minimum level predefined in this sub-band. subband, usually set at -14.5 dB (sub-band extinction level) relative to a reference level.

Thus, in order to extinguish a sub-band, steps 54 and 56 can be repeated several times. Alternatively, a new data field can be defined in the fast swap request, this field directly containing a minimum level indicator. predefined, ie -14.5 dB above the reference level.

The field may thus comprise a data bit, a value of this bit indicating the predefined minimum level, the other value of this bit indicating the reference level.

Note that, in the example described, the fast swap message is issued as a conventional fast swap message flowing through the overhead control channel in accordance with at least one of the xDSL standards, to which it is added. the data field previously described.

In addition, the activation message is also issued as a fast swap request flowing through the overhead control channel in accordance with at least one of the xDSL standards. It further includes a data field containing an indicator of a predefined minimum level of power spectral density modification, and a "vendor-specific" type message header.

It will be appreciated that the method described above can be used to restore the initial level of subband power spectral density, for example for the recovery provided in step 33 of the method of FIG. 2. Thus, it is possible to use the new data field in the fast swap request, this field containing in this case an indicator of the initial level.

A power spectral density modification method according to the invention can be executed at any time, including during the use of lines 12a, 12b, ..., 12c to perform services to which they are subscribed. It allows to adjust the capabilities of lines in real time.

In addition, it is clear that the device and the adjustment method described above allow optimal overall management capabilities to transmit data of a set of lines.

Claims

REVENDICATION8 A method for modifying the power spectral density of a telecommunication line transmitting data from a transmitting terminal (16a, 16b, ..., 16c) to a receiving terminal (18a, 18b, ..., 18c) , the power spectral density being assigned to frequency sub-bands for transmitting the data of the line, comprising a step of transmitting (54) a power spectral density modification request message transmitted in a sub-transmission selected band, from the receiving terminal to the transmitting terminal (16a, 16b, ..., 16c), characterized in that: - an activation message is transmitted (52) from the transmitting terminal (16a, 16b, ..., 16c) to the receiving terminal (18a, 18b 18c); and the reception of this activation message by the receiving terminal (18a, 18b,..., 18c) causes the emission (54) of the request message for modification of the power spectral density emitted in the selected subband. . The method of modifying the power spectral density of a line according to claim 1, wherein the activation message is issued as a "vendor-specific" type message flowing through a control channel. overhead complies with at least one of the xDSL standards. A method for changing the power spectral density of a line according to claim 1 or 2, wherein the power spectral density change request message transmitted in the selected subband is transmitted as a a fast swap request flowing through an overhead control channel according to at least one of the xDSL standards. A method for changing the power spectral density of a line according to claim 3, wherein the fast swap request comprises a data field containing an indicator of a predefined minimum level of power spectral density change. The method of modifying the power spectral density of a line according to claim 4, wherein the data field comprises a data bit, a value of this bit indicating the predefined minimum level, the other value of this bit. indicating a reference level. A method for changing the power spectral density of a line according to claim 4 or 5, wherein the activation message is transmitted as a fast swap request via an overhead control channel in accordance with at least one of the xDSL standards, includes a data field containing an indicator of a predefined minimum level of power spectral density modification, and further includes a "vendor specific" message header. The use of a method for modifying the power spectral density of a line according to any one of the preceding claims to restore an initial level of power spectral density. A method of controlling power spectral densities of a plurality of data transmitting telecommunication lines, a power spectral density being assigned to frequency subbands of each data transmitting line, characterized in that: selecting (32) at least one line, called "donor line", whose capacity to transmit data is greater than a predetermined reference capacity, called "donor capacity"; - selecting (36) at least one sub-band of this donor line; and - reducing (40) the power spectral density assigned to the selected subband to a predefined minimum power level in that subband, by applying a modification method according to any one of Claims 1 to 6.