WO2010004230A2

WO2010004230A2 - Method and device for correcting transmission errors

Info

Publication number: WO2010004230A2
Application number: PCT/FR2009/051387
Authority: WO
Inventors: Gautier Avril; Ahmed Zeddam
Original assignee: France Telecom
Priority date: 2008-07-10
Filing date: 2009-07-10
Publication date: 2010-01-14
Also published as: WO2010004230A3; FR2933830A1

Abstract

The method of the invention for correcting errors that disrupt a data transmission carried out via at least one transmission channel (6) separating a sender and a receiver is characterized by: - monitoring (20) said sender-side transmission channel during the resending of data by the sender; and – in the event that a disruption is detected, automatically activating a data correction broadcast (30) by the sender.

Description

METHOD AND DEVICE FOR CORRECTING ERRORS OF

TRANSMISSION

The present invention relates to a method and an error correction device during the transmission of data.

In general, any digital communication system between a transmitter and one or more receivers is subjected to various disturbances and in particular impulsive noises or modifications of the transmission channel.

The physical link between the transmitter and the receiver is called the transmission channel. This link is defined by certain parameters and in particular by the nature of the link (radiofrequency, wired, carrier current, etc.). Some intermediate equipment such as couplers or repeaters are considered part of the transmission channel. Indeed, these devices participate only in the transmission of the physical signal and are transparent from the point of view of the transmitters and receivers.

A transmission channel is therefore defined for each transmitter / receiver pair. In a broadcast situation with one transmitter and several receivers, several transmission channels are processed simultaneously. The disturbances on the transmission channel cause variations in the quality of transmission and result in transmission errors, that is to say to data that can not be exploited at the receiver.

Conventionally, there are two approaches to managing and correcting transmission errors, these two approaches being freely combinable. According to a first approach, the transmitter sends the data redundantly, for example on a plurality of different channels.

According to a second approach, transmitter and receiver use acknowledgments. Depending on the case, these are positive acknowledgments, ie the receiver sends an acknowledgment of receipt for each well-received packet or negative acknowledgments that is to say that the receiver asks for the retransmission of data for each badly received packet. The retransmitted data is called correction data.

These acknowledgments, or indicators of transmission errors, form what is commonly referred to as a return channel. Receipt acknowledgments received on the return channel allow the sender to trigger retransmission of the data.

In some embodiments, the return channel is implemented at the physical layer as in the protocols known as ARQ or "Automatic Repeat Request" or RPHY ("Physical Layer Retransmission"). In other systems, the return channel is implemented on a higher layer of the protocol, such as for example the TCP / IP layer.

In all cases, the use of a return channel imposes a significant delay on the transmission of the correction data. Indeed, the receiver must wait for the end of the received frame and the execution of the correction calculations to request a return. In addition, the return request message takes a certain amount of time and, when it receives the forwarding request, the sender must interrupt the current transmission to transmit the correction data.

Moreover, in the case where the disturbance is due to a variation of the transmission channel, the retransmission will be made with the same errors. Indeed, the receiver is not able to distinguish a channel variation from an impulsive noise. The correction data will therefore suffer the same disturbances as the initial data and it will be necessary to wait for the transmission of a new equalization sequence to allow the resumption of data transmission.

These problems are magnified in the case of multicast or broadcast broadcast, that is, a situation where an issuer communicates with multiple receivers. Indeed, the multiplication of receivers leads to a multiplication of acknowledgments and a loss of time and significant bandwidth. It turns out that the existing solutions for management and error correction with retransmission of data lead to significant delays.

The present invention seeks to remedy this problem in particular.

For this purpose, the subject of the present invention is a method for transmitting data via at least one transmission channel separating a transmitter from said data and a receiver, according to which the method comprises, on the transmitter side, a monitoring of said transmission channel at the transmitter. during transmission of data by the transmitter, detection of a disturbance of the data transmission, and automatic triggering of a transmission of correction data by the transmitter.

Thus, the transmitter proceeds to send correction data automatically ie without waiting for instructions or information from the receiver or receivers resulting in faster and more reliable error correction. According to a particular embodiment, the detected disturbance belonging to a group comprising: an impulsive noise received through the transmission channel, a variation of the transmission channel, the correction data transmitted differ according to the disturbance detected.

By distinguishing between impulse noise and channel variations, the transmitter can adapt the correction data to the situation.

Advantageously, during a detection of an impulsive noise, the automatic transmission of correction data comprises a retransmission of data during transmission during the detection of a disturbance.

In a variant, during a detection of a variation of the channel, the automatic transmission of correction data comprises a transmission of an equalization sequence and a retransmission of data being transmitted when a signal is detected. disturbance.

According to a particular embodiment, the monitoring of the channel comprises reception of a signal on the transmitter side and via the transmission channel, evaluation of the performance of an echo cancellation applied to said received signal representative of the variation of the transmission channel, and an evaluation of the power of the impulsive noise.

Advantageously, said evaluation of the performance of the echo cancellation and said evaluation of the power of the impulsive noise are compared with predetermined thresholds to determine the presence of a disturbance.

This comparison system makes it easy to make the decision relating to the presence of a disturbance using parameters available in existing equipment which limits the modifications to be made to this equipment. Furthermore, the invention also relates to a computer program for a transmission error correction device, an error correction device, a transmitter incorporating such a device and a system using such a device.

Other features and advantages of the present invention will appear in the description given below, without limitation, and with reference to the accompanying drawings in which:

FIG. 1 represents a block diagram of a data transmission system,

- Figures 2A and 2B respectively represent a flowchart of the transmission and reception of data.

According to the embodiment described, and illustrated with reference to FIG. 1, a data transmission is carried out between a transmitter 2 and a receiver 4 connected by a transmission channel 6. For example, the link between the entities 2 and 4 is a digital bidirectional bidirectional link powerline, so that each of the entities 2 and 4 is alternately transmitter and receiver.

Each of the entities 2 and 4 has both a module for transmitting and receiving data. It should be noted that, according to the embodiment described, the transmissions and receptions of data are carried out on the same bandwidth so that a transmitter receives an echo signal when it transmits data on the transmission channel. This echo signal corresponds to a kind of reflection of the signal issued. Indeed, transmission and reception being made on the same bandwidth, the transmitted signal is also received at the transmitter.

The noises likely to disturb the data transmission are modeled in the form of a transmitter 8 also connected to the transmission channel 6.

Furthermore, according to the embodiment described, an error management and correction device 10 is connected to the transmitter 2. This device is adapted to monitor the transmission channel 6 and to control the transmitter in case of detection of disruptions. According to the embodiments, the management and error correction device is integrated in the transmitter or constitutes a separate equipment.

With reference to FIGS. 2A and 2B, an embodiment of the method of the invention will now be described.

The transmission begins with a step 12 of data transmission by the transmitter 2 to the receiver 4. These data are denoted SE for transmitted signal.

During the transmission, the transmitted signal SE is altered by the transfer function of the transmission channel 6 between the transmitter and the receiver. This transfer function is denoted HER. The transmitted signal is transformed into SE x HER. In the context of this patent application this notation and the use of the sign "x" signify that the transfer function is applied to the signal. According to the calculation method, the frequency or time domain, the mathematical operations implemented differ.

The receiver also receives patterned noise in the form of a noise signal SB received through a transmission channel between the noise source and the receiver. The transfer function of this channel is denoted HBR.

Accordingly, in a step 14, the receiver 4 receives a SR signal which is written SR = SExHER + SBxHBR. As before, the sign

"+" Means that the signals are summed after being transformed by the transfer functions. Again, the mathematical operations put implemented to accomplish this operation may differ and be more complex than an addition.

The receiver has an evaluation of the transfer function of the channel between the transmitter and the receiver. This evaluation is obtained during a prior transmission of a known equalization sequence of the receiver. This estimation of the channel is noted H'ER and is obtained in a conventional manner so that this step will not be described in more detail.

After reception, the receiver performs an equalization of the received signal. This equalization corresponds to a compensation of the impact of the transmission channel using the evaluated transfer function.

The signal then becomes S'R = SR / H'ER = SExHER / H'ER + SBxHBR / H'ER.

As in the previous equations, the sign "/" means that the term H'ER is taken into account in an inverse manner to the terms HER and HBR without however limiting the implementation of this operation to a mathematical division. As indicated above, a sudden change in the transfer function of the transmission channel HER and / or a high impulse noise SB result in poor reception.

Simultaneously, the method also comprises, at the level of the transmitter 2, that is to say on the transmitter side, a monitoring of the transmission channel.

This monitoring begins with a reception 22, the side of the transmitter of a signal SEE. This signal corresponds to the transmitted signal SE modified by the transfer function HEE corresponding to the transfer function of the echo perceived from the side of the transmitter. As indicated above, this echo corresponds to the perception, on the side of the transmitter, of the emitted signal SE. The signal SEE also comprises a component linked to the noise signal SB modified by a transfer function modeling the transmission channel between the noise source and the transmitter and is denoted HBE. Thus, the SEE signal is written in the following form: SEE = SExHEE +

SBxHBE. This monitoring further includes an echo cancellation 24 applied to the SEE signal. This echo cancellation is performed in a conventional manner in itself. According to the embodiment described, the echo cancellation comprises an estimate of the echo transfer function denoted H ¹ EE from the comparison of the known transmitted signal and the received echo signal. Once the estimated echo transfer function, it is possible to compensate in the signal a SExH'EE term corresponding to the estimated echo.

The method then comprises an evaluation of the impulsive noise. As previously indicated, using the estimated transfer function and the transmitted signal, the error correction device isolates the noise-related term and measures its power. The noise power is then compared with predetermined thresholds and, if this power is greater than a predetermined threshold, the transmitter considers that the transmission has been disturbed by impulsive noise and that the receiver could not receive the data.

Indeed, even if the received noise power spectral density at the transmission is potentially different from that received at the reception, it is possible to determine a correspondence between these noise levels during a prior calibration or at the reception. simulations help.

In addition, according to the described embodiment, the method includes an evaluation of the level of performance of the echo cancellation. In the case of a modification of the transmission channel resulting for example from the connection of a new device or a modification of the reflections of the wave paths, the echo cancellation will have a low level of performance because the function Echo transfer estimated HΕE must be recalculated.

The evaluation of the echo cancellation is compared with predetermined thresholds and, if this evaluation is too low, the transmitter considers that the transmission has been disturbed by a variation of the channel.

In the event that the monitoring results in the identification of a disturbance, the method automatically initiates a transmission of correction data.

In this context, "automatic transmission" means that this emission is initiated spontaneously at the transmitter without waiting for information or instructions from the receiver on a return channel. Depending on the situation, the correction data differs. If the detected disturbance is an impulsive noise, the transmitter automatically transmits the data that was being transmitted when the disturbance was detected, that is to say the signal SE. In the case where the disturbance detected is a variation of the channel, the transmitter automatically initiates the transmission of an equalization sequence. Indeed, if the transfer function of the channel has evolved, the equalization performed by the receiver loses efficiency since the compensation of the transfer function is no longer suitable. Subsequently and as in the previous case, the transmitter automatically transmits the SE data that was being transmitted when the disturbance was detected.

The correction data may also correspond to the useful data of the SE signal encoded in another form. For example, in the case of video encodings, the image data may be encoded with respect to other images (inter coding) or autonomously (intra coding). In some cases, the initial data is transmitted according to an inter coding and the correction data is transmitted according to an intra coding.

These automatically transmitted correction data are received by the receiver 4 in a step 32. As a result, the monitoring of the transmission channel by the transmitter as well as its ability to detect a disturbance and to distinguish the disturbances resulting from impulsive noises. and variations of the channel allow better management and correction of transmission errors. Depending on the case, the transmitter is automatically retransmitted data whose transmission had been disturbed, or an equalization sequence, then these data.

Of course, the correction data can be adapted to the situation in a conventional manner. For example, only part of a frame is retransmitted, or a frame is dropped, and the next frame is transmitted without reference to the previous frame. The transmission of the correction data is triggered automatically, that is to say without using a return channel as in the case the ARQ and without having to wait for the receiver to complete the data quality calculations. As a result, management and error correction is improved.

Of course, the invention can also be combined with an existing technique of redundancy or return channel.

Preferably, this error correction is applied in environments in which the physical distance between emitters and receivers is short so that the same disturbances are detectable at both ends. For example, so-called PLT, VDSL, wifi or other systems are particularly suitable for the application of the invention.

In addition, the invention can be implemented in a multicast system between a transmitter and a plurality of receivers. In such an embodiment, the time and bandwidth gain increases considerably with the number of receivers.

In another particular embodiment, the monitoring of the channel comprises receiving signals on carriers or frequencies not used for transmission. Thus, in certain environments, certain frequencies or carriers are reserved and must not be used. These frequencies or carriers are reserved by virtue of standards, legislations or others. For example, some frequencies or carriers are reserved for applications such as private radio broadcasts or security (police, emergency ...).

Thus, the transmitters and receivers of the system are not supposed to use these frequencies or carriers. As a result, the detection of a signal on these frequencies or carriers is necessarily a noise signal.

Advantageously, the invention is implemented by a computer program comprising code instructions, which, when executed by a computer of a management and error correction device implement the method as described above. . This computer program can be implemented in the transmitter or in a device separate from the transmitter and interacting with the latter.

Claims

Method for transmitting data via at least one transmission channel (6) separating a transmitter (2) from said data and a receiver (4), characterized in that the method comprises transmitter side:

a monitoring (20) of said transmission channel, during the transmission of data by the transmitter,

a detection of a disturbance of the data transmission, and an automatic triggering of a transmission (30) of correction data by the transmitter.

2. Method according to claim 1 wherein the detected disturbance belonging to a group comprising: an impulsive noise received through the transmission channel,

a variation of the transmission channel, the correction data transmitted differ according to the detected disturbance.

3. The method of claim 2, wherein, during the detection of an impulsive noise, the automatic transmission of correction data comprises a retransmission of data during transmission during the detection of the disturbance.

4. The method according to claim 2, wherein, when detecting a variation of the channel, the automatic transmission of correction data comprises a transmission of an equalization sequence and a retransmission of data being transmitted. when detecting the disturbance.

The method of claim 2, wherein the monitoring of the channel comprises: a reception (22) of a signal on the transmitter side and via the transmission channel,

an evaluation (28) of the performance of an echo cancellation applied to said received signal representative of the variation of the transmission channel, and an evaluation (26) of the power of the impulsive noise.

The method of claim 5, wherein said evaluation of the performance of the echo cancellation and said evaluation of the power of the impulsive noise are compared with predetermined thresholds to determine the presence of a disturbance.

7. Computer program for an error correction device, characterized in that this program comprises code instructions which, when executed by a computer of said device involve the implementation of a method according to any one Claims 1 to 6.

8. Device for error correction via a transmission channel (6) separating a transmitter (2) from said data and at least one receiver (4), characterized in that the device comprises: - a unit (10) for monitoring said issuer-side transmission channel, during the issuance of data by the issuer; and

a transmitter control unit (10) for detecting a disturbance of the data transmission, and automatically triggering transmission of correction data by the transmitter.

The apparatus of claim 8, wherein said transmission channel monitoring unit comprises an impulse noise detection module and a transmission channel variation detection module.

10. Device according to claim 9, wherein the driving unit is adapted for, upon detection of an impulsive noise, trigger automatically transmitting correction data including data being transmitted upon detection of a disturbance.

11. Device according to claim 9, wherein the control unit is adapted for, when detecting a variation of the channel, automatically trigger a correction data transmission comprising an equalization sequence and a data transmission. during transmission during the detection of a disturbance.

The device of claim 9, wherein said transmission channel monitoring unit comprises:

a module for receiving a signal at the transmitter and on said transmission channel,

a module for evaluating the performance of an echo cancellation applied to said received signal representative of the variation of the transmission channel, and

a module for evaluating the power of the impulsive noise.

The device of claim 12, wherein said channel monitoring unit comprises a comparison unit of the evaluation of the performance of the echo cancellation and said evaluation of the power of the impulsive noise with predetermined thresholds for determine the presence of a disturbance.

Data transmitter comprising an integrated error correction device, characterized in that said device comprises:

a unit (10) for monitoring said transmitter-side transmission channel during transmission of data by the transmitter; and

15. A data transmission system comprising a transmitter and at least one receiver connected by a transmission channel, characterized in that the system comprises, connected to said transmitter, an error correction device comprising: