Method for reducing interference in data transmission via power cables

Abstract

Method for reducing interference in a data transmission via a power cable with at least three wires, wherein a first conductor pair is used for transmitting user data signals, characterized in that a second conductor pair of the power cable, different from the first, is used to detect and form a reference signal for interference, wherein no user data signal is transmitted on the second conductor pair.

Description

[0001] The invention relates to a method for reducing interference in data transmission via a power cable with at least three wires, wherein at least one pair of conductors is used for transmitting user data signals.

[0002] Transmission over multiple pairs of conductors (MIMO, Multiple-Input Multiple-Output) is known from the state of the art. US Patent No. 9 035 484 B2 describes this as an example for power cables. In the DSL sector, this was already published in 2000 in G. Tauböck and W. Henkel: "MIMO Systems in the Subscriber-Line Network," 5th International OFDM Workshop, Hamburg, 2000, along with the use of crosstalk functions.

[0003] Furthermore, methods for reducing interference are known. For example, CH 670 923 A5, for the application of ripple control technology, proposes suppressing line frequency harmonics in AC distribution networks. A filter has a stage for delaying the input signal by the inverse of the line frequency and an adder stage for subtracting the delayed signal from the input signal. The filter thus affects line frequency harmonics in AC distribution networks, but not impulse interference that occurs in domestic installations.

[0004] EP 1 271 773 A1 describes specific detection and suppression measures, but these refer to one pair of conductors without including another pair of conductors. Instead, the common mode component of the interference is used.

[0005] To reduce crosstalk coupling in telephone conversations, DE 40 32 068 A1 proposes installing a stub line with a matched terminating resistor as a reference line. Impulse interference then affects both the payload line and the stub line in a similar way, so a converter acts as a subtraction element to partially compensate for the impulsive interference in the receive line. The disadvantage of this solution is that an additional stub line is required, and even with partial compensation, the integrity of the payload data may still not be ensured.

[0006] EP 1 858 174 A1 discloses a method for reducing interference in data transmissions via power cables, in which two transmission modes are used on the conductor pair formed by the phase and neutral conductors. The differential mode and common mode are combined in order to reduce the known asymmetries and to increase the range. Object of the invention

[0007] The object of the invention is to improve the state of the art and, in particular, to provide a method for reducing interference during data transmission via power cables, which compensates for impulse interference and improves the quality of the data transmission. Furthermore, the object of the invention is to provide a device for implementing such a method.

[0008] The object is achieved by a method for reducing interference in data transmission via an at least three-wire power cable according to claim 1, wherein a first conductor pair is used to transmit user data signals, and a second conductor pair of the power cable, different from the first, is used to detect and form a reference signal for interference. Advantageous embodiments are the subject of the dependent claims.

[0009] The object is further achieved by a communication device for carrying out such a method according to claim 8 and by a supply network according to claim 9.

[0010] Interference that complicates the transmission of user data signals over power cables often occurs in buildings in a correlated form on multiple wire pairs. This is particularly evident in pulse interference that occurs in the same network segment and is caused, for example, by switching operations. The invention is based on the finding that a separate protective earth provides an additional means of detecting interference signals.

[0011] Devices for transmitting user data over power cables, so-called powerline modems, represent transmitters and / or receivers for a data stream. These devices typically operate on the LN wire pair, meaning they transmit the user data via the phase (L) and neutral (N) conductors. In all buildings with state-of-the-art electrical installations, the earthing is not established by a neutral connection at the respective socket (NPE), but rather by a separate protective earth (PE).

[0012] As a rule, the neutral conductor and the protective earth are at the same or almost the same potential, so that the useful data signal is preferably transmitted via the phase. The invention utilizes the effect that the equipotentiality does not apply to high-frequency, coupled interference such as pulse interference. It is therefore provided to use an additional conductor pair of the power cable, which has at least three conductors, for detecting interference. In particular, this allows the protective earth to be used to determine the interference and thus to generate a reference signal for interference reduction.

[0013] With the separate protective earth as a third conductor, several additional conductor pairs are available that can be used for measurement purposes, referred to below as measurement channels. In the case of impulse interference, the measurement channels contain interference that is strongly correlated with that occurring in the data channel used for transmission. This high correlation makes it possible to approximately determine at least the duration of the interference, and in principle also the type and magnitude of the interference in the data channel.

[0014] In a three-core cable of an AC domestic installation, the measuring channel can be formed by the phase and the protective earth, L-PE, or by the neutral conductor and the protective earth, N-PE.

[0015] The measurement channel is preferably formed by the N-PE conductor pair. This takes advantage of the fact that potential equality or low-resistance grounding does not apply to high-frequency interference. The payload signals are then preferably transmitted via the LN conductor pair.

[0016] In the case of three-phase current or other power cables with multiple phases or more than three conductors, additional conductor pairs can be used as measuring channels.

[0017] In one embodiment, multiple conductor pairs can also form multiple measurement channels. The interference detected on the multiple measurement channels can be averaged or otherwise used to form a reference signal for interference. In another embodiment, multiple conductor pairs form separate payload signal transmission paths, and one conductor pair functions as the measurement channel.

[0018] According to the invention, no user data is transmitted via the measurement channel. It is used solely to generate the reference signal and thus to determine whether or not a disturbance is present and to what extent.

[0019] In a first variant of the method, the information from the measurement channel about a disturbance can be used to identify the corresponding payload data as being influenced by a disturbance and to mark it in an optional additional step. The reference signal can therefore represent a probability value or contain digital information about whether a disturbance is present or not. The information about the detection of a disturbance can then be used in a further processing step, for example - possibly even at a higher protocol level - to discard the payload data in whole or in part and request it again, or to provide a decoder with the reliability of the data.

[0020] In a second variant, the interference affecting the measurement channel or multiple measurement channels is used to suppress the interference from the payload signal. Due to the high correlation, noise cancellation can be achieved in the simplest case by directly subtracting the signals of the measurement channel from the signals of the payload channel. The relationship between the payload signal and the measurement channel can be described by a filter.

[0021] Instead of subtracting the direct measurement signal as a reference signal, the measurement signal can first be processed. It can be formed as the average of several measurement channels, or it can be modified in the time or frequency spectrum using additional filters, for example, before being compared or subtracted from the payload signal.

[0022] A suitable type of processing may be to not mark the reference signal in every case of interfering interference, but only when a certain threshold is exceeded. The required exceeding of the threshold can be specified, for example, by the interference exceeding a certain duration, a certain amplitude, or reaching a predetermined value in a transformation range, such as a sufficiently broad frequency band interference. The processing can be carried out by marking the threshold exceedances of interference pulses in the measurement channel in a transformation range, e.g. after performing a discrete Fourier transform (DFT) on the spectral components, possibly including the filter function between the two channels.

[0023] To mark corrupted payload data, the payload signal and the reference signal can be viewed, for example, in time windows (frames) of a specified length. If a fault is present, the fault can then be marked, discarded, or error-handled window-by-window. Threshold violations can be used to detect potential error locations and, in the decoding of error-correcting codes, to mark the error locations (erasures), thus increasing the correction capability.

[0024] In a further embodiment of the method, it can be provided that, after a fault is detected, the identified data is reprocessed immediately or at a later time. For this purpose, the error-correcting code can be applied to the data, which may be adapted to the type and duration of the fault. Reed-Solomon codes, for example, allow the correction of twice as many erasures (errors at known locations) as errors at unknown locations.

[0025] The invention also relates to a communication device for implementing the proposed methods. The communication device can be provided for solely transmitting the payload signal or solely receiving the payload signal and the measurement signals. It is preferably designed for both transmitting and receiving. All components required for receiving and further processing the payload signal are preferably arranged in a common housing.

[0026] In one embodiment, the communication device is intended for use in a domestic electrical installation. At least part of the domestic installation forms a supply network with at least one phase, a neutral conductor, and a protective earth cable, which has a transmitting device for transmitting a user data signal and a communication device for receiving the user data signal and a reference signal.

[0027] The invention will be explained below with reference to exemplary embodiments. Fig. 1 a representation of a first pulse event in the useful channel (upper graphic) and in the measuring channel (lower graphic), Fig. 2 a representation of a second pulse event in the useful channel (upper graphic) and in the measuring channel (lower graphic), Fig. 3 a representation of a third pulse event in the useful channel (upper graphic) and in the measuring channel (lower graphic), Fig. 4 the frequency-dependent correlation factor averaged over several pulse events and Fig. 5 a block diagram of a filter of a powerline communication device.

[0028] The Fig. Figures 1-3 show examples of interference signals from one channel of a power line. As can be seen from the comparison of the LN segment (data channel) and the NPE segment (measurement channel), the pulse events in the data channel and the measurement channel correlate in their temporal progression within the time window.

[0029] The striking correlation of the disturbances in the comparison of the channels is in Fig. 4 is illustrated by the correlation factor, which is often close to 1 over a wide frequency range. This high correlation offers the possibility of interference suppression or at least reduction by approximately determining the interference in the useful channel and subtracting it (noise cancellation).

[0030] The relationship between the measuring channel and the useful channel can be described by a filter. Fig.Figure 5 shows a circuit diagram of such an arrangement for noise reduction by filtering the signal of the measuring channel and subtracting it from the signal of the useful channel.

Claims

[1] Method for reducing interference in a data transmission via a power cable with at least three conductors, wherein a first pair of conductors is used for transmitting user data signals, characterized by that a second conductor pair of the power cable, different from the first, is used to detect and form a reference signal for disturbances, whereby no useful data signal is transmitted on the second conductor pair. [2] Method according to claim 1, characterized by that the second conductor pair is formed by the protective earth (PE) with the neutral conductor (N) or the protective earth (PE) with one of the phases (L). [3] Method according to claim 2, characterized by that the first pair of conductors is formed by the neutral conductor (N) and one of the phases (L). [4] Method according to one of the preceding claims, characterized by that the reference signal is used to detect or suppress interference that affects the user data signals. [5] Method according to claim 5, characterized by that the detection of disturbances occurs by exceeding threshold values in a time or frequency window. [6] Method according to claim 4 or 5, characterized by that when a fault is detected, the affected user data is marked so that an error-correcting code can be applied. [7] Method according to one of the preceding claims, characterized by that after suitable filtering the reference signal is subtracted from the useful data signal. [8] Communication device for carrying out a method according to one of the preceding claims. [9] Supply network with a power cable having at least one phase (L), a neutral conductor (N) and a protective earth (PE), a transmitting device for transmitting a user data signal and a communication device according to claim 8 for receiving the user data signal and a reference signal.

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