DE102018216949A1 - Method for transmitting at least one useful signal between two transceiver units, transceiver unit and vehicle - Google Patents

Abstract

The invention relates to a method for transmitting at least one useful signal between two transceiver units (TRX1, TRX2) via a transmission medium (TL), with a first of the two transceiver units (TRX1) during a first transmission phase (P1). a first useful signal (UTX1) with a useful voltage level (LTX) is sent via the transmission medium (TL) to a second of the two transceiver units (TRX2). The invention provides that the second transmit / receive unit (TRX2) sends a first interference signal (UN2) with an interference voltage level during the first transmit phase (P1) via the transmission medium (TL) to the first transmit / receive unit (TRX1) (LN) is sent, with which the first useful signal (UTX1) is completely or temporarily superimposed.

Description

The invention relates to a method for transmitting at least one useful signal between two transceiver units, the transceiver unit and a vehicle equipped with the transceiver units.

Motor vehicle electronics can be subjected to numerous manipulation attempts. Such manipulation attempts are often made for the unauthorized adaptation of motor vehicle behavior. This includes, in particular, the so-called chip tuning, which is intended to improve the driving behavior of a motor vehicle, but is accompanied by greater wear on the vehicle parts and can thus impair the proper functioning of the motor vehicle. A starting point of such a manipulation attempt is to listen to signals which are transmitted via serial data transmission networks of the motor vehicle, such as the LIN bus or the CAN bus, or between associated memory chips.

A countermeasure to prevent eavesdropping is to provide a way to perform secure serial data transmission. Secure serial data transmission has so far only been possible using encryption methods such as AES or RSA.

A disadvantage of securing by means of encryption methods is the computing effort of the encryption, which causes an increase in the computing time or an additional hardware effort. Another problem is the secure storage of the keys required for the encryption processes. In the case of smaller microcontrollers and external components in particular, encryption is a computationally complex process, so that they cannot be secured using encryption processes.

A solution is therefore required to enable tap-proof serial data transmission without complex encryption methods, so that tap-proof serial data transmission between smaller microcontrollers with external components, such as RAM, flash, which can be connected via SPI, for example, is made possible.

It is an object of the invention to provide a solution which enables tap-proof transmission on lines.

According to the invention, a method for transmitting at least one useful signal between two transceiver units via a transmission medium is provided. A first useful signal with a useful voltage level is sent via the transmission medium to a second of the two transmit / receive units by a first of the two transmit / receive units during a first transmit phase. During the first transmission phase, the second transceiver unit sends a first interference signal with an interference voltage level to the first transceiver unit via the transmission medium. The two transmissions take place on the same line. The first useful signal is completely or temporarily superimposed on the first interference signal.

In other words, during the first transmission phase, the transmission of the first useful signal from the first transmission / reception unit to the second transmission / reception unit takes place via the transmission medium. In order to make it more difficult to intercept the first useful signal during transmission via the transmission medium, the first interference signal is sent to the first transceiver unit by the second transceiver unit in the first transmission phase. The first useful signal has the useful voltage level and the first interference signal has the interference voltage level. In the first transmission phase, the first useful signal and the first interference signal are at least temporarily superimposed.

The advantage of the invention is that listening to the first useful signal is made more difficult due to the superposition of the first useful signal with the first interference signal on the duplex line. In addition, the effort is reduced compared to the classic encryption method, so that the method can be carried out by components that do not have sufficient computing capacity for encryption methods.

The transceiver units can be combined electronic components, for example, which are set up both for transmitting and for receiving signals. Such transceivers are also known as transceivers. The method can be carried out by the two transceiver units, which can be connected to one another via a duplex line. During the first transmission phase, a first input signal with a signal voltage level at a first input of the first transmission / reception unit can be received by the first transmission / reception unit. The first input signal can be adjusted to the first useful signal with the useful voltage level by a first input driver of the first transceiver unit. The first useful signal can then be sent to the second transceiver unit via the transmission medium. The second transceiver unit can receive the first useful signal and by means of a transform the second output driver to a second output signal with the signal voltage level. The useful signal can thus be output at a second output of the second transceiver unit as the second output signal. During the first transmission phase, the first interference signal can be sent by the second transceiver unit to the first transceiver unit via the transmission medium in the opposite direction to the first useful signal. To generate the first interference signal, the second transceiver unit can have a second interference voltage source. This can generate a random signal as the first interference signal with the interference voltage level. So that the first interference signal is not output at the second output of the second transceiver unit, the second transceiver unit can have a hybrid circuit, as a result of which the first interference signal can be canceled on the feed line to the second output, so that at the second output only the output signal generated from the first useful signal is made available to the second transceiver unit.

The invention also includes further developments which result in additional advantages.

A further development of the invention provides that the second of the two transmit / receive units sends a second useful signal with the useful voltage level via the transmission medium to the first of the two transmit / receive units during a second transmission phase. During the second transmission phase, the first of the two transmit / receive units sends a second interference signal with the interference voltage level to the second transmit / receive unit via the transmission medium. In other words, the second useful signal is transmitted from the second transceiver unit via the transmission medium to the first transceiver unit during the second transmission phase. In order to superimpose the second useful signal, the first transceiver unit sends the second interference signal to the second transceiver unit via the transmission medium. Thus, during the second transmission phase, the second useful signal is superimposed in whole or in part by the second interference signal.

This has the advantage that transmission of useful signals from the second transceiver unit to the first transceiver unit is also made possible.

For example, it can be provided that in the second transmission phase a second input signal is received by a second input of the second transmission / reception unit. The second input signal can be transformed by a second input driver of the second transceiver unit to the second useful signal with the useful voltage level and can be sent to the first of the two transceiver units via the transmission medium. The second useful signal can be received by the first transceiver unit, transformed by a first output driver to a first output signal with the signal voltage level and made available at a first output of the first transceiver unit. During the second transmission phase, the second interference signal with the interference voltage level can be generated by a first interference voltage source of the first transceiver unit and can be sent to the second transceiver unit via the transmission medium. The second interference signal and the second useful signal can at least temporarily overlap on the duplex line. So that the second interference signal of the first transceiver unit is not output at the first output of the first transceiver unit, the first transceiver unit can have a hybrid circuit, as a result of which the second interference signal is filtered out.

A further development of the invention provides that a half-duplex transmission of the useful signals is carried out by the two transceiver units, a transmission being carried out alternately during the first transmission phase or the second transmission phase.

In other words, it is provided that the first transmission phase and the second transmission phase alternate, the first useful signal being sent from the first transmission-reception unit to the second transmission-reception unit in the first transmission phase and that in the second transmission phase second useful signal is transmitted from the second transceiver to the first transceiver. To conceal the respective useful signals, the respective interference signal is transmitted alternately, the first interference signal being sent from the second transceiver unit to the first transceiver unit during the first transmission phase and the second interference signal from the first during the second transmission phase Transceiver unit is sent to the second transceiver unit.

This has the advantage that a two-sided transmission between the two transceiver units is made possible.

It can be provided, for example, that the first transmission-reception unit and the second transmission-reception unit are synchronized in time and that each transmission phase has a predetermined duration. The first transceiver unit and the second transceiver unit can each at the end of one of the transmission phases initiate another transmission phase, so that one after the other there is a change between the first and the second transmission phase. Useful signals can thus be transmitted alternately from the first transceiver unit to the second transceiver unit and from the second transceiver unit to the first transceiver unit.

A further development of the invention provides that the first interference signal and / or the second interference signal are generated randomly.

In other words, the first interference signal and / or the second interference signal are generated by a respective interference voltage source, the interference signals having non-reproducible voltage fluctuations.

This has the advantage that it is not possible to calculate the interference signal from the superimposed signal in order to access the useful signal.

It can be provided, for example, that the respective transceiver unit has an electronic circuit which, for example, generates a random noise which is increased to the interference voltage level in order to generate the interference signal.

A further development of the invention provides that the first interference signal is transmitted continuously during the first transmission phase and / or the second interference signal is transmitted continuously during the second transmission phase.

In other words, the first interference signal is continuously transmitted in the first transmission phase and the second interference signal is transmitted continuously in the second transmission phase.

This has the advantage that a complete transmission takes place, and it is also possible to disguise whether a useful signal is being transmitted at all during the respective transmission phase.

It can be provided, for example, that the respective interference signal is generated by the respective transceiver unit and sent to the other transceiver unit from the beginning and to the end of the respective transmission phase. This can take place regardless of whether the respective useful signal is sent during the transmission phase. It can be provided that the interference signal is triggered when a first part of the useful signal is received. Then the generation takes place only when required.

A further development of the invention provides that the interference voltage level is at least a factor 10 larger than the useful voltage level. In other words, the interference signals have an interference voltage level which is at least ten times greater than the useful voltage level of the useful signals. This has the advantage that there is a very low signal-to-noise ratio on the duplex line, which makes it difficult to intercept the useful signals. It can be provided, for example, that the useful voltage level of the useful signal is 100 millivolts or less, whereas the interference voltage level of the interference signal is 5 volts or more, for example.

A further development of the invention provides that the first interference signal and / or the second interference signal are rejected when received by one of the transmit / receive units. In other words, it is provided that the first interference signal is filtered out or rejected when received by the first transceiver unit and / or the second interference signal is filtered out or rejected when received by the second transceiver unit. This has the advantage that the interference signal is not output at the output of the transceiver unit which receives the interference signal. It can be provided, for example, that a respective transceiver unit is switched during the transmission of the respective useful signal in such a way that the interference signal is not received via the transmission medium, or the interference signal is not routed to the output.

A further development of the invention provides that the first useful signal and / or the second useful signal has binary coding. In other words, the first useful signal and / or the second useful signal is a binary-coded signal. This has the advantage that digital signal transmission is possible. For example, it can be provided that the useful signals have either a lower voltage value or a higher voltage value. The lower voltage value can be assigned a value 0 and the higher voltage value can be assigned a value 1.

A further development of the invention provides that the transmission medium is a duplex line or at least includes sections. In other words, the signals are sent at least in sections over a duplex line. This has the advantage that listening to a duplex line is made more difficult. For example, it can be provided that the transceiver units are connected to the duplex line.

A further development of the invention provides that the transmission medium is an air route or at least includes routes. In other words, the signals are sent via radio. This has the advantage that listening to radio signals is made more difficult. The transceiver units can be set up for sparking, for example. It can be provided, for example, that signals are transmitted by the transceiver units, in particular via short-range radio, such as NFC. In this case, a key exchange via the useful signals for symmetrical cryptography (for example with AES) may be necessary. To prevent eavesdropping, a transceiver can send out the interference signals. In this case, an unauthorized receiver can receive the superimposed signal, including the useful signal and the interference signal. Because of the superimposition, reading out the useful signal is difficult for him. Another possibility would be to use the method during radio communication between vehicles (Car-2-Car). Transceiver units of vehicles traveling in succession can send useful signals to one another. Interception by third parties is made more difficult by the interference signals.

The invention also includes a transceiver unit which is set up to carry out the method.

In other words, the invention also comprises a combined unit which is set up both as a transmitter and as a receiver. The transceiver unit is set up to send or receive a useful signal with a useful voltage level via a transmission medium during a transmission phase. The transceiver unit is set up to generate an interference signal with an interference voltage level by means of an interference voltage source and to transmit it via the transmission medium.

The transceiver unit can be set up, for example, as a hybrid circuit, which is set up to separate forward and returning voltage waves on the duplex line by a resistance voltage.

The invention also includes a vehicle which has at least one of the transceiver units. The vehicle can be, for example, a passenger car, a truck, a motorcycle, a bicycle, or a bicycle with an electric drive (e-bike).

The invention also includes further developments of the transceiver unit according to the invention and the vehicle according to the invention, which have features as have already been described in connection with the further developments of the method according to the invention. For this reason, the corresponding developments of the transceiver unit according to the invention and the vehicle according to the invention are not described again here.

The invention also includes combinations of the features of the described embodiments.

• 1 ein System von zwei Ausführungsformen der erfindungsgemäßen Sende-Empfangs-Einheit, welche über die Duplexleitung miteinander verbunden sind;
• 2 mögliche Signalverläufe während einer Durchführung einer Ausführungsform des erfindungsgemäßen Verfahrens; und
• 3 ein Ablauf einer Ausführungsform des erfindungsgemäßen Verfahrens.

An exemplary embodiment of the invention is described below. This shows:

• 1 a system of two embodiments of the transceiver unit according to the invention, which are interconnected via the duplex line;
• 2nd possible signal profiles during the execution of an embodiment of the method according to the invention; and
• 3rd a sequence of an embodiment of the method according to the invention.

The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual features of the invention that are to be considered independently of one another, which further develop the invention independently of one another and are therefore also to be regarded individually or in a combination other than the one shown as part of the invention. Furthermore, the described embodiment can also be supplemented by further features of the invention that have already been described.

In the figures, elements with the same function are each provided with the same reference symbols.

1 shows a possible system with two embodiments of the transceiver units, which are interconnected via the duplex line. The send-receive units ( TRX1 , TRX2 ) can be arranged in a vehicle. The system can be the first transceiver unit TRX1 and the second TRX2 include which through the duplex line TL can be connected. The task of the transceiver units TRX1 and TRX2 can consist of tap-proof transmission of useful signals UTX1 , UTX2 over the duplex line TL to enable.

It can be provided that in the first transmission phase P1 a sends the useful signal UTX1 from the first transceiver unit TRX1 over the duplex line TL to the second transceiver unit TRX2 is carried out. A first input signal TX1 with a signal voltage level LRX can from the first transceiver unit TRX1 at the first entrance IN1 be received. Using the first input driver LT1 may be the first Input signal TX1 on the first useful signal UTX1 with the useful voltage level LTX be set.

The first useful signal UTX1 can from the first transceiver unit TRX1 over the duplex line TL to be dispatched. Via the duplex line TL can be the first useful signal UTX1 to the second transceiver unit TRX2 are transmitted and by the second transceiver unit TRX2 be received. Via the second output driver LR2 the second transceiver unit TRX2 can be the first useful signal UTX1 from the useful voltage level LTX to the signal voltage level LRX be set and at a second output OUT2 as the first output signal RX2 the second transceiver unit TRX2 to be provided.

Listening to the first useful signal UTX1 on the duplex line TL is difficult, it can be provided that the second transceiver TRX2 the second interference voltage source G2 which is set up to provide the first interference signal UN2 to create. The first interference signal UN2 can reduce the interference voltage level ULN have, which can be, for example, 5 volts. The first interference signal UN2 can be a noise signal that is randomly generated. The resistances R the second transceiver unit TRX2 can be matched to one another in such a way that at the output driver LR2 an extinction of the first interference signal UN2 takes place so that the first interference signal UN2 not at the second exit OUT2 the second transceiver unit TRX2 is issued.

The first interference signal UN2 can over the duplex line TL to the first transceiver unit TRX1 to be dispatched. This can lead to a partial or complete superimposition of the first useful signal UTX1 with the first interference signal UN2 to the line signal UTL come. It is therefore not possible for the first useful signal to be protected UTX1 alone on the duplex line TL to eat. The useful voltage level LTX can be, for example, 100 millivolts. It can be provided that the system is operated in a half-duplex transmission method. This can mean that the first broadcast phase P1 and the second broadcast phase P2 alternate. The change between the transmission phases P1 , P2 can take place after a predetermined time, for example. In the second broadcast phase P2 it can be provided that a transmission of the second useful signal UTX2 from the second transceiver unit TRX2 to the first transceiver unit TRX1 is carried out.

A second input signal TX2 can by the second transceiver unit TRX2 at a second entrance IIN2 be received. Using a second input driver LT2 the second transceiver unit TRX2 can the second input signal TX2 into the second useful signal UTX2 with the useful voltage level ULTX be transformed. The second useful signal UTX2 can over the duplex line TL from the second transceiver unit TRX2 to the first transceiver unit TRX1 be transmitted. By a first output driver LR1 the first transceiver unit TRX1 can the second useful signal UTX2 from the useful voltage level LTX to the signal voltage level LRX be set and as a second output signal RX1 at a first exit OUT1 the first transceiver unit TRX1 be issued. During the second broadcast phase P2 can be the second interference signal UN1 by means of a first interference signal generator G1 the first transceiver unit TRX1 generated and over the duplex line TL to the second transceiver unit TRX2 be transmitted. Thus takes place on the duplex line TL again a superimposition of the second useful signal UTX2 with the second interference signal UN1 to the line signal UTL instead of. The first transceiver TRX1 can also have a hybrid circuit, the resistors R are coordinated such that the second interference signal UN1 on the first output driver LR1 picks up.

The binary TTL input signals TX1 and TX2 (Typ. NRZ coding [0,1] assignment to [0, 5] V) can be done by the input driver LT1 , LT2 according to the invention on the useful signals UTX1 and UTX2 with a useful voltage level LTX being transformed. This useful voltage level LTX of the useful signals UTX1 and UTX2 is small compared to the noise level LN the intentionally superimposed interference signals UN1 and UN2 . A factor c is therefore smaller than 1. c << 1:

$$\text{UTX2}=\text{c*TX2}+\text{UN2}$$

$$\text{UTL}=\mathrm{0,5}\text{*UTX1}+\mathrm{0,5}*\text{UTX2}$$

$$\text{URX1}=0\text{*UTX1}+\mathrm{0,5}*\text{UTX2}=\text{UTL}-\mathrm{0,5}*\text{UTX1}$$

$$\text{UTL}=\mathrm{0,5}\text{*UTX1}+\mathrm{0,5}*\text{UTX2}$$

$$\text{URX2}=\mathrm{0,5}\text{*UTX1}+0*\text{UTX2}=\text{UTL}-\mathrm{0,5}*\text{UTX2}$$

In the example, the following relationships exist between the signals: $$\text{UTX1}=\text{c * TX1}+\text{UN1}$$

$$\text{UTX2}=\text{c * TX2}+\text{UN2}$$

$$\text{UTL}=0.5\text{* UTX1}+0.5*\text{UTX2}$$

$$\text{URX1}=0\text{* UTX1}+0.5*\text{UTX2}=\text{UTL}-0.5*\text{UTX1}$$

$$\text{UTL}=0.5\text{* UTX1}+0.5*\text{UTX2}$$

$$\text{URX2}=0.5\text{* UTX1}+0*\text{UTX2}=\text{UTL}-0.5*\text{UTX2}$$

Transmission line according to the invention for a connecting line ( TL ) whose voltage (or current) can in principle be monitored. Without the arrangement of the transmitter drivers according to the invention in series switched interference voltage sources G1 and G2 the left or right-hand transceiver is a classic full-duplex transmission (hybrid circuit), in which the forward and returning voltage waves on the line are separated by the resistance balance (Eq. 1). So that the left-hand receive voltage URX1 only dependent on the opposite transmission voltage Um, and thus of UTX2 , but not from the left-hand transmitter voltage Um, which according to the invention is formed by a left-hand interference signal, while the right-hand transmitter user data ( UTX2 ) sends. According to the invention, in favor of a very small signal-to-interference ratio, the information-carrying signal on the line is overlaid with a strong interference signal, which is neither known on the line nor at the opposite receiver and can therefore be eliminated. Listening to the information on the line is therefore made considerably more difficult, especially if the transmission level is selected to be much lower than the mean amplitude of the interference signals, this does not lead to any problems with the bit error rate for short lines.

2nd shows waveforms on the connecting line during a possible embodiment of the method according to the invention. A possible time course of the respective signals is shown during the second transmission phase P2 and the first broadcast phase P1 . The second input signal TX2 can, for example, as a binary coded signal by the second transceiver TRX2 be received. The second interference signal UN1 can during the second broadcast phase P2 by the first transceiver unit TRX1 over the duplex line TL be transmitted. This can be caused by the first interference voltage source G1 act randomly generated signal. During the second broadcast phase P2 can that on the useful voltage level LTX regulated second useful signal UTX2 over the duplex line TL be transmitted so that there is a superimposed signal UTL on the duplex line TL forms. The second useful signal UTX2 can through the first output driver LR1 the first transceiver unit TRX1 to the signal voltage level LRX be set and as a second output signal RX1 at the first exit OUT1 the first transceiver unit TRX1 be issued. After the end of the second broadcast phase P2 it can be provided that the first input signal TX1 by the first transceiver unit TRX1 is received and on the first useful signal UTX1 with the useful voltage level UTX is regulated. The first useful signal UTX1 can over the duplex line TL to the second transceiver unit TRX2 be transmitted. During the first broadcast phase P1 can be the first interference signal UN2 through the second interference voltage source G2 the second transceiver unit TRX2 generated and over the duplex line TL are transmitted so that the superimposed signal is on the duplex line UTL can form. That through the second transceiver unit TRX2 received useful signal UTX1 can on the signal voltage level LRX be reset and as the first output signal RX2 at the second exit OUT2 the second transceiver unit TRX2 be issued.

3rd shows a possible embodiment of the method according to the invention. In a first step, the first transceiver unit TRX1 at the first entrance IIN1 the first input signal TX1 be received. This can be, for example, a binary coded signal with the signal voltage level LRX act ( S1 ).

In a second step S2 can be the first input signal TX1 by means of the first input driver LT1 on the first useful signal UTX1 with the useful voltage level LTX be set. The useful voltage level LTX can be, for example, 100 millivolts.

In one step S3 can be the first useful signal UTX1 over the duplex line TL from the first transceiver unit TRX1 to the second transceiver unit TRX2 be transmitted. At the same time, the second random number generator G2 the second transceiver unit TRX2 the first interference signal UN2 with the interference voltage level LN generated and over the duplex line TL be transmitted. The first useful signal is thus superimposed UTX1 and the first interference signal UN2 to the superimposed signal UTL .

In one step S4 can the second transceiver unit TRX2 the first useful signal UTX1 received and at the second output driver LR2 direct which of the first useful signal UTX1 with the useful voltage level LTX into the first output signal RX2 with the signal voltage level LRX converts. The first interference signal UN2 can also by the second output driver LR2 be received. It can be provided that the resistors R the second transceiver unit TRX2 are matched to one another in such a way that on two feed lines of the second output driver LR2 an identical signal arrives, which cancels them.

In a final step S5 can be the first output signal RX2 at the second exit OUT2 the second transceiver unit TRX2 be issued.

• - Vollduplex-Übertragung von rechtsseitigem nach linksseitigem Transceiver
• - Nutzsignal wird von rechts nach links mit reduziertem Spannungspegel übertragen (z.B. 100 mV)
• - Rauschsignal wird von links nach rechts mit vollem Pegel übertragen (z.B. 5 V)
• - Auf der Übertragungsleitung ist nur die Summe beider Signale messbar, mit sehr niedrigem Signal- zu Rauschverhältnis
• - Auf dem linksseitigen Transceiver ist jedoch das Rauschsignal bekannt und kann vom Nutzsignal getrennt werden (z.B. mittels Gabelschaltung)

2nd : Typical signal curves of the transmission link according to the invention for a connecting line ( TL ) after 1 . Above: Transceiver transmission 2nd to transceiver 1 (right to left), below: transmission from left to right (transceiver 1 after 2). In both cases, the useful signal on the line is deliberately chosen to be small, so that mainly the intentionally superimposed interference voltages UN1 and UN2 as line voltage LN are observable. This makes undesired eavesdropping considerably more difficult.

• - Full duplex transmission from right-hand to left-hand transceiver
• - The useful signal is transmitted from right to left with a reduced voltage level (e.g. 100 mV)
• - Noise signal is transmitted from left to right at full level (e.g. 5 V)
• - Only the sum of both signals can be measured on the transmission line, with a very low signal to noise ratio
• - However, the noise signal is known on the left-hand transceiver and can be separated from the useful signal (e.g. using a hook-up)

This enables tap-proof transmission on lines without the expense of traditional encryption. It is a pure hardware solution in the transceiver. The transmission can be possible in full duplex or half duplex mode. The method can be used for peer-to-peer standard transmissions with short lines, such as with SPI or I2C, or for onboard communication on a circuit board.

Overall, the example shows how tap-proof serial duplex data transmission can be provided by the invention.

Reference list

G1

first interference voltage source

G2

second interference voltage source

IN1

first entrance

IN 2

second entrance

LT1

first input driver

LT2

second input driver

LR1

first output driver

LR2

second output driver

UN1

second interference signal

UN2

first interference signal

P1

first broadcast phase

P2

second broadcast phase

R

resistance

RX1

first output signal

RX2

second output signal

OUT1

first exit

OUT2

second exit

TL

Duplex line

TRX1

first transceiver unit

TRX2

second transceiver unit

UTX1

first useful signal

UTX2

second useful signal

LN

Interference voltage level

TX1

first input signal

TX2

second input signal

UTL

superimposed signal

LTX

Useful voltage level

LRX

Signal voltage level

Motor vehicle

vehicle

Claims (12)

Method for transmitting at least one useful signal between two transmit / receive units (TRX1, TRX2) via a transmission medium (TL), whereby a first useful signal () is transmitted through a first of the two transmit / receive units (TRX1) during a first transmit phase (P1). UTX1) with a useful voltage level (LTX) via the transmission medium (TL) to a second of the two transceiver units (TRX2), characterized in that the second transceiver unit (TRX2) during the first transmission phase ( P1) a first interference signal (UN2) with an interference voltage level (LN) is sent via the transmission medium (TL) to the first transceiver unit (TRX1), with which the first useful signal (UTX1) is completely or temporarily superimposed. Procedure according to Claim 1 , characterized in that the second of the two transmit / receive units (TRX2) during a second transmit phase (P2) transmits a second useful signal (UTX2) with the useful voltage level (LTX) via the transmission medium (TL) to the first of the two transmitters Receiving units (TRX1) is sent, and by the first of the two transmitting / receiving units (TRX1) during the second transmission phase (P2) a second interference signal (UN1) with the interference voltage level (LN) via the transmission medium (TL) to the second transmit / receive unit (TRX2) is sent, with which the second useful signal (UTX2) is completely or temporarily superimposed. Procedure according to Claim 2 characterized in that a half-duplex transmission of the useful signals (UTX1, UTX2) is carried out by the two transceiver units (TRX1, TRX2), the first transmission phase (P1) or the second transmission phase (P2) being carried out alternately. Method according to one of the preceding claims, characterized in that the first interference signal (UN2) and / or the second interference signal (UN1) are generated randomly. Method according to one of the preceding claims, characterized in that the first interference signal (UN2) is transmitted continuously during the first transmission phase (P1) and / or the second interference signal (UN1) is transmitted continuously during the second transmission phase (P2). Method according to one of the preceding claims, characterized in that the interference voltage level (LN) is at least a factor 10 greater than the useful voltage level (LTX). Method according to one of the preceding claims, characterized in that the first interference signal (UN2) and / or the second interference signal (UN1) are rejected when received. Method according to one of the preceding claims, characterized in that the first useful signal (UTX1) and / or the second useful signal (UTX1) have NRZ coding. Method according to one of the preceding claims, characterized in that the transmission medium (TL) is a duplex line or at least includes sections. Method according to one of the preceding claims, characterized in that the transmission medium (TL) is an air route or at least includes routes. Transceiver unit, set up to carry out one of the methods according to one of the Claims 1 to 10th . Vehicle (vehicle) with a transceiver unit (TRX1, TRX2) Claim 11 .

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