Communication apparatus with antenna attenuation compensation

1. A communication system for a motor vehicle, the system comprising:

a transceiver unit for generating transmission signals at a transmission output of the transceiver unit, wherein at least two of the transmission signals differ in terms of their signal power;

a cable coupled to the transmission output to transmit the transmission signals to an antenna connected to an antenna end of the cable via a controllable amplifier device amplifying the transmission signals transmitted via the cable;

a power detector device capturing a respective power value correlated with a power of the transmission signals at a tapping point between the antenna end of the cable and the antenna; and

a control device controlling the amplifier device on the basis of the captured power values;

wherein the transceiver device generates at least one of the transmission signals with a predetermined reference power;

a reference value describing the reference power is permanently predefined in the control device; and

the control device selects one of the power values as an actual value of the power of the at least one transmission signal generated with the reference power at the tapping point and sets a transmission gain value of the amplifier device on the basis of a discrepancy between the reference value and the actual value.

2. The communication system as claimed in claim 1 , wherein:

the transceiver device generates the transmission signals at the transmission output each solely with a transmission power selected from one of at least two predefined power levels;

the reference power corresponds to one of the power levels, and

the control device selects, as the actual value, that power value indicating a power between the power level of the reference power and the next lower power level.

3. The communication apparatus as claimed in claim 1 , wherein:

the transceiver device generates, as a transmission signal, a calibration signal with the reference power on the basis of a trigger signal; and

the control device selects the actual value on the basis of the trigger signal.

4. The communication apparatus as claimed in claim 1 , wherein the reference power corresponds to a maximum or a minimum transmission power, and the control device selects a maximum value or a minimum value of the power values as the actual value.

5. The communication apparatus as claimed in claim 1 , wherein:

the amplifier device amplifies reception signals received via the antenna on the basis of a reception gain value and then forwards them to the cable; and

the control device sets the reception gain value on the basis of the discrepancy.

6. The communication apparatus as claimed in claim 5 , wherein:

the amplifier device is connected to the cable via a multiplexer;

the transceiver device changes over the multiplexer between a transmission position and a reception position by means of a switching signal;

the control device distinguishes between power values of the transmission signals and power values of the reception signals on the basis of the switching signal and account only for power values of the transmission signals for the purpose of determining the discrepancy.

7. The communication apparatus as claimed in claim 1 , wherein the control device takes into account only power values captured between the antenna end of the cable and the antenna for the purpose of determining the discrepancy.

8. The communication apparatus as claimed in claim 1 , wherein the control device is electrically coupled to the transceiver device solely via the cable.

9. The communication apparatus as claimed in claim 1 , wherein the power detector device comprises a diode-based envelope demodulator.

10. The communication apparatus as claimed in claim 1 , wherein the communication device generates the transmission signals according to a car-to-car communication protocol.

11. A method for compensating for cable attenuation in a communication apparatus, the method comprising:

generating transmission signals with a transceiver unit, wherein at least two of the transmission signals differ in their signal power;

transmitting the transmission signals through a cable coupled to an output of the transceiver unit and to an antenna, wherein a controllable amplifier device is connected between an antenna end of the cable and the antenna;

capturing respective signal power values with a power detector sensing a power of the transmission signals at a tapping point between the antenna end of the cable and the antenna; and

controlling the amplifier on the basis of the captured power values;

wherein the transceiver device generates at least one of the transmission signals with a predetermined reference power;

a reference value describing the reference power is permanently predefined; and

an actual value is selected from the power values, the actual value corresponding to the power of the at least one transmission signal generated with the reference power at the tapping point; and

a transmission gain value of the amplifier device is set on the basis of a discrepancy between the reference value and the actual value.