| 摘要 |
Disclosed is a radio installation for a road toll system (1) which determines the distance (a1, a2) of a passing vehicle (12). The vehicle has an on-board unit (11) which emits a signal (10) with a known curve of its frequency over time. The radio installation (1) contains a receiver (8) configured to receive the signal (10) of a passing vehicle (12) and a memory connected to the receiver (8). The memory is configured to record the curve of the frequency of the received signal (10) over time in relation to the known frequency curve over time. A detector is provided to detect a change in the recorded frequency curve. The system also includes an evaluation device which is connected to the memory and detector and is configured to look for two far regions in the frequency curve. These far regions lie before and after the detected change in time and show a frequency change below a threshold value. A scaling device is connected to the memory and the evaluation device and is configured to scale the recorded frequency curve so that the far regions assume predetermined values. A differentiator then determines the gradient of the scaled frequency curve at an inflection point and determines the distance (a1, a2) between the passing vehicle (12) and the installation from this gradient. |
