Apparatus for determining the relative velocity between a transmitting and a receiving device

A data transmission system (1) comprises a transmitter (2) and receiving means (3) for transmitting data by radio. The transmitting device (2) includes a transmitting unit (4, 5) for transmitting a pilot signal (20), which (3) contains one of the receiving means known symbol sequence. The receiving device (3) comprises a counting unit (10, 11) for counting crossings of the received symbol sequence by a predetermined threshold value and an evaluation unit (13) for calculating the velocity between the transmitter (2) and the receiving device (3) from the count value ,