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1. A system comprising a first radio device, acting as master and a second radio device, acting as slave, each of the first and second radio devices having a time reference and being arranged for transmitting and receiving radio signals that include a plurality of chirps, said first and second radio devices having a ranging mode in which the first radio device transmits to the second radio device a ranging request containing ranging chirps, and the second radio device responds to the ranging request transmitting to the first radio device a ranging reply containing reply chirps, the second radio device is configured to align the reply chirps in time and frequency with the ranging chirps, the system being configured to determine a range between the first radio device and the second radio device, based on time shifts between the ranging chirps and the reply chirps, wherein the ranging chirps do not have all the same slope, the system being configured to determine a Doppler-unbiased range and a Doppler shift between the first radio device and the second radio device, based on time shifts between the ranging chirps and the reply chirps, wherein the first radio device has a plurality of receiving antennas at known positions, and a switch for selecting each receiving antenna in turn, the first radio device being configured to switch between the antennas during the reception of the ranging chirps, such that each antenna is used to receive ranging chirps of different slopes, the master being configured to determine phases of ranging chirps received by each receiving antenna from the second radio device, and an angle of arrival of the radio signal based on said phases.
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