Determining distance between two radio transceivers

A reflector radio transceiver for use in a method for determining a distance between an initiator radio transceiver and the reflector radio transceiver, wherein the reflector radio transceiver is configured to:

• determine a frequency offset of a sampling clock signal from one or more radio signals received by the reflector radio transceiver, and determine an adjustment factor in dependence on the determined frequency offset;
• receive a first radio signal from the initiator radio transceiver at a first reception time;
• generate an electrical signal representative of the received first radio signal;
• generate a sampled signal by sampling the electrical signal using the sampling clock signal;
• process the sampled signal to determine a first reception-time value, representative of the first reception time, at a temporal resolution that is finer than a sampling period of the sampling clock signal, whereby the first reception-time value comprises a fractional component representative of a fraction of the sampling period;
• and
• use the fractional component and the adjustment factor to transmit a second radio signal at a second transmission time that follows a pulse of the sampling clock signal by an offset amount that is equal to said fractional component plus the adjustment factor, such that the second transmission time is delayed from the first reception time by a predetermined dwell time that is determined to an accuracy finer than the sampling period.

A non-transitory computer-readable storage medium comprising instructions that, when executed by a processing system of a reflector radio transceiver, cause the processing system to:

• receive a sampled signal representative of a received first radio signal received by the reflector radio transceiver at a first reception time, wherein the sampled signal is sampled according to a sampling clock signal having a sampling period;
• process the sampled signal to determine a first reception-time value, representative of the first reception time, at a temporal resolution that is finer than the sampling period, whereby the first reception-time value comprises a fractional component representative of a fraction of the sampling period;
• determine an adjustment factor in dependence on a frequency offset of the sampling clock signal;
• and
• use the fractional component and the adjustment factor to control the reflector radio transceiver to transmit a second radio signal at a second transmission time that follows a pulse of the sampling clock signal by an amount that is equal to said fractional component plus the adjustment factor, such that the second transmission time is delayed from the first reception time by a predetermined dwell time that is determined to an accuracy finer than the sampling period.