A method of determining a distance between a radio frequency device (2, 102) and a target (18, 122), the method comprising: the radio frequency device (2, 102) receiving a radio frequency signal (16, 146) from the target; determining a time domain channel response (202, 302, 600, 700, 800, 900) from the received radio frequency signal (16, 146); determining an amplitude of a largest peak (204, 304, 902) in the time domain channel response (202, 302, 600, 700, 800, 900); determining an amplitude of a second, earlier, peak (306, 904) in the time domain channel response (202, 302, 600, 700, 800, 900); comparing the second peak amplitude to a threshold based on the largest peak amplitude; identifying the largest peak (204, 304, 902) as a shortest path peak if the second peak amplitude is less than the threshold; identifying the second peak (306, 904) as a shortest path peak if the second peak amplitude is greater than the threshold; identifying a closest local minimum in the time domain channel response (202, 302, 600, 700, 800, 900) earlier than the shortest path peak; determining a time separation between the closest local minimum and the shortest path peak; comparing the time separation to an expected time separation based on a bandwidth of the received radio frequency signal (16, 146); calculating the distance between the radio frequency device (2, 102) and the target (18, 122) based on a time corresponding to the shortest path peak; and if the time separation is greater than the expected time separation, calculating said time corresponding to the shortest path peak as a time corresponding to the closest local minimum plus the expected time separation. the radio frequency device (2, 102) receiving a radio frequency signal (16, 146) from the target; determining a time domain channel response (202, 302, 600, 700, 800, 900) from the received radio frequency signal (16, 146); determining an amplitude of a largest peak (204, 304, 902) in the time domain channel response (202, 302, 600, 700, 800, 900); determining an amplitude of a second, earlier, peak (306, 904) in the time domain channel response (202, 302, 600, 700, 800, 900); comparing the second peak amplitude to a threshold based on the largest peak amplitude; identifying the largest peak (204, 304, 902) as a shortest path peak if the second peak amplitude is less than the threshold; identifying the second peak (306, 904) as a shortest path peak if the second peak amplitude is greater than the threshold; identifying a closest local minimum in the time domain channel response (202, 302, 600, 700, 800, 900) earlier than the shortest path peak; determining a time separation between the closest local minimum and the shortest path peak; comparing the time separation to an expected time separation based on a bandwidth of the received radio frequency signal (16, 146); calculating the distance between the radio frequency device (2, 102) and the target (18, 122) based on a time corresponding to the shortest path peak; and if the time separation is greater than the expected time separation, calculating said time corresponding to the shortest path peak as a time corresponding to the closest local minimum plus the expected time separation.