Positioning device, communications system and method

A communications system, the communications system comprising:

• a device;
• a first base station;
• and
• a second base station,
• wherein the first base station is arranged to transmit a first signal to the second base station,
• the second base station is arranged receive the first signal and transmit a second signal to the first base station in response to the first signal,
• the first base station is arranged to receive the second signal and transmit a third signal to the second base station in response to the second signal,
• wherein the device includes:
• a receiving unit arranged to receive each of the first and third signals from the first base station and the second signal from the second base station;
• a delay time measuring unit arranged to measure a first delay time as a time between receiving the first signal from the first base station and receiving the second signal from the second base station;
• a round trip time measuring unit arranged to measure a first round trip time as a time between receiving the second signal from the second base station and receiving the third signal from the first base station;
• a base station timings unit arranged to determine a round trip time of the first base station and a delay time of the first base station from the third signal;
• and
• a calculating unit arranged to calculate a first time difference of arrival based on the first round trip time, first delay time, round trip time of the first base station, delay time of the first base station, the speed of light and a value indicative of a distance between the first base station and the second base station,
• wherein the first base station is arranged to measure the round trip time of the first base station as a time between transmitting the first signal and receiving the second signal, and
• the first base station is further arranged to measure the delay time of the first base station as a time between receiving the second signal and transmitting the third signal, and
• the third signal includes information indicative of the measured round trip time of the first base station and the measured delay time of the first base station,
• wherein the base station timings unit is arranged to determine the round trip time of the first base station and delay time of the first base station by decoding the round trip time of the first base station and delay time of the first base station from the third signal, and
• wherein the first time difference of arrival relates to the difference in time of signal propagation between the first base station and the device and between the second base station and the device.