US Patent 10251077 Proximity detection

A method of estimating the proximity of a first device to a second device in a network causes the first device to perform a first measurement in a first period during which a control message broadcasted over the network instructs devices in the network to not transmit during the first period, wherein the second device disregards the control message and transmits a first signal during the first period which is measured by the first device during the first period, and forms a measure of the proximity of the first device to the second device in dependence on a strength of the first signal.