There is provided an apparatus including receiving, at a second node, a signal including contributions of at least one backscatter signal and at least one further signal, the at least one backscatter signal being transmitted by a respective at least one passive device in response to a first node transmitting a first signal to the at least one passive device; isolating the contribution of the at least one backscatter signal from the at least one further signal; and based on the contribution of the at least one backscatter signal, determining, by the second node, one or more parameters associated with the respective at least one passive device.