Abstract: A method of inferring a state of activity of a carrier of a mobile communication device, the method comprising a. monitoring a parameter of a transmitter serving the mobile communication device and of a plurality of neighbouring transmitters; b. acquiring data relating to the monitored parameter of the serving transmitter and the neighbouring transmitters during a time window; c. processing the acquired data to generate a time window parameter associated with the time window; d. repeating steps b and c for one or more further time windows; and e. inferring the state of activity of the carrier of the mobile communication device from the time window parameters generated in steps b and c.