A method is provided of replacing a first drone base station with a second drone base station, the first drone base station, the method comprising: sending by the first drone base station first pilot signals indicating a cell identifier; receiving by the first drone base station information that the second drone base station is in the vicinity of the first drone base station; sending by the second drone base station second pilot signals which indicate the same cell identifier as the first drone base station; receiving by the first drone base station from the second drone base station an indication to cease to send first pilot signals; and dependent upon receiving by the first drone base station from the second drone base station the indication to cease to send first pilot signals, ceasing by the first drone base station the sending of first pilot signals.