The invention discloses a method (800) for use in a cellular wireless system (100) with a base station (120), a cell (110) in the system and a first user terminal (130) which can be scheduled for receiving traffic from the base station during a down link period, and for transmitting traffic to the base station during an up link period. There is a first guard period (TUD) between the up link period and the down link period, and a second guard period (TDU) between the down link period and the up link period. The method (800) comprises measuring the interference level in the cell for part of the time between two consecutive down link periods, and varying at least one of the following in accordance with the measured interference level: the duration of the first or second guard period, the duration of the up link period, or the traffic sent in the up link period.