The invention concerns a method and a 
base station (21) for controlling beam forming in a mobile 
cellular network: Antenna units (212) of base stations (21) of a cluster of neighbored base stations (21) apply a respective 
beam pattern sequence on each sector of a 
cell served by the respective 
base station (21). The 
beam pattern sequence is selected from a respective predefined set of 
beam pattern sequences and each beam 
pattern sequence defines a sequence of beam subsets used for communication with mobile units (41, 42, 43, 44). One of the base stations (21) of the cluster which acts as trigger 
base station informs all neighbored base stations of the cluster of neighbored base stations (21, 22, 23, 24, 25, 26, 27) not to change their beam pattern sequences. The trigger base 
station (21) controls the antenna unit (212) of the trigger base 
station (21) to change the beam 
pattern sequence applied on the sectors of the 
cell and sequently apply two or more different beam pattern sequences of the predefined set of beam pattern sequences on the respective sector. The trigger base 
station (21) triggers one or more mobile units (41, 42, 43, 44) located in the cluster of neighbored base stations to calculate one or more 
signal quality parameters for currently applied beam pattern sequences of the trigger base station (21). The trigger base station (21) selects an optimal beam 
pattern sequence from the set of the predefined beam pattern sequences based on the one or more calculated 
signal quality parameters and the antenna unit (212) of the trigger base station (21) applies the optimal beam pattern sequence as a new beam pattern sequence on the respective sector.