A central node/database receives from each mth one of a plurality of M user devices at least one of geographic location information of the mth user device and type information of the mth user device. The node/database registers the M user devices to different groups according to at least one of location criteria based on the received geographic location information and type criteria based on the received type information. Then the node/database sends to each mth one of the plurality of M user devices a set of parameters that define a periodic time window that is specific to the group to which the mth user device is registered. The time window restricts times at which the mth user device can access a data source of spectrum use information. Balancing the number of user devices among the groups, spreads database accesses in time and overloads are less frequent and less severe.