A first method comprises transmitting data (83) of a first kind during a first part of a first time slot (ti1) of a plurality of time slots (ti1-ti4) of equal length according to a regular slot schedule, transmitting a preamble (84) in a second part of the first time slot, and transmitting data of the second kind during one or more mini-slots of a first part of a second time slot (ti2) of the time slots according to a mini-slot schedule. The second time slot succeeds the first time slot and the first part of the second time slot comprises a plurality of mini-slots (85). A second method comprises receiving the data of the first kind during the first part of the first time slot, receiving the preamble in the first time slot, and receiving data during a plurality of the mini-slots of the second time slot.