This disclosure relates to performing cellular communication in unlicensed spectrum using a flexible slot structure. A cellular base station may perform a listen-before-talk procedure, and may transmit a reservation frame when the listen-before-talk procedure is successful. The reservation frame may reserve a wireless medium for a transmit opportunity. Transmission slots may be scheduled for communication with one or more wireless devices during the transmit opportunity. The transmission slots may be selected from multiple possible uplink transmission slot types and multiple possible downlink transmission slot types. Indications of the scheduled transmission slots, including indications of slot types of the scheduled transmission slots, may be provided to the wireless devices. Wireless communication may be performed between the cellular base station and the wireless devices according to the scheduled transmission slots.