This disclosure relates to performing uplink cellular communication in unlicensed frequency bands using Wi-Fi preamble information. A wireless device may receive downlink control information from a cellular base station. The downlink control information may indicate an uplink transmit opportunity for licensed assisted access communication for the wireless device. A length of the uplink transmit opportunity may be determined. Licensed assisted access uplink communication may be performed during the uplink transmit opportunity. A Wi-Fi physical layer preamble may be transmitted as part of the licensed assisted access uplink communication. A type of the Wi-Fi physical layer preamble may depend at least in part on the length of the uplink transmit opportunity.