A mobile device transmits data over a shared spectrum in an uplink channel to a base station in a contention-based access scheme. The mobile device obtains data to be wirelessly transmitted over the shared spectrum in the uplink channel to the base station. The uplink channel is formatted with a frame/subframe structure with a predetermined timing. The mobile device determines whether the shared spectrum is free for transmission according to a listen before transmit procedure. When the shared spectrum is free for transmission, the mobile device contends with other mobile device to gain access to the uplink channel. After gaining access to the uplink channel, the mobile device transmits the data over the shared spectrum in the uplink channel to the base station.