A mobile device obtains data to be wirelessly transmitted over a shared spectrum in an uplink channel to a 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 selects a start time in the uplink channel that mitigates interference from other mobile devices in proximity to the mobile device. Beginning at the start time, the mobile device transmits the data over the shared spectrum in the uplink channel to the base station.