A first base station receives a first message comprising one or more first parameters identifying one or more first subframes as a listen-before-talk (LBT) subframe. One or more second subframes are selected as an LBT subframe by the first base station employing the one or more first parameters. An LBT procedure is performed in a subframe in the one or more subframes. A burst is transmitted when the LBT procedure indicates a clear channel.