Methods, systems, and devices for wireless communication are described. A base station may perform a clear channel assessment (CCA) procedure on a channel that includes multiple sub-bands of a radio frequency spectrum band. The base station may determine that the channel is available based on the CCA and transmit a special header in the channel. In some examples, the special header may include multiple transmission time intervals (TTIs), where each TTI may include a header packet in each sub-band of the radio frequency spectrum band. In some cases, the header packet may include a clear to send (CTS)-to-self frame structure. The base station may transmit a first TTI across each of the sub-bands at a first power level, and transmit additional TTIs across the sub-bands at a different power level. Additional header packets may be transmitted at the boundaries of subsequent subframes.