Methods, systems, and devices for wireless communication are described. A base station may establish a transmission gap between downlink (DL) and uplink (UL) transmissions on a shared radio frequency (RF) spectrum band using time division duplex (TDD). A length of the gap may be based at least in part on a maximum allowed length of a filler signal corresponding to a coverage area of the base station. To reserve the shared band, a user equipment (UE) may communicate the filler signal for a length of time that is based at least in part on the maximum allowed length and a geographic distance between the UE and the base station. UEs farther from the base station transmit the filler signal of shorter lengths before sending an UL transmission, so that the UL transmissions from different UEs arrive at the same time at the base station regardless of the geographic distance between the UEs.