A method is performed by a wireless transmitting device for a communication network. The communication network implements a standard in which transmitting devices contend for access to a wireless transmission medium, a transmitting device being permitted to transmit using the wireless transmission medium for a window of time upon winning contention. The method includes initiating a first, initial transmission to one or more wireless receiving devices in the window of time, the first transmission including a first preamble; and, subsequent to the first transmission, initiating a second transmission to one or more wireless receiving devices in the window of time, the second transmission including a second preamble which is shorter than the first preamble, or including no preamble.