Channel characterization and training within multiple user, multiple access, and/or MIMO wireless communications. Within such communication systems, there can be a number of devices (e.g., STAs) that communicate with a single device (e.g., AP). A multi-cast sounding frame may be transmitted from a transmitting device to a number of receiving devices. Appropriate scheduling or ordering of feedback signals from some or all of the receiving devices may be performed explicitly (e.g., sounding frame sent from the transmitting device to a receiving device) or implicitly (e.g., control information sent from the transmitting device to the receiving device, sounding frame sent to the transmitting device from the receiving device). Such characterization and training is with respect to a channel or path in which data will subsequently follow. Such characterization and training can be performed in accordance with group membership (e.g., with respect to only some of the receiving devices).