A first communication device receives respective beamforming training packets as part of a procedure for developing respective transmit beamforming matrices for use by a plurality of second communication devices during a subsequent UL MU transmission. The first communication device generates respective beamforming feedback information based on reception of the respective beamforming training packets, and transmits the respective beamforming feedback information to the plurality of second communication devices. The first communication device transmits a synchronization signal to a group of multiple second communication devices to the group to simultaneously transmit to the first communication device at a particular time as part of the UL MU transmission, and receives simultaneous transmissions from the group responsive to the synchronization signal, the simultaneous transmissions having been beamformed by second communication devices in the group using transmit beamforming matrices.