Systems and techniques relating to wireless communications are described. A described technique includes determining a primary access category for a transmission opportunity (TXOP) to transmit data to a primary wireless communication device, the primary access category being an access category included in a group of access categories that are associated with different transmission priorities, respectively; retrieving one or more primary data units belonging to the primary access category to transmit to the primary wireless communication device during the TXOP; determining a secondary access category for the TXOP, the secondary access category being an access category included in the group of access categories, the secondary access category having a transmission priority different from the primary access category; retrieving one or more secondary data units belonging to the secondary access category to transmit to a secondary wireless communication device during the TXOP; and transmitting spatially steered streams during the TXOP, the steered streams embodying the one or more primary data units and the one or more secondary data units.