A packet transmitter in a wireless communication system can perform a method for preparing transmission of physical layer protocol data units (PDUs). The method includes detecting a need to transmit a second stream of symbols having higher priority than a first stream of symbols currently being transmitted from the packet transmitter to a packet receiver. The first and second streams of symbols are each part of a respective physical layer PDU. A dedicated tag is inserted after a recent-most transmitted symbol of the first stream of symbols. The dedicated tag indicates that the first stream of symbols is subjected to pre-emption at the physical layer. Symbols of the second stream of symbols are inserted following the dedicated tag for transmission of the second stream of symbols to the packet receiver.