Method and apparatus for variable length Physical Layer (PL) packet generation. Multiple Security Layer (SL) packets may be multiplexed into a single PL packet to increase efficiency wherein the SL packets may have variable lengths. In one embodiment different format SL packets for different users are combined into capsules that form the PL packet. Shorter packets are for users in poor channel conditions or requiring smaller amounts of data due to the applications and the accompanying Quality of Service (QoS) requirements. In one embodiment a modified Preamble structure provides for Unicast or multi-user packets. Alternate embodiment provides modified Rate Sets a mechanism for identifying ACK from a single-user packet or a multiplexed packet (delayed ACK). ON/OFF keying for ACK channel v/s bi-polar keying used in IS-856 and/or multi-valued interpretation of DRC.