Admission control is a key mecha-nism to manage the increasing number of the simultaneous demanding services, requiring a desired Quality of Service (QoS) in a spec-trum efficient manner. To address this issue, we investigate in this work, the use of the superposition coding technique to increase the system capacity through multiuser diver-sity exploitation. We propose a novel joint admission control and superposition coding formalism based on different utility functions:Opportunistic (OPSC), Great Faess (GFSC) and Proportional Faess (PFSC). Simulation results show the superiority of our proposed approaches over other by providing higher mean of served VoIP users and higher through-put while maintaining an average VoIP packet transmission delay lower than 0.6 ms.