tems. The prin- ciples of capacity and coverage gaining mechanisms, explained in Section 10.4, are: limiting the IP-header overhead, multiuser channel sharing, VoIP specific packet schedulers, and advanced receivers. ROHC, a solution for the first mechanism, enables the system to perform more efficiently by reducing the overhead and has been widely studied and recognized as an essential optimization for VoIP. The other gaining mechanisms enhance the capacity and the coverage by helping to guaran- tee the quality also at the cell edge. Control channel overhead and the co-channel interference, as explained in Section 10.5, are severe obstacles to the VoIP performance. To enable the whole potential offered by the different gaining mechanisms in the networks with the practical limitations and further gain in capacity and coverage, several methods were explained in Section 10.6. These solutions (packet bundling, UL gating, HS-SCCH-less operation, semi-persistent allocation, distributed allocation, adap- tive HARQ, TTI bundling) with VoIP optimization provide an optimistic sight for the VoIP success. The simulation results of Section 10.7 show that especially the control channel overhead reduction solutions adopted by 3GPP are attractive, as they provide very good performance. References 1. H. Holma and A. Toskala, "WCDMA for UMTS-HSPA evolution and LTE," 4th ed., John Wiley, 2007. R. Cuny and A. Lakaniemi, "VoIP in 3G networks: An end-to-end quality of service analysis," IEEE, VTC Spring, vol. 2, April 2003, pp. 930-934. 3. H. Holma and A. Toskala, "HSDPA/HSUPA for UMTS," John Wiley, 2006. 4. 3GPP TS 25.309, "FDD enhanced UL; Overall description; Stage 2." 5. 3GPP TR 25.896, "Feasibility study for enhanced UL (FDD)." 6. 3GPP TS 25.308, "HSDPA; Overall description; Stage 2." 7. H. Holma, M. Kuusela, E. Malkamäki, K. Ranta-aho, and T. Chen, "VoIP over HSPA with 3GPP, Release 7," PIMRC 2006, Helsinki. 8. 3GPP TS 36.300, "Evolved universal terrestrial radio access (E-UTRA) and evolved universal terrestrial radio access ne