UMTS Release 99/4 airlink enhancement for supporting MBMS services

In this paper, we first describe the UMTS architecture for supporting MBMS. Then, we describe various airlink options for carrying multicast traffic in UMTS Release 99/4 system. One can carry it over FACH or DSCH channel. We discuss why DSCH channel is not an attractive solution. Then, we discuss how rate splitting, longer TTI and STTD techniques can be used to reduce the power requirement of delivering multicast traffic over the FACH channel for MBMS users. Another possibility is to use a combination of multicast as well as dedicated channels to serve all MBMS users. Some users who are in bad conditions are served using dedicated channels and those who are in relatively good conditions are served using a multicast channel. Last but not least, we present simulation results to give us an idea of how much power is required to support MBMS.