ease 5 initiated the High Speed Downlink Packet Access (HSDPA) in March 2002. Further Release 6 followed with High Speed Uplink Packet Access (HSUPA) was standardized in 2004. HSDPA and HSUPA are commonly referred to as High-Speed Packet Access (HSPA). The first commercial HSDPA network started in fall of 2005, and the first HSUPA network was launched in February 2007. The latest step being studied and developed in 3GPP is an evolution of 3G into an evolved radio access referred to as the Long-Term Evolution (LTE) and an evolved packet access core network in the System Architecture Evolution (SAE). By 2009-2010, LTE and SAE are expected to be deployed. In the following a more detailed introduction of the UMTS network architecture and key UMTS evolution technologies are presented. 2.2 UMTS Network Architecture A UMTS network comprises three main parts: User Equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and Core Network (CN). Their individual functionalities as well as the logical interfaces between them are specified in the 3GPP standards. More detailed 2.2 UMTS Network Architecture introductions on the fundamentals of UMTS can be found in [KAL*01], [WSA03] and [HT04]. Figure 2.1 presents the schematic view of the structure of a UMTS network. The UE includes two parts: the Mobile Equipment (ME), which is a radio terminal handling the communications on the Uu interface (radio interface), and the UMTS Subscriber Identity Module (USIM), which is a smart card that contains the subscriber's confidential data such as identity, authentication algorithm and subscription information. USIM and ME communicate over the internal Cu interface. The UE accesses the fixed network via the Uu radio interface. The UTRAN contains one or more Radio Network Subsystems (RNS) each of which comprises one Radio Network Controller (RNC) and a number of Node Bs in a UMTS network, which make up the UMTS radio access network. The RNC is the central element of the UTRAN responsible for the control of the radio resources in all a