bandwidth, lower latency and packet-optimized radio access technology with highly improved peak data rate capability, in order to meet the rapidly growing demand for bandwidth and mobility of the global nomadic users. This chapter will give a brief introduction of the evolution of the UMTS standard, from its first release (Release 99) to the latest Release 8 (still being standardized). The purpose of this chapter is to provide background knowledge of the evolution of the UMTS to help understand the new requirements of the evolved UMTS radio access networks. 2.1 Background of UMTS In parallel with the widespread deployment and evolution of Second Generation (2G) mobile communication systems during the 1990s, the International Telecommunication Union (ITU) started the process of defining the standard for Third Generation (3G) mobile systems, referred to as International Mobile Telecommunications 2000 (IMT-2000). Universal Mobile Telecommunication System (UMTS) is a key member of the global family of 3G mobile communication systems. It was initiated by the European Telecommunications Standards Institute (ETSI) in Europe. In 1998, the 3rd Generation Partnership Project (3GPP) was formed by standards-developing organizations from all regions of the world to continue the technical specification work for UMTS. This solved the problem of trying to maintain parallel development of aligned specifications in multiple regions. The major standardization bodies of 3GPP are ARIB (Japan), CCSA (China), ETSI (Europe), ATIS (USA), TTA (Korea) and TTC (Japan). UMTS is seen as the successor to 2G mobile communication systems such as Global System for Mobile communications (GSM) and to evolved 2G systems such as the General Packet Radio Service (GPRS). 3G UMTS brings an evolution in terms of greatly enhanced capacity, data rates and new service capabilities from 2G systems. It provides global mobility and high speed transmissions with a wide range of services including voice telephony, messaging, images, video, Internet access, and b