 as well as supply certain QoS for various traffic types. In Rel99, Asynchronous Transfer Mode (ATM) has been chosen for the radio access network transport. In addition, the ATM Adaptation Layer type 2 (AAL2) [ITU00] was selected by the 3GPP Re199 to be used on top of the ATM to transport user data within the UTRAN (User Plane) because of its ability to perform multiplexing of low bit rate traffic such as voice traffic, and thus can efficiently support the QoS and link transmission utilization. A more detailed introduction on UTRAN of UMTS Rel99 is given in Chapter 3 including the defined network architecture, channels, protocol stacks, transport network and its related resource management functions. An essential part of this thesis focuses on the UMTS Rel99 system. It is the basic UMTS release and considered as the reference system for the other evolved UMTS networks. 2 UMTS Evolution 2.3.2 High Speed Downlink Packet Access (HSDPA) With the gradual development of UMTS, the offered services by UMTS rapidly extend from primarily voice telephony to a variety of appealing data and multimedia-based applications. The offered data services, such as Internet access, remote database access, email or ftp, are now contributing a substantial traffic share in the UMTS networks. In order to greatly enhance the capability of transmitting such delay-tolerant data services with improved resource efficiency and service quality, 3GPP Release 5 specifications introduce the High Speed Downlink Packet Access (HSDPA) as a key evolution of the WCDMA radio interface to significantly improve the downlink packet data transmissions. Compared to the UMTS Rel99, HSDPA makes a significant improvement in peak data rate on the downlink for transmitting the packet data. It provides a maximum data transmission rate of up to 14.4 Mbps per user, the current HSDPA deployments support downlink speeds of 1.8, 3.6, 7.2 and 14.4 Mbps. The main features of HSDPA are its high data transmission rate, low latency, and high throughput, which facilitate a not