WCDMA/UMTS

This chapter gives an overview of the Wideband Code Division Multiple Access (WCDMA) standard for third generation (3G) cellular telephony – part of a group of standards known as Universal Mobile Telecommunication System (UMTS), Third Generation Partnership Project (3GPP), and International Mobile Telecommunications (IMT-2000). A WCDMA system consists of the Core Network (CN) and the UMTS Terrestrial Radio Access Network (UTRAN), which in turn consists of multiple Radio Network Subsystems (RNSs), containing Radio Network Controllers (RNCs), and base stations (Node-Bs). For the physical layer we concentrate on the UMTS-FDD mode. Aspects related to RF implementation include frequency bands, out-of-band emissions, and power classes. We then discuss logical channels or transport channels (describing the type of data that are transmitted) and physical channels (time/frequency/code resources). Transport channels include: common transport channels (broadcast channel BCH, paging channel PCH, random access channel RACH, forward access channel FACH, common packet Channel CPCH, and downlink shared channel DSCH), and dedicated (transport) channels DCH. Control and user data of a DCH are transmitted on the physical coded composite traffic channel (CCTrCH). We next describe coding, spreading, and multiplexing for uplink and downlink. The speech coder in UMTS is an adaptive multirate (AMR) coder. Data are segmented into blocks and encoded with convolutional or turbo codes. UMTS then uses channelization codes and scrambling codes for spreading and multiple access. Channelization codes are Orthogonal Variable Spreading Factor (OVSF) codes; spreading codes are either short codes (Kasami), or long codes (Gold). We finally describe physical layer procedures, including cell search and synchronization, the steps involved in establishing a connection, power control (which involves both closed-loop and open-loop control), transmit diversity, and overload control.