rates some of the UTRA Frequency Division Duplexing (FDD) charac- teristics. This mode uses Wide-band Direct-Sequence Code Division Multiple Access (DS-CDMA), denoted WCDMA. To support bit rates up to 2 Mbps, it utilizes a variable spreading factor and multi-code links. It supports highly variable user data rates through the allocation of 10 ms frames, during which the user data rate remains constant, al- though the latter may change from frame to frame depending on the network control. It realizes a chip rate of 3.84 Mcps within 5 MHz carrier bandwidth, although the actual carrier spacing can be selected on a 200 kHz grid between approximately 4.4 and 5 MHz, depending on the interference situation between the carriers. Frequency Variable bit rate services Power High bit rate 4.4-5.0 MHz services Different spreading factors 10 ms (e.g. allowing 8-384 kpbs) Figure 2.1 The UTRA WCDMA or FDD mode characteristics. 2 Direct Sequence Code Division Multiple Access. System Analysis Fundamentals The FDD has a self timing point of reference through the operation of asynchronous BSs, and it uses coherent detection in the up- and downlink based on the use of pilot reference symbols. Its architecture allows the introduction of advanced capacity and coverage enhancing CDMA receiver techniques, e.g. multi-user detection and smart adaptive antennas. In addition, it will seamlessly co-exist with GSM networks through its inter-system handover functions of WCDMA. 2.1.1.4 The UTRA TDD Mode: TD/CDMA The 2nd UTRA mode results from the combination of TDMA-FDMA and exploits spreading as part of its CDMA component. It operates in Time Division Duplexing using the same frequency channel. Frequency Power 4.4-5.0 MHz Multicode Multislot 10 ms frame Multicode / Multislot Variable Spreading Figure 2.2 UTRA TDD mode characteristics. In this mode, the MSs can only access a Frequency Division Multiplexing (FDM) chan- nel at specific times and only for a specific period of time. Thus, if a mobile gets one or more Time Slots (TS) allocated, it can