Introduction to WCDMA
This chapter introduces the principles of the WCDMA air interface. Special attention is drawn to those features by which WCDMA differs from GSM and IS-95. The main parameters of the WCDMA physical layer are introduced in Section 3.2. The concept of spreading and despreading is described in Section 3.3, followed by a presentation of the multipath radio channel and Rake receiver in Section 3.4. Other key elements of the WCDMA air interface discussed in this chapter are power control and soft and softer handovers. The need for power control and its implementation are described in Section 3.5, and soft and softer handover in Section 3.6.
3.2 Summary of the Main Parameters in WCDMA
We present the main system design parameters of WCDMA in this section and give brief explanations for most of them. Table 3.1 summarizes the main parameters related to the WCDMA air interface. Here we highlight some of the items that characterize WCDMA:
- WCDMA is a wideband Direct-Sequence Code Division Multiple Access (DS-CDMA) system, i.e. user information bits are spread over a wide bandwidth by multiplying the user data with quasi-random bits (called chips) derived from CDMA spreading codes. In order to support very high bit rates (up to 2 Mbps), the use of a variable spreading factor and multicode connections is supported. An example of this arrangement is shown in Figure 3.1.
- The chip rate of 3.84 Mcps leads to a carrier bandwidth ...