 at a reduced signal/interference ratio and the inhibiting flexibility1 of bit rate capabilities outweigh the benefits. TDMA allows flexible rates in multiples of basic single channels and sub-multiples for low-bit rate broadcast transmis- sion. It offers frame-by-frame signal management with efficient guard band arrange- ments to control signal events. However, it requires substantial amounts of signal proc- essing resources to cope with matched filtering and synchronization needs. 1 The maximum bit per channel remains fixed and low. The UMTS Network and Radio Access Technology 2.1.1.2 Wide-band Digital Channel Systems Some of the drawbacks and limitations in the narrow-band channel systems made room for wide-band channel system designs. In wide-band systems the entire bandwidth re- mains available to each user, even if it is many times larger than the bandwidth required to convey the information. These systems include primarily Spread Spectrum (SS) sys- items, e.g. Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS). In DSSS, emphasized in this book, the transmission bandwidth ex- ceeds the coherent bandwidth, i.e. the received signal after de-spreading resolves into multiple time-varying delay signals that a RAKE receiver can exploit to provide an in- herent time diversity receiver in a fading environment. In addition, DSSS has greater resistance to interference effects when compared to FDMA and TDMA. The latter greatly simplifies frequency band assignment and adjacent cell interference. In addition, capacity improvements with DSSS or more commonly referred to as DS-CDMA², re- sulting from the voice activity factor, which we cannot apply effectively to FDMA or TDMA. With DS-CDMA, e.g. adjacent micro-cells share the same frequencies, whereas interference in FDMA and TDMA does not allow this. Other benefits and features can be found in [10-12]. Here we focus on the WCDMA or FDD mode and TDMA/ CDMA or TDD mode of the UTRA solution. 2.1.1.3 The UTRA FDD Mode: WCDMA Figure 2.1 illust