Service Access Points Physical layer Figure 4.1 A radio interface protocol architecture around L1. The data transport services offered to higher layers by L1 occurs through the use of transport channels via the MAC sub-layer. Table 4.1 illustrates some of the L1 or physi- cal layer services. Through inter-working (e.g. a UE) provision of compatible bearers is assured. The UMTS Network and Radio Access Technology Based on the types of physical channels L1 has two multiple access techniques: a Direct-Sequence Code Division Multiple Access (DS-CDMA) with the informa- tion spread within 5 MHz bandwidth, also referred to as Wide-band CDMA (WCDMA; and a Time Division Multiple Access (TDMA) + CDMA often denoted as TDMA/ CDMA or TD/CDMA resulting from the extra slotted feature. Table 4.1 Main Functions of the UTRA Physical Layer Macro-diversity distribution/combining Power weighting and combining of and soft handover execution physical channels Error detection on transport channels and Modulation and spreading/ indication to higher layers demodulation and de-spreading of physical channels FEC encoding/decoding of transport chan- Frequency and time (chip, bit, slot, frame) synchronization Multiplexing of transport channels and de- Radio characteristics measurements multiplexing of coded composite transport including FER, SIR, interference channels power, etc., and indication to higher layers Rate matching (data multiplexed on DCH) 10. Inner-loop power control 11. Mapping of coded composite transport 12. RF processing channels on physical channels The two access schemes afford UTRA two transmission modes, i.e. Frequency Division Duplex (FDD) corresponding to WCDMA operating with pair bands, and Time Divi- sion Duplex (TDD) corresponding to TD/CDMA operating with unpaired bands. The flexibility to operate in either FDD or TDD mode allows efficient spectrum utilization within the frequency allocation in different regions, e.g. Europe, Asia, etc. The FDD mode or WCDMA is thus a duplex method where uplink and downlink transmis