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PACKET ACCESS IN UTRA FDD AND UTRA TDD In this chapter, first a brief introduction to UMTS Terrestrial Radio Access (UTRA) matters is provided, such as fundamental radio access network concepts, basics of, for example, the physical and the MAC layer, and the types of channels defined (namely logical, transport and physical channels). This is followed by a discussion of certain UTRA FDD features, such as soft handover, fast power control and compressed mode operation. | Multiple Access Protocols for Mobile Communications GPRS UMTS and Beyond Alex Brand Hamid Aghvami Copyright 2002 John Wiley Sons Ltd ISBNs 0-471-49877-7 Hardback 0-470-84622-4 Electronic 10 PACKET ACCESS IN UTRA FDD AND UTRA TDD In this chapter first a brief introduction to UMTS Terrestrial Radio Access UTRA matters is provided such as fundamental radio access network concepts basics of for example the physical and the MAC layer and the types of channels defined namely logical transport and physical channels . This is followed by a discussion of certain UTRA FDD features such as soft handover fast power control and compressed mode operation. The main focus is on the mechanisms that are available for packet access on UTRA FDD and UTRA TDD air interfaces as provided by release 1999 of the 3GPP specifications. Improvements being considered for further releases currently mostly dealt with in 3GPP under the heading of High Speed Downlink Packet Access HSDPA are also discussed. For more general information on UMTS the reader is referred to dedicated texts such as Reference 86 . UTRAN and Radio Interface Protocol Architecture UTRAN Architecture The UMTS terrestrial radio access network UTRAN consists of one or more Radio Network Subsystems RNS which in turn are composed of a Radio Network Controller RNC and multiple base stations. In UMTS terminology base stations are referred to as node B in the following both terms will be used. A single node B may serve one or more cells . different sectors served from one site . A node B is connected to its RNC via the Iub interface. The RNC is said to be the Controlling RNC CRNC of that node B. The RNC is connected to the Core Network CN via the Iu interface see Figure . To be precise two variants of the latter are discerned namely Iu-CS which provides the connection to the circuit-switched core network . to an MSC and Iu-PS providing the connection to the packet-switched core network . to an SGSN . .