GSM - Architecture, Protocols and Services, Third Edition

Chapter 9. Beyond GSM and UMTS: 4G

Today, many network operators have already introduced UMTS and most of them have integrated the UMTS Terrestrial Radio Access Network (UTRAN) into existing GSM backbone infrastructure and architecture. Figure 9.1 shows the respective evolution scenario for the migration from GSM to UMTS. On the basis of the existing circuit- and packet-switched infrastructure (GSM/GPRS) and entities for mobility management (HLR, MAP), the UTRAN with the new air interface has already been introduced (UMTS Phase 1). Here, UTRANs are installed in parallel to BSSs of GSM and partly even reusing existing locations. In a further step (UMTS Phase 2) the network architecture and backbone transportation facilities are adapted to the requirements of broadband packet-switched services, as the systems evolve.

In the meantime, the UMTS air interface has already been extended by the development of the fast-scheduled, packet-switched data services High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA). Both, HSDPA and HSUPA have already been fully specified through standardization within 3GPP. Similar to EDGE in GSM, the HSxPA services apply higher-order modulation schemes and offer a series of different coding schemes, such that the data rate can be adapted to the channel conditions through the process of link adaptation. In addition, fast scheduling is applied utilizing a channel feedback with a frequency of up to once per 2 ms. Combined with clever ...