3GPP Broadband Evolution to IMT-Advanced - 4G Americas

Operators can also use their entire available spectrum for both voice and high-speed dataservices.Additionally, operators can use a common core network that supports multiple radioaccessnetworks including GSM, EDGE, WCDMA, HSPA, and evolutions of thesetechnologies. This is called the UMTS multi-radio network, and it gives operatorsmaximum flexibility in providing different services across their coverage areas (see Figure31).Figure 31: UMTS Multi-radio NetworkGSM/EDGEPacket-SwitchedNetworksWCDMA,HSDPAUMTSCore Network(MSC, HLR,SGSN, GGSN)Circuit-SwitchedNetworksOthere.g., WLANOther CellularOperatorsRadio-Access NetworksExternal NetworksThe UMTS radio-access network consists of base stations referred to as Node B(corresponding to GSM base transceiver systems) that connect to RNCs (corresponding toGSM base station controllers [BSCs]). The RNCs connect to the core network as do theBSCs. When both GSM and WCDMA access networks are available, the network can handover users between these networks. This is important for managing capacity, as well asin areas in which the operator has continuous GSM coverage, but has only deployedWCDMA in some locations.Whereas GSM can effectively operate like a spread-spectrum system 101 , based on timedivision in combination with frequency hopping, WCDMA is a direct-sequence, spreadspectrumsystem. WCDMA is spectrally more efficient than GSM, but it is the widebandnature of WCDMA that provides its greatest advantage—the ability to translate theavailable spectrum into high data rates. This wideband technology approach results in theflexibility to manage multiple traffic types including voice, narrowband data, andwideband data.WCDMA allocates different codes for different channels, whether for voice or data, and itcan adjust the amount of capacity, or code space, of each channel every 10 msec withWCDMA Release 99 and every 2 msec with HSPA. WCDMA creates high-bandwidth trafficchannels by reducing the amount of spreading (using a shorter code) with WCDMARelease 99 and higher-order modulation schemes for HSPA. Packet data users can sharethe same codes as other users, or the network can assign dedicated channels to users.101 Spread spectrum systems can either be direct sequence or frequency hopping.Transition to 4G: 3GPP Broadband Evolution to IMT-Advanced, Rysavy Research/3G Americas, Aug 2010 Page 79