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Figure 3Interoperability of mobile terminals andnetwork equipment from different vendorsis crucial for handover between WCDMAand GSM. Ericsson network equipment, incommercial operation in Japan since 2002(here represented by the Indoor MacroRBS 3202), has been publicly shown (at3GSM World Congress in Cannes, February18-21) to interoperate in WCDMA withall major mobile terminal vendors—hererepresented by two Sony Ericsson Z1010terminals.Figure 4Overview of the GSM and WCDMA nodesand interfaces involved in the cell reselectionand handover procedures.As mentioned above, a mobile terminal inWCDMA makes use of compressed mode tomeasure GSM. That is, if the mobile terminalhas a single radio receiver, it requirescompressed mode. If, on the other hand, themobile terminal contains separateWCDMA and GSM radio receivers, it canuse each receiver in parallel, performingGSM measurements without compressedmode in the downlink. Notwithstanding,each solution—compressed mode and dualreceivers—reduces talk time due to higherpower consumption in the terminal.In idle mode, standby time of the mobileterminal is mainly affected by how often itneeds to wake up to monitor radio channelsand perform measurements for cell reselection.Since a dual-mode terminal mustmeasure WCDMA and GSM cells, this hasa negative effect on standby time comparedto GSM-only mobile terminals. To improvestandby time, the mobile terminal is allowedto inhibit measurements on the otheraccess technology (for example, WCDMAwhen in GSM) when the quality of the currentaccess technology is adequate for thenetwork settings. Furthermore, comparedto re-selection between GSM cells, the measurementrequirements in the standard aremore relaxed for re-selection betweenWCDMA and GSM cells.Mobility procedures for interworkingbetween WCDMA and GSMThere are two basic modes of operation forhandling mobility:• the mobile terminal-controlled mode;and• the network-controlled mode.In the mobile terminal-controlled mode, themobile terminal selects the cell to which itwill connect. However, the network canbroadcast various parameters to influencethis process.In the network-controlled mode, the networkexplicitly orders the mobile terminalto connect to a specific cell. Ordinarily, thenetwork bases its decisions on measurementinformation provided by the mobile terminal.For either mode of operation, the networkshould consider cells that use each accesstechnology. Besides radio link quality,the network might also consider other aspectswhen selecting the cell, for example,the current load of the established service.Two procedures have been defined bywhich the network can order the mobile terminalto connect to a cell using another technology,namely the handover and cellchange order procedures. These are employedwhen the mobile terminal uses a dedicatedchannel. The handover procedureprovides a higher level of service, since it involvesa preparation phase in which resourcesin the target cell are reserved priorto the actual handover. Accordingly, thehandover procedure is employed when themobile terminal is providing circuitswitchedservice—for instance, voice. Thecell change order procedure applies whenthe mobile terminal is providing packetswitchedservice, such as Web browsing.Cell re-selection betweenWCDMA and GSMWhile in WCDMA, the mobile terminalperforms cell re-selection• in idle mode; and• in connected mode when common channelsare used for packet-switched service.The dual-mode mobile terminal re-selects aGSM cell when that cell is ranked higherthan the current WCDMA cell or any otherWCDMA cell. WCDMA and GSM cells areranked together according to signalstrength. This same type of ranking appliesin GSM.When performing cell re-selection inWCDMA, the mobile terminal either measuresGSM cells continuously or when thequality of the serving WCDMA cell fallsbelow a given threshold. The mobile terminalis solely allowed to select a newWCDMA or GSM cell when the average receivedquality and average signal strengthexceed a minimum threshold. Theminimum-quality threshold (signal-tonoiseratio) ensures that the mobile terminalcan receive the information transmittedEricsson Review No. 1, 2003
y the potential target cell. The minimumthreshold for signal strength ensures thatthe network can receive the information forcell re-selection transmitted by the mobileterminal in the target cell. This criterionalso takes into account• the maximum transmit power that themobile terminal is allowed to use whenaccessing the cell; and• the maximum radio frequency (RF) outputpower that the mobile terminal cantransmit.Frequent re-selections can be avoided withmechanisms such as penalty time and temporaryoffset. Likewise, mechanisms are definedto keep fast-moving mobile terminalsfrom re-selecting small-sized cells when alarge overlay cell has been configured.The network can configure these optionsby broadcasting parameters in theWCDMA cell.When the mobile terminal is actively providingpacket-switched data service in aWCDMA cell and re-selects a GSM cell, itestablishes the radio connection to the GSMbase station subsystem (BSS) and then initiatesthe routing area update procedure.During this procedure, the core networkmay retrieve information from the UMTStertestrial radio access network (UTRAN)on the context ofthe mobile terminal, whichincludes any data packets waiting in thedownlink queue. When complete, the connectionto UTRAN is released. Finally, thecore network confirms the routing area update.Figure 5 shows the message sequenceafter cell re-selection from WCDMA to aGSM cell in idle mode.Figure 5WCDMA-to-GSM cell re-selection.the mobile terminal has a circuit-switchedservice and the signal strength falls below agiven threshold, the WCDMA network ordersthe mobile terminal to perform GSMmeasurements. Typically, the mobile terminalis instructed to send a measurementFigure 6Handover from WCDMA to GSM.WCDMA-to-GSM cell change orderThe mobile terminal measures GSM cellsand sends measurement reports to che network,which orders the mobile terminal toswitch to GSM. The measurement procedureand the use of compressed mode areidentical to that described below for theWCDMA-to-GSM handover procedure.The signaling in the cell-change-orderprocedure is identical to that in the cell reselectionprocedure described in Figure 5 exceptthat the network selects the target GSMcell and initiates the procedure by sendinga cell-change-order from the UTRAN message.This message includes the infotmationon the target GSM cell.Handover from WCDMA to GSMFigure 6 shows the message sequence forhandover from WCDMA to GSM. WhenEricsson Review No. 1, 2003 9
Page 1 and 2: Ericsson 1/2003REVIEWTHE TELECOMMUN
Page 3 and 4: EricssonREVIEWTHE TELECOMMUNICATION
Page 5 and 6: systems built from Ericsson's produ
Page 7: EditorialEric PetersonSince joining
Page 12 and 13: Figure 7Handover from GSM to WCDMA.
Page 14 and 15: OMA—Changing the mobile standards
Page 16 and 17: Figure 3The OMA enables wireless co
Page 18 and 19: instance, the WAP Forum created mob
Page 20 and 21: The service network framework—An
Page 22 and 23: Figure 3Architectural views of the
Page 24 and 25: Figure 7SNF system type view.Sysfem
Page 26 and 27: Figure 9High-availability deploymen
Page 28 and 29: Realizing the operator's service ne
Page 30 and 31: Figure 3Consultative approach to me
Page 32 and 33: Figure 4MMS integration interfaces.
Page 34 and 35: Advanced baseband technology in thi
Page 36 and 37: channels. A channel element is defi
Page 38 and 39: Figure 6Backward hardware compatibi
Page 40 and 41: Figure 9TX board of the RBS3000 ser
Page 42 and 43: Figure 11RAX board implementation.
Page 44: Previous issuesNo. 3, 2002Packet da

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