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Figure 7Handover from GSM to WCDMA.Figure 8System capacity can be increased by selecting service-based radio access technology.The blue and red triangles describe system capacity to handle voice and data traffic in twoseparate access technologies, blue and red. If we combine these technologies and enableservice-based handover between them, the capacity can vary depending on how the serviceis allocated. To achieve maximum capacity, all data users should be allocated to theblue technology and all voice users to the red (dashed black line). Minimum capacity willresult if all data users are allocated to the red technology and all voice users to the blue(solid black line).10report when the quality of a neighboringGSM cell exceeds a given threshold and thequality from WCDMA is unsatisfactory.When UTRAN receives the measurementreport message, it initiates the handover,given that all the criteria for handoverhave been fulfilled—for example, providedthe mobile terminal is not involved in servicesthat require WCDMA. UTRAN thenasks the target BSS to reserve resources. Thetarget BSS prepares a handover commandmessage, which includes the details of theallocated resources. This GSM message,which is sent to the mobile terminal via theWCDMA radio interface, is transferredwithin a container that is transparentlypassed on by the different network nodes.When the mobile terminal receives thehandover command, it moves to the targetGSM cell and establishes the radio connectionin accordance with the parameters includedin the handover command message.The mobile terminal indicates successfulcompletion of the handover by sending ahandover complete message to the BSS, afterwhich the GSM network initiates the releaseof the WCDMA radio connection.Handover from GSM to WCDMAFigure 7 shows the message sequence forhandover from GSM to WCDMA. The networkorders the dual-mode mobile terminalto perform WCDMA measurements bysending the measurement information message,which contains information on neighboringWCDMA cells and the criteria forperforming and reporting measurements.When the criteria for handover toWCDMA have been met, the BSS initiatesthe allocation of resources to the WCDMAcell. Encapsulated in these messages, the BSSalso sends information to UTRAN on theWCDMA capabilities of the mobile terminal.When the resources of the WCDMA targetcell have been allocated, UTRAN compilesthe handover-to-UTRAN-commandmessage, which typically includes the identityof the pre-defined configuration for theservice in use. This message is then senttransparently to the mobile terminalthrough the core network and BSS.When the mobile terminal receives thehandover-to-UTRAN command message ittunes to the WCDMA frequency and beginsradio synchronization. The mobile terminalthen indicates that the handover was successfulby sending the handover-to-UTRAN-complete message, after which theresources in GSM are released.Ericsson Review No. 1, 2003
Figure 9Successful handover between WCDMAand GSM requires a holistic perspective.From coverage fallback tonetwork optimizationAs described above, the first WCDMA commercialnetworks provide basic coveragefallback to GSM. This fallback is merely thefirst step on the way toward a true seamlessnetwork 2 , where WCDMA and GSM, togetherwith other access technologies, combineto form a single network.There are two important areas in this evolution.The first relates to minimizing theperceived impact on the user when the mobileterminal changes between WCDMAand GSM. The Third-generation PartnershipProject (3GPP) is currently working onenhancements to the WCDMA and GSMstandards (such as inter-system packethandover) that will reduce the actual interruptionin user data transfer from seconds tofractions of a second during packet-switchedservice.The other area relates to the ability of thesystem to select the access technology thatis best capable of providing the requestedservice and quality. This includes the triggercriteria for moving between GSM andWCDMA access technologies. By triggeringa change of radio access technology on,for example, the requested service type, it ispossible to provide the appropriate qualityof service for the call, and to increase theoverall capacity of the system. Figure 8shows the increase in system capacity thatcan be obtained, provided the system—onthe basis of requested services—can allocatetraffic on access technologies.ConclusionThanks to interworking between WCDMAand GSM, users of third-generation mobileterminals can enjoy seamless coverage fromthe very start. The challenges of interworkingbetween WCDMA and GSM havebeen overcome using• dual-mode mobile terminals;• compressed mode channel measurements;• cell re-selection between WCDMA andGSM;• WCDMA-to-GSM cell change order; and• handover between WCDMA and GSM.Ericsson has successfully demonstrated handoverbetween WCDMA and GSM using dualmodemobile terminals in a live network. Thisevent, which required a holistic perspective,was the tesult of a long-term effort (ten years)in research, standardization, system developmentand interoperability testing.Ericsson is also a total system provider inthe area of WCDMA-to-GSM interworking.The set of features described in this article,such as compressed mode and handoverfrom WCDMA to GSM, is available inthe Ericsson WCDMA and GSM networkinfrastructure and in the mobile terminalplatform products being commerciallylaunched in 2003.REFERENCESBirkedal, A., Corbett, E., Jamai, K. andWoodfield, K.: Experiences of operating apre-commercial WCDMA network.Ericsson Review Vol. 79(2002): 2, pp. 50-61.Heickero, R. Jelvin, S. and Josefsson, B.:Ericsson seamless network. EricssonReview Vol. 79(2002):2, pp.76-83.Hedberg, T. and Parkvall, S.: EvolvingWCDMA. Ericsson Review Vol.78(2001 ):3, pp. 124-131.Aimers, P., Birkedal, A., Seungtai, K.Lundqvist, A. and Milen, A.: Experiencesof the live WCDMA network in Stockholm,Sweden. Ericsson Review Vol. 77(2000):4,pp. 204-215.Ericsson Review No. 1, 2003 11
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 10 and 11: Figure 3Interoperability of mobile
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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