ericssonhistory.com

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