An analytical model for intersystem handover

Universal Mobile Telecommunication Systems (UMTS) shall be developed in such a way that it supports compatibility with an evolved Global System for Mobile Ccommunications (GSM). In this paper, we investigate intersystem handover between GSM and UMTS based on wideband code division multiple access (WCDMA) air-interface. A mathematical model is proposed to evaluate the handover performance. The handover initiation algorithm is based on the absolute value of averaged signal strength thresholds. Average number of handovers and handover initiation delay are used as performance measures. Based on numerical results, it is observed that handover initiation algorithm based on absolute thresholds induces large number of handovers near the cell boundary. Finally, threshold levels are optimized for given system parameters.