DESIGN AND SIMULATION STUDY OF AN INTER-SYSTEM HANDOVER ALGORITHM IN UMTS

摘要

In this paper, we present a (UMTS -^sGSM) inter-system handover algorithm which uses two pairs of UMTS and GSM HO thresholds (E{sub}c/I{sub}o threshold for UMTS and RSSI threshold for GSM); one pair of thresholds for making a decision to handover from UMTS to GSM and another pair of thresholds for making a decision to handover from GSM to UMTS. We build a simulation model of a 37-cell UMTS/GSM system consisting of an island of 7 UMTS cells surrounded by 30 GSM cells. The simulation model includes mobility of all users in the system and spatial correlation of the log-normal shadow losses in the 2.1 GHz (for UMTS) and 900 MHz (for GSM) frequency bands. We allow a test mobile to move along the boundary of the UMTS and GSM cells and evaluate the handover rate performance as a function of the various handover thresholds involved. We show that by properly building a hysteresis between the UMTS-to-GSM-HO threshold pair and the GSM-to-UMTS-HO threshold pair, a good compromise between call drop rate, and intra- and inter-system handover rates can be achieved.