AN important aspect of wireless system is the maintenance of a reliable and good radio link quality between the mobile station and the fixed system. When the mobile station crosses the cell boundary, handoff is required to switch the link from one base-station to another to preserve the quality and existence of the call. As cell size shrinks for more capacity, handoff becomes a critical issue. Unnecessary handoff not only increase the system burden, but also jeopardize voice quality and increase the change of lost call....[ Read more ]

AN important aspect of wireless system is the maintenance of a reliable and good radio link quality between the mobile station and the fixed system. When the mobile station crosses the cell boundary, handoff is required to switch the link from one base-station to another to preserve the quality and existence of the call. As cell size shrinks for more capacity, handoff becomes a critical issue. Unnecessary handoff not only increase the system burden, but also jeopardize voice quality and increase the change of lost call.

In this thesis, a handoff algorithm referred to as the Fuzzy Adaptive Averaging-interval and Hysteresis-threshold handoff (FAAH) is introduced. FAAH utilizes the soft decision of fuzzy logic to control the handoff parameters. The fuzzy logic controller takes into the account for signal variation and to change the averaging interval accordingly, and dynamically adapts the hysteresis level with signal differences between the base-stations. Conventional algorithms with fixed signal averaging interval and/or fixed hysteresis level are lack of flexibility under changing mobile environment. The FAAH is designed to minimize handoff frequency, averaging delay, and the chance of lost call. FAAH is shown to enhance the system handoff performance over convent ion al algorithms under various mobile velocity and channel fading.