Mobility management in ubiquitous environments

Ubiquitous computing is aiming at providing users with intelligent human-centric context-aware services at anytime anywhere. However, mobility increases dynamism and uncertainty conditions. This study therefore explores the management and uses of various contexts for automatically providing appropriate services to individual users. This issue is explored from an open framework perspective referred to as ubiquitous gate (U-gate). In this framework, a distributed context management architecture and a communication model based on standard protocols are proposed. To fit user requirements and to achieve complete mobility management, a context-aware path planning mechanism (UbiPaPaGo) and a context-aware handoff mechanism (UbiHandoff) are proposed based on context stored in an open and distributed context management server U-gate. Based on the path planning results of UbiPaPaGo, UbiHandoff derives a minimum access point (AP) handoff plan that satisfies multiple QoS requirements for individual users and services. The UbiHandoff mechanism includes multiple-attribute decision making method (MADM)-based handoff planning, referred to as MADM-based UbiHandoff, and genetic algorithm (GA)-based handoff planning, referred to as GA-based UbiHandoff. In the proposed MADMbased UbiHandoff, analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) provide efficient and seamless AP handoff to gain higher QoS performance. In GA-based UbiHandoff, genetic algorithm is employed to minimize handoff by finding appropriate APs along the path under QoS constraints. Finally, the effectiveness of the proposed mechanisms is evaluated through simulations. Numerical results demonstrate that both mechanisms minimize handoffs and ensure compliance with QoS requirements.