| Summary: | 碩士 === 朝陽科技大學 === 資訊工程系碩士班 === 93 === The demand and amount of data transfer in heterogeneous wireless network increases as the techniques of the third/fourth generation mobile communications (3G/4G) are progressed significantly. Vertical handoff provides continuous and seamless transfer between various wireless mobile networks, which have different data transmission techniques and standards such as GPRS, UMTS, cdma2000 and IEEE 802.11 family WLANs. In contrast to the horizontal handoff, the vertical handoff should consider not only the strength of signal power but also QoS classes, network bandwidth and service types, etc. Most of the previous works proposed the Received Signal Strength (RSS) based methods to set thresholds for making the decision of performing vertical handoff or not. The RSS-based approach yields serious ping-pong effect when the mobile node moves around the overlay area of two heterogeneous wireless networks, which causes unnecessary handoff and increases the handoff overhead. Although the RSS-based approach with the hysteresis technique decreases the number of unnecessary handoffs, it remains large overhead of handoff, which causes some drawbacks, including low network throughput, long handoff delay and high dropping probability. Therefore, an efficient cost-based vertical handoff algorithm is proposed herein to reduce unnecessary handoffs while increasing network throughput, decreasing handoff delay and avoiding connection dropping. Two primary motivations of this paper include the prediction of node mobility from RSS and the adaptive cost-based competitive on-line (COL) method to determine the optimal network for handoff from several available wireless networks. Furthermore, message flows of vertical handoff between 3G/UMTS and WLAN with mobile IPv6 protocol are investigated in detail. Numerical results demonstrate that the proposed cost-based approach outperforms other approaches in the number of vertical handoffs and connection dropping while yielding competitive throughput.
|
|---|
