| Summary: | 碩士 === 朝陽科技大學 === 資訊工程系碩士班 === 94 === Recently, many wireless access techniques are developed rapidly. The wireless networks which consist of several kinds of wireless access techniques, such as 802.11, 802.16 and 3G/UMTS, etc., are formed heterogeneous wireless networks. In such heterogeneous wireless network, vertical roaming allows user moving between wireless networks which have different access techniques. However, too much unnecessary vertical roaming may result in some drawbacks, including long roaming delay, connection dropping and low utilization. Besides, the fast changes of bandwidth cause by vertical roaming will lead to the low performance of TCP. Therefore, in this paper we proposed an efficient vertical roaming approach that uses the RSS prediction to reduce the unnecessary vertical roaming, and a cross layer-based approach that uses cross layer mechanism to adjust the TCP when vertical roaming is performed to improve the performance of TCP in heterogeneous wireless networks. Numerical results show that the proposed efficient vertical roaming approach yields less number of roams and low grade of service while yielding competitive utilization. The proposed cross layer-based approach improves the performance of TCP Reno and TCP NewReno.
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