在異質性無線網路上利用封包遺失資訊輔助換手決策研究

近年來無線行動通訊網蓬勃發展，各種不同型態的無線網路提供了不同涵蓋範圍與傳輸品質。在未來，行動裝置將普遍的裝設多個不同無線網路介面，使它可以隨時依據它所在的地點連線上網。當需要時，它也必須在無線網路之間換手，以達到無礙、高品質的通訊服務。本論文提出一創新的輔助機制來改善過去學者所提出的網路探索演算法-NDMD (Network Discovery with user Motion Detection)的效能。NDMD以移動感知來啟動網路探索，然而，因多路徑衰退，無線網路的傳輸訊號受環境影響極大，因此，以訊號強度為換手的依據往往造成NDMD誤判。本論文使用TCP的CWND(Congestion Window Size)來當作封包遺失的指標，以輔助NDMD來更精準的量測使用者的接收品質，並改善換手的決策的品質，此換手演算法稱為封包遺失感知packet loss aware NDMD，又簡稱為PLA-NDMD。實驗結果顯示PLA-NDMD演算法可以在較佳的時間驅動換手且有效提升資料傳輸效能。

關鍵字

換手；網路探索；動態偵測；封包遺失；接收訊號強度；壅塞視窗

並列摘要

Integration of different wireless network environments can provide a universal ubiquitous coverage and various transmission rates for Mobile Terminals (MTs). In the future, many MTs will be featured with several interfaces to access these networks. Such a multi-mode MT can access an appropriate wireless network wherever they go. To achieve ubiquitous computing, an MT needs to switch or handoff its connection between different or similar types of wireless networks. This thesis presents a novel mechanism to improve a previous work called NDMD (Network Discovery based on user Motion Detection), which triggers network discovery based on an MT’s motion and Received Signal Strength (RSS). However, due to multipath fading, a wireless signal is strongly affected by environment. Hence the motion detection based on RSS in NDMD may cause an MT to make poor handoff decision. Thus, in this thesis, we exploit TCP CWND (Congestion Window Size) as a packet loss index to cope with the problem. The presented algorithm is called packet loss aware NDMD, or PLA-NDMD. Experiment results show that PLA-NDMD can trigger a MT to perform handoff at appropriate timings and improve the data transmission throughput between MT and a wired station.

並列關鍵字

Packet Loss ； RSS ； CWND ； Handoff ； Network Discovery ； Motion Detection

參考文獻

[2]V. Hector and K. Gunnar, “Techniques to reduce IEEE 802.11b MAC layer

Internetworking of WLANs and Cellular Networks: Architecture and Performance Issues in A Mobile IPv6 Scenario,” In IEEE Wireless Communications Magazine, Vol. 12, No. 3, pp. 42-49, June 2005.

[6]W.-T. Chen and Y.-Y. Shu, “Active application oriented vertical handoff in next-generation wireless networks,” in Proceedings of IEEE Wireless Communications and Networking Conference (WCNC ’05), Vol. 3, pp. 1383-1388, March 2005.

[7]M. Ylianttila, J. M’akel’a, and K. Pahlavan, “Analysis of handoff in a location-aware vertical multi-access network,” Computer Networks, Vol. 47, No. 2, pp. 185-201, 2005.

[9]W.-T. Chen, J.-C. Liu and H.-K. Huang, “An adaptive scheme for vertical handoff in wireless overlay networks,” in Proceedings of the 10th International Conference on Parallel and Distributed Systems (ICPADS ’04), pp. 541-548, July 2004.

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在異質性無線網路上利用封包遺失資訊輔助換手決策研究

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