隨著科技日新月異，無線網路系統的使用越來越普遍，其建置成本亦日益低廉，創造出許多新穎的應用，如何在此應用環境中提供實用的加值服務，實為無線網路系統之主要課題，一方面能藉由傳輸技術之高延展性，來確保眾多行動裝置接收視訊影音資料之即時性，而無庸冗長的等待耗時，另一方面又能自動地判定行動裝置的所在，暨以選擇性地擷取與該位置相關的服務項目，提供連續性查詢貼切的服務內容，而不需操作者僵化的反覆輸入，誠能妥善地發揮無線網路有別於有線網路之特點，增益其應用服務之實質內涵。
本論文提出了兩項技術：第一項是高效率廣播技術，解決為了使伺服器頻寬更為有效地利用，必需對多媒體檔案做精細的切割，所產生封包檔頭負擔的問題。這個新的方法為了不使封包檔頭的負擔過大，將每個片斷都維持填滿封包的大小，再針對第一個片斷做額外的分割，來有效地避免過多檔頭的負擔，亦能維持伺服器在傳輸低位元率的多媒體檔案時原應有的效能表現。第二項為位址預測技術，提出有效的演算法來預測位置，解決室內定位的問題，藉由所接收的無線網路封包中，擷取出訊號強度，並和之前所搜集的訊號強度資訊做比對。為了減少雜訊的干擾，我們使用四分位數去描繪訊號強度的分布情況，能改善使用平均值時容易被極大或極小值影響的情況，查詢中也不需要大量的訊號資料，加快了查詢的速度，只需要少量運算便可得到不錯的結果。

With the advances of technologies, wireless connectivity becomes a critical component of networking infrastructure due to the favorable mobility and incessant reduction of hardware cost. Many creative wireless applications are feasible. On one hand, the scalable services allow numerous mobile users to receive the audiovisual streams on demand with short delays. On the other hand, the system should recognize the user positions to fulfill the pertinent location-aware contents as responses from the continuous queries without repetitive explicit specification from users. Both desirable features discern the very characteristics of wireless networks, and honestly give free rein to their applications.
In this thesis, we propose two techniques. First is an efficient periodic broadcast scheme that preserves bandwidth efficiency when extensive segmentation on stream contents is necessary to initial service delay reduction. Our new design elegantly controls the effect of the packet overhead on the bandwidth efficiency by only fragmenting the very first segment. The latter segments are kept constant as the size of the full-sized packets. As a result, the proposed scheme can avoid the performance deterioration due to the induced overhead of segmentation, while accommodate the available server capacity to reduce the service latency. The performance study indicates our new scheme is constantly better than the existing competitors with all possible design options for the delivery of low bit-rate media streams. The second one is the location estimation problem. Our solution exploits the signal strengths of packets on wireless Ethernet networks to predict the location from the previously collected knowledge. To reduce the noise effects on signals, we use the quartiles to portrait strength distributions seen from the positions. We can deliver more reliable results than the techniques based on the average signal strengths, which are greatly biased by the strongest signals. Particularly, using quartiles allows us to answer the location query more accurately than the schemes that employ numerous strength data in each query. As a result, our solution scales gracefully in terms of computation cost, a favorable feature particularly suitable to the hand-held devices with limiting computing and storage resources.

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