Browsing by Author "Tientsung Tai"

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Achieving time-based fairness for VoIP applications in IEEE 802.11 WLAN using a cross-layer approach
(2010-09-30) Chiapin Wang; Tientsung Tai
IEEE 802.11 Wireless Local Area Network (WLAN) Physical Layer (PHY) offers multiple data rates. In multi-rate WLANs, 802.11 Medium Access Control (MAC) protocol, Distributed Coordination Function (DCF), essentially provides equal transmission opportunities to each sender host, causing the degradation of system throughput due to some hosts using low rates. In this paper we propose a cross-layer link adaptation scheme which improves throughput by adjusting MAC parameters according to PHY data rates to achieve time-based fairness instead of throughput-based fairness. Most importantly, in comparison with other approaches using a deterministic manner for temporal fairness (e.g. OAR), our random-access-based approach in statistic can be more effective to restrict the maximum packet delay within a bound when the number of stations grows. We conduct the transmission scenario of VoIP applications to evaluate the performance of our proposed scheme and the results demonstrate its effectiveness.
Application of Neural Networks on Rate Adaptation in IEEE 802.11 WLAN with Multiples Nodes
(2010-07-11) Chiapin Wang; Jungyi Hsu; Kueihsiang Liang; Tientsung Tai
The paper presents an adaptive Auto Rate Fallback (ARF) scheme to improve the performance of aggregate throughput in IEEE 802.11 Wireless Local Area Network (WLAN) with multiple nodes. When the number of contending nodes increases, using ARF will be likely to degrade transmission rates due to increasing packet collisions and can consequently cause a decline of the overall throughput. In this paper we propose a neural-network based adaptive ARF scheme which improves the throughput performance by dynamically adjusting the system parameters that determine the transmission rates according to the contention situations including the amount of contending nodes and traffic intensity. The performance of our scheme is evaluated and compared with that of other LA schemes by using the Qualnet simulator. Simulator results demonstrate the effectiveness of the propose algorithm to improve the performance of aggregate throughput in a variety of 802.11 WLAN environments.
於移動WiMAX網路提出延伸即時性輪詢服務演算法改進上行資源分配之研究
(2011) 戴天縱; Tientsung Tai
雖然在IEEE 802.16e標準規範中，針對不同物理特徵的訊務流定義五種不同服務品質要求(Quality of Service, QoS)的資源分配演算法，但是標準規範中並沒有明確提出具體解決方案保證維持服務品質，而這些種種問題近年來就成為許多實驗室研究的重點。在本研究中，我們針對使用延伸即時性輪詢服務演算法，運用在點對多點的無線網路模式上的移動終端裝置，提出了一種改進的上行鏈路資源分配演算法。該演算法可用來解決在不可預測的多變無線通訊環境裡，移動終端裝置因服VBR(Variable bit rate, VBR)訊務流的資料量會是週期性可變動的特徵，所造成移動終端裝置請求資源與獲得可傳輸資源的不匹配所面臨的問題。該演算法依據各個移動裝置請求表頭統計次數的變化，使基地台作到主動分配合理的上行資源給需求持續增加的移動裝置；改善原始延伸即時性輪詢服務演算法的缺點，降低資料封包遺失率及滿足延遲的要求。在模擬的結果顯示，此演算法的確可以有效地降低移動裝置在上行鏈路傳輸資料延遲時間及達到減少封包遺失率，維持服務品質的要求。