教師著作
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Item A Cross-Layer Link Adaptation Algorithm for IEEE 802.11 WLAN with Multiple Nodes(2008-12-12) Chiapin Wang; Tsungnan LinIEEE 802.11 wireless local area network (WLAN) physical layer (PHY) offers multiple data rates. In multi-rate WLANs, 802.11 distributed coordination function (DCF) presents the phenomenon so called ldquoperformance anomalyrdquo: when some hosts transmit at lower data rates, throughput of others at high rates will be restricted within the lowest rate, leading to the degradation of overall performance. Therefore, the link adaptation scheme for 802.11 WLAN should consider not only throughput of the observed host but also system throughput in order to optimize the overall performance. In this paper we propose a cross-layer link adaptation algorithm which improves system throughput by regarding the situation of PHY rate degradation more thoughtfully and critically, and meanwhile compensates the throughput of hosts with bad link qualities by applying differentiated channel access parameters. Simulation results demonstrate the effectiveness of the propose algorithm.Item A Cross-Layer Adaptive Handoff Algorithm in Wireless Multimedia Environments(2007-09-12) Tsungnan Lin; Chiapin WangProviding multimedia services in wireless networks is concerned about the performance of handoff algorithms because of the irretrievable property of real-time data delivery. To lessen unnecessary handoffs and handoff latencies which can cause media disruption perceived by users, we present in this paper a cross-layer handoff algorithm base on link quality. Neural networks are used to learn the cross-layer correlation between the link quality estimator such as packet success rate and the corresponding context metric indictors, e.g. the transmitting packet length, received signal strength, and signal to noise ratio. Based on a pre-processed learning of link quality profile, our approach makes handoff decisions intelligently and efficiently with the evaluations of link quality instead of the comparisons between relative signal strength. The experiment and simulation results show that the proposed method outperforms RSS-based handoff algorithms in a transmission scenario of VoIP applications.Item Improving 802.11 QoS in Heterogeneous Channels Using an Adaptive Scheme(2006-01-01) Chiapin Wang; Tsungnan LinItem A Context-Aware Approach for Multimedia Performance Optimization using Neural Networks in Wireless LAN Environments(2006-07-12) Po-Chiang Lin; Chiapin Wang; Tsungnan LinPacket size is one of the most important factors that would affect the user-perceived multimedia QoS in the wireless LAN environments. The time-varying channel characteristics make it difficult to find the exact relationship between the packet size and the throughput and decide an optimal packet size in advance. Furthermore, every node would suffer different channel conditions. In this paper, we tackle this problem by an optimization approach. A context-aware framework is designed to optimize the packet size adaptively in order to maximize the throughput. In this approach each node abstracts its specific context via the throughput from the time-varying wireless environments. The obtained throughput information is the instantaneous integrated effect of all contexts in wireless LAN environments. This approach adopts neural networks to learn the complex nonlinear function between the packet size and the throughput and adaptively adjusts the packet size. Simulation results show that out method can cope with the time-varying wireless channel conditions and improve the perceived QoS of wireless multimedia servicesItem A Neural Network Based Adaptive Algorithm for Multimedia Quality Fairness in WLAN Environments(2006-07-12) Chiapin Wang; Tsungnan LinThis paper investigates multimedia quality fairness in wireless LAN environments where channel are error-prone due to mobility and fading. The experimental results show that using fixed MAC arguments for nodes in heterogeneous channel conditions leads to unequal throughput performance and that may incur the degradation of multimedia QoS. To overcome the unfairness problem for provisioning QoS, we propose a cross-layer adaptation scheme by on-line adapting the multidimensional MAC-layer backoff parameters depending on the application-layer QoS requirements and PHY-layer channel conditions. Our solution is based on an optimization approach which utilizes neural networks to learn the cross-layer function. Simulation results demonstrate that our adaptive scheme can tackle a variety of channel condition to provide fair throughput for nodes in heterogeneous channel conditionsItem 以跨層式鏈結調整演算法提升無線區域網路之吞吐量效能(行政院國家科學委員會, 2009-07-31) 王嘉斌在本計畫中，我們研究在IEEE 802.11 無線區域網路(WLAN)中有多個工作站使用 不同傳輸速率時的吞吐量(throughput)效能。無線網路在實體層(PHY)使用不同的調變與 編碼技術(Modulation and Coding Schemes， MCS)支援多重傳輸速率。當某一個工作站 的通道品質變差時，它會使用較低的傳輸速率來獲得較佳的連線品質。然而，IEEE 802.11 媒體存取控制層(Medium Access Control， MAC)所使用的分散協調式功能 (Distributed Coordination Function， DCF)對於每一個工作站提供了相同的傳輸機會， 無論它們所使用的傳輸速率為何。這將導致使用高速率的工作站其資料傳輸率被限制 在某一個使用中的最低速率，使得整體系統的吞吐量下降。這種現象稱為IEEE 802.11 無線區域網路的傳輸效能不規則(performance anomaly)，而這個現象在提供高範圍傳輸 速率的網路例如IEEE 802.11g 網路中將會是更為嚴重的問題。 我們將會以理論推導的方式深入分析效能不規則現象，並且研究既有鏈結調整(link adaptation， LA)演算法的效能。我們也將提出我們包括實體層及媒體存取控制層的跨 層最佳化鏈結調整演算法，並且評估比較我們方法與其他文獻提出方法的效能。我們 提出的演算法考慮實體層及媒體存取控制層之間的交互影響並進行跨層效能最佳化， 預期將能提高系統吞吐量，並且同時維持工作站之間使用通道的公平性。在本計畫中 所提出的理論分析以及跨層最佳化解決方法，希望可作為未來無線區域網路系統設計 之參考。Item Cross-Layer Analysis and Design for Multimedia Services in IEEE 802.11 WLANs(2008-01-01) Chiapin Wang; Po-Chiang Lin; Tsungnan LinIEEE 802.11 Wireless Local Area Networks (WLAN) supply broadband data accesses and evolve a growing demand of multimedia services for mobile users. To provide quality of service (QoS) for multimedia applications in WLANs, it is important to analyze the performance of 802.11 Medium Access Control (MAC) protocols under varying heterogeneous channel conditions. In this paper, we focus on 802.11 WLANs which adopt the MAC protocol of Distributed Coordination Function (DCF), and provide performance analyses to show the interlayer effect of physical-layer (PHY) channel diversities on DCF protocol as well as the consequent impact on multimedia QoS at application (APP) layer. We then discuss some feasible crosslayer designs for overall optimizing QoS performance in 802.11 WLANs. We also take example of the QoS unfairness problem due to the interlayer impact of PHY channel diversities and illustrate a solution of our cross-layer approach.Item 無線區域網路中鏈結調整演算法之跨層最佳化設計(教育部, 2009-08-31) 王嘉斌Item On Fairness in Heterogeneous WLAN Environments(2006-12-01) Chiapin Wang; Tsungnan LinWe analyze the fairness of IEEE 802.11 DCF in heterogeneous wireless LAN environments where users experience unequal channel conditions due to the mobility and fading effects. Previous works [3] [4] show that the 802.11 CSMA/CA can present fairness characteristics in both long- term and short-term. However, the conclusion is only valid under the condition of homogeneous link qualities, which may be impractical. In this paper, we consider heterogeneous channel conditions based on an analytical approach of extending a verified two dimensional Markov chain model of DCF proposed by Bianchi [10]. From our analytical results, it is shown that 802.11 CSMA/CA can present fairness among hosts with identical link qualities regardless of equal or different data rates applied, which is consistent with the observations of previous works. Our analytical results also demonstrate that the presence of heterogeneous channel conditions can pose significant unfairness of channel sharing even with a link adaptation mechanism since the MCSs (modulation and coding schemes) available are limited.Item A Cognitive Approach to Achieve Fair Uplink and Downlink Utilities in Wireless Networks(2009-08-31) Chiapin Wang; Kueihsiang LiangThe paper investigates on fairness of utilities between uplink and downlink traffic flows in IEEE 802.11 Wireless Local Area Networks (WLAN) with an infrastructure mode. We propose a cognitive resource allocation scheme to tackle the fairness problem. The proposed scheme is cognitive by using neural networks to on-line learn the nonlinear function between the adopted Medium Access Control (MAC) parameters and the corresponding throughput. Thus, the learned knowledge can be exploited to adjust MAC parameters dynamically toward the utility fairness between uplink and downlink flows. Simulations results demonstrate that our adaptive scheme can effectively provide fair uplink and downlink utilities in a varying heterogeneous WLAN environment.