Wifly或Wiflop:Qware是否能為全球最大的都市無線網路創造出一個有效可行的商業模式? / Taipei City has made a bold step as a first mover in the increasingly popular municipal wireless movement. Currently Taipei’s WiFly service holds the distinction of operating the largest Wi-Fi network in the world. But there are issues that go beyond the accolades Taipei has received in the press. A municipal wireless network is a complex system that involves more than simply setting up a large number of outdoor wireless antennas. While most city leaders around the world cite social improvement as goals for setting up the networks, the reality if that these networks are large scale business ventures. In most large scale projects, private companies are funding municipal networks. Taipei’s network is no exception. The WiFly network must be also able to support the services that will allow the private company Qware to create a workable business model in order to recoup the high setup costs it spent. Looking into Taipei’s experience with WiFly is important because it is currently the only network of its kind and there is a massive amount of money that other cities around the world are investing in their own municipal networks without any evidence that they work. Unfortunately the value of WiFly is mostly as a lesson to other cities considering such a municipal wireless project. The actual subscriber numbers for WiFly are far below initial projects. Qware faces a daunting task of creating a workable business model with WiFly. The difficulties lie in a chicken and egg type scenario in which the Wi-Fi infrastructure does not support the wireless services that citizens would pay for and the lack of a sufficient wireless infrastructure, including location based services, does not allow smaller companies to invest in the development of wireless services. Making the situation even more difficult for Qware is the fact that the wireless industry is evolving so quickly with new standards like Mobile WiMAX that better support outdoor mobile use and the probable convergence of cellular and IP based broadband. By the time the wireless service industry evolves, WiFly’s Wi-Fi infrastructure may be obsolete.

本論文對IEEE 802.16 協調分散式之網狀網路提出一允入控制之演算法。在此類網路中，控制子訊框交換各站台之排程訊息，並預留資料子訊框之時槽作為實際資料傳輸之用。我們利用令牌桶機制來控制網路訊流之流量特徵，如此可簡單的估計各訊流所需之頻寬。我們使用了所提出的頻寬估計方法，並一起考慮各訊流之跳接數與延遲時間之需求，提出的允入控制演算法能夠保證即時性串流之延遲時間需求，且可避免低等級訊流發生飢餓情形。模擬結果顯示，所提出的允入控制方法可以有效的把超過延遲時間需求之即時性訊流封包數目降低，並且低等級訊流在網路負載大時仍然可以存取頻道。 / We propose a routing metric (SWEB: Shortest-Widest Efficient Bandwidth) and an admission control (TAC: Token bucket-based Admission Control) algorithm under IEEE 802.16 coordinated, distributed mesh networks. In such network architectures, all scheduling messages are exchanged in the control subframes to reserve the timeslots in data subframes for the actual data transmissions. The token bucket mechanism is utilized to control the traffic pattern for easily estimating the bandwidth of a connection. We apply the bandwidth estimation and take the hop count and delay requirements into consideration. TAC is designed to guarantee the delay requirements of the real-time traffic flows, and avoid the starvation of the low priority ones. Simulation results show that TAC algorithm can effectively reduce the number of real-time packets that exceed the delay requirements and low priority flows still can access the channel when the network is heavily-loaded.

隨著網路訊務流量的快速成長和無線網路技術日漸成熟，如何妥善的運用有限的網路資源是一個成功擁塞控制機制要面對的根本問題。TCP為現行網路上最廣為使用的傳輸層協定，並且有許多的不同版本被提出來改進其效能上的問題，例如TCP NewReno，TCP SACK 及TCP Vegas等。然而由於TCP傳送端並未具有網路內部狀態的資訊，如可用頻寬等，大部份的TCP擁塞控制機制僅能依賴封包遺失做為觸發擁塞控制的指標。許多研究指出在無線的環境下TCP無法有效使用有限的資源並且分辨封包遺失的原因，因而造成整體的效能不佳。本篇研究提出一個藉由路由器輔助的TCP擁塞控制協定－TCP Muzha，仰賴路由器提供調速資訊，以幫助傳送端能不依靠封包遺失進行傳輸速度控制，並可更快速的達到最佳的傳輸速度。本研究同時提出模糊化的多層級速率調整方法，藉由動態所獲得的細膩資訊做擁塞避免及因應無線環境下因路由改變或傳輸介質不穩所產生的不必要傳輸速度減低。最後我們在NS2模擬器上對所提出的協定做效能評估，實驗結果顯示本協定除了能有效的避免擁塞外，並能減少不必要的降速及重傳封包的次數。 / Communication networks have evolved tremendously in the past decades. TCP is the most dominant and deployed end-to-end transport protocol across Internet today and will continue to be in the foresee future. It has numerous enhancing versions for wired network such as TCP Reno, TCP NewReno and TCP Vegas to improve the drawbacks of initial version of TCP. As IEEE 802.11 wireless network technology gains popularity, TCP is very likely to be popular for existing applications so far. However due to unawareness of network conditions, regular TCP is not able to fully control the limited resources and distinguish packet loss from congestion loss and random loss. Based on such implicit assumption, many studies have shown this would results in serious performance degradation in wireless environment. In this paper, we proposed a new TCP congestion control mechanism by router-assisted approach which is inspired by the concept of each wireless node playing the roles of terminal and router simultaneously. Based on the information feedback from routers, sender is able to adjust the sending speed dynamically in order to avoid overshooting problem. We also proposed a multilevel date rate adjustment method to control the date rate more precisely. Finally we evaluate the performance of our approach by NS2 simulator. Our proposed protocol has 5~10% higher throughput than TCP NewReno and much less number of retransmission. The fairness requirement is also achieved while our proposed protocol coexists with other major TCP variants.

隨著無線網路的興起，許多相關的研究議題也應運而生，利用無線網路(WLAN)對於使用者位置的判斷與追蹤就是其中相當熱門的一塊。經過近幾年的發展，室內WLAN定位誤差的進步空間已達到極限，其原因主要出在無線訊號傳播的物理性質所產生的侷限。然而，大部分擁有良好精準度的定位系統是建立在不切實際的人力成本上，故我們將著眼點放在如何減少收集大量訊號所耗費的人力，同時保持不錯的精準度。取得AP位置所消耗的人力資源也是我們考慮的一環。 因此，我們提出一套新的定位系統：首先建立少數的資料點，再透過推測基地台位置和插入機制來完成訊號資料庫的初步建置。然後在定位的同時收集使用者接收到連續的訊號強度，透過隱馬可夫鏈建立的模型，再配合其他演算法來更新訊號資料庫。實驗結果顯示，相較於其他兩個定位系統，我們的系統能夠減少最多的人力建置資源，並且達到有競爭力的定位精準度。除此之外，我們也分析了系統在使用舊的資料庫或是不同的實驗環境下，能夠展現怎樣的定位結果。 / Following the raise of Wireless LAN networks, there are a lot of relative research issues in today’s life. Tracking and locating mobile users in RF-based WLAN (IEEE 802.11) is a very important issue in location-based applications area. The error distances of indoor WLAN locating was decreased to approximately 1.5 meter in recent years. However, the improvement in accuracy was limited due to the nature of radio propagation. Many researches which contain precise accuracy were based on an impractical effort of collecting too much signal data which we usually called “calibration” in this area. So this thesis focuses on how to reduce the calibration efforts without losing too much accuracy. Confirming the allocation of access points is another kind of calibration effort we concerned. As a consequence, we proposed a new locating system: first we calibrated few points and utilized inferring AP’s position and interpolation to complete radio map. During location estimation phase, radio map could be updated dynamically using learning mechanism modeled by HMM and other algorithms. In the experimental results, we proved our system maintained a comparable accuracy under reducing much calibration effort than other two locating systems. Besides, we analyzed the performance of our system with elder radio map and in two different experimental environments.

網路使用率逐漸普及、傳輸技術的進步以及通訊網路蓬勃發展，提供人們許多生活上的便利，無線網路已經成為現代通訊市場上的新寵兒。其中，IEEE於1999年開始制定與修正WiMAX，此協定在無線網路的應用視為解決”最後一哩”接取問題的利器。然而，無線網路仍舊會遇到傳送訊號耗弱、通訊死角或是氣候干擾等種種原因造成傳輸失敗的問題。 MPEG-4編碼上，考慮影音封包具有不同重要性的意義，針對影音封包需制定不同的重傳機制，本研究先行改善WiMAX中ARQ（Auto Repeat Request）的流程，再利用跨層設計使得MAC層可以辨識影音封包資訊，確保GOP-tree中之＂骨幹＂節點穩定的抵達率，再利用Lagrange’s Method of Multiplier方法，針對GOP-tree中非骨幹部分提出合適的trade-off客製化。最後本研究藉由網路模擬器NS-2(Network Simulater ver. 2)與myEvalvid-NT的實驗架構，做不同效能的評比，並以PSNR值評估所提出之方法的有效性。 / The growing of network popularity, progressing of trasmission technology and development of communication network have facilitated our daily life these years. Wireless network has become a new favor at modern communication market. Among of them, IEEE has started to design and modify specification of WiMAX since 1999, which has been thought to be the solution toward “last mile”. But, there still exist problems such as Doppler effect, blind corner of communication and obstruction of weather condition, which cause the failure of communication. MPEG-4 coding would concern the different significances of distinct types of packets, we should define retransmission strategies for different multimedia packets, respectively. Firstly, we improve the process of ARQ(Auto Repeat reQuest). Secondly, we use MAC-centric design to distinguish multimedia packets and guarantee the arrival rate of packets in the “backbone nodes” of a group of pictures tree. Thirdly, Lagrange’s Method of Multiplier is used to customize the trade-off of “non-backbone node”. In the end, we have performance evaluations by NS-2(Network Simulator ver. 2) and myEvalvid-NT, to verify the efficiency of the proposed method using Peak Signal to Noise Ratio.

藉由許多配備無線通訊能力的嵌入式系統裝置，如筆記型電腦、行動電話、PDA、車用導航系統及車用電腦等，不同的裝置透過無線通訊的能力，將彼此連接，構成行動隨意網路 (Mobile Ad Hoc Network) 的環境。這些網路上的節點可能任意且快速移動，隨時改變既有網路拓樸，造成原先已經建立好的路由中斷。採用被動式路由協定 (Reactive Routing Protocol) 的路由重建，往往增加了資料傳送的延遲及重建路由時所需要大量路由發現 (Route Discovery) 的封包，造成廣播風暴 (Broadcast Storm)，嚴重影響整個網路的效能。 在論文中，我們提出一個利用節點的移動方向做為選擇適當中繼節點 (Relay Node) 的策略，稱之為Directive Location-Aided Routing，簡稱DLAR。DLAR將節點的移動方向因素加入於既有的LAR中做為選擇中繼節點的考量。中繼節點的決定，需要符合與來源節點相同的移動方向，目的是維持較長的連線時間，且讓路由中斷的位置靠近目的節點，並使用AODV的Local Repair的機制做為路由搜尋的協定，加速路由的恢復。 實驗模擬結果顯示，DLAR與AODV、DSR及LAR比較，在減少找尋路由路徑時所需的路由請求封包、降低點對點 (End -To-End) 的延遲及資料成功送達率，都有較佳的表現。在網路中節點數較多時，DLAR在封包送達率能有6%– 55%的改善，降低搜尋及維持路由時需要的控制封包量達40%以上，降低廣播風暴發生的機率， DLAR也同時在End-to-End Delay的表現較之於其他路由機制，有20%以上的改善。 / In MANET the nodes may move fast and unpredictable, this may cause the original set up route well broken. Adopt those Reactive Routing Protocols may not only cause seriously data delivery delay but also produce a large number of control packages (RREQ) thus reducing network capacity. This is known as Broadcast Storm Problem. In this thesis, we proposed a routing protocol, Directive Location-Aided Routing (DLAR), that helps to choose appropriate relay nodes (intermediate nodes) in MANET. DLAR considers the node movement direction factor in deciding a stable route. Relay node is considered to be the same movement direction as source node. The goal is to maintain longer path lifetime, and make the broken very close to the destination node. DLAR adopts AODV to discovery route and accelerate the route recovery using Local Repair mechanism. Simulations show that as the network loading is high, DLAR can increase the packet delivery ratio by 6% ~ 55 % and increase the bandwidth utility by 40%, reduce the largely broadcast storm probability, and reduce end-to-end delay by 20%.

隨著無線網路環境的普及，越來越多行動工作者可以透過隨身的手持設備進行網路漫遊，即時地存取不同的服務。另外亦可以經由公司的虛擬專有網路來存取企業內部資料、電子郵件及其它應用程式。不論是針對企業或是網路服務業者而言，為了要能夠確保網路環境上的安全性，眾多的行動工作者在進行漫遊時，身分必須被驗證，進而才能被授予各項服務的存取權。此外，還必需根據使用者服務使用的情況進行計費，來提升服務提供者的收益。 因此在無線區域網路中，結合一套認證、授權、計費的架構(Authentication, Authorization, Accounting Architecture, AAA Architecture)，使得網路服務業者能夠有效地來管理龐大行動工作者的跨網路漫遊服務。 本研究提出一個以情境知覺運算(context-aware computing)為基礎的AAA架構。以情境來設計資源存取政策，因此系統偵測到行動工作者情境上的改變，根據已定義好的存取政策，動態地進行身分驗證及調整授權服務，最後再依不同的服務使用等級、連線時間與網路使用量等來計費。本論文以漫遊服務與企業虛擬專有網路為例，說明在此架構下如何針對不同的情境進行身分認證、與服務授權。 / With the popularity of the Wireless LAN, mobile workers are able to access various services or resources with seamless roaming, as well as mobile VPN, just via their handheld devices. Not only for the corporations but the Internet Service Providers(ISP), a secure and trusted remote access is required. User identity should be authenticated in advance, and the service providers grant or deny mobile users the access to resources according to their statuses. Besides, a usage-based accounting and billing is crucial to provide commercialized services within WLAN, and to benefit those service providers. As a result, a AAA architecture designed for coordinating the authentication, authorization and accounting between different administrative networks is required with urgent need. The objective of this research is to provide a context-aware based AAA architecture which adopts context as the design principle to define access control policies. So the system can detect the changing contexts of mobile workers, re-authenticate user identity, adjust dynamically service permissions in the light of context-based access control policies, and bill the user taking into account the contexts efficiently. In this research, we take examples of roaming services and VPN to describe how the architecture works.

現今我們所住的世界不再只是一個單純的有線網路，隨著WLAN的無線區域網路的存取點越來越普遍，每個家庭使用有線網路做為後端網路然後使用無線區域網路的存取點作為最後一哩的情況也隨著變的常見了，所以現在的網路世界不再只是一個單純的有線網路而是一個有線跨無線的異質性無線網路了，TCP一個我們所常用的傳輸層的協定當遇到異質性無線網路時已經被證實會對封包遺失的原因有誤判，在無線傳輸時封包遺失的理由包括訊號品質不好以及用戶端之間在無線介質中的競爭，因此我們設計了一個具有跨層考量的EATCP-Assisted模組來幫助傳送端收集媒體存取控制層的資訊並使的傳送端在調整競爭視窗上面更有效率，在EATCP中有兩大部分：第一部份是估算階段，第二階段就是EATCP的擁塞控制機制，藉由EATCP-Assisted模組所收集到的wirelessRTT以及utilization我們可以有效的估算出wiredBW以及wirelessBW，並藉由這兩個參數我們可以準確的將封包遺失的原因從頻道衰減以及用戶端之間的競爭中分別出來，因此一個適當的競爭視窗就可以藉由這些資訊來調整出來。 / Recently, with the growth of WLAN, the world we live today is no longer a pure wired network, it’s a heterogeneous wireless network. The TCP that we commonly used has been proven to have misjudgements of packet loss in heterogeneous wireless networks. We design a cross-layer architecture called EATCP-Assisted module to help the sender collect MAC layer information, and adjust the congestion window more efficiently. In EATCP, there are two important parts: the first is estimation phase; the second is congestion control algorithm. By collecting the wirelessRTT, and utilization we can estimate the wiredBW and wirelessBW. The EATCP will distinguish the causes of packet loss from network congestion, channel fading, or contention between wireless clients. Thus, appropriate congestion window adjustment can be done accordingly. The simulation results show that our EATCP outperforms other versions of TCP.

隨著多元智慧型設備(如智慧型手機、筆記型電腦與平板電腦)的迅速普及，以及高效能行動網路之導入，行動寬頻市場之接受度持續快速提升中。已有越來越多的智慧型手機用戶，會在移動狀態中使用各式各樣應用及網際網路服務，預計未來十年內資訊流量將成長近百倍。 然而面對行動數據傳輸量的暴增，如何利用small-cell進行行動數據傳輸量的分流，是目前全球所有電信營運商及行動網路設備供應商所面臨的一大課題。若毫無篩選規劃的廣泛建置small-cell將耗費龐大的建置維護成本(包含設備、電路、人力及維運等支出)，卻無法得到與投入成本相對應的行動數據傳輸量分流效益。 於本研究中，我們將建立一個small-cell覓點模型來有效找出真正需要分流行動數據傳輸量的地點來建置small-cell。由2010年Informa的統計資料可知，行動數據來源有住家屋內、辦公場所、交通運輸據點及公眾開放空間等四大部分。因交通運輸據點及公眾開放空間有直接較明顯的目標地點，如何精準找出住家及辦公場所亟需分流的地點為本論文研究之重點。 最後我們透過實驗並以off-load、throughput、建置成本及選點準確率等指標，驗證本研究所建立之small-cell覓點模型確實可有效找出需要分流行動數據傳輸量的地點。

近十年來，由於無線網路的普及與人們對於影像串流服務的需求愈高，導致人們迫切需要更好的服務品質。但在IEEE 802.11無線網路中，本身的設計並非針對影像串流來設計，為讓影像串流能在無線網路更有效率，我們必須重新設計適合影像串流的無線網路。本研究首先探討IEEE 802.11 MAC層DCF (Distributed Coordination Function)與802.11e EDCA (Enhanced Distributed Channel Access)機制的潛在問題。由於DCF與EDCA並未特別對影像串流做設計，會導致具有時延(delay time)限制的影像封包等待過久造成失效，卻仍繼續傳送。本研究提出幾個有效方法，改善原本IEEE 802.11無線網路對影像串流傳輸效能不彰的現象。我們將利用跨層設計使MAC層能取得影像串流封包資訊，並改善DCF與EDCA的重傳(retransmission)機制，使用time limit與retry limit混和設計節省不必要的等待時間，並使用single-video multi-level queue改善傳輸效能。最後本研究將利用網路模擬器NS-2 (Network Simulater ver. 2)與影像串流測試實驗架構myEvalvid-NT作不同效能的驗證比較並評估我們所提出方法的有效性。 / Over the past decade, wireless network access and video streaming services have become more popular than ever. People are eager to have better quality of video streaming services over wireless network. However, IEEE 802.11 DCF and IEEE 802.11e EDCA are not specifically designed for video streaming. This leads to the problem of transmitting overdue video packets and thus degrades both the network performance and video quality. In this paper, we propose a hybrid design framework to improve the quality of video streaming. This framework consists of a MAC-centric cross-layer architecture to allow MAC-layer to retrieve video streaming packet information (slice type and transmission deadline), a retransmission mechanism of hybrid retransmission deadline and retry limit to save unnecessary packet waiting time, and a single-video multi-level queue to prioritize I/P/B slice delivery. Simulations show that the proposed methodology outperforms IEEE 802.11e, IEEE 802.11e Timebase and IEEE 802.11e MultiQ in packet loss rate, invalid packet ratio, lost and invalid packet ratio, delay time, jitter, and PSNR.