Increasing capacity in wireless mesh networks can be achieved by using multiple channels and radios. By using different channels, two nodes can send packets at the same time without interfering with each other. To utilize diversity of available frequency, typically cards use channel-switching, which implies significant overhead in terms of delay. Assignment of which channels to use needs to be coupled with routing decisions as routing influences topology and traffic demands, which in turn impacts the channel assignment. Routing algorithms for wireless mesh networks differ from routing algorithms that are used in wired networks. In wired networks, the number of hops is usually the only metric that matters. Wireless networks, on the other hand, must consider the quality of different links, as it is possible for a path with a larger amount of hops to be better than a path with fewer hops. Typical routing protocols for wireless mesh networks such as Optimized Link State Routing (OLSR) use a single path to send packets from source to destination. This path is precomputed based on link state information received through control packets. The consideration of more information than hop-count in the routing process has shown to be beneficial as for example link quality and physical layer data rate determines the quality of the end-to-end path. In multi-channel mesh networks, also channel switching overhead and channel diversity need to be considered as a routing metric. However, a major drawback of current approaches is that a path is precomputed and used as long as the path is available and shows a good enough metric. As a result, short term variations on link quality or channel switching are not considered. In this thesis, a new routing protocol is designed that provides a set of alternative forwarding candidates for each destination. To minimize delay (from both transmission and channel switching), a forwarding mechanism is developed to select one of the available forwarding candidates for each packet. The implementation was tested on an ARM based multi-radio platform, of which the results show that in a simple evaluation scenario the average delay was reduced by 22 % when compared to single path routing.

As the need to remain connected increases, more and more people are turning to wireless mesh networks because they reduce the need for network infrastructure. Unfortunately, TCP does not perform well in such networks. HxH, an alternate protocol, has shown great promise in simulations, but since it relies on exploiting passive feedback, real measurements are needed to determine how effective the protocol really is. This thesis uses a measurement study on a wireless mesh network to characterize the performance of the HxH protocol in real-world networks. Several aspects of the HxH protocol do in fact perform well on real networks, but the high rate of packet loss renders other aspects of the protocol ineffective.

A wireless imaging system for monitoring strawberry fields provides enough quality image data for computer vision algorithms to make meaningful yield predictions. This report contains a design for a wireless sensor network modified with mesh networking techniques to extend coverage range and a solar energy harvesting system to improve sensor node lifetime. A two hop system with six nodes is implemented in a laboratory environment validating the communication systems integrity over an 800’ range. Moving from a primary battery system to solar energy harvesting increases the module lifetime indefinitely.

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<p>This thesis presents the lessons learned from building an IEEE 802.11 wireless mesh network (WMN) test-bed. Each network node consists of a Linux processor with multiple IEEE 802.11b/g transceivers operating in the 2.4 GHz band. Each transceiver consists of a medium access control (MAC) and base-band processor (BBP) in addition to a radio. A device driver was modified to control some of the key transceiver functions. The test-bed's Wi-Fi interfaces can be programmed to implement any mesh communication topology. All Wi-Fi interfaces use omni-directional antennas and the IEEE 802.11b operation mode.</p> <p>The test-bed design is easily extendable to incorporate newer Wi-Fi technologies. Measurements of co-channel interference in each Wi-Fi channel including received signal strength (RSS) and signal-to-interference-and-noise ratio (SINR) are presented. The AutoMin algorithm was developed in order to use the captured physical layer (PHY) metrics to avoid Wi-Fi congestion during test-bed operation. A comparison of a software-based spectrum analyzer to a commercial one is described. Key Wi-Fi functions in the Ralink driver source code are explored in depth. The compliance of the Ralink chip-set to the IEEE 802.11b spectral mask was verified. The maximum driver-induced retuning rate for the popular Ralink radio was found experimentally. This data can be used to optimize the performance of IEEE 802.11 WMNs.</p> / Master of Applied Science (MASc)

<p>In this thesis we study a wireless mesh network (WMN), where a number of access points (APs) form a wireless infrastructure and provide communications to the mobile stations (MSs). Different APs share the same frequency channel. We study how to provide fair throughput for the MSs while efficiently utilizing the channel resources through effective handoff management and channel timeline allocations.</p> <p>In the first part of the thesis, we assume that the channel time allocations at the AP level are given, and jointly consider the handoff management of the MSs and the channel time allocations at the MS level. An optimization problem is formulated based on long-term proportional fairness (PF) and solved. A heuristic distributed scheme is then proposed, which can be easily implemented in a practical WMN.</p> <p>In the second part, we jointly study the channel time allocations at the AP level and the MS level together with the MS handoff management. An optimization problem is first formulated and solved as a benchmark. Two distributed schemes are proposed by decoupling the handoff management and time allocations. The HO-CA scheme performs heuristic handoff decisions for the MSs and then optimizes the channel time allocations. The CA-HO scheme allocates the channel time to individual APs based on the neighboring relationship of the APs, and then makes handoff.</p> <p>Numerical results indicate that our proposed distributed schemes can achieve close-to-optimum fairness, improve the network utilization and balance the traffic load under uneven MSs geographical distributions.</p> / Master of Applied Science (MASc)

近年來興起一個前瞻性無線技術，稱之為無線網狀網路（Wireless Mesh Networks；WMNs） 以所費低廉方式提供無線網路最後一哩存取Internet，同時具備ad hoc網路全部優點。例如自我組織（self-organization）、自我組態（self-configuration）等。而802.11協議已經納入802.11s草案。雖然802.11的實體層支持多元速率，大多數研究為了簡化多假設在單一速率的情況下。但事實上，802.11可以支援的Automatic Rate Fallback (ARF)多元速率演算法；換句話說，由於信號雜訊比和資料錯誤率的不同，資料傳輸速率將自動調整。在這裡，我們假定在WMNs上使用 802.11協定，並且考慮路徑容量，延遲，流量公平及多元速率多跳接的環境。為了設法指出和改善這方面的議題，我們提出了經由改進802.11競爭視窗和加權公平調度機制的跨階層設計。透過一系列的模擬指出問題並找出合適的解決方案。結果顯示，如果增加低速率連結的優先權和考慮流量公平問題，容量及延遲將得到改善。 / A new promising wireless technology has emerged recently, called wireless mesh networks (WMNs). WMNs are an inexpensive way to provide wireless last-mile broadband Internet access and have all the advantages of ad hoc networks, such as self-organization, self-configuration. IEEE 802.11 MAC protocol has been adopted in 802.11s draft. Although IEEE 802.11 physical layer supports multiple rates, most researches assume single rate environment for simplicity. However, in reality, 802.11 adopts automatic rate fallback (ARF) multi-rate algorithm. In other words, the data rate will be automatically adjusted due to its signal-to-noise ratio, or error rate. Here, we assume the fitness of IEEE 802.11 over WMNs, and considering path capacity, delay, flow fairness, in multi-hop multi-rate environments. They all are affected by data rates on the links along the path. In order to address and improve the above issues, we propose a cross layer scheme which is modified by the contention window of IEEE 802.11 DCF MAC and weighted fairness scheduling mechanism. We point out the problem and find out the suitable solution via a series of scenarios simulations. The results show that if increasing the priority of the low data link and taking care about flow fairness problem, the capacity and delay will be improved.

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.