Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-09-27 21:48:20.594 / Wireless networks are less reliable than wired networks because channels are “exposed” to the surrounding environment that is susceptible to interference and noise. To minimize losses of data due to collisions, wireless networks need a mechanism to regulate the access on the transmission medium. Medium Access Control (MAC) protocols control access to the shared communication medium so that it can be used efficiently. In this thesis, we first describe the collision-controlled Dual Prohibition Multiple Access (DPMA) protocol [45]. The main mechanisms implemented in DPMA, such as binary dual prohibition, power control, interference control, and support for differentiated services (DiffServ), are presented in detail. We conducted a thorough simulation study on DPMA protocol from several aspects. First, we conduct simulations to observe the effects of binary competition number (BCN), unit slot length and safe margin on the performance of DPMA. Secondly, the DiffServ capability of DPMA is demonstrated through simulation results. Finally, we compare the DPMA protocol with the CSMA/CA protocol and find that DPMA with optimal configuration has better performance than CSMA/CA under both low and high network density. / Master

Mobile ad hoc networks consist of potentially moving, computing nodes that communicate via radio and do not have access to any fixed infrastructure. The knowl- edge about nearby nodes is a fundamental requirement and is part of many of the known solutions to problems in mobile and wireless networks including routing, broad- casting, distributed token circulation, etc. The existing solutions for this problem of knowing about neighbors are probabilistic. In this thesis, we give a first step towards a distributed, deterministic algorithm for finding out about the neighboring nodes. In particular, we focus on the problem of maintaining information about neighboring nodes in a one dimensional mobile and wireless ad hoc environment. Under some simplifying assumptions, we give an algorithm for the problem and a proof of correctness for the algorithm. We deal with efficiency in terms of both time and space. We prove a tight bound on the speed of propagation of the message when the nodes are sufficiently dense. We also consider the case when multiple clusters merge together. Our algorithm is space efficient in that the nodes do not include information about all the nodes they know in their broadcast message at all times. Nodes also store only the information about relevant nodes in their local store and purge information about nodes that have moved out of range. Our work shows that it is possible to solve the problem deterministically, and with reasonable values of the parameters, under some simplifying assumptions. Numerous interesting open questions remain in the area regarding how to relax the assumptions to make the approach more practical.

With rapidly development of wireless network technology in the past few years, hand-held devices can connect to Internet everywhere conveniently by equipped with wireless card. IEEE 802.11 defined two types of wireless networks: infrastructure networks and ad hoc networks. Since ad hoc networks are a kind of networks without access points, efficient routing is an important issue for these networks. A more efficient routing approach involves dividing the network into several clusters by using a clustering algorithm. The purpose of this paper is to investigate a hybrid cluster routing algorithm in mobile ad hoc networks. This investigation proposed a double-manager K-hop clustering algorithm based on the link evaluation. This algorithm not only can elect a more suitable node as the cluster head but also can reduce the overhead of the managers. Furthermore, this study devised maintenance and backup mechanisms to stabilize network performance in the face of network topology changes. The simulation results demonstrate that our proposed algorithm outperforms other clustering algorithm in terms of number of clusters, routing overhead of managers and cluster stability.

In an ad hoc networks, it is an important problem about how to increase the bandwidth utilization and guarantee Quality-of-Service. In order to increase the bandwidth utilization under the situation of limited bandwidth, we want to achieve the target by using the bitty residual bandwidth in the ad hoc networks. Hence we integrate several single paths into a multi-path that satisfies QoS requirement. In this paper, we present a policy to look up, maintain, and reroute the virtual circuit in the ad hoc networks. From the result of simulation, we obtain that our proposal indeed can increase the bandwidth utilization of ad hoc networks. But the condition of splitting also increases the overhead of connection, and affects the forced terminated ratio and packets lost ratio under mobility.

An ad hoc network is formed by a group of self-configuring nodes, typically deployed in two or three dimensional spaces, and communicating with each other through wireless or some other media. The distinct characteristics of ad hoc networks include the lack of pre-designed infrastructure, the natural correlation between the network topology and geometry, and limited communication and computation resources. These characteristics introduce new challenges and opportunities for de- signing ad hoc network applications. This dissertation studies various optimization problems in ad hoc network information retrieval and transmission. Information stored in ad hoc networks is naturally associated with its location. To effectively retrieve such information, we study two fundamental problems, range search and object locating, from a distance sensitive point of view, where the retrieval cost depends on the distance between the user and the target information. We develop a general framework that is applicable to both problems for optimizing the storage overhead while maintaining the distance sensitive retrieval requirement. In addition, we derive a lowerbound result for the object locating problem which shows that logarithmic storage overhead is asymptotically optimal to achieve linear retrieval cost for growth bounded networks. Bandwidth is a scarce resource for wireless ad hoc networks, and its proper utilization is crucial to effective information transmission. To avoid conflict of wireless transmissions, links need to be carefully scheduled to satisfy various constraints. In this part of the study, we first consider an optimization problem of end-to-end on- demand bandwidth allocation with the single transceiver constraint. We study its complexity and present a 2-approximation algorithm. We then discuss how to estimate the end-to-end throughput under a widely adopted model for radio signal interference. A method based on identifying certain clique patterns is proposed and shown to have good practical performance.

The key challenge in mobile ad-hoc network (MANET) is the design of routing protocol which adapting their behavior to frequency with rapid changes in the network. As we have known, there are two main kinds of routing protocols in MANET: proactive and reactive routing protocol; and in addition, authors [1] proposed to use location information provided by positioning devices such as global positioning systems (GPS) to assist routing. We wonder whether the assumption of all devices in the communication area have the GPS ability is reasonable; furthermore, a GPS-enabled device has its own limitation on working areas; for example, the GPS ability cannot work in the indoor environments. In this paper, (1) we tried to addition the mechanism of probing routing redirection/discovery at routing protocol in AODV. Using overheard node avoid route breaking and select route batter than origin.(2)we tried to use the property of GPS to solve the routing problems in MANET, which like broadcast storm in the route discovery, device power saving and optimal one-hop destination, channel reuse rate, and optimal routing path. According to 802.11 specification, the best way to reach the goal of device power saving is putting device into the sleep mode. In this routing protocol, we let most mobile devices stay in the sleep mode until it sends or receives data or acts as an intermediate node to forward data. Last, we use simulations and implementation to validate the effectiveness of our design.

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This paper presents a method for managing a Mixed Network with multiple ground stations and Test Articles (TA) preferences. The main difference between a Ground Station (cellular) network and the over the horizon (ad-hoc) network is that the ad-hoc method has no fixed infrastructure. This paper presents the computation and performance of a clustering technique for mobile nodes within the simulated mixed network environment with multiple ground stations and users preferences for those ground stations. This includes organization for multiple ground stations and for TA's gravitating toward a ground station of their choice on the basis of service and performance.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / This paper presents a case study of the commercialisation of an ad-hoc wireless network technology from a subsidiary of a multinational company. The paper does not disclose any intellectual property specifics, the organisations or individuals involved. Instead the paper focuses on generic issues associated with technology transfer; exploration of market opportunities, market validation, the identification of a novel business model and economic validation. The paper wraps the case study within the academic context of commercialisation providing substantive literature sources, tools and techniques for readers faced with similar challenges; tools and techniques that can be applied irrespective of the underlying technology.

In the past decades, mobile traffic generated by devices such as smartphones, iphones, laptops and mobile gateways has been growing rapidly. While traditional direct connection techniques evolve to provide better access to the Internet, a new type of wireless network, mobile ad hoc network (MANET), has emerged. A MANET differs from a direct connection network in the way that it is multi-hopping and self-organizing and thus able to operate without the help of prefixed infrastructures. However, challenges such dynamic topology, unreliable wireless links and resource constraints impede the wide applications of MANETs. Routing in a MANET is complex because it has to react efficiently to unfavourable conditions and support traditional IP services. In addition, Quality of Service (QoS) provision is required to support the rapid growth of video in mobile traffic. As a consequence, tremendous efforts have been devoted to the design of QoS routing in MANETs, leading to the emergence of a number of QoS support techniques. However, the application independent nature of QoS routing protocols results in the absence of a one-for-all solution for MANETs. Meanwhile, the relative importance of QoS metrics in real applications is not considered in many studies. A Best Effort QoS support (BEQoS) routing model which evaluates and ranks alternative routing protocols by considering the relative importance of multiple QoS metrics is proposed in this thesis. BEQoS has two algorithms, SAW-AHP and FPP for different scenarios. The former is suitable for cases where uncertainty factors such as standard deviation can be neglected while the latter considers uncertainty of the problems. SAW-AHP is a combination of Simple Additive Weighting and Analytic Hierarchical Process in which the decision maker or network operator is firstly required to assign his/her preference of metrics with a specific number according to given rules. The comparison matrices are composed accordingly, based on which the synthetic weights for alternatives are gained. The one with the highest weight is the optimal protocol among all alternatives. The reliability and efficiency of SAW-AHP are validated through simulations. An integrated architecture, using evaluation results of SAW-AHP is proposed which incorporates the ad hoc technology into the existing WLAN and therefore provides a solution for the last mile access problems. The protocol selection induced cost and gains are also discussed. The thesis concludes by describing the potential application area of the proposed method. Fuzzy SAW-AHP is extended to accommodate the vagueness of the decision maker and complexity of problems such as standard deviation in simulations. The fuzzy triangular numbers are used to substitute the crisp numbers in comparison matrices in traditional AHP. Fuzzy Preference Programming (FPP) is employed to obtain the crisp synthetic weight for alternatives based on which they are ranked. The reliability and efficiency of SAW-FPP are demonstrated by simulations.

Mobile collaborative work is a developing sub-area of Computer Supported Collaborative Work (CSCW). The future of this field will be marked by a significant increase in mobile device usage as a tool for co-workers to cooperate, collaborate and work on a shared workspace in real-time to produce artefacts such as diagrams, text and graphics regardless of their geographical locations. A real-time collaboration editor can utilise a centralised or a replicated architecture. In a centralised architecture, a central server holds the shared document as well as manages the various aspects of the collaboration, such as the document consistency, ordering of updates, resolving conflicts and the session membership. Every user's action needs to be propagated to the central server, and the server will apply it to the document to ensure it results in the intended document state. Alternatively, a decentralised or replicated architecture can be used where there is no central server to store the shared document. Every participating site contains a copy of the shared document (replica) to work on separately. Using this architecture, every user's action needs to be broadcast to all participating sites so each site can update their replicas accordingly. The replicated architecture is attractive for such applications, especially in wireless and ad-hoc networks, since it does not rely on a central server and a user can continue to work on his or her own local document replica even during disconnection period. However, in the absence of a dedicated server, the collaboration is managed by individual devices. This presents challenges to implement collaborative editors in a replicated architecture, especially in a mobile network which is characterised by limited resource reliability and availability. This thesis addresses challenges and requirements to implement group editors in wireless ad-hoc network environments where resources are scarce and the network is significantly less stable and less robust than wired fixed networks. The major contribution of this thesis is a proposed framework that comprises the proposed algorithms and techniques to allow each device to manage the important aspects of collaboration such as document consistency, conflict handling and resolution, session membership and document partitioning. Firstly, the proposed document consistency algorithm ensures the document replicas held by each device are kept consistent despite the concurrent updates by the collaboration participants while taking into account the limited resource of mobile devices and mobile networks. Secondly, the proposed conflict management technique provides users with conflict status and information so that users can handle and resolve conflicts appropriately. Thirdly, the proposed membership management algorithm ensures all participants receive all necessary updates and allows users to join a currently active collaboration session. Fourthly, the proposed document partitioning algorithm provides flexibility for users to work on selected parts of the document and reduces the resource consumption. Finally, a basic implementation of the framework is presented to show how it can support a real time collaboration scenario.