Ad hoc wireless networks are quite convenient local area networks. Because ad hoc wireless networks have a property what its topology is changed as hosts move. In order to efficiently and quickly broadcasting data, it is very important to have efficacious protocols in MAC (Medium Access Control) layer. In this paper, we propose a new broadcast protocol, Contention-based Broadcast Protocol (CBP). CBP is a TDMA-based protocol. There are three characteristics which make CBP an efficient protocol. They are (1) CBP utilize a backoff algorithm and some mini slot in contention request phase to avoid collisions. Most protocols do not implement a backoff algorithm. (2) A host only reserves a data slot each time instead of many slots in most TDMA-based protocol. It has the advantage of reducing the influence of host mobility because the time between a data slot is reserved and the time the data slot is utilized has greatly decreased, and (3) CBP differentiates unicast data and broadcast data and allows a host to reuse by channel for a unicast if it is impossible for a broadcast.

Many large-scale random graphs (e.g., the Internet) exhibit complex topology, nonhomogeneous spatial node distribution, and preferential attachment of new nodes. Current topology models for ad-hoc networks mostly consider a uniform spatial distribution of nodes and do not capture the dynamics of evolving, real-world graphs, in which nodes "gravitate" toward popular locations and self-organize into non-uniform clusters. In this thesis, we first investigate two constraints on scalability of ad-hoc networks – network reliability and node capacity. Unlike other studies, we analyze network resilience to node and link failure with an emphasis on the growth (i.e., evolution) dynamics of the entire system. Along the way, we also study important graph-theoretic properties of ad-hoc networks (including the clustering coefficient and the expected path length) and strengthen our generic understanding of these systems. Finally, recognizing that under existing uniform models future ad-hoc networks cannot scale beyond trivial sizes, we argue that ad-hoc networks should be modeled from an evolution standpoint, which takes into account the well-known "clustering" phenomena observed in all real-world graphs. This model is likely to describe how future ad-hoc networks will self-organize since it is well documented that information content distribution among end-users (as well as among spatial locations) is non-uniform (often heavy-tailed). Results show that node capacity in the proposed evolution model scales to larger network sizes than in traditional approaches, which suggest that non-uniformly clustered, self-organizing, very large-scale ad-hoc networks may become feasible in the future.

In this dissertation, we investigate the capacity and performance of wireless networks with an emphasis on multicast traffic. The defining characteristic of a multicast network is a network where a number of different destinations all require the information generated by a single source. The models that we explore differ in the nature of the nodes from all-mobile case where all nodes are mobile to hybrid case where some nodes are mobile and some are static. We investigate different performance measure for these wireless multicast networks: upper bounds, capacity scaling laws, and achievable rates. The understanding of these measures for such networks helps in the development of efficient algorithms for operating these networks. In addition, we study the practical realization of algorithms for real-time streaming of rich multimedia content in the context of mobile wireless networks for embedded and cyberphysical systems. Our initial work is in the context of unicast and multiple unicast systems over an autonomous aerial vehicle (AAV) network. Bandwidth requirements and stringent delay constraints of real-time video streaming, paired with limitations on computational complexity and power consumptions imposed by the underlying implementation platform, make cross-layer and cross-domain co-design approaches a necessity. In this dissertation, we propose a novel, low-complexity rate-distortion optimized (RDO) protocol specifically targeted at video streaming over mobile embedded networks. First, we test the performance of our RDO algorithm on simulation models developed for aerial mobility of multiple wirelessly communicating AAVs. Second, we test the performance of our RDO algorithm and other proposed adaptive algorithms on a real network of AAVs and present a comparative study between these different algorithms. Note that generalizing these algorithms to multicast settings is relatively straightforward and thus is not highlighted to a great degree in this thesis. / text

The focus of this dissertation is the task of resource allocation in multi- server systems arising from two applications – multi-channel wireless com- munication networks and large-scale content delivery networks. The unifying theme behind all the problems studied in this dissertation is the large-scale nature of the underlying networks, which necessitate the design of algorithms which are simple/greedy and therefore scalable, and yet, have good perfor- mance guarantees. For the multi-channel multi-hop wireless communication networks we consider, the goal is to design scalable routing and scheduling policies which stabilize the system and perform well from a queue-length and end-to-end delay perspective. We first focus on relay assisted downlink networks where it is well understood that the BackPressure algorithm is stabilizing, but, its delay performance can be poor. We propose an alternative algorithm - an iterative MaxWeight algorithm and show that it stabilizes the system and outperforms the BackPressure algorithm. Next, we focus on wireless networks which serve mobile users via a wide-area base-station and multiple densely deployed short- range access nodes (e.g., small cells). We show that traditional algorithms that forward each packet at most once, either to a single access node or a mobile user, do not have good delay performance and propose an algorithm (a distributed scheduler - DIST) and show that it can stabilize the system and performs well from a queue-length/delay perspective. In content delivery networks, each arriving job can only be served by servers storing the requested content piece. Motivated by this, we consider two settings. In the first setting, each job, on arrival, reveals a deadline and a subset of servers that can serve it and the goal is to maximize the fraction of jobs that are served before their deadlines. We propose an online load balanc- ing algorithm which uses correlated randomness and prove its optimality. In the second setting, we study content placement in a content delivery network where a large number of servers, serve a correspondingly large volume of con- tent requests arriving according to an unknown stochastic process. The main takeaway from our results for this setting is that separating the estimation of demands and the subsequent use of the estimations to design optimal content placement policies (learn-and-optimize approach) is suboptimal. In addition, we study two simple adaptive content replication policies and show that they outperform all learning-based static storage policies. / text

The recent proliferation of personal wireless devices has led to the emergence of disruption-tolerant networks (DTNs), which are characterized by intermittent connectivity among some or all participating nodes and a consequent lack of contemporaneous end-to-end paths between the source and consumer of information. However, the success of DTNs as a communication paradigm is critically dependent on the following challenges being addressed: (1) How to enable popular but demanding applications, such as video-on-demand, to operate in such constrained network settings, and (2) How to incentivize individual devices to cooperate when network operation is only possible under, or greatly benefits from cooperation. In this dissertation, we present a novel set of protocols and develop real systems that effectively meet the above challenges. We make the following contributions: First, we design and implement a novel system for enabling high bandwidth content distribution in vehicular DTNs by leveraging infrastructure access points (APs). We predict which APs will soon be visited by a vehicular node and then proactively push content-of-interest to those APs. Our replication schemes optimize content delivery by exploiting Internet connectivity, local wireless connectivity, node relay connectivity and mesh connectivity among APs. We demonstrate the effectiveness of our system through trace-driven simulation and Emulab emulation using real taxi and bus traces. We further deploy our system in two vehicular networks: a fourteen AP 802.11b network and a four AP 802.11n network with smartphones and laptops as clients. Second, we propose an incentive-aware routing protocol for DTNs. In DTNs, routing takes place in a store-and-forward fashion with the help of relay nodes. If the nodes in a DTN are controlled by rational entities, such as people or organizations, the nodes can be expected to behave selfishly by attempting to maximize their utilities and conserve their resources. Since routing is inherently a cooperative activity, system operation will be critically impaired unless cooperation is incentivized. We propose the use of pair-wise tit-for-tat (TFT) as a simple, robust and practical incentive mechanism for DTNs. We then develop an incentive-aware routing protocol that allows selfish nodes to maximize their own performance while conforming to TFT constraints. / text

Αντικείμενο αυτής της διπλωματικής είναι ο χαρακτηρισμός του ασύρματου καναλιού σύγχρονων ασύρματων δικτύων με εφαρμογές για κάλυψη σε τούνελ. Ο χαρακτηρισμός του ασύρματου καναλιού μέσα σε περιβάλλον τούνελ γίνετε στατιστικά. Παρότι είναι δυνατή η αναλυτική και αριθμητική επίλυση του προβλήματος τα στοχαστικά φαινόμενα που επικρατούν κάνουν ιδανικότερη τη στατιστική επίλυση του προβλήματος. Με τον όρο χαρακτηρισμό του ασύρματου καναλιού εννοείται ο προσδιορισμός τριών χαρακτηριστικών του ασύρματου καναλιού. Ο υπολογισμός των απωλειών ισχύος στη διαδρομή που παρεμβάλλεται μεταξύ πομπού και δέκτη και κατά επέκταση ο υπολογισμός της λαμβανόμενης ισχύος στη κεραία το δέκτη. Επίσης, ο υπολογισμός των διακυμάνσεων που υφίσταται το πλάτος του σήματος που λαμβάνεται στο δέκτη. Το πλάτος δεν είναι σταθερό αλλά μεταβάλλεται καθώς ο δέκτης μετακινείται σε μικρές αποστάσεις συγκρίσιμες με το μήκος κύματος του σήματος. Τέλος, η σύγκριση της ληφθείσας ισχύος στο δέκτη με το κατώφλι ευαισθησίας της συσκευής επικοινωνίας του δέκτη με σκοπό τον υπολογισμό της πιθανότητας ‘’να έχει σήμα ο δέκτης’’ δηλαδή να είναι δυνατή η επικοινωνία πομπού και δέκτη. Για να γίνουν αυτοί οι υπολογισμοί χρησιμοποιούνται ανάλογες προσομοιώσεις σε πρόγραμμα λογισμικού προσομοιώσεων. / The subject of this thesis is the characterization of modern and wireless channel networks with applications for coverage in tunnels. The characterization of the wireless channel inside tunnel environments is studied and modeled statistically. While analytical and numerical solutions of the problem are possible, the stochastic nature of the parameters make ideal the statistical approach of the problem. The characterization of a wireless channel aims to identify three characteristics of the wireless channel. First goal is the calculation of the power loss in the path between the transmitter and receiver. Thus the first goal is the calculation of the received power. The second goal is the calculation of the fading and the fluctuations of the received signal. The amplitude of the received signal is not stable but varies as the receiver moves over short distances comparable to the wavelength of the signal. Finally the third goal is to make a comparison of the received power with the sensitivity threshold of the communication device of the receiver in order to calculate the probability that the receiver has acceptable quality signal. To make these calculations there are used software simulations.

Heterogeneous Wireless Networks (HWNs) are composite networks made of different wireless access technologies, possibly with overlapping coverage. Users with multi-mode terminals in HWNs will be able to initiate connectivity in the access technology that best suits their attributes and the requirements of their applications. The true potential of HWNs, however, is only realized through allowing users to maintain their sessions when toggling from one access technology to another. Such inter-technology handoffs, called vertical handoffs, will enable users to persistently select the most appropriate network, and not just at session initiation. For operators, HWNs pave the road to higher profitability through more capable networks where the complementary advantages of individual access technologies are combined. However, the characteristics of HWNs challenge traditional arguments for designing Radio Resource Management (RRM) frameworks. Managing the resources of an access technology in an HWN independently of other networks with which its overlaid risks underutilization and resource mismanagement. The dynamic nature of user demands in HWNs also calls for RRM modules with controlled operational cost. More importantly, the unique characteristics of HWNs call for non-traditional solutions that exploit the ``complementarity" of the individual networks. In this thesis, we address these issues through proposing a framework for RRM in HWNs. Our framework comprises three key components. The first component is aimed at improving allocation policies in HWNs through joint allocation policies involving provisioning and admission control. In addition, we outline the basis for achieving robust provisioning that accommodates variability in user demands, but also in network capabilities. The second component is concerned with controlling the operational cost of RRM modules. As a case study, we choose bandwidth adaptation algorithms and optimize their performance. We also introduce the notion of stochastic triggers which enables operators to direct the operation of a RRM module based on the operator's objectives and network conditions. In the third component, we introduce a new module that exploits vertical handoffs to the benefit of network operators. Such operator motivated vertical handoffs can be utilized in instances of congestion control. They can also be used proactively to achieve long-term objectives such as load balancing or service delivery cost reduction. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2007-09-28 04:54:46.819

Wireless Local Area Networks (WLANs) provide an affordable solution for last mile network access. They also allow for extension of a network by configuring a Wireless Mesh Network (WMN) where it may otherwise be physically infeasible or cost prohibitive to do so. With the increasing use of real-time applications such as video conferencing and Voice over IP (VoIP), networks are stressed to guarantee Quality of Service (QoS) requirements for these applications. Examples of key requirements include bounded delay and packet loss ratios. Addressing this issue in WLANs, the IEEE 802.11e amendment was proposed to provide a QoS mechanism. However, the performance of 802.11e in meshed environments is yet to be studied. In this work, we study VoIP call quality in a meshed environment with provisions for QoS. We study the call quality and throughput of background traffic in an experimental WMN testbed in order to test how well the IEEE 802.11e QoS provisions support voice calls. Call quality is tested in different configurations and scenarios. We study the effect of the number of wireless hops on VoIP call quality. In addition, we investigate the number of VoIP calls that can be supported simultaneously for different numbers of wireless hops. We also study how fairly the network treats different calls in different configurations. Then, we look at how much effective bandwidth a VoIP call uses on the network. Finally, we examine the VoIP call quality of different calls when calls have different QoS parameters and study the effect that a busy central node has on traffic passing through it. We provide suggestions to improve call quality on a WMN and hint at possible future work. / Thesis (Master, Computing) -- Queen's University, 2008-05-30 09:55:45.535

The problem of multicasting in wireless multihop networks was studied in this dissertation. Nodes in the multicast routing structures were classified into different classes based on their roles in the multicast routing structures. Optimal multicast routing strategies for different classes were analyzed using the most accurate interference model. Based on the analyses, two algorithms to create interference-aware multicast routing tree and three algorithms to create interference-aware multicast routing mesh were proposed. The proposed multicast routing structures were evaluated using wireless network simulations. To improve the credibility of the wireless network simulations, a frame-level bursty link model was proposed and implemented in ns-3 network simulator. The results showed that, by taking interference into account when building multicast routing structures, the proposed multicast routing structures provided improved performance over other multicast routing structures that do not consider wireless interference when building multicast routing structures.

How to improve the radio resource utilization and provide better quality-of-service (QoS) is an everlasting challenge to the designers of wireless networks. As an indispensable element of the solution to the above task, medium access control (MAC) protocols coordinate the stations and resolve the channel access contentions so that the scarce radio resources are shared fairly and efficiently among the participating users. With a given physical layer, a properly designed MAC protocol is the key to desired system performance, and directly affects the perceived QoS of end users. Distributed random access protocols are widely used MAC protocols in both infrastructure-based and infrastructureless wireless networks. To understand the characteristics of these protocols, there have been enormous efforts on their performance study by means of analytical modeling in the literature. However, the existing approaches are inflexible to adapt to different protocol variants and traffic situations, due to either many unrealistic assumptions or high complexity. In this thesis, we propose a simple and scalable generic performance analysis framework for a family of carrier sense multiple access with collision avoidance (CSMA/CA) based distributed MAC protocols, regardless of the detailed backoff and channel access policies, with more realistic and fewer assumptions. It provides a systematic approach to the performance study and comparison of diverse MAC protocols in various situations. Developed from the viewpoint of a tagged station, the proposed framework focuses on modeling the backoff and channel access behavior of an individual station. A set of fixed point equations is obtained based on a novel three-level renewal process concept, which leads to the fundamental MAC performance metric, average frame service time. With this result, the important network saturation throughput is then obtained straightforwardly. The above distinctive approach makes the proposed analytical framework unified for both saturated and unsaturated stations. The proposed framework is successfully applied to study and compare the performance of three representative distributed MAC protocols: the legacy p-persistent CSMA/CA protocol, the IEEE 802.15.4 contention access period MAC protocol, and the IEEE 802.11 distributed coordination function, in a network with homogeneous service. It is also extended naturally to study the effects of three prevalent mechanisms for prioritized channel access in a network with service differentiation. In particular, the novel concepts of ``virtual backoff event'' and ``pre-backoff waiting periods'' greatly simplify the analysis of the arbitration interframe space mechanism, which is the most challenging one among the three, as shown in the previous works reported in the literature. The comparison with comprehensive simulations shows that the proposed analytical framework provides accurate performance predictions in a broad range of stations. The results obtained provide many helpful insights into how to improve the performance of current protocols and design better new ones.