<p>Communicating over a wireless channel poses many unique challenges not found in wired communication because of the special characteristics of the wireless channel. The capacity in a wireless network is typically scarce as a result of the limited bandwidth and many distinct phenomenons, like attenuation and interference, that work destructively on the received signals.</p><p>The Medium Access Control (MAC) layer is responsible for sharing this limited resource among the users. This allocation problem should be handled by considering the Quality of Service (QoS) requirements of each user as to maximize the utility. Efficient MAC algorithms are crucial in minimizing collisions between transmissions and thus achieving high utilization of the channel.</p><p>This thesis focuses on conflict resolution and service differentiation algorithms for wireless local area networks, where there is no central control of the channel and each sender independently contends for access.</p><p>In part I, we study three approaches to improve the IEEE 802.11(e) standards with focus on QoS. In the first approach, utility functions are considered, that model application preferences, to achieve service differentiation and maximize the aggregated utility. We provide algorithms for two subsidiary problems that arise from the maximization problem, and show that a near--optimal solution is found. In the second approach a collision detection algorithm for multicast transmissions is proposed, that increases the reliability for multicast compared to the protected unicast traffic. The third approach is an improved MAC algorithm for the QoS standard IEEE 802.11e. The improved algorithm outperforms the standard and achieves close to optimal performance for large number of scenarios, which significantly reduces the need of adjusting the contention parameters.</p><p>In part II, we focus on channel bursting protocols that use noise bursts to resolve channel conflicts. These protocols is capable of achieving very low collision probability. We propose two new bursting protocols, that achieve very high channel utilization, and show that the bursting technique has good fairness properties and provides efficient support for service differentiation. We also show that it is possible to reduce the number of bursts without loosing performance.</p><p>In part III, the optimal backoff distribution that minimizes the collision probability is derived. We then propose a heuristic backoff distribution with similar properties that yields high channel utilization. An extension for service differentiation is provided where the sizes of the backoff windows are adjusted.</p>

Communicating over a wireless channel poses many unique challenges not found in wired communication because of the special characteristics of the wireless channel. The capacity in a wireless network is typically scarce as a result of the limited bandwidth and many distinct phenomenons, like attenuation and interference, that work destructively on the received signals. The Medium Access Control (MAC) layer is responsible for sharing this limited resource among the users. This allocation problem should be handled by considering the Quality of Service (QoS) requirements of each user as to maximize the utility. Efficient MAC algorithms are crucial in minimizing collisions between transmissions and thus achieving high utilization of the channel. This thesis focuses on conflict resolution and service differentiation algorithms for wireless local area networks, where there is no central control of the channel and each sender independently contends for access. In part I, we study three approaches to improve the IEEE 802.11(e) standards with focus on QoS. In the first approach, utility functions are considered, that model application preferences, to achieve service differentiation and maximize the aggregated utility. We provide algorithms for two subsidiary problems that arise from the maximization problem, and show that a near--optimal solution is found. In the second approach a collision detection algorithm for multicast transmissions is proposed, that increases the reliability for multicast compared to the protected unicast traffic. The third approach is an improved MAC algorithm for the QoS standard IEEE 802.11e. The improved algorithm outperforms the standard and achieves close to optimal performance for large number of scenarios, which significantly reduces the need of adjusting the contention parameters. In part II, we focus on channel bursting protocols that use noise bursts to resolve channel conflicts. These protocols is capable of achieving very low collision probability. We propose two new bursting protocols, that achieve very high channel utilization, and show that the bursting technique has good fairness properties and provides efficient support for service differentiation. We also show that it is possible to reduce the number of bursts without loosing performance. In part III, the optimal backoff distribution that minimizes the collision probability is derived. We then propose a heuristic backoff distribution with similar properties that yields high channel utilization. An extension for service differentiation is provided where the sizes of the backoff windows are adjusted.

In this thesis, we propose a power saving strategy based on tree splitting algorithm in wireless sensor network with multiple packet reception. We concentrate on the case that maximum queue size is 1. We derive both analytical results and simulation results. We use theory of Markov chain to analyze the evolution of the system state. In addition, we propose to use Renewal theory to calculate the throughput. Furthermore, we obtain the average system size, the packet blocking probability, and the average packet delay. Because the network model is distributed, we can¡¦t understand the state of network all the time. So we use the length of last collision resolution cycle to predict the length of next cycle, and determine the sleeping time by the predicted length of next cycle to implement power saving. At last we will use the simulation result to show the performance of our power saving strategy.

Title from PDF of title page. / Document formatted into pages; contains 84 pages. / Thesis (M.S.C.S.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: New generations of video surveillance systems are expected to possess a large-scale network of intelligent video cameras with built-in image processing capabilities. These systems need to be tethered for reasons of bandwidth and power requirements. To support economical installation of video cameras and to manage the huge volume of information flow in these networks, there is a need for new shared-medium daisy-chained physical and medium access control (bus arbitration) layer communication protocols. This thesis describes the design principles of Spatial reuse FireWire Protocol (SFP), a novel request/grant bus arbitration protocol, architected for an acyclic daisy-chained network topology. SFP is a new extension of the IEEE 1394b FireWire architecture. / ABSTRACT: SFP preserves the simple repeat path functionality of FireWire while offering two significant advantages: 1) SFP supports concurrent data transmissions over disjoint segments of the network (spatial reuse of bandwidth), which increases the effective throughput and 2) SFP provides support for priority traffic, which is necessary to handle real-time applications (like packet video), and mission critical applications (like event notifications between cameras) that have strict delay and jitter constraints. The delay and throughput performance of FireWire and SFP were evaluated using discrete-event queuing simulation models built with the CSIM-18 simulation library. Simulation results show that for a homogeneous traffic pattern SFP improves upon the throughput of IEEE 1394b by a factor of 2. For a traffic pattern typical of video surveillance applications, throughput increases by a factor of 7. / ABSTRACT: Simulation results demonstrate that IEEE 1394b asynchronous stream based packet transactions offer better delay performance than isochronous transactions for variable bit rate video like MPEG-2 and MPEG-4. SFP extends this observation by supporting priority traffic. QoS for packet video is provided in SFP by mapping individual asynchronous stream packets to the three priority classes. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Ad hoc network is intrinsically autonomous and self-configuring network that does not require any dedicated centralized management. For specialized applications such as, military operations, search-and-rescue missions, security and surveillance, patient monitoring, hazardous material monitoring, 4G (4th Generation) coverage extension, and rural communication; ad hoc networks provide an intelligent, robust, flexible and cost effective solution for the wireless communication needs. As in centralized wireless systems, ad hoc networks are also expected to support high data rates, low delays, and large node density in addition to many other QoS (Quality of Service) requirements. However, due to unique ad hoc network characteristics, spectrum scarcity, computational limit of current state-of-the-art technology, power consumption, and memory; meeting QoS requirements is very challenging in ad hoc networks. Studies have shown cross layer to be very effective in enhancing QoS performance under spectrum scarcity and other constraints. In this dissertation, our main goal is to enhance performance (e.g., throughput, delay, scalability, fairness) by developing novel cross layer techniques in single-hop single channel general ad hoc networks. Our dissertation mainly consists of three main sections. In the first section, we identify major challenges intrinsic to ad hoc networks that affect QoS performance under spectrum constraint (i.e., single channel). In the later parts of the dissertation, we investigate and propose novel distributed techniques for ad hoc networks to tackle identified challenges. Different from our main goal, albeit closely related; in the first section we propose a conceptual cross layer frame work for interaction control and coordination. In this context, we identify various functional blocks, and show through simulations that global and local perturbations through parametric correlation can be used for performance optimization. In the second section, we propose MAC (Medium Access Control) scheduling approaches for omni-directional antenna environment to enhance throughput, delay, scalability and fairness performance under channel fading conditions. First, we propose a novel cooperative ratio-based MAC scheduling scheme for finite horizon applications. In this scheduling scheme, each node cooperatively adapts access probability in every window based on its own and neighbors` backlogs and channel states to enhance throughput, scalability and fairness performance. Further, in the second section, we propose two novel relay based MAC scheduling protocols (termed as 2rcMAC and IrcMAC) that make use of relays for reliable transmission with enhanced throughput and delay performance. The proposed protocols make use of spatial diversity due to relay path(s) provided they offer higher data rates compared to the direct path. Simulation results confirm improved performance compared to existing relay based protocols. In the third section, we make use of directional antenna technology to enhance spatial reuse and thus increase network throughput and scalability in ad hoc networks. In this section, we introduce problems that arise as a result of directional communication. We consider two such problems and propose techniques that consequently lead to throughput, delay and scalability enhancement. Specifically, we consider destination location and tracking problem as our first problem. We propose a novel neighbor discovery DMAC (Directional MAC) protocol that probabilistically searches for the destination based on elapsed time, distance, average velocity and beam-width. Results confirm improved performance compared to commonly used random sector and last sector based directional MAC protocols. Further, we identify RTS/CTS collisions as our second problem which leads to appreciable throughput degradation in ad hoc networks. In this respect, we investigate and propose a fully distributed asynchronous polarization based DMAC protocol. In this protocol, each node senses its neighborhood on both linear polarization channels and adapts polarization to enhance throughput and scalability. Throughput and delay comparisons against the basic DMAC protocol clearly show throughput, scalability and delay improvements.

There is growing interest in developing reliable, high performance, underwater acoustic networks (UWANs). However, the acoustic communication channel, with its slow sound propagation, high signal attenuation, and low bandwidth, presents significant challenges to network designers. One advantage offered by the acoustic channel is the ability to form directional communication beams, which improve signal strength and reduce interference. The work presented here describes a novel medium access control protocol for UWANs designated Beam-Enabled Acoustic Link Establishment (BEALE). BEALE addresses the inherent challenges of the acoustic channel by incorporating two techniques: link-level scheduling and dynamic directional beam steering. BEALE neighbors exchange packets based on a link-level schedule negotiated between the two nodes. This scheduling allows nodes to steer transmit and receive beams in the appropriate direction at the appropriate time while minimizing control overhead. Using steered, directional beams increases the gain between sender and receiver, reduces the senders interference with other nodes, and, at the receiver, rejects possible interference from other nodes and noise sources common in the ocean, resulting in increased spatial reuse. The core protocol has been modeled in a UWAN simulator developed specifically for this research. The results demonstrate significant improvement in throughput and packet loss over two benchmark UWAN random access protocols when evaluated over a variety of spatial node topologies and traffic patterns. The core BEALE protocol is further enhanced herein by a Half-Duplex Sliding Window algorithm. The HDX Sliding window is shown through point-to-point simulation to markedly improve bandwidth utilization and error rate in large Bandwidth Delay Product (BDP) situations. Extension of the HDX Sliding Window to more complex multi-flow, two-way and multi-hop cases requires an additional level of communication coordination provided by the BEALE Sliding Window Scheduler presented here. The functional challenges and novel concept of the scheduler are described in detail. The BEALE protocol performance promotes a rich list of potential future research, such as rigorous characterization of the BEALE Sliding Window Scheduler, BEALE accommodation of mobile nodes, conceptual operability of a BEALE-enabled network of a central multi-beam sink node supporting large numbers of simple source nodes, and rate adaptation. / text

Wireless Sensor Network (WSN) is an emerging multi-hop wireless network technology, and the greenhouse network monitoring system is one of the key applications of WSNs in which various parameters such as temperature, humidity, pressure and power can be monitored. Here, we aim to study the performance of a simulation-based greenhouse monitoring system. To design the greenhouse monitoring system based on WSN, we have used ZigBee-based devices (end devices, routers, coordinators, and actuators. Our proposed greenhouse monitoring network has been designed and simulated using the network simulator OPNET Modeller.The investigation is split into two; first, the aim is to find the optimal Transmit (Tx) power set out at sensor nodes and second, the focus is on studying how increasing the number of sensor nodes in the same greenhouse network will affect the overall network performance. ZigBee-based greenhouses corresponded to 4 network scenarios and are simulated using OPNET Modeller in which 22 different transmit (Tx) power (22 cases) in Scenario 1 is simulated, scenario 2, 3 and 4 estimated to 63, 126, 189 number of sensor nodes respectively. Investigating the performance of the greenhouse monitoring network performance metrics such as network load, throughput, packets sent/received and packets loss are considered to be evaluated under varied transmit (Tx) power and increasing number of sensor nodes. Out of the comprehensive studies concerning simulation results for 22 different transmit (Tx) power cases underlying the greenhouse monitoring network (Scenario1), it is found that packets sent/received and packets loss perform the best with the transmitted (Tx) power falling in a range of 0.9 mWatt to 1.0 mWatt while packet sent/received and packet loss are found to perform moderately with the transmitted (Tx) power values that lie in a range of 0.05 mWatt to 0.8 mWatt. Less than 0.05 mWatt and greater than 0.01 microWatt Tx power experience, the worst performance in terms of particularly packet dropped case. For instance, in the case of the packet dropped (not joined packet, i.e., generated at the application layer but not able to join the network due to lack of Tx power), with a Tx power of 0.01 mWatt, 384 packets dropped with a Tx power of 0.02 and 0.03 mWatt, 366 packets dropped, and with a Tx power of 0.04 and 0.05, 336 packet dropped.While increasing the number of sensor nodes, as in scenario 2, 3 and 4, dealing with sensor nodes 63, 126 and 189 correspondingly, the MAC load, MAC throughput, packet sent/received in scenario 2 are found to perform better than that of scenario 3 and scenario 4, while packet loss in scenarios 2, 3 and 4 appeared to be 15%, 12% and 83% correspondingly.

Ultra-wideband (UWB) technologies with higher data rates and lower transmission power over shorter ranges, have enabled a new set of applications in Wireless Personal Area Networks (WPANs). For example, UWB can offer data rates 50 to 500 times higher than the current WPAN technologies such as Bluetooth. This property makes UWB a primary candidate for indoor high-speed multimedia applications such as whole-house Internet Protocol Television (IPTV) and Personal Video Recorder (PVR). Lower power emission brings less interference to other devices, and larger bandwidth makes UWB less affected by interference from others, which are very attractive attributes in a household environment. However, the effective and efficient utilization of such high data rate wireless channel represents a new challenge to WPAN Media Access Control (MAC), especially for high quality video streaming applications. To meet the minimum bandwidth and maximum delay requirement for Quality-of-Service (QoS) guarantee, high-definition IPTV and PVR services usually need to reserve a certain amount of channel time for exclusive access in a dynamic manner, since the number of video flows may change over time in a piconet. WiMedia Alliances MAC protocols for UWB-based WPANs have become an international standard. The Distributed Reservation Protocol (DRP) is part of this standard that reserves the wireless channel on a slot-by-slot basis for different flows. However, not much work has been done on DRP reservation algorithms and their performance. In this research, we propose, analyze and evaluate two application-aware reservation algorithms. One algorithm allocates time slots based on the first-fit idea whereas the other takes one step further by doing a best-fit reservation according to the maximum tolerable delay bound. Our proposed algorithms try to find the best possible time slots for any requests with respect to the existing reservations in the piconet and those arriving later. With these algorithms, devices in the same piconet that have data to transmit can negotiate and reserve time slots based on their traffic specification and QoS requirement while following WiMedia MAC reservation policies. We analyze the reservation algorithms and policies with a tiered overflow model, and evaluate their performance with Network Simulator (NS-2 ) and an MPEG-4 video traffic generator. We further discuss the ways of improving video streaming quality and system resource utilization in UWB networks.

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This paper presents a scheduling algorithm for point to point wireless power transfer system (WPTS) to sensor nodes of wireless body area networks (WBAN). Since the sensors of wireless body area networks are continuously monitoring and sending data to remote central unit, power crisis for these sensor nodes degrades the data transfer of patient monitoring system. Although energy harvesting from ambient sources using electromagnetic induction enhances the longevity of sensor performance, continuous operation in the primary side decreases the overall efficiency. With such paradigm in sight, a framework is proposed for increasing the primary battery longevity and reducing the transmission loss, inductive power is transmitted from primary to secondary unit using medium access control (MAC) protocols for underlying the centralized scheduling opportunity in a collision free scheme for channel access of rare yet critical emergency situation. In a preliminary study, the proposed scheduling for charging sensor nodes in a wireless body area network (WBAN) is evaluated in a case consideration.