• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 291
  • 73
  • 43
  • 24
  • 24
  • 14
  • 8
  • 5
  • 4
  • 3
  • 3
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 622
  • 622
  • 121
  • 121
  • 103
  • 95
  • 80
  • 69
  • 66
  • 63
  • 62
  • 61
  • 61
  • 58
  • 54
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

An Efficient Hybrid Objects Selection Protocol for 3D Streaming over Mobile Devices

Alja'afreh, Mohammad Mahmoud January 2012 (has links)
With the rapid development in the areas of mobile manufacturing and multimedia communications, there is an increasing demand for Networked Virtual Environment (NVE) applications, such as Augmented Reality (AR), virtual walk-throughs, and massively multiplayer online games (MMOGs), on hand-held devices. Unfortunately, downloading and rendering a complex 3D scene is very computationally intensive and is not compatible with current mobile hardware specifications nor with available wireless bandwidth. Existing NVE applications deploy client/server based 3D streaming over thin mobile devices, which suffer from single point of failure, latency, and scalability issues. To address these issues, image-based rendering (IBR) and cloud-based 3D streaming have been introduced. The former introduces visual artifacts that reduce, and usually cancel, the realistic behaviors of the Virtual Environment (VE) application, while the latter is considered very expensive to implement. Peer-to-peer (P2P) 3D streaming is promising and affordable, but it has to tackle issues in object discovery and selection as well as content provider strategies. Distributing VE content over a mobile ad-hoc network (MANET) makes the system difficult to update due to the dynamic nature of the mobile clients. In order to tackle these issues, we came up with a novel protocol that combines the pros of both central and distributed approaches. Our proposed hybrid protocol, called OCTET, enables 3D scene streaming over thin devices in a way that can cope with current mobile hardware capabilities and mitigate the challenges of client/server and P2P 3D streaming. In fact, OCTET provides strategies that select, prioritize, and deliver only those objects that contribute to the user’s visible scene. OCTET is implemented using the "ns-2" simulation environment, and extensive experiments have clearly demonstrated significant achievements in mobile resource utilization, throughput, and system scalability.
162

Connectivity-Aware Routing Algorithms for Cognitive Radio Networks

Gad, Mahmoud M. January 2015 (has links)
The increased demand on wireless applications, coupled with the current inefficiency in spectrum usage, mandate a new communication paradigm shift from fixed spectrum assignment to dynamic spectrum sharing which can be achieved using the cognitive radio technology. Cognitive radio allows unlicensed secondary nodes to form communication links over licensed spectrum bands on an opportunistic basis which increases the spectrum management efficiency. Cognitive radio networks (CRN), however, impose unique challenges due to the fluctuation in the available spectrum as well as the diverse quality of service requirements. One of the main challenges is the establishment and maintenance of routes in multi-hop CRNs. In this thesis, we critically investigate the problem of routing in multi-hop CRNs. The main objective of this research is to maximize network connectivity while limiting routing delay. We developed a general connectivity metric for single-band and multi-band CRNs based on the properties of the Laplacian matrix eigenvalues spectrum. We show through analytical and simulation results that the developed metric is more robust and has lower computational complexity than the previously proposed metrics. Furthermore, we propose a new position-based routing algorithm for large scale CRNs which significantly reduces the routing computational complexity with negligible performance degradation compared to the traditional full node search algorithm. In addition, the connectivity metric developed in this thesis is used to develop a connectivity-aware distributed routing protocol for CRNs. Finally, we use a commodity cognitive radio testbed to demonstrate the concept of CR Wi-Fi networks.
163

Relay Selection for Heterogeneous Transmission Powers in Connected Vehicles

Alotaibi, Maryam January 2017 (has links)
It is widely believed that the advances of Vehicle-to-Vehicle (V2V) communications will help to remodel the prospect of road transportation systems. By virtue of V2V communications, information generated by the vehicle control system, on-board sensors or passengers can be effectively disseminated among vehicles in proximity, or to vehicles in multiple hops away in a vehicular ad-hoc network (VANET). Without assistance from any built infrastructure, a variety of active road safety applications (e.g., Vehicle-Based Road Condition Warning, Cooperative Collision Warning, Approaching Emergency Vehicle Warning) and traffic efficiency management applications (e.g., Wrong Way Driver Warning) are enabled by inter-vehicle wireless links. The purpose of connecting vehicle technologies is to improve road safety, awareness, and transportation systems efficiency. The Wireless Access for Vehicular Environments (WAVE) technology/Dedicated Short-Range Communications (DSRC) is the main enabling wireless technology for both V2V and vehicle-to-Infrastructure (V2I) communications. From USDOT and stakeholders detailed analysis, it is resolved that WAVE is the only viable option for critical safety and other low latency mobility and environmental applications. WAVE technology has reached to a mature stage and a basic V2V system is expected to be deployed in the next few years. In the late part of 2015, USDOT announce that WAVE is sufficiently robust to proceed with the preparation for deployment of connected vehicle environments. The USDOT has created a roadmap with preliminary plans to guide industries and public agencies implementation efforts. However, there are persisting major concerns regarding the V2V initiative needing more analysis and testing. One of the concerns is the channel congestion. Channel congestion may impact WAVE effectiveness, which may in turn impact the effectiveness of supported safety applications. Suggested solutions to mitigate congestion are focused on supporting adaptive control of the message transmission power. The Institute of Electrical and Electronics Engineers (IEEE), and European Telecommunications Standards Institute (ETSI) have included transmit power component per packet to be used for channel congestion control mechanism. The adjustment of transmission powers has created an environment of vehicles with different transmission powers. Such environment will affect the performance of the proposed protocols to disseminate warning messages. It may also affect the performance of periodic beaconing that is required by most of the safety applications. Thus far, several protocols have been proposed to help identify appropriate relay vehicles. However, such approaches neglect the fact that vehicle transmission ranges are typically heterogeneous due to different transmission power values or dynamic adjustment of power to alleviate congestion. The proper selection of relay nodes governs high delivery ratio, acceptable overall end-to-end delay and efficient bandwidth usage. In this work, area-based relay selection protocols that work in heterogeneous transmission powers are introduced. Mathematical functions are developed for a timer and decision probability to be used by each vehicle receiving the message. The values of the two functions allow the vehicle to determine if it is the next to act as relay node or not. Geometric taxonomy for all possible overlap patterns in wireless environment is constructed with the related math calculations. Moreover, an adaptive expiry time for neighbours-table entries that harmonizes with dynamic beacon scheduling is proposed.
164

Simulation-Assisted QoS-Aware VHO in Wireless Heterogeneous Networks

Al Ridhawi, Ismaeel January 2014 (has links)
The main goal of today’s wireless Service Providers (SPs) is to provide optimum and ubiquitous service for roaming users while maximizing the SPs own monetary profits. The fundamental objective is to support such requirements by providing solutions that are adaptive to varying conditions in highly mobile and heterogeneous, as well as dynamically changing wireless network infrastructures. This can only be achieved through well-designed management systems. Most techniques fail to utilize the knowledge gained from previously tested reconfiguration strategies on system and network behaviour. This dissertation presents a novel framework that automates the cooperation among a number of wireless SPs facing the challenge of meeting strict service demands for a large number of mobile users. The proposed work employs a novel policy-based system configuration model to automate the process of adapting new network policies. The proposed framework relies on the assistance of a real-time simulator that runs as a constant background process in order to continuously find optimal policy configurations for the SPs’ networks. To minimize the computational time needed to find these configurations, a modified tabu-search scheme is proposed. An objective is to efficiently explore the space of network configurations in order to find optimal network decisions and provide a service performance that adheres to contracted service level agreements. This framework also relies on a distributed Quality of Service (QoS) monitoring scheme. The proposed scheme relies on the efficient identification of candidate QoS monitoring users that can efficiently submit QoS related measurements on behalf of their neighbors. These candidate users are chosen according to their devices’ residual power and transmission capabilities and their estimated remaining service lifetime. Service monitoring users are then selected from these candidates using a novel user-to-user semantic similarity matching algorithm. This step ensures that the monitoring users are reporting on behalf of other users that are highly similar to them in terms of their mobility, used services and device profiles. Experimental results demonstrate the significant gains achieved in terms of the reduced traffic overhead and overall consumed users’ devices power while achieving a high monitoring accuracy, adaptation time speedup, base station load balancing, and individual providers’ payoffs.
165

3GPP Long Term Evolution LTE Scheduling

Alotaibi, Sultan 12 1900 (has links)
Future generation cellular networks are expected to deliver an omnipresent broadband access network for an endlessly increasing number of subscribers. Long term Evolution (LTE) represents a significant milestone towards wireless networks known as 4G cellular networks. A key feature of LTE is the implementation of enhanced Radio Resource Management (RRM) mechanism to improve the system performance. The structure of LTE networks was simplified by diminishing the number of the nodes of the core network. Also, the design of the radio protocol architecture is quite unique. In order to achieve high data rate in LTE, 3rd Generation Partnership Project (3GPP) has selected Orthogonal Frequency Division Multiplexing (OFDM) as an appropriate scheme in terms of downlinks. However, the proper scheme for an uplink is the Single-Carrier Frequency Domain Multiple Access due to the peak-to-average-power-ratio (PAPR) constraint. LTE packet scheduling plays a primary role as part of RRM to improve the system’s data rate as well as supporting various QoS requirements of mobile services. The major function of the LTE packet scheduler is to assign Physical Resource Blocks (PRBs) to mobile User Equipment (UE). In our work, we formed a proposed packet scheduler algorithm. The proposed scheduler algorithm acts based on the number of UEs attached to the eNodeB. To evaluate the proposed scheduler algorithm, we assumed two different scenarios based on a number of UEs. When the number of UE is lower than the number of PRBs, the UEs with highest Channel Quality Indicator (CQI) will be assigned PRBs. Otherwise, the scheduler will assign PRBs based on a given proportional fairness metric. The eNodeB’s throughput is increased when the proposed algorithm was implemented.
166

Určování polohy zařízení v bezdrátovém systému / Localization of device in wireless environment

František, Milan January 2016 (has links)
The work is focused on localization in wireless networks and localization using inertial measurement units. There is also included a theoretical analysis of used localization techniques. The work also describes how to create application for data collection, application for receiving and processing data and used database. In conclusion of this work is verifying the functionality of whole system.
167

Green Frame Aggregation Scheme for IEEE 802.11n Networks

Alaslani, Maha S. 04 1900 (has links)
Frame aggregation is one of the major MAC layer enhancements in the IEEE 802.11 family that boosts the network throughput performance. It aims to achieve higher throughput by transmitting huge amount of data in a single transmit oppor- tunity. With the increasing awareness of energy e ciency, it has become vital to rethink about the design of such frame aggregation protocol. Aggregation techniques help to reduce energy consumption over ideal channel conditions. However, in a noisy channel environment, a new energy-aware frame aggregation scheme is required. In this thesis, a novel Green Frame Aggregation (GFA) scheduling scheme has been proposed and evaluated. GFA optimizes the aggregate size based on channel quality in order to minimize the consumed energy. GFA selects the optimal sub-frame size that satisfies the loss constraint for real-time applications as well as the energy budget of the ideal channel situations. The design, the implementation, and evaluation of GFA using testbed deployment is done. The experimental analysis shows that GFA outperforms the conventional frame aggregation methodology in terms of energy e ciency by about 6⇥ in the presence of severe interference conditions. Moreover, GFA also outperforms the static frame sizing method in terms of network goodput and maintains almost the same end- to-end latency.
168

Gateways between ad hoc and other networks

Ha, Nguyen Manh January 2007 (has links)
Multi-hop wireless ad hoc wireless networks have no fixed network infrastructure. Such a network consists of multiple nodes that maintain network connectivity through wireless links. Additionally, these nodes may be mobile and thus the topology of the network may change with time. It will be useful if the nodes in this network could communicate with the Internet; this can be done via gateways which in turn interconnect to the Internet. This functionality requires that the nodes in the ad hoc network to discover the gateway, using a gateway discovery protocol. However, a limiting factor (particularly for mobile nodes) is suing their limited energy supply provided by batteries. In order to understand the potential effect this thesis considers two key areas: internetworking between a multi-hop mobile wireless ad hoc network and the Internet and the energy utilization as a function of number of gateways and the mobility pattern of nodes. Using simulation on various mobility patterns and networks density scenarios, we show that increase the number of gateways in ad hoc network significantly improves the power efficiency of mobile node and therefore prevent network partition due to death nodes. The thesis also discusses about the impact of different environment and mobility patterns on the power consumption of mobile nodes which is a very important factor in the building and deployment of the cost-effective high performance wireless ad hoc networks.
169

Performance Analysis of Wireless Multiplayer Games on Terraplay Systems

Chen, Xu January 2005 (has links)
This thesis project was sponsored by Terraplay System AB. Terraplay System is a wireless online multiplayer game service provider in Europe. The purpose of this project was to provide a convenient and free latency test tool named Terraplay Test Toolkit (TTK) for game developers who utilize the Terraplay platform. Since wireless multiplayer games are latency sensitive, it’s necessary for game developers to estimate the real-time game latency before their development. TTK is based on Java Mobile Edition (J2me) technology, it can performs a real-time Round Trip Time (RTT) latency test. This project explored the application of the mobile development. Mobile development is a brand new field and becoming more and more popular. The design process and source code can be used as reference for mobile developers. Based on the Terraplay Test Toolkit, a series of experiments were conducted to test the ability of TTK. These experiments focused on end-to-end latency effects of wireless multiplayer games under different situations such as different packet size, different sending rates, high speed movement, and so on. Although TTK is not a professional test tool, it still reflects the latency variance under different conditions correctly. From these experiments, it was found that for the Terraplay enabled wireless multiplayer games, large average packet size (300 bytes) is NOT a factor with regard to the latency on the Terraplay System; the packet rate can affect the game latency. In a high speed-moving environment, game latency doesn’t obvious increase. Using HTTP can cause three times higher latency than simply using TCP. These conclusions are based on experimental results. These conclusions should guide wireless multiplayer game developers and game players. / Denna avhandling är sponsrad av Terraplay System AB. Terraplay System är en trådlös multiplayer-spelservice i Sverige. Syftet med detta projekt var att ge ett lättillgängligt och gratis testverktyg för fördröjning kallat Terraplay Test Toolkit (TTK) till spelutvecklare som använder Terraplays plattform. Eftersom trådlösa multispel är känsliga för fördröjning, är det nödvändigt för spelutvecklare att innan de börjar göra en uppskattning av denna. TTK är baserat på Java Mobile Edition-teknologi (J2me), och kan utföra ett fördröjningstest i realtid, kallat Round Trip Time (RTT). Detta projekt undersökte tillämpningen av den mobila utvecklingen. Mobil utveckling är ett helt nytt fält och blir mer och mer populärt. Designprocessen och källkoden kan användas som referenser för mobila utvecklare. Baserat på Terraplay Test Toolkit gjordes en serie experiment för att testa TTK:s förmåga. Dessa experiment fokuserade på fördröjda effekter av trådlösa multiplayerspel under olika situationer så som olika paketstorlek, olika leveranshastigheter, höghastighetsrörelser och så vidare. Även fast TTK inte är ett professionellt testverktyg, och inte kan användas för exakta fördröjningsanalyser, återger det ändå fördröjningens variationer under olika villkor. Dessa experiment visade att trådlösa multiplayerspel anpassade till Terraplay, med genomsnittlig paketstorlek (300 bite) INTE är en faktor med avseende på fördröjningen till Terraplay System; paketets hastighet kan påverka paketets fördröjning. I en miljö med hög rörelsehastighet, ökar inte påtagligt spelets fördröjning. Användandet av HTTP kan orsaka en tre gånger så lång fördröjning, jämfört med att bara använda TCP. Slutsatserna är baserade på experimentresultaten. Dessa slutsatser kan hjälpa utvecklare av trådlösa multiplayerspel[.]
170

Real-time services and multihop networks : Delay analysis of a multihop CDMA fixed relay network

Gaitan, Ivar January 2005 (has links)
The next generation of cellular networks is expected to carry high speed IP traffic in a packet switched environment in order to accommodate data traffic for a wide range of services. Much research is thus focused on how to increase the transmission rate in cellular networks. A general consequence of increasing transmission rate in a radio link is a corresponding increase in transmit power, resulting in increased interference and reduced network capacity. The straightforward way to reduce this effect is to shorten the link distance, which in the cellular case means shrinking the cells. This, however, means increased control traffic for handoffs and location registration, as well as increased infrastructure costs. An alternative approach, which has received increased attention lately, is the introduction of wireless multihop access networks to relay traffic between the wired infrastructure and the users. Such an access network must clearly accommodate all types of services expected to operate in next generation systems, including real-time services. However, wireless multihop networks have traditionally had problems meeting the delay requirements posed by such services. In this thesis, we will study the delay performance through analysis and simulation of such a network, based on the Virtual Cellular Network proposal [1], in which geographically fixed wireless relays are deployed to act as both network nodes and user relays. / Nästa generations mobilnät förväntas bära paketväxlad höghastighetstraffik för att kunna stödja en stor mängd varierande tjänster. Mycket forskning har däför fokuserat på transmissionshastigheten i mobilnäten. En generell konsekvens av att öka transmissionshastigheten i ett radiobaserat nätverk är en motsvarande ökning i transmissionsstyrkan, vilket resulterar i ökad interferens och följaktligen minskad kapacitet. En lösning på det problemet är att minska avståndet mellan sändare och mottagare, vilket i fallet med dagens mobila infrastruktur innebär mindre, och fler celler. Detta skulle dock innebära både ökad kontrolltraffik och större kostnader för planering och underhåll av infrastruktur. En alternativ väg, som den senaste tiden fått ökad uppmärksamhet, är införandet av ett trådlöst vidarebefordrande accessnätverk mellan de mobila stationerna och det fasta nätet. Ett sådant nätverk måste naturligtvis kunna ackommodera samtliga typer av tjänster som förväntas utnyttja nästa generations mobilnät, inklusive realtidstjänster. Dock har kraven på låg fördröjning hos denna typ av tjänster traditionellt inneburit problem problem för vidarebefordrande trådlösa nätverk. I denna rapport studeras fördröjningskaraktären hos ett sådant nätverk, baserat på konceptet Virtual Cellular Network [1], i vilket geografiskt fixerade radionoder vidarebefordrar traffik mellan mobila stationer och det fasta nätet.

Page generated in 0.0804 seconds