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Design techniques for high performance optical wireless front-ends

Alves, Luís Nero; Aguiar, Rui L.
Fonte: Instituto de Telecomunicações Publicador: Instituto de Telecomunicações
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
56.35%
Wireless optical networks usually have demanding specifications in terms of bandwidth, dynamic range and sensitivity. The front-end is a critical element for the fulfillment of these demands. This paper discusses several design aspects of front-ends for optical wireless communications, covering techniques for achieving high gains, high input dynamic ranges, improving noise performance, and reducing electromagnetic interference (EMI). The paper further presents some experimental results of many of the techniques here described. The cumulative usage of those techniques significantly increases system performance, in terms of sensitivity, power and bandwidth even with low cost, CMOS technologies.

Towards Flexible Time Triggered Wireless Communications

Bartolomeu, Paulo; Fonseca, José Alberto
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
56.39%
The adoption of established fieldbus technologies in demanding scenarios has been supported by the lack of reliability of wireless communications, for example, under the influence of interference. In the last few years, new methods such as channel hoping and blacklisting have been proposed to cope with these vulnerabilities, but their effectiveness is limited. This paper proposes a wireless protocol featuring a novel approach to real-time medium access building on features provided by the bandjacking technique to support deterministic, reliable and flexible communications.

Enforcing flexibility in real-time wireless communications: A bandjacking enabled protocol

Bartolomeu, Paulo; Ferreira, Joaquim; Fonseca, José Alberto
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
66.55%
Wireless communications are being applied in heterogeneous domains ranging from healthcare to industrial manufacturing. However, as wireless channels are highly unreliable, the support of applications having tight hard real-time and fault-tolerance requirements has been provided by dedicated wired communications. Recently, a technique named bandjacking has been evaluated as a feasible solution to mitigate the unreliability associated with wireless channels in contention-based communications environments. This paper builds on this technique to propose an FTT inspired protocol aiming to provide deterministic, reliable and flexible wireless communications.

Dependable wireless real-time communications for open environments; Comunicações sem-fios de tempo-real para ambientes abertos

Bartolomeu, Paulo Jorge de Campos
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
56.64%
Wireless communication technologies have become widely adopted, appearing in heterogeneous applications ranging from tracking victims, responders and equipments in disaster scenarios to machine health monitoring in networked manufacturing systems. Very often, applications demand a strictly bounded timing response, which, in distributed systems, is generally highly dependent on the performance of the underlying communication technology. These systems are said to have real-time timeliness requirements since data communication must be conducted within predefined temporal bounds, whose unfulfillment may compromise the correct behavior of the system and cause economic losses or endanger human lives. The potential adoption of wireless technologies for an increasingly broad range of application scenarios has made the operational requirements more complex and heterogeneous than before for wired technologies. On par with this trend, there is an increasing demand for the provision of cost-effective distributed systems with improved deployment, maintenance and adaptation features. These systems tend to require operational flexibility, which can only be ensured if the underlying communication technology provides both time and event triggered data transmission services while supporting on-line...

Characterization of Network Inaccessibility in IEEE 802.15.4 Wireless Networks

Rufino, José; Souza, Jeferson Luiz Rodrigues
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Relatório
Publicado em 17/01/2013 Português
Relevância na Pesquisa
56.47%
Wireless communications are vulnerable to the presence of errors during the network operation. These errors may be originated from different sources such as external electromagnetic interferences, obstacles in communication path, or even glitches in the communication circuitry. Such origins may lead the medium access control (MAC) layer to deviate from its normal operation (without presence of errors), forcing the execution of additional actions to maintain the network operational. The execution of such actions may imply the occurrence of periods of "communication silence", where the network, although not being failed, is not performing communications. These periods of ``communication silence" are dubbed network inaccessibility, which may induce inaccurate fault detections and deadline misses. Additionally, the occurrence of network inaccessibility may compromise network properties such as predictability, dependability, and timeliness. Thus, this report presents an exhaustive study about network inaccessibility, using the 802.15.4 standard as a case study. All network inaccessibility scenarios are presented, discussing important steps to achieve predictability, dependability, and timeliness in wireless communications.

Some Economics of Wireless Communications

Benkler, Yochai
Fonte: Harvard University, Harvard Law School Publicador: Harvard University, Harvard Law School
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.65%
Spectrum policy appears to be coming to a turning point. After half a century of criticism from economists, the FCC and Congress seem poised to undertake substantial reform of a system that almost all commentators criticize as outdated and inefficient. Two radical alternatives have emerged as major approaches towards reform. The first, more widely known, is the proposal to create a system of property rights in spectrum that would form the basis for a market in spectrum to replace the existing regulatory system. The second, less widely recognized, is the proposal to permit greater deployment of wireless equipment that relies neither on a license nor on a property right. This open wireless network approach—often called “spectrum commons” or “open spectrum”—aims to provide a space for a market in intelligent end user equipment, rather than a market in infrastructure rights. This article provides an economic analysis of wireless communications that offers a framework for evaluating the relative desirability of the two proposed alternatives. First, it provides a concise description of the technological changes that have made open wireless networks a feasible alternative to licensing and spectrum property. Second, it offers a new way of describing the social cost of wireless communications that enables one to specify more precisely the tradeoff between property rights in spectrum and open wireless networks. I explain why spectrum property based systems will have systematically lower capacity than open wireless networks...

Future Directions of Personal Multimedia Communication Space: Investigation of Wireless Markets, Systems, and Standards in Regard to Multimedia over IP

Englund, Christer
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 501452 bytes; 808287 bytes; 409179 bytes; 560718 bytes; application/pdf; application/pdf; application/pdf; application/pdf
Português
Relevância na Pesquisa
46.69%
Mobile communications and Internet based computer communications are the two fastest growing areas of communications indicating an enormous business potential in the intersection of these two domains. Since the introduction of cellular networks, wireless communications have focused on speech only, while mobile data has played a minor role. This paradigm is likely to change drastically in the near future. A new phenomenon, reflected by a nomadic lifestyle, is spreading all over the industrialized countries. Clear evidence of this is discernible particularly in Japan and Scandinavia. Nomadic lifestyle suggests that we are now at the advent of a new era of mobile communications, which will be fueled by rapid evolution of key technologies such as mobile computing, low-power consuming RISC and signal processor technologies, wireless channel aggregation, wireless packet data, and Internet based multimedia communications. The current trend of network evolution implies that the Internet will serve as a core for future service provision, whereas traditional telecommunication networks offer access paths to those services. Internet telephony reflects the beginning of a new communication era, which is characterized by running real-time applications over Internet/Intranet based computer communication infrastructure. We can envision that soon they not only contain speech...

Multitier Wireless Communications

Aazhang, Behnaam; Cavallaro, Joseph R.; Aazhang, Behnaam; Cavallaro, Joseph R.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.35%
Journal Paper; Next-generation computing systems will be highly integrated using wireless networking. The Rice Everywhere NEtwork (RENE) project is exploring the integration of WCDMA cellular systems, high speed wireless LANs, and home wireless networks to produce a seamless multitier network interface. We are currently developing a simulation acceleration testbed and a multitier network interface card (mNIC) consisting of DSP processors, custom VLSI ASICs, and FPGAs for baseband signal processing to interact with the various RF units and the host processor. This testbed will also allow us to explore high performance algorithm alternatives through computer aided design tools for rapid prototyping and hardware/software co-design of embedded systems.

A Reconfigurable Decoder Architecture for Wireless LAN and Cellular Systems

Chadha, Kanu; Chadha, Kanu
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
56.43%
Masters Thesis; The rapid growth of wireless communications has led to the demand for communication devices which can support multiple standards and have the capability of switching from one to another on-the-fly. For instance, a device which could support the Wireless Local Area Network (WLAN) and Wideband Code Division Multiple Access (WCDMA) standards would enable seamless communications in the indoor LAN network as well as the outdoor cellular environment. A key challenge involved in the building of such a communications device is the design of a flexible hardware architecture that can dynamically reconfigure itself to run different algorithms as required to support the different standards. In particular, the Viterbi decoding algorithm is used at the receiver of both WCDMA and WLAN systems to decode the convolutionally encoded data. The difference lies in the encoding parameters such as the constraint length, code rate and generator polynomials. In this thesis, we propose an architecture for a reconfigurable Viterbi decoder that can dynamically adapt to changes in the encoding parameters. The proposed architecture is implemented on a Field Programmable Gate Array (FPGA) device. The proposed architecture can be used to realize a Viterbi decoder which can support constraint lengths from 3 to 9 and rates 1/2 and 1/3.

Computationally Efficient Multiuser Detectors

Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
Relevância na Pesquisa
56.24%
Conference paper; CDMA is becoming an increasingly popular multiplexing scheme in wireless communications and this has necessitated the development of efficient detection techniques. The exponential complexity of the optimal detector on one end and inferior performance of conventional single-user detctor at the other have led to the development of suboptimal multiuser detectors with lower complexity. Most of these detection techniques involve solution of a linear system. In their naive implementation this requires O(n³) operations in the size of the matrix. This cost can be reduced if we move towards modern iterative techniques for solution of the system. However maximum benefit can be achieved if we fully exploit the structure of the system. In this paper we have proposed several methods of reducing the computational complexity utilizing the above ideas. We have also come up with algorighms which computationally can achieve the lower bound in complexity.

Rapid Prototyping of Wireless Communications Systems

Jones, Bryan Allen; Jones, Bryan Allen
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
76.43%
Masters Thesis; This thesis introduces rapid prototyping methodology which overcomes important barriers in the design and implementation of digital signal processing (DSP) algorithms and systems on embedded hardware platforms, such as cellular phones. This thesis describes rapid prototyping in terms of a simulation/prototype bridge and in terms of appropriate language design. The simulation/prototype bridge combines the strengths of simulation and of prototyping, allowing the designer to develop and evaluate next-generation communications systems partly in simulation on a host computer, and partly as a prototype on embedded hardware. Appropriate language design allows engineers to express a communications system as a block diagram, in which each block represents an algorithm specified by a set of equations. Software tools developed for this thesis implement both concepts, and have been successfully used in the development of a type-based detector for a code-division multiple access (CDMA) cellular wireless communications system.

Prototyping Platforms for Multiple Antenna Wireless Communications

Murphy, Patrick; Murphy, Patrick
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
56.47%
Masters Thesis; As the demand for higher performance wireless communications continues to grow, novel algorithms have been developed which provide increased performance and efficiency. One such class of algorithms involves the use of multiple antennas on either end of a wireless link. Many of these multiple input multiple output (MIMO) algorithms offer impressive performance gains over their single antenna counterparts. The practicality of implementing such algorithms in a real system, however, has received far less attention. A primary reason for this is the scarcity of hardware platforms suitable for implementing and evaluating complex wireless communications algorithms. We present in this thesis two such platforms designed specifically to fill this void. The first platform is constructed from commercial off the shelf hardware, including equipment for baseband processing, RF up/downconversion and wireless channel emulation. The second, more ambitious platform, is built from custom hardware designed specifically for flexible MIMO prototyping.

Baseband Architecture Design for Future Wireless Base-Station Receivers

Rajagopal, Sridhar; Rajagopal, Sridhar
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
56.35%
Masters Thesis; This thesis demonstrates designing efficient algorithms and architectures to meet the real-time requirements of future wireless base-station receivers. Next generation receivers require orders-of-magnitude performance improvements in order to provide support for features such as Multimedia, Quality-Of-Service and extremely high data rates. The sophisticated, compute-intensive algorithms proposed to integrate these features make their real-time implementation difficult on current DSP-based receivers. A real-time implementation can be achieved by (1.) making the algorithms computationally efficient, without significant loss in error rate performance, (2.) task partitioning, and (3.) designing hardware to exploit available pipelining, parallelism and bit-level computations. Multiuser Channel Estimation and Detection, two of the most compute-intensive baseband tasks in the receiver, are studied on DSPs for performance evaluation. A reduced complexity iterative channel estimation scheme for slow fading channels is proposed for a fixed point, area-time efficient and real-time VLSI architecture. The multiuser detection algorithm is modified for a simple, pipelined structure. A GPP or DSP based architecture with reconfigurable support suited for wireless communications is proposed and extensions are developed to accelerate the implementation of wireless communication algorithms.

Wireless system application for in-scale marine vehicles

Velasco González, Francisco Jesús; Revestido Herrero, Elías; Hombreiro Noriega, Tomás José; Moyano Pérez, Emiliano; López García, Eloy
Fonte: Sociedad Española de Estudios Cientificos Marinos (SEECMAR) Publicador: Sociedad Española de Estudios Cientificos Marinos (SEECMAR)
Tipo: info:eu-repo/semantics/article; publishedVersion
Português
Relevância na Pesquisa
56.5%
Advances in information and communications technology have enabled the use of wireless communication techniques in all sectors for the transmission of information in different forms. Wireless communications and distributed computing have made it possible to develop the remote experimentation environment for in-scale marine vehicles which is the subject of this work. The present article describes a wireless system architecture suitable for communication among several in-scale vehicles and a station base located on land, which can control the vehicles and acquire data from all of the sensors on board the different vehicles at a distance via wireless communications.

Algorithms for MIMO-OFDM wireless communications

García-Armada, Ana
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Relatório Formato: application/pdf
Publicado em 15/04/2008 Português
Relevância na Pesquisa
66.34%
Communications Group of University Carlos III of Madrid has designed and implemented algorithms for the improvement of the performance of MIMO-OFDM systems. This technology is capable of providing high data rate wireless communications. The developed algorithms allow, on one side, the correction of the imperfections introduced by radio-frequency equipment and, on the other side, adaptation of the transmission to the channel characteristics.

Data-parallel Digital Signal Processors: Algorithm Mapping, Architecture Scaling and Workload Adaptation

Rajagopal, Sridhar; Rajagopal, Sridhar
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text; Text
Português
Relevância na Pesquisa
56.38%
PhD Thesis; Emerging applications such as high definition television (HDTV), streaming video, image processing in embedded applications and signal processing in high-speed wireless communications are driving a need for high performance digital signal processors (DSPs) with real-time processing. This class of applications demonstrates significant data parallelism, finite precision, need for power-efficiency and the need for 100's of arithmetic units in the DSP to meet real-time requirements. Data-parallel DSPs meet these requirements by employing clusters of functional units, enabling 100's of computations every clock cycle. These DSPs exploit instruction level parallelism and subword parallelism within clusters, similar to a traditional VLIW (Very Long Instruction Word) DSP, and exploit data parallelism across clusters, similar to vector processors. Stream processors are data-parallel DSPs that use a bandwidth hierarchy to support dataflow to 100's of arithmetic units and are used for evaluating the contributions of this thesis. Different software realizations of the dataflow in the algorithms can affect the performance of stream processors by greater than an order-of-magnitude. The thesis first presents the design of signal processing algorithms that map efficiently on stream processors by parallelizing the algorithms and by re-ordering the flow of data. The design space for stream processors also exhibits trade-offs between arithmetic units per cluster...

Blind Estimation of Perceptual Quality for Modern Speech Communications

Falk, Tiago
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1412501 bytes; application/pdf
Português
Relevância na Pesquisa
56.58%
Modern speech communication technologies expose users to perceptual quality degradations that were not experienced earlier with conventional telephone systems. Since perceived speech quality is a major contributor to the end user's perception of quality of service, speech quality estimation has become an important research field. In this dissertation, perceptual quality estimators are proposed for several emerging speech communication applications, in particular for i) wireless communications with noise suppression capabilities, ii) wireless-VoIP communications, iii) far-field hands-free speech communications, and iv) text-to-speech systems. First, a general-purpose speech quality estimator is proposed based on statistical models of normative speech behaviour and on innovative techniques to detect multiple signal distortions. The estimators do not depend on a clean reference signal hence are termed ``blind." Quality meters are then distributed along the network chain to allow for both quality degradations and quality enhancements to be handled. In order to improve estimation performance for wireless communications, statistical models of noise-suppressed speech are also incorporated. Next, a hybrid signal-and-link-parametric quality estimation paradigm is proposed for emerging wireless-VoIP communications. The algorithm uses VoIP connection parameters to estimate a base quality representative of the packet switching network. Signal-based distortions are then detected and quantified in order to adjust the base quality accordingly. The proposed hybrid methodology is shown to overcome the limitations of existing pure signal-based and pure link parametric algorithms. Temporal dynamics information is then investigated for quality diagnosis for hands-free speech communications. A spectro-temporal signal representation...

Hybrid wired/wireless PROFIBUS architectures: performance study based on simulation models

Sousa, Paulo Baltarejo; Ferreira, Luís Lino
Fonte: SpringerOpen Publicador: SpringerOpen
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
Relevância na Pesquisa
56.35%
The problem of providing a hybrid wired/wireless communications for factory automation systems is still an open issue, notwithstanding the fact that already there are some solutions. This paper describes the role of simulation tools on the validation and performance analysis of two wireless extensions for the PROFIBUS protocol. In one of them, the Intermediate Systems, which connect wired and wireless network segments, operate as repeaters. In the other one the Intermediate Systems operate as bridge. We also describe how the analytical analysis proposed for these kinds of networks can be used for the setting of some network parameters and for the guaranteeing real-time behaviour of the system. Additionally, we also compare the bridge-based solution simulation results with the analytical results.

Segurança em sistemas de comunicação pessoal : um modelo de arquitetura de protocolos para a interconexão de sistemas heterogêneos; Security in personal communications systems. one model of protocol architecture for the interworking of heterogeneous systems

Luna Galiano, Herbert
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
56.59%
A evolução dos sistemas de comunicação sem fio ou wireless apresentam até agora três gerações em menos de duas décadas. Fazendo parte desta evolução estão os sistemas de telefonia celular e os emergentes Sistemas de Comunicação Pessoal ou PCS (Personal Communications Systems). Este trabalho visa apresentar duas questões importantes na evolução destes sistemas, primeiro a questão da segurança e segundo a questão da interconexão com redes heterogêneas. No trabalho, abordando a questão de segurança, são estudados, analisados e comparados os mecanismos de autenticação e privacidade implementados nos atuais padrões de telefonia celular digital e analógico, como sistemas AMPS (celular analógico americano), USCD (celular digital americano) e GSM (celular digital europeu). São identificadas a vulnerabilidade e os fraudes mais comuns nestes sistemas. Também são analisados as propostas das recentes pesquisas e o state of art em termos de segurança, para os sistemas PCS emergentes. Como conclusão apresentado um quadro comparativo resumindo as principais características de segurança adotados pelos sistemas abordados neste estudo. Uma vez apresentado os aspectos de segurança em forma isolada para cada um dos sistemas acima mencionados...

Wireless communications in the new millennium and third generation wireless networks

Yakuphanogullarindan, Oz
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
56.58%
At the end of the 20 century, and at the beginning of this one, wireless communications are making large advances. The new technologies are on the way to provide a high-speed, high-quality information exchange between handheld terminals, and information repositories. The so called 2,5 generation networks, using the techniques like the HSCSD1, GPRS2, EDGE3, and the 3r generation wireless systems will help the wireless world to reach those goals. In this thesis I will start from the first and second-generation wireless networks, and then look into the 2,5 generation and 3rd generation wireless communications more in detail. The latest advances in the wireless world are the main focus of this paper although a short history of wireless communications is also given. The various aspects related to 3rd generation systems will be explored in this thesis, for example the air interface discussions, its time scale, its elements like the mobile equipment, software and security, USLM4, services that will be offered, etc. In addition, the technical factors and key technologies that are likely to shape the wireless network environment of the future will be explored. This part is expected to help us to see beyond the 3rd generation.