97 research outputs found
Towards a more efficient spectrum usage: spectrum sensing and cognitive radio techniques
The traditional approach of dealing with spectrum management in wireless communications has been through the definition on a license user granted exclusive exploitation rights for a specific frequency.Peer ReviewedPostprint (published version
Sparse Bases and Bayesian Inference of Electromagnetic Scattering
Many approaches in CEM rely on the decomposition of complex radiation and scattering behavior with a set of basis vectors. Accurate estimation of the quantities of interest can be synthesized through a weighted sum of these vectors. In addition to basis decompositions, sparse signal processing techniques developed in the CS community can be leveraged when only a small subset of the basis vectors are required to sufficiently represent the quantity of interest. We investigate several concepts in which novel bases are applied to common electromagnetic problems and leverage the sparsity property to improve performance and/or reduce computational burden. The first concept explores the use of multiple types of scattering primitives to reconstruct scattering patterns of electrically large targets. Using a combination of isotropic point scatterers and wedge diffraction primitives as our bases, a 40% reduction in reconstruction error can be achieved. Next, a sparse basis is used to improve DOA estimation. We implement the BSBL technique to determine the angle of arrival of multiple incident signals with only a single snapshot of data from an arbitrary arrangement of non-isotropic antennas. This is an improvement over the current state-of-the-art, where restrictions on the antenna type, configuration, and a priori knowledge of the number of signals are often assumed. Lastly, we investigate the feasibility of a basis set to reconstruct the scattering patterns of electrically small targets. The basis is derived from the TCM and can capture non-localized scattering behavior. Preliminary results indicate that this basis may be used in an interpolation and extrapolation scheme to generate scattering patterns over multiple frequencies
Otimização do fronthaul ótico para redes de acesso de rádio (baseadas) em computação em nuvem (CC-RANs)
Doutoramento conjunto (MAP-Tele) em Engenharia Eletrotécnica/TelecomunicaçõesA proliferação de diversos tipos de dispositivos moveis, aplicações e serviços
com grande necessidade de largura de banda têm contribuído para o aumento
de ligações de banda larga e ao aumento do volume de trafego das
redes de telecomunicações moveis. Este aumento exponencial tem posto
uma enorme pressão nos mobile operadores de redes móveis (MNOs). Um
dos aspetos principais deste recente desenvolvimento, é a necessidade que as
redes têm de oferecer baixa complexidade nas ligações, como também baixo
consumo energético, muito baixa latência e ao mesmo tempo uma grande
capacidade por baixo usto. De maneira a resolver estas questões, os MNOs
têm focado a sua atenção na redes de acesso por rádio em nuvem (C-RAN)
principalmente devido aos seus benefícios em termos de otimização de performance
e relação qualidade preço. O standard para a distribuição de sinais
sem fios por um fronthaul C-RAN é o common public radio interface (CPRI).
No entanto, ligações óticas baseadas em interfaces CPRI necessitam de uma
grande largura de banda. Estes requerimentos podem também ser atingidos
com uma implementação em ligação free space optical (FSO) que é um sistema
ótico que usa comunicação sem fios. O FSO tem sido uma alternativa
muito apelativa aos sistemas de comunicação rádio (RF) pois combinam a
flexibilidade e mobilidade das redes RF ao mesmo tempo que permitem a
elevada largura de banda permitida pelo sistema ótico. No entanto, as ligações
FSO são suscetíveis a alterações atmosféricas que podem prejudicar
o desempenho do sistema de comunicação. Estas limitações têm evitado o
FSO de ser tornar uma excelente solução para o fronthaul. Uma caracterização
precisa do canal e tecnologias mais avançadas são então necessárias
para uma implementação pratica de ligações FSO. Nesta tese, vamos estudar
uma implementação eficiente para fronthaul baseada em tecnologia
á rádio-sobre-FSO (RoFSO). Propomos expressões em forma fechada para
mitigação das perdas de propagação e para a estimação da capacidade do
canal de maneira a aliviar a complexidade do sistema de comunicação. Simulações
numéricas são também apresentadas para formatos de modulação
adaptativas. São também considerados esquemas como um sistema hibrido
RF/FSO e tecnologias de transmissão apoiadas por retransmissores
que ajudam a alivar os requerimentos impostos por um backhaul/fronthaul
de C-RAN. Os modelos propostos não só reduzem o esforço computacional,
como também têm outros méritos, tais como, uma elevada precisão na estimação
do canal e desempenho, baixo requisitos na capacidade de memória
e uma rápida e estável operação comparativamente com o estado da arte
em sistemas analíticos (PON)-FSO. Este sistema é implementado num recetor
em tempo real que é emulado através de uma field-programmable gate
array (FPGA) comercial. Permitindo assim um sistema aberto, interoperabilidade,
portabilidade e também obedecer a standards de software aberto.
Os esquemas híbridos têm a habilidade de suportar diferentes aplicações,
serviços e múltiplos operadores a partilharem a mesma infraestrutura de
fibra ótica.The proliferation of different mobile devices, bandwidth-intensive applications
and services contribute to the increase in the broadband connections
and the volume of traffic on the mobile networks. This exponential growth
has put considerable pressure on the mobile network operators (MNOs). In
principal, there is a need for networks that not only offer low-complexity,
low-energy consumption, and extremely low-latency but also high-capacity
at relatively low cost. In order to address the demand, MNOs have given significant
attention to the cloud radio access network (C-RAN) due to its beneficial
features in terms of performance optimization and cost-effectiveness.
The de facto standard for distributing wireless signal over the C-RAN fronthaul
is the common public radio interface (CPRI). However, optical links
based on CPRI interfaces requires large bandwidth. Also, the aforementioned
requirements can be realized with the implementation of free space
optical (FSO) link, which is an optical wireless system. The FSO is an appealing
alternative to the radio frequency (RF) communication system that
combines the flexibility and mobility offered by the RF networks with the
high-data rates provided by the optical systems. However, the FSO links are
susceptible to atmospheric impairments which eventually hinder the system
performance. Consequently, these limitations prevent FSO from being an
efficient standalone fronthaul solution. So, precise channel characterizations
and advanced technologies are required for practical FSO link deployment
and operation. In this thesis, we study an efficient fronthaul implementation
that is based on radio-on-FSO (RoFSO) technologies. We propose closedform
expressions for fading-mitigation and for the estimation of channel
capacity so as to alleviate the system complexity. Numerical simulations
are presented for adaptive modulation scheme using advanced modulation
formats. We also consider schemes like hybrid RF/FSO and relay-assisted
transmission technologies that can help in alleviating the stringent requirements
by the C-RAN backhaul/fronthaul. The propose models not only
reduce the computational requirements/efforts, but also have a number of
diverse merits such as high-accuracy, low-memory requirements, fast and
stable operation compared to the current state-of-the-art analytical based
approaches. In addition to the FSO channel characterization, we present
a proof-of-concept experiment in which we study the transmission capabilities
of a hybrid passive optical network (PON)-FSO system. This is
implemented with the real-time receiver that is emulated by a commercial
field-programmable gate array (FPGA). This helps in facilitating an
open system and hence enables interoperability, portability, and open software
standards. The hybrid schemes have the ability to support different
applications, services, and multiple operators over a shared optical fiber
infrastructure
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression
Analysis and design of smart antenna arrays (SAAs) for improved directivity at GHz range for wireless communication systems.
Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2018.Abstract available in PDF file
Abstracts on Radio Direction Finding (1899 - 1995)
The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography).
Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM.
The contents of these files are:
1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format];
2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format];
3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion
Mobile Ad-Hoc Networks
Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
Proceedings of the Fifth International Mobile Satellite Conference 1997
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments
- …