43 research outputs found
Radio Communications
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modiďŹed our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the ďŹeld of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks
Enhancing spectrum utilization through cooperation and cognition in wireless systems
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."February 2013." Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 201-217).We have seen a proliferation of wireless technologies and devices in recent years. The resulting explosion of wireless demand has put immense pressure on available spectrum. Improving spectrum utilization is therefore necessary to enable wireless networks to keep up with burgeoning demand. This dissertation presents a cognitive and cooperative wireless architecture that significantly enhances spectrum utilization. Specifically, it introduces four new systems that embody a cross-layer design for cognition and cooperation. The first system, SWIFT, is a cognitive cross technology solution that enables wideband devices to exploit higher layer network semantics to adaptively sense which portions of the spectrum are occupied by unknown narrowband devices, and weave the remaining unoccupied spectrum bands into a single high-throughput wideband link. Second, FARA is a cooperative system that enables multi-channel wireless solutions like 802.11 to dynamically use all available channels for all devices in a performance-aware manner by using information from the physical layer and allocating to each link the frequency bands that show the highest performance for that link. SourceSync, the third system, enables wireless nodes in last-hop and wireless mesh networks to cooperatively transmit synchronously in order to exploit channel diversity and increase reliability. Finally, MegaMIMO enables wireless throughput to scale linearly with the number of transmitters by enabling multiple wireless transmitters to transmit simultaneously in the same frequency bands to multiple wireless receivers without interfering with each other. The systems in this dissertation demonstrate the practicality of cognitive and cooperative wireless systems to enable spectrum sharing. Further, as part of these systems, we design several novel primitives - adaptive spectrum sensing, time alignment, frequency synchronization, and distributed phase-coherent transmission, that can serve as fundamental building blocks for wireless cognition and cooperation. Finally, we have implemented all four systems described in this dissertation, and evaluated them in wireless testbeds, demonstrating large gains in practice.by Hariharan Shankar Rahul.Ph.D
Design, Modeling, and Analysis for MAC Protocols in Ultra-wideband Networks
Ultra-wideband (UWB) is an appealing transmission technology for
short-range, bandwidth demanded wireless communications. With the
data rate of several hundred megabits per second, UWB demonstrates
great potential in supporting multimedia streams such as
high-definition television (HDTV), voice over Internet Protocol
(VoIP), and console gaming in office or home networks, known as the
wireless personal area network (WPAN). While vast research effort
has been made on the physical layer issues of UWB, the corresponding
medium access control (MAC) protocols that exploit UWB technology
have not been well developed.
Given an extremely wide bandwidth of UWB, a fundamental problem on
how to manage multiple users to efficiently utilize the bandwidth is
a MAC design issue. Without explicitly considering the physical
properties of UWB, existing MAC protocols are not optimized for
UWB-based networks. In addition, the limited processing capability
of UWB devices poses challenges to the design of low-complexity MAC
protocols. In this thesis, we comprehensively investigate the MAC
protocols for UWB networks. The objective is to link the physical
characteristics of UWB with the MAC protocols to fully exploit its
advantage. We consider two themes: centralized and distributed UWB
networks.
For centralized networks, the most critical issue surrounding the
MAC protocol is the resource allocation with fairness and quality of
service (QoS) provisioning. We address this issue by breaking down
into two scenarios: homogeneous and heterogeneous network
configurations. In the homogeneous case, users have the same
bandwidth requirement, and the objective of resource allocation is
to maximize the network throughput. In the heterogeneous case, users
have different bandwidth requirements, and the objective of resource
allocation is to provide differentiated services. For both design
objectives, the optimal scheduling problem is NP-hard. Our
contributions lie in the development of low-complexity scheduling
algorithms that fully exploit the characteristics of UWB.
For distributed networks, the MAC becomes node-based problems,
rather than link-based problems as in centralized networks. Each
node either contends for channel access or reserves transmission
opportunity through negotiation. We investigate two representative
protocols that have been adopted in the WiMedia specification for
future UWB-based WPANs. One is a contention-based protocol called
prioritized channel access (PCA), which employs the same mechanisms
as the enhanced distributed channel access (EDCA) in IEEE 802.11e
for providing differentiated services. The other is a
reservation-based protocol called distributed reservation protocol
(DRP), which allows time slots to be reserved in a distributed
manner. Our goal is to identify the capabilities of these two
protocols in supporting multimedia applications for UWB networks. To
achieve this, we develop analytical models and conduct detailed
analysis for respective protocols. The proposed analytical models
have several merits. They are accurate and provide close-form
expressions with low computational effort. Through a cross-layer
approach, our analytical models can capture the near-realistic
protocol behaviors, thus useful insights into the protocol can be
obtained to improve or fine-tune the protocol operations. The
proposed models can also be readily extended to incorporate more
sophisticated considerations, which should benefit future UWB
network design
Heterogeneous integration of optical wireless communications within next generation networks
Unprecedented traffic growth is expected in future wireless networks and new
technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical
cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing
the RF cell for highly mobile devices and devices that lack a reliable OW connection.
Visible light communication (VLC) is considered as a potential OW technology due
to the increasing adoption of solid state lighting for indoor illumination.
Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF
small cell implementations is evaluated. A media independent model is developed
and results are presented that provide motivation for the adoption of hyper dense
small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are
evaluated in order to define methods for fair comparison when user-centric channel
selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated
to show errors in excess of 100x when dominant interferers are present. Finally,
dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model
is presented to predict device motion for improved channel selection and a novel OW
range expansion technique is presented that dynamically alters coverage regions of
OW cells by 50%.
In addition to analytical results, the dissertation describes two tools that have
been created for evaluation of RF/OW HetNets. A communication and lighting
simulation toolkit has been developed for modeling and evaluation of environments
with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse
response simulator model to utilize GPU acceleration and achieves 10x speedup over
the previous model. A software defined testbed for OW has also been proposed
and applied. The testbed implements a VLC link and a heterogeneous RF/VLC
connection that demonstrates the RF/OW HetNet concept as proof of concept
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: ⢠Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments⢠Measurements, characterization, and modelling of radio channels beyond 4G networks⢠Key issues in Vehicle (V2X) communication⢠Wireless Body Area Networks, including specific Radio Channel Models for WBANs⢠Energy efficiency and resource management enhancements in Radio Access Networks⢠Definitions and models for the virtualised and cloud RAN architectures⢠Advances on feasible indoor localization and tracking techniques⢠Recent findings and innovations in antenna systems for communications⢠Physical Layer Network Coding for next generation wireless systems⢠Methods and techniques for MIMO Over the Air (OTA) testin
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: ⢠Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments⢠Measurements, characterization, and modelling of radio channels beyond 4G networks⢠Key issues in Vehicle (V2X) communication⢠Wireless Body Area Networks, including specific Radio Channel Models for WBANs⢠Energy efficiency and resource management enhancements in Radio Access Networks⢠Definitions and models for the virtualised and cloud RAN architectures⢠Advances on feasible indoor localization and tracking techniques⢠Recent findings and innovations in antenna systems for communications⢠Physical Layer Network Coding for next generation wireless systems⢠Methods and techniques for MIMO Over the Air (OTA) testin
Real-time wireless networks for industrial control systems
The next generation of industrial systems (Industry 4.0) will dramatically transform manyproductive sectors, integrating emerging concepts such as Internet of Things, artificialintelligence, big data, cloud robotics and virtual reality, to name a few. Most of thesetechnologies heavily rely on the availability of communication networks able to offernearlyâistantaneous, secure and reliable data transfer. In the industrial sector, these
tasks are nowadays mainly accomplished by wired networks, that combine the speed ofoptical fiber media with collisionâfree switching technology.
However, driven by the pervasive deployment of mobile devices for personal com-munications in the last years, more and more industrial applications require wireless connectivity, which can bring enormous advantages in terms of cost reduction and flex-ibility. Designing timely, reliable and deterministic industrial wireless networks is a complicated task, due to the nature of the wireless channel, intrinsically errorâprone andshared among all the devices transmitting on the same frequency band.
In this thesis, several solutions to enhance the performance of wireless networks employed in industrial control applications are proposed. The presented approaches differ in terms of achieved performance and target applications, but they are all characterized by an improvement over existing industrial wireless solutions in terms of timeliness, reliability and determinism. When possible, an experimental validation of the designed
solutions is provided.
The obtained results prove that significant performance improvements are already possible, often using commercially available devices and preserving compliance to existing standards. Future research efforts, combined with the availability of new chipsets and
standards, could lead to a world where wireless links effectively replace most of the existing cables in industrial environments, as it is already the case in the consumer market
Applications
Volume 3 describes how resource-aware machine learning methods and techniques are used to successfully solve real-world problems. The book provides numerous specific application examples: in health and medicine for risk modelling, diagnosis, and treatment selection for diseases in electronics, steel production and milling for quality control during manufacturing processes in traffic, logistics for smart cities and for mobile communications