565 research outputs found
Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage
With the rapid growth of demand for ever-increasing data rate, spectrum
resources have become more and more scarce. As a promising technique to
increase the efficiency of the spectrum utilization, cognitive radio (CR)
technique has the great potential to meet such a requirement by allowing
un-licensed users to coexist in licensed bands. In conventional CR systems, the
spectrum sensing is performed at the beginning of each time slot before the
data transmission. This unfortunately results in two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. To tackle these problems, in this paper we present a
new design paradigm for future CR by exploring the full-duplex (FD) techniques
to achieve the simultaneous spectrum sensing and data transmission. With FD
radios equipped at the secondary users (SUs), SUs can simultaneously sense and
access the vacant spectrum, and thus, significantly improve sensing
performances and meanwhile increase data transmission efficiency. The aim of
this article is to transform the promising conceptual framework into the
practical wireless network design by addressing a diverse set of challenges
such as protocol design and theoretical analysis. Several application scenarios
with FD enabled CR are elaborated, and key open research directions and novel
algorithms in these systems are discussed
Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks
Soaring capacity and coverage demands dictate that future cellular networks
need to soon migrate towards ultra-dense networks. However, network
densification comes with a host of challenges that include compromised energy
efficiency, complex interference management, cumbersome mobility management,
burdensome signaling overheads and higher backhaul costs. Interestingly, most
of the problems, that beleaguer network densification, stem from legacy
networks' one common feature i.e., tight coupling between the control and data
planes regardless of their degree of heterogeneity and cell density.
Consequently, in wake of 5G, control and data planes separation architecture
(SARC) has recently been conceived as a promising paradigm that has potential
to address most of aforementioned challenges. In this article, we review
various proposals that have been presented in literature so far to enable SARC.
More specifically, we analyze how and to what degree various SARC proposals
address the four main challenges in network densification namely: energy
efficiency, system level capacity maximization, interference management and
mobility management. We then focus on two salient features of future cellular
networks that have not yet been adapted in legacy networks at wide scale and
thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and
device-to-device (D2D) communications. After providing necessary background on
CoMP and D2D, we analyze how SARC can particularly act as a major enabler for
CoMP and D2D in context of 5G. This article thus serves as both a tutorial as
well as an up to date survey on SARC, CoMP and D2D. Most importantly, the
article provides an extensive outlook of challenges and opportunities that lie
at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201
A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends
This paper examines the security vulnerabilities and threats imposed by the
inherent open nature of wireless communications and to devise efficient defense
mechanisms for improving the wireless network security. We first summarize the
security requirements of wireless networks, including their authenticity,
confidentiality, integrity and availability issues. Next, a comprehensive
overview of security attacks encountered in wireless networks is presented in
view of the network protocol architecture, where the potential security threats
are discussed at each protocol layer. We also provide a survey of the existing
security protocols and algorithms that are adopted in the existing wireless
network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term
evolution (LTE) systems. Then, we discuss the state-of-the-art in
physical-layer security, which is an emerging technique of securing the open
communications environment against eavesdropping attacks at the physical layer.
We also introduce the family of various jamming attacks and their
counter-measures, including the constant jammer, intermittent jammer, reactive
jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the
integration of physical-layer security into existing authentication and
cryptography mechanisms for further securing wireless networks. Finally, some
technical challenges which remain unresolved at the time of writing are
summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201
Cooperative communication in wireless networks: algorithms, protocols and systems
Current wireless network solutions are based on a link abstraction where a
single co-channel transmitter transmits in any time duration. This model severely
limits the performance that can be obtained from the network. Being inherently an
extension of a wired network model, this model is also incapable of handling the
unique challenges that arise in a wireless medium. The prevailing theme of this
research is to explore wireless link abstractions that incorporate the broadcast and
space-time varying nature of the wireless channel. Recently, a new paradigm for
wireless networks which uses the idea of 'cooperative transmissions' (CT) has garnered
significant attention. Unlike current approaches where a single transmitter transmits
at a time in any channel, with CT, multiple transmitters transmit concurrently after
appropriately encoding their transmissions. While the physical layer mechanisms for
CT have been well studied, the higher layer applicability of CT has been relatively
unexplored. In this work, we show that when wireless links use CT, several network
performance metrics such as aggregate throughput, security and spatial reuse can
be improved significantly compared to the current state of the art. In this context,
our first contribution is Aegis, a framework for securing wireless networks against
eavesdropping which uses CT with intelligent scheduling and coding in Wireless Local
Area networks. The second contribution is Symbiotic Coding, an approach to encode
information such that successful reception is possible even upon collisions. The third
contribution is Proteus, a routing protocol that improves aggregate throughput in
multi-hop networks by leveraging CT to adapt the rate and range of links in a flow.
Finally, we also explore the practical aspects of realizing CT using real systems.PhDCommittee Chair: Sivakumar, Raghupathy; Committee Member: Ammar, Mostafa; Committee Member: Ingram, Mary Ann; Committee Member: Jayant, Nikil; Committee Member: Riley, Georg
Collaborative Broadcast in O(log log n) Rounds
We consider the multihop broadcasting problem for nodes placed uniformly
at random in a disk and investigate the number of hops required to transmit a
signal from the central node to all other nodes under three communication
models: Unit-Disk-Graph (UDG), Signal-to-Noise-Ratio (SNR), and the wave
superposition model of multiple input/multiple output (MIMO). In the MIMO
model, informed nodes cooperate to produce a stronger superposed signal. We do
not consider the problem of transmitting a full message nor do we consider
interference. In each round, the informed senders try to deliver to other nodes
the required signal strength such that the received signal can be distinguished
from the noise. We assume sufficiently high node density . In the unit-disk graph model, broadcasting needs
rounds. In the other models, we use an Expanding Disk Broadcasting Algorithm,
where in a round only triggered nodes within a certain distance from the
initiator node contribute to the broadcasting operation. This algorithm
achieves a broadcast in only rounds in the
SNR-model. Adapted to the MIMO model, it broadcasts within rounds. All bounds are asymptotically tight and hold with high
probability, i.e. .Comment: extended abstract accepted for ALGOSENSORS 201
Architectures and synchronization techniques for distributed satellite systems: a survey
Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements before their use is generalized. When clock or local oscillator signals are generated locally at each of the distributed nodes, achieving exact synchronization in absolute phase, frequency, and time is a complex problem. In addition, satellite systems have significant resource constraints, especially for small satellites, which are envisioned to be part of the future CDSSs. Thus, the development of precise, robust, and resource-efficient synchronization techniques is essential for the advancement of future CDSSs. In this context, this survey aims to summarize and categorize the most relevant results on synchronization techniques for Distributed Satellite Systems (DSSs). First, some important architecture and system concepts are defined. Then, the synchronization methods reported in the literature are reviewed and categorized. This article also provides an extensive list of applications and examples of synchronization techniques for DSSs in addition to the most significant advances in other operations closely related to synchronization, such as inter-satellite ranging and relative position. The survey also provides a discussion on emerging data-driven synchronization techniques based on Machine Learning (ML). Finally, a compilation of current research activities and potential research topics is proposed, identifying problems and open challenges that can be useful for researchers in the field.This work was supported by the Luxembourg National Research Fund (FNR), through the CORE Project COHEsive SATellite (COHESAT): Cognitive Cohesive Networks of Distributed Units for Active and Passive Space Applications, under Grant FNR11689919.Award-winningPostprint (published version
Localization of sound sources : a systematic review
Sound localization is a vast field of research and advancement which is used in many useful applications to facilitate communication, radars, medical aid, and speech enhancement to but name a few. Many different methods are presented in recent times in this field to gain benefits. Various types of microphone arrays serve the purpose of sensing the incoming sound. This paper presents an overview of the importance of using sound localization in different applications along with the use and limitations of ad-hoc microphones over other microphones. In order to overcome these limitations certain approaches are also presented. Detailed explanation of some of the existing methods that are used for sound localization using microphone arrays in the recent literature is given. Existing methods are studied in a comparative fashion along with the factors that influence the choice
of one method over the others. This review is done in order to form a basis for choosing the best fit method for our use
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