740 research outputs found
Frequency-domain transmit processing for MIMO SC-FDMA in wideband propagation channels
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Exploiting Multi-Antennas for Opportunistic Spectrum Sharing in Cognitive Radio Networks
In cognitive radio (CR) networks, there are scenarios where the secondary
(lower priority) users intend to communicate with each other by
opportunistically utilizing the transmit spectrum originally allocated to the
existing primary (higher priority) users. For such a scenario, a secondary user
usually has to trade off between two conflicting goals at the same time: one is
to maximize its own transmit throughput; and the other is to minimize the
amount of interference it produces at each primary receiver. In this paper, we
study this fundamental tradeoff from an information-theoretic perspective by
characterizing the secondary user's channel capacity under both its own
transmit-power constraint as well as a set of interference-power constraints
each imposed at one of the primary receivers. In particular, this paper
exploits multi-antennas at the secondary transmitter to effectively balance
between spatial multiplexing for the secondary transmission and interference
avoidance at the primary receivers. Convex optimization techniques are used to
design algorithms for the optimal secondary transmit spatial spectrum that
achieves the capacity of the secondary transmission. Suboptimal solutions for
ease of implementation are also presented and their performances are compared
with the optimal solution. Furthermore, algorithms developed for the
single-channel transmission are also extended to the case of multi-channel
transmission whereby the secondary user is able to achieve opportunistic
spectrum sharing via transmit adaptations not only in space, but in time and
frequency domains as well.Comment: Extension of IEEE PIMRC 2007. 35 pages, 6 figures. Submitted to IEEE
Journal of Special Topics in Signal Processing, special issue on Signal
Processing and Networking for Dynamic Spectrum Acces
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Physical Layer Service Integration in 5G: Potentials and Challenges
High transmission rate and secure communication have been identified as the
key targets that need to be effectively addressed by fifth generation (5G)
wireless systems. In this context, the concept of physical-layer security
becomes attractive, as it can establish perfect security using only the
characteristics of wireless medium. Nonetheless, to further increase the
spectral efficiency, an emerging concept, termed physical-layer service
integration (PHY-SI), has been recognized as an effective means. Its basic idea
is to combine multiple coexisting services, i.e., multicast/broadcast service
and confidential service, into one integral service for one-time transmission
at the transmitter side. This article first provides a tutorial on typical
PHY-SI models. Furthermore, we propose some state-of-the-art solutions to
improve the overall performance of PHY-SI in certain important communication
scenarios. In particular, we highlight the extension of several concepts
borrowed from conventional single-service communications, such as artificial
noise (AN), eigenmode transmission etc., to the scenario of PHY-SI. These
techniques are shown to be effective in the design of reliable and robust
PHY-SI schemes. Finally, several potential research directions are identified
for future work.Comment: 12 pages, 7 figure
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Spatially Selective Artificial-Noise Aided Transmit Optimization for MISO Multi-Eves Secrecy Rate Maximization
Consider an MISO channel overheard by multiple eavesdroppers. Our goal is to
design an artificial noise (AN)-aided transmit strategy, such that the
achievable secrecy rate is maximized subject to the sum power constraint.
AN-aided secure transmission has recently been found to be a promising approach
for blocking eavesdropping attempts. In many existing studies, the confidential
information transmit covariance and the AN covariance are not simultaneously
optimized. In particular, for design convenience, it is common to prefix the AN
covariance as a specific kind of spatially isotropic covariance. This paper
considers joint optimization of the transmit and AN covariances for secrecy
rate maximization (SRM), with a design flexibility that the AN can take any
spatial pattern. Hence, the proposed design has potential in jamming the
eavesdroppers more effectively, based upon the channel state information (CSI).
We derive an optimization approach to the SRM problem through both analysis and
convex conic optimization machinery. We show that the SRM problem can be recast
as a single-variable optimization problem, and that resultant problem can be
efficiently handled by solving a sequence of semidefinite programs. Our
framework deals with a general setup of multiple multi-antenna eavesdroppers,
and can cater for additional constraints arising from specific application
scenarios, such as interference temperature constraints in interference
networks. We also generalize the framework to an imperfect CSI case where a
worst-case robust SRM formulation is considered. A suboptimal but safe solution
to the outage-constrained robust SRM design is also investigated. Simulation
results show that the proposed AN-aided SRM design yields significant secrecy
rate gains over an optimal no-AN design and the isotropic AN design, especially
when there are more eavesdroppers.Comment: To appear in IEEE Trans. Signal Process., 201
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