3,652 research outputs found
Achieving secrecy without knowing the number of eavesdropper antennas
The existing research on physical layer security commonly assumes the number
of eavesdropper antennas to be known. Although this assumption allows one to
easily compute the achievable secrecy rate, it can hardly be realized in
practice. In this paper, we provide an innovative approach to study secure
communication systems without knowing the number of eavesdropper antennas by
introducing the concept of spatial constraint into physical layer security.
Specifically, the eavesdropper is assumed to have a limited spatial region to
place (possibly an infinite number of) antennas. From a practical point of
view, knowing the spatial constraint of the eavesdropper is much easier than
knowing the number of eavesdropper antennas. We derive the achievable secrecy
rates of the spatially-constrained system with and without friendly jamming. We
show that a non-zero secrecy rate is achievable with the help of a friendly
jammer, even if the eavesdropper places an infinite number of antennas in its
spatial region. Furthermore, we find that the achievable secrecy rate does not
monotonically increase with the jamming power, and hence, we obtain the
closed-form solution of the optimal jamming power that maximizes the secrecy
rate.Comment: IEEE transactions on wireless communications, accepted to appea
On the transfer matrix of a MIMO system
We develop a deterministic ab-initio model for the input-output relationship
of a multiple-input multiple-output (MIMO) wireless channel, starting from the
Maxwell equations combined with Ohm's Law. The main technical tools are
scattering and geometric perturbation theories. The derived relationship can
lead us to a deep understanding of how the propagation conditions and the
coupling effects between the elements of multiple-element arrays affect the
properties of a MIMO channel, e.g. its capacity and its number of degrees of
freedom.Comment: Accepted for publication in Mathematical Methods in the Applied
Science
MIMO-aided near-capacity turbo transceivers: taxonomy and performance versus complexity
In this treatise, we firstly review the associated Multiple-Input Multiple-Output (MIMO) system theory and review the family of hard-decision and soft-decision based detection algorithms in the context of Spatial Division Multiplexing (SDM) systems. Our discussions culminate in the introduction of a range of powerful novel MIMO detectors, such as for example Markov Chain assisted Minimum Bit-Error Rate (MC-MBER) detectors, which are capable of reliably operating in the challenging high-importance rank-deficient scenarios, where there are more transmitters than receivers and hence the resultant channel-matrix becomes non-invertible. As a result, conventional detectors would exhibit a high residual error floor. We then invoke the Soft-Input Soft-Output (SISO) MIMO detectors for creating turbo-detected two- or three-stage concatenated SDM schemes and investigate their attainable performance in the light of their computational complexity. Finally, we introduce the powerful design tools of EXtrinsic Information Transfer (EXIT)-charts and characterize the achievable performance of the diverse near- capacity SISO detectors with the aid of EXIT charts
Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments
The paper describes the implementation and performance analysis of the first
fully-operational beam-space MIMO antenna for the spatial multiplexing of two
QPSK streams. The antenna is composed of a planar three-port radiator with two
varactor diodes terminating the passive ports. Pattern reconfiguration is used
to encode the MIMO information onto orthogonal virtual basis patterns in the
far-field. A measurement campaign was conducted to compare the performance of
the beam-space MIMO system with a conventional 2-by-?2 MIMO system under
realistic propagation conditions. Propagation measurements were conducted for
both systems and the mutual information and symbol error rates were estimated
from Monte-Carlo simulations over the measured channel matrices. The results
show the beam-space MIMO system and the conventional MIMO system exhibit
similar finite-constellation capacity and error performance in NLOS scenarios
when there is sufficient scattering in the channel. In comparison, in LOS
channels, the capacity performance is observed to depend on the relative
polarization of the receiving antennas.Comment: 31 pages, 23 figure
Interference-Aware RZF Precoding for Multi Cell Downlink Systems
Recently, a structure of an optimal linear precoder for multi cell downlink
systems has been described in [1, Eq (3.33)]. Other references (e.g., [2,3])
have used simplified versions of the precoder to obtain promising performance
gains. These gains have been hypothesized to stem from the additional degrees
of freedom that allow for interference mitigation through interference
relegation to orthogonal subspaces. However, no conclusive or rigorous
understanding has yet been developed. In this paper, we build on an intuitive
interference induction trade-off and the aforementioned precoding structure to
propose an interference aware RZF (iaRZF) precoding scheme for multi cell
downlink systems and we analyze its rate performance. Special emphasis is
placed on the induced interference mitigation mechanism of iaRZF. For example,
we will verify the intuitive expectation that the precoder structure can either
completely remove induced inter-cell or intra-cell interference. We state new
results from large-scale random matrix theory that make it possible to give
more intuitive and insightful explanations of the precoder behavior, also for
cases involving imperfect channel state information (CSI). We remark especially
that the interference-aware precoder makes use of all available information
about interfering channels to improve performance. Even very poor CSI allows
for significant sum-rate gains. Our obtained insights are then used to propose
heuristic precoder parameters for arbitrary systems, whose effectiveness are
shown in more involved system scenarios. Furthermore, calculation and
implementation of these parameters does not require explicit inter base station
cooperation.Comment: Accepted for publication in IEEE Transactions on Signal Processing,
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