211 research outputs found
Precoding and Beamforming Design for Intelligent Reconfigurable Surface-Aided Hybrid Secure Spatial Modulation
Intelligent reflecting surface (IRS) is an emerging technology for wireless
communication composed of a large number of low-cost passive devices with
reconfigurable parameters, which can reflect signals with a certain phase shift
and is capable of building programmable communication environment. In this
paper, to avoid the high hardware cost and energy consumption in spatial
modulation (SM), an IRS-aided hybrid secure SM (SSM) system with a hybrid
precoder is proposed. To improve the security performance, we formulate an
optimization problem to maximize the secrecy rate (SR) by jointly optimizing
the beamforming at IRS and hybrid precoding at the transmitter. Considering
that the SR has no closed form expression, an approximate SR (ASR) expression
is derived as the objective function. To improve the SR performance, three IRS
beamforming methods, called IRS alternating direction method of multipliers
(IRS-ADMM), IRS block coordinate ascend (IRS-BCA) and IRS semi-definite
relaxation (IRS-SDR), are proposed. As for the hybrid precoding design,
approximated secrecy rate-successive convex approximation (ASR-SCA) method and
cut-off rate-gradient ascend (COR-GA) method are proposed. Simulation results
demonstrate that the proposed IRS-SDR and IRS-ADMM beamformers harvest
substantial SR performance gains over IRS-BCA. Particularly, the proposed
IRS-ADMM and IRS-BCA are of low-complexity at the expense of a little
performance loss compared with IRS-SDR. For hybrid precoding, the proposed
ASR-SCA performs better than COR-GA in the high transmit power region.Comment: 14pages,8figure
An Overview of Physical Layer Security with Finite-Alphabet Signaling
Providing secure communications over the physical layer with the objective of
achieving perfect secrecy without requiring a secret key has been receiving
growing attention within the past decade. The vast majority of the existing
studies in the area of physical layer security focus exclusively on the
scenarios where the channel inputs are Gaussian distributed. However, in
practice, the signals employed for transmission are drawn from discrete signal
constellations such as phase shift keying and quadrature amplitude modulation.
Hence, understanding the impact of the finite-alphabet input constraints and
designing secure transmission schemes under this assumption is a mandatory step
towards a practical implementation of physical layer security. With this
motivation, this article reviews recent developments on physical layer security
with finite-alphabet inputs. We explore transmit signal design algorithms for
single-antenna as well as multi-antenna wiretap channels under different
assumptions on the channel state information at the transmitter. Moreover, we
present a review of the recent results on secure transmission with discrete
signaling for various scenarios including multi-carrier transmission systems,
broadcast channels with confidential messages, cognitive multiple access and
relay networks. Throughout the article, we stress the important behavioral
differences of discrete versus Gaussian inputs in the context of the physical
layer security. We also present an overview of practical code construction over
Gaussian and fading wiretap channels, and we discuss some open problems and
directions for future research.Comment: Submitted to IEEE Communications Surveys & Tutorials (1st Revision
An Anti-Eavesdropping Strategy for Precoding-Aided Spatial Modulation With Rough CSI of Eve
In this paper, an anti-eavesdropping strategy is proposed for secure precoding-aided spatial modulation networks, under the assumption that the rough channel state information of eavesdropper can be obtained at the transmitter. Traditionally, artificial noise (AN) can be always projected into the null-space of the legitimate channel, however it may lead to some security loss since this strategy dispenses with a holistic consideration for secure transmissions. To reduce the computational complexity of our optimization problem, we derive a closed-form expression that is a loose bound of the approximate rate over the illegitimate channel. Then a concave maximization problem is formulated for optimizing the covariance matrix of AN. Simulation results show that our proposed low-complexity scheme performs closely to the method which directly maximizes the approximate secrecy rate expression, and harvests significant secrecy rate gains compared with the traditional null-space projection benchmark
Spatial Coded Modulation
In this paper, we propose a spatial coded modulation (SCM) scheme, which
improves the accuracy of the active antenna detection by coding over the
transmit antennas. Specifically, the antenna activation pattern in the SCM
corresponds to a codeword in a properly designed codebook with a larger minimum
Hamming distance than its counterpart conventional spatial modulation. As the
minimum Hamming distance increases, the reliability of the active antenna
detection is directly enhanced, which in turn improves the demodulation of the
modulated symbols and yields a better system reliability. In addition to the
reliability, the proposed SCM scheme also achieves a higher capacity with the
identical antenna configuration compared to the conventional spatial modulation
technique. Moreover, the proposed SCM scheme strikes a balance between spectral
efficiency and reliability by trading off the minimum Hamming distance with the
number of available codewords. The optimal maximum likelihood detector is first
formulated. Then, a low-complexity suboptimal detector is proposed to reduce
the computational complexity, which has a two-step detection. Theoretical
derivations of the channel capacity and the bit error rate are presented in
various channel scenarios, i.e., Rayleigh, Rician, Nakagami-m, imperfect
channel state information, and spatial correlation. Further derivation on
performance bounding is also provided to reveal the insight of the benefit of
increasing the minimum Hamming distance. Numerical results validate the
analysis and demonstrate that the proposed SCM outperforms the conventional
spatial modulation techniques in both channel capacity and system reliability.Comment: 30 pages, 17 figure
Interference Suppression in Massive MIMO VLC Systems
The focus of this dissertation is on the development and evaluation of methods and principles to mitigate interference in multiuser visible light communication (VLC) systems using several transmitters. All components of such a massive multiple-input multiple-output (MIMO) system are considered and transformed into a communication system model, while also paying particular attention to the hardware requirements of different modulation schemes. By analyzing all steps in the communication process, the inter-channel interference between users is identified as the most critical aspect. Several methods of suppressing this kind of interference, i.e. to split the MIMO channel into parallel single channels, are discussed, and a novel active LCD-based interference suppression principle at the receiver side is introduced as main aspect of this work. This technique enables a dynamic adaption of the physical channel: compared to solely software-based or static approaches, the LCD interference suppression filter achieves adaptive channel separation without altering the characteristics of the transmitter lights. This is especially advantageous in dual-use scenarios with illumination requirements. Additionally, external interferers, like natural light or transmitter light sources of neighboring cells in a multicell setting, can also be suppressed without requiring any control over them. Each user's LCD filter is placed in front of the corresponding photodetector and configured in such a way that only light from desired transmitters can reach the detector by setting only the appropriate pixels to transparent, while light from unwanted transmitters remains blocked. The effectiveness of this method is tested and benchmarked against zero-forcing (ZF) precoding in different scenarios and applications by numerical simulations and also verified experimentally in a large MIMO VLC testbed created specifically for this purpose
- …