258 research outputs found
Study of Opportunistic Cooperation Techniques using Jamming and Relays for Physical-Layer Security in Buffer-aided Relay Networks
In this paper, we investigate opportunistic relay and jammer cooperation
schemes in multiple-input multiple-output (MIMO) buffer-aided relay networks.
The network consists of one source, an arbitrary number of relay nodes,
legitimate users and eavesdroppers, with the constraints of physical layer
security. We propose an algorithm to select a set of relay nodes to enhance the
legitimate users' transmission and another set of relay nodes to perform
jamming of the eavesdroppers. With Inter-Relay interference (IRI) taken into
account, interference cancellation can be implemented to assist the
transmission of the legitimate users. Secondly, IRI can also be used to further
increase the level of harm of the jamming signal to the eavesdroppers. By
exploiting the fact that the jamming signal can be stored at the relay nodes,
we also propose a hybrid algorithm to set a signal-to-interference and noise
ratio (SINR) threshold at the node to determine the type of signal stored at
the relay node. With this separation, the signals with high SINR are delivered
to the users as conventional relay systems and the low SINR performance signals
are stored as potential jamming signals. Simulation results show that the
proposed techniques obtain a significant improvement in secrecy rate over
previously reported algorithms.Comment: 8 pages, 3 figure
Multi-Antenna Relay Aided Wireless Physical Layer Security
With growing popularity of mobile Internet, providing secure wireless
services has become a critical issue. Physical layer security (PHY-security)
has been recognized as an effective means to enhance wireless security by
exploiting wireless medium characteristics, e.g., fading, noise, and
interference. A particularly interesting PHY-security technology is cooperative
relay due to the fact that it helps to provide distributed diversity and
shorten access distance. This article offers a tutorial on various
multi-antenna relaying technologies to improve security at physical layer. The
state of the art research results on multi-antenna relay aided PHY-security as
well as some secrecy performance optimization schemes are presented. In
particular, we focus on large-scale MIMO (LS-MIMO) relaying technology, which
is effective to tackle various challenging issues for implementing wireless
PHY-security, such as short-distance interception without eavesdropper channel
state information (CSI) and with imperfect legitimate CSI. Moreover, the future
directions are identified for further enhancement of secrecy performance.Comment: 17 pages, 4 figures, IEEE Communications Magazine, 201
A Tutorial on Nonorthogonal Multiple Access for 5G and Beyond
Today's wireless networks allocate radio resources to users based on the
orthogonal multiple access (OMA) principle. However, as the number of users
increases, OMA based approaches may not meet the stringent emerging
requirements including very high spectral efficiency, very low latency, and
massive device connectivity. Nonorthogonal multiple access (NOMA) principle
emerges as a solution to improve the spectral efficiency while allowing some
degree of multiple access interference at receivers. In this tutorial style
paper, we target providing a unified model for NOMA, including uplink and
downlink transmissions, along with the extensions tomultiple inputmultiple
output and cooperative communication scenarios. Through numerical examples, we
compare the performances of OMA and NOMA networks. Implementation aspects and
open issues are also detailed.Comment: 25 pages, 10 figure
A Survey of Optimization Approaches for Wireless Physical Layer Security
Due to the malicious attacks in wireless networks, physical layer security
has attracted increasing concerns from both academia and industry. The research
on physical layer security mainly focuses either on the secrecy
capacity/achievable secrecy rate/capacity-equivocation region from the
perspective of information theory, or on the security designs from the
viewpoints of optimization and signal processing. Because of its importance in
security designs, the latter research direction is surveyed in a comprehensive
way in this paper. The survey begins with typical wiretap channel models to
cover common scenarios and systems. The topics on physical-layer security
designs are then summarized from resource allocation, beamforming/precoding,
and antenna/node selection and cooperation. Based on the aforementioned
schemes, the performance metrics and fundamental optimization problems are
discussed, which are generally adopted in security designs. Thereafter, the
state of the art of optimization approaches on each research topic of physical
layer security is reviewed from four categories of optimization problems, such
as secrecy rate maximization, secrecy outrage probability minimization, power
consumption minimization, and secure energy efficiency maximization.
Furthermore, the impacts of channel state information on optimization and
design are discussed. Finally, the survey concludes with the observations on
potential future directions and open challenges.Comment: to appear in IEEE Communications Surveys & Tutorial
Virtual Full-Duplex Buffer-Aided Relaying in the Presence of Inter-Relay Interference
In this paper, we study virtual full-duplex (FD) buffer-aided relaying to
recover the loss of multiplexing gain caused by half-duplex (HD) relaying in a
multiple relay network, where each relay is equipped with a buffer and multiple
antennas, through joint opportunistic relay selection (RS) and beamforming (BF)
design. The main idea of virtual FD buffer-aided relaying is that the source
and one of the relays simultaneously transmit their own information to another
relay and the destination, respectively. In such networks, inter-relay
interference (IRI) is a crucial problem which has to be resolved like
self-interference in the FD relaying. In contrast to previous work that
neglected IRI, we propose joint RS and BF schemes taking IRI into consideration
by using multiple antennas at the relays. In order to maximize average
end-to-end rate, we propose a weighted sum-rate maximization strategy assuming
that adaptive rate transmission is employed in both the source to relay and
relay to destination links. Then, we propose several BF schemes cancelling or
suppressing IRI in order to maximize the weighted sum-rate. Numerical results
show that our proposed optimal, zero forcing, and minimum mean square error
BF-based RS schemes asymptotically approach the ideal FD relaying upper bound
when increasing the number of antennas and/or the number of relays.Comment: Accepted for publication to IEEE Transactions on Wireless
Communication
Switched Max-Link Relay Selection Algorithms for Buffer-Aided Relay Systems
In this paper, we investigate relay selection for cooperative
multiple-antenna systems that are equipped with buffers, which increase the
reliability of wireless links. In particular, we present a novel relay
selection technique based on switching and the selection of the best link, that
is named Switched Max-Link. We also introduce a novel relay selection criterion
based on the Maximum Likelihood (ML) principle and the Pairwise Error
Probability (PEP) denoted Maximum Minimum Distance (MMD) that is incorporated
into the proposed Switched Max-Link protocol. We compare the proposed MMD to
the existing Quadratic Norm (QN), in terms of PEP and computational complexity.
Simulations are then employed to evaluate the performance of the proposed and
existing techniques.Comment: 8 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1807.0364
Alternate Distributed Beamforming for Decode-and-Forward Multi-Relay Systems Using Buffers
In this paper, link selection for half-duplex buffer-aided relay systems is
revisited. A new fixed scheduling policy referred as alternate distributed
beamforming (ADB) is proposed, in which the relays are divided into two groups,
with one group receiving the same information broadcast from the source and the
other group transmitting the common messages to the destination via distributed
beamforming in each time slot. It is worth noting that the relays used for
reception and transmission are determined without the need of instantaneous
channel state information (CSI). Theoretical analysis of the achievable
throughput of the proposed scheme in Rayleigh fading is provided and the
approximate closed-form expressions are derived. Through numerical results, it
is shown that compared with existing link selection policies, the proposed
fixed scheduling ADB achieves a significant improvement in achievable
throughput
Weighted Sum-Rate Optimization for Intelligent Reflecting Surface Enhanced Wireless Networks
Intelligent reflecting surface (IRS) is a promising solution to build a
programmable wireless environment for future communication systems. In
practice, an IRS consists of massive low-cost elements, which can steer the
incident signal in fully customizable ways by passive beamforming. In this
paper, we consider an IRS-aided multiuser multiple-input single-output (MISO)
downlink communication system. In particular, the weighted sum-rate of all
users is maximized by joint optimizing the active beamforming at the
base-station (BS) and the passive beamforming at the IRS. In addition, we
consider a practical IRS assumption, in which the passive elements can only
shift the incident signal to discrete phase levels. This non-convex problem is
firstly decoupled via Lagrangian dual transform, and then the active and
passive beamforming can be optimized alternatingly. The active beamforming at
BS is optimized based on the fractional programming method. Then, three
efficient algorithms with closed-form expressions are proposed for the passive
beamforming at IRS. Simulation results have verified the effectiveness of the
proposed algorithms as compared to different benchmark schemes.Comment: 13 pages, 8 figure
Low-Complexity QL-QR Decomposition Based Beamforming Design for Two-Way MIMO Relay Networks
In this paper, we investigate the optimization problem of joint source and
relay beamforming matrices for a twoway amplify-and-forward (AF) multi-input
multi-output (MIMO) relay system. The system consisting of two source nodes and
two relay nodes is considered and the linear minimum meansquare- error (MMSE)
is employed at both receivers. We assume individual relay power constraints and
study an important design problem, a so-called determinant maximization (DM)
problem. Since this DM problem is nonconvex, we consider an efficient iterative
algorithm by using an MSE balancing result to obtain at least a locally optimal
solution. The proposed algorithm is developed based on QL, QR and Choleskey
decompositions which differ in the complexity and performance. Analytical and
simulation results show that the proposed algorithm can significantly reduce
computational complexity compared with their existing two-way relay systems and
have equivalent bit-error-rate (BER) performance to the singular value
decomposition (SVD) based on a regular block diagonal (RBD) scheme
Joint resource allocation in SWIPT-based multi-antenna decode-and-forward relay networks
In this paper, we consider relay-assisted simultaneous wireless information
and power transfer (SWIPT) for two-hop cooperative transmission, where a
half-duplex multi-antenna relay adopts decode-and-forward (DF) relaying
strategy for information forwarding. The relay is assumed to be energy-free and
needs to harvest energy from the source node. By embedding power splitting (PS)
at each relay antenna to coordinate the received energy and information, joint
problem of determining PS ratios and power allocation at the multi-antenna
relay node is formulated to maximize the end-to-end achievable rate. We show
that the multi-antenna relay is equivalent to a virtual single-antenna relay in
such a SWIPT system, and the problem is optimally solved with closed-form. To
reduce the hardware cost of the PS scheme, we further propose the antenna
clustering scheme, where the multiple antennas at the relay are partitioned
into two disjoint groups which are exclusively used for information decoding
and energy harvesting, respectively. Optimal clustering algorithm is first
proposed but with exponential complexity. Then a greedy clustering algorithms
is introduced with linear complexity and approaching to the optimal
performance. Several valuable insights are provided via theoretical analysis
and simulation results.Comment: To appear in IEEE TV
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