1,209 research outputs found
Robust Cooperative Relay Beamforming
In this paper, the robust distributed relay beamforming problem is solved
using the worst case approach, where the problem solution has been involved
because of the effect of uncertainty of channel knowledge on the quality of
service (QoS) constraints. It is shown that the original robust design, which
is a non-convex semi-infinite problem (SIP), can be relaxed and reformed to a
semi-definite problem (SDP). Monte-Carlo simulations are presented to verify
the performance improvement of our proposed robust problem over existing robust
and non-robust problems in terms of transmit power and symbol error
probability.Comment: IEEE Wireless Communications Letter
Cooperative Beamforming for Cognitive Radio-Based Broadcasting Systems with Asynchronous Interferences
In order to address the asynchronous interference issue for a generalized
scenario with multiple primary and multiple secondary receivers, in this paper,
we propose an innovative cooperative beamforming technique. In particular, the
cooperative beamforming design is formulated as an optimization problem that
maximizes the weighted sum achievable transmission rate of secondary
destinations while it maintains the asynchronous interferences at the primary
receivers below their target thresholds. In light of the intractability of the
problem, we propose a two-phase suboptimal cooperative beamforming technique.
First, it finds the beamforming directions corresponding to different secondary
destinations. Second, it allocates the power among different beamforming
directions. Due to the multiple interference constraints corresponding to
multiple primary receivers, the power allocation scheme in the second phase is
still complex. Therefore, we also propose a low complex power allocation
algorithm. The proposed beamforming technique is extended for the cases, when
cooperating CR nodes (CCRNs) have statistical or erroneous channel knowledge of
the primary receivers. We also investigate the performance of joint CCRN
selection and beamforming technique. The presented numerical results show that
the proposed beamforming technique can significantly reduce the asynchronous
interference signals at the primary receivers and increase the sum transmission
rate of secondary destinations compared to the well known zero-forcing
beamforming (ZFBF) technique.Comment: Submitted to the IEEE Transactions on Wireless Communication
Simultaneous Wireless Information Power Transfer for MISO Secrecy Channel
This paper investigates simultaneous wireless information and power transfer
(SWIPT) for multiuser multiple-input-single-output (MISO) secrecy channel.
First, transmit beamfoming without artificial noise (AN) design is considered,
where two secrecy rate optimization frameworks (i.e., secrecy rate maximization
and harvested energy maximization) are investigated. These two optimization
problems are not convex, and cannot be solved directly. For secrecy rate
maximization problem, we employ bisection method to optimize the associated
power minimization problem, and first-order Taylor series expansion is consider
to approximate the energy harvesting (EH) constraint and the harvested energy
maximization problem. Moreover, we extend our proposed algorithm to the
associated robust schemes by incorporating with channel uncertainties, where
two-level method is proposed for the harvested energy maximization problem.
Then, transmit beamforming with AN design is studied for the same secrecy rate
maximization problem, which are reformulated into semidefinite programming
(SDP) based on one-dimensional search and successive convex approximation
(SCA), respectively. Moreover, tightness analysis of rank relaxation is
provided to show the optimal transmit covariance matrix exactly returns
rank-one. Simulation results is provided to validate the performance of the
proposed algorithm.Comment: 14 pages, 7 figure
Secure MIMO Relaying Network: An Artificial Noise Aided Robust Design Approach
Owing to the vulnerability of relay-assisted and device-to-device (D2D)
communications, improving wireless security from a physical layer signal
processing perspective is attracting increasing interest. Hence we address the
problem of secure transmission in a relay-assisted network, where a pair of
legitimate user equipments (UEs) communicate with the aid of a multiple-input
multiple output (MIMO) relay in the presence of multiple eavesdroppers (eves).
Assuming imperfect knowledge of the eves' channels, we jointly optimize the
power of the source UE, the amplify-and-forward (AF) relaying matrix and the
covariance of the artificial noise (AN) transmitted by the relay, in order to
maximize the received signal-to-interference-plus-noise ratio (SINR) at the
destination, while imposing a set of robust secrecy constraints. To tackle the
resultant nonconvex optimization problem, a globally optimal solution based on
a bi-level optimization framework is proposed, but with high complexity. Then a
low-complexity sub-optimal method relying on a new penalized
difference-of-convex (DC) algorithmic framework is proposed, which is
specifically designed for non-convex semidefinite programs (SDPs). We show how
this penalized DC framework can be invoked for solving our robust secure
relaying problem with proven convergence. Our extensive simulation results show
that both proposed solutions are capable of ensuring the secrecy of the
relay-aided transmission and significantly improve the robustness towards the
eves' channel uncertainties as compared to the non-robust counterparts. It is
also demonstrated the penalized DC-based method advocated yields a performance
close to the globally optimal solution.Comment: 13 pages, 6 figures, one table and one supplementary documen
A Survey on MIMO Transmission with Discrete Input Signals: Technical Challenges, Advances, and Future Trends
Multiple antennas have been exploited for spatial multiplexing and diversity
transmission in a wide range of communication applications. However, most of
the advances in the design of high speed wireless multiple-input multiple
output (MIMO) systems are based on information-theoretic principles that
demonstrate how to efficiently transmit signals conforming to Gaussian
distribution. Although the Gaussian signal is capacity-achieving, signals
conforming to discrete constellations are transmitted in practical
communication systems. As a result, this paper is motivated to provide a
comprehensive overview on MIMO transmission design with discrete input signals.
We first summarize the existing fundamental results for MIMO systems with
discrete input signals. Then, focusing on the basic point-to-point MIMO
systems, we examine transmission schemes based on three most important criteria
for communication systems: the mutual information driven designs, the mean
square error driven designs, and the diversity driven designs. Particularly, a
unified framework which designs low complexity transmission schemes applicable
to massive MIMO systems in upcoming 5G wireless networks is provided in the
first time. Moreover, adaptive transmission designs which switch among these
criteria based on the channel conditions to formulate the best transmission
strategy are discussed. Then, we provide a survey of the transmission designs
with discrete input signals for multiuser MIMO scenarios, including MIMO uplink
transmission, MIMO downlink transmission, MIMO interference channel, and MIMO
wiretap channel. Additionally, we discuss the transmission designs with
discrete input signals for other systems using MIMO technology. Finally,
technical challenges which remain unresolved at the time of writing are
summarized and the future trends of transmission designs with discrete input
signals are addressed.Comment: 110 pages, 512 references, submit to Proceedings of the IEE
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
How to Understand LMMSE Transceiver Design for MIMO Systems From Quadratic Matrix Programming
In this paper, a unified linear minimum mean-square-error (LMMSE) transceiver
design framework is investigated, which is suitable for a wide range of
wireless systems. The unified design is based on an elegant and powerful
mathematical programming technology termed as quadratic matrix programming
(QMP). Based on QMP it can be observed that for different wireless systems,
there are certain common characteristics which can be exploited to design LMMSE
transceivers e.g., the quadratic forms. It is also discovered that evolving
from a point-to-point MIMO system to various advanced wireless systems such as
multi-cell coordinated systems, multi-user MIMO systems, MIMO cognitive radio
systems, amplify-and-forward MIMO relaying systems and so on, the quadratic
nature is always kept and the LMMSE transceiver designs can always be carried
out via iteratively solving a number of QMP problems. A comprehensive framework
on how to solve QMP problems is also given. The work presented in this paper is
likely to be the first shoot for the transceiver design for the future
ever-changing wireless systems.Comment: 31 pages, 4 figures, Accepted by IET Communication
Directional Relays for Multi-Hop Cooperative Cognitive Radio Networks
In this paper, we investigate power allocation and beamforming in a relay assisted cognitive radio (CR) network. Our objective is to maximize the performance of the CR network while limiting interference in the direction of the primary users (PUs). In order to achieve these goals, we first consider joint power allocation and beamforming for cognitive nodes in direct links. Then, we propose an optimal power allocation strategy for relay nodes in indirect transmissions. Unlike the conventional cooperative relaying networks, the applied relays are equipped with directional antennas to further reduce the interference to PUs and meet the CR network requirements. The proposed approach employs genetic algorithm (GA) to solve the optimization problems. Numerical simulation results illustrate the quality of service (QoS) satisfaction in both primary and secondary networks. These results also show that notable improvements are achieved in the system performance if the conventional omni-directional relays are replaced with directional ones
Secure SWIPT for Directional Modulation Aided AF Relaying Networks
Secure wireless information and power transfer based on directional
modulation is conceived for amplify-and-forward (AF) relaying networks.
Explicitly, we first formulate a secrecy rate maximization (SRM) problem, which
can be decomposed into a twin-level optimization problem and solved by a
one-dimensional (1D) search and semidefinite relaxation (SDR) technique. Then
in order to reduce the search complexity, we formulate an optimization problem
based on maximizing the signal-to-leakage-AN-noise-ratio (Max-SLANR) criterion,
and transform it into a SDR problem. Additionally, the relaxation is proved to
be tight according to the classic Karush-Kuhn-Tucker (KKT) conditions. Finally,
to reduce the computational complexity, a successive convex approximation (SCA)
scheme is proposed to find a near-optimal solution. The complexity of the SCA
scheme is much lower than that of the SRM and the Max-SLANR schemes. Simulation
results demonstrate that the performance of the SCA scheme is very close to
that of the SRM scheme in terms of its secrecy rate and bit error rate (BER),
but much better than that of the zero forcing (ZF) scheme
Cooperative Communication Based on Random Beamforming Strategy in Wireless Sensor Networks
This paper presents a two-phase cooperative communication strategy and an
optimal power allocation strategy to transmit sensor observations to a fusion
center in a large-scale sensor network. Outage probability is used to evaluate
the performance of the proposed system. Simulation results demonstrate that: 1)
when signal-to-noise ratio is low, the performance of the proposed system is
better than that of the multiple-input and multiple-output system over
uncorrelated slow fading Rayleigh channels; 2) given the transmission rate and
the total transmission SNR, there exists an optimal power allocation that
minimizes the outage probability; 3) on correlated slow fading Rayleigh
channels, channel correlation will degrade the system performance in linear
proportion to the correlation level.Comment: 6 pages and 7 figure
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