27 research outputs found
Secure Wireless Communication via Movable-Antenna Array
Movable antenna (MA) array is a novel technology recently developed where
positions of transmit/receive antennas can be flexibly adjusted in the
specified region to reconfigure the wireless channel and achieve a higher
capacity. In this letter, we, for the first time, investigate the MA
array-assisted physical-layer security where the confidential information is
transmitted from a MA array-enabled Alice to a single-antenna Bob, in the
presence of multiple single-antenna and colluding eavesdroppers. We aim to
maximize the achievable secrecy rate by jointly designing the transmit
beamforming and positions of all antennas at Alice subject to the transmit
power budget and specified regions for positions of all transmit antennas. The
resulting problem is highly non-convex, for which the projected gradient ascent
(PGA) and the alternating optimization methods are utilized to obtain a
high-quality suboptimal solution. Simulation results demonstrate that since the
additional spatial degree of freedom (DoF) can be fully exploited, the MA array
significantly enhances the secrecy rate compared to the conventional
fixed-position antenna (FPA) array
Fluid Antennas-Enabled Multiuser Uplink: A Low-Complexity Gradient Descent for Total Transmit Power Minimization
We investigate multiuser uplink communication from multiple single-antenna
users to a base station (BS), which is equipped with a movable-antenna (MA)
array and adopts zero-forcing receivers to decode multiple signals. We aim to
optimize the MAs' positions at the BS, to minimize the total transmit power of
all users subject to the minimum rate requirement. After applying
transformations, we show that the problem is equivalent to minimizing the sum
of each eigenvalue's reciprocal of a matrix, which is a function of all MAs'
positions. Subsequently, the projected gradient descent (PGD) method is
utilized to find a locally optimal solution. In particular, different from the
latest related work, we exploit the eigenvalue decomposition to successfully
derive a closed-form gradient for the PGD, which facilitates the practical
implementation greatly. We demonstrate by simulations that via careful
optimization for all MAs' positions in our proposed design, the total transmit
power of all users can be decreased significantly as compared to competitive
benchmarks
A Cooperative Deception Strategy for Covert Communication in Presence of a Multi-antenna Adversary
Covert transmission is investigated for a cooperative deception strategy,
where a cooperative jammer (Jammer) tries to attract a multi-antenna adversary
(Willie) and degrade the adversary's reception ability for the signal from a
transmitter (Alice). For this strategy, we formulate an optimization problem to
maximize the covert rate when three different types of channel state
information (CSI) are available. The total power is optimally allocated between
Alice and Jammer subject to Kullback-Leibler (KL) divergence constraint.
Different from the existing literature, in our proposed strategy, we also
determine the optimal transmission power at the jammer when Alice is silent,
while existing works always assume that the jammer's power is fixed.
Specifically, we apply the S-procedure to convert infinite constraints into
linear-matrix-inequalities (LMI) constraints. When statistical CSI at Willie is
available, we convert double integration to single integration using asymptotic
approximation and substitution method. In addition, the transmission strategy
without jammer deception is studied as a benchmark. Finally, our simulation
results show that for the proposed strategy, the covert rate is increased with
the number of antennas at Willie. Moreover, compared to the benchmark, our
proposed strategy is more robust in face of imperfect CSI.Comment: 33 pages, 8 Figure
Security-Reliability Tradeoff Analysis in Multisource Multirelay Cooperative Networks with Multiple Cochannel Interferers
Cooperative relaying communication is one of the green communication technologies since it shortens the communication distance and saves the transmit power. In this paper, the physical-layer security (PLS) of a multisource multirelay cooperative relaying communication network is investigated by considering the influence of cochannel interference from a security-reliability tradeoff (SRT) perspective. First, the SRT performance is characterized by the outage probability (OP) and the intercept probability (IP). In particular, the IP encountered at the eavesdropper is used to evaluate the security performance, while the reliability performance is analyzed in terms of the OP experienced at the destination. Then, under the impact of multiple cochannel interferers, the intercept probabilities and the outage probabilities of both the conventional direct transmission (DT) strategy and relay selection (RS) strategy are derived in closed-form expressions over Rayleigh fading channels, respectively. Simulation results are provided to validate the theoretical analysis. It is shown that when the OP (reliability) requirement is relaxed, the IP (security) performance improves and vice versa. It confirms that there is an SRT existing between the OP and the IP. Meanwhile, a better SRT performance can be achieved by increasing the number of sources, relays, and cochannel interferers. In addition, it is also shown that the RS strategy generally outperforms the conventional DT strategy in terms of the product of the IP and the OP