Phased array (PA) has received considerable attention as a representative multiantenna technique due to its inherent advantages of superior directionality, spatial multiplexing capabilities, and robust anti-jamming characteristics. However, PA suffers from relatively high hardware complexity and power consumption. As a low-complexity array technology with excellent beamforming capability, time modulated array (TMA) has attracted much attention in recent years. In this article, we exploit a TMA for enhancing the Age of Information (AoI) of covert communication. Specifically, we first propose the transmitter structures and the corresponding beamforming methods for the TMA scheme and the PA scheme as a benchmark. Subsequently, the closed-form expressions of the Kullback-Leibler (KL) divergence is derived to serve as the quantitative measure of communication covertness under both schemes, based on which the average covert AoI (CAoI) is derived to jointly characterize the covertness and timeliness performance. Then, to minimize the average CAoI, the optimization problems of the block-length and beamforming parameters for both the TMA and PA schemes are formulated and solved. Finally, the numerical results are provided to show that the proposed TMA scheme surpasses the PA scheme in terms of both the convergence rate and the average CAoI.

Energy efficiency (EE) has become a key design metric for the sustainable development of future wireless communications. Dynamic metasurface antennas (DMAs), with their compact size and low power consumption, are considered a promising solution for improving EE. In this letter, we investigate the energy-efficient beamforming design for downlink multiple-input single-output communication systems, where the DMA-equipped base station serves multiple users simultaneously. We aim to maximize the energy efficiency by jointly optimizing the DMA weight matrix and the digital precoder, subject to the constraints of power budget and Lorentzian-phase. To address this complicated non-convex optimization problem, we develop an alternating optimization algorithm based on manifold optimization and sequential convex approximation. Numerical results verify the effectiveness of the proposed method.

In recent years, physical-layer security (PLS) techniques have been paid considerable attention due to their high-security level and strong compatibility. However, the request of the superior legitimate channel is the Achilles’ Heel of PLS. A significant challenge exists in ensuring information confidentiality when the eavesdropper is located at the user’s direction in the multiantenna system. To overcome this limitation, we propose a novel framework to achieve secure communication via a distributed split single-sideband (SSB) time-modulated array (TMA). By strategically dividing the I/Q paths of the transmitted signals into geographically separated subarrays, we establish the nonaliasing zone to achieve error-free communication for legitimate users (LU), while the eavesdropper positioned in the aliasing zone receives an irrecoverably disturbed waveform. To assess performance, we adopt the encoder–decoder-based deep neural network to optimize the time-switching sequence, ensuring the subarrays’ spatial radiation areas overlap exclusively at the LU. A specialized loss function is formulated to enhance the interference-to-signal ratio (ISR) by increasing the −1st to the +1st harmonic power ratio in non-LU regions. Furthermore, the joint optimization improves security by focusing energy on the LU while generating interference in non-LU areas. The bit error ratio (BER) is used as the metric, and the simulation results validate the effectiveness of the proposed method, ensuring reliable transmission and increasing Eve’s BER to approximately 0.5, thereby compromising her ability to intercept the communication.

In this letter, we propose a novel method to improve the performance of covert communication via using movable time modulated array (MTMA). Compared with the conventional time modulated array (TMA), we leverage the spatial position of the antenna as a new dimension to enhance the degree of freedom in MTMA. First, we derive the closed-form expression for the covertness constraint by considering the characteristics of MTMA. On the basis, we jointly optimize the transmit power, blocklength, antenna position, and switch states of the MTMA to maximize the covert throughput, in which we propose an attention-enhanced swish deep neural network (ASDNN) to address the intractable optimization problem. Finally, numerical results demonstrate the superiority of the proposed scheme over benchmark schemes in terms of covert throughput.

Time-modulated array (TMA) has garnered significant interest in recent years as an alternative to phased arrays for certain applications. The TMA offer advantages such as simplicity and high accuracy when employed in scanning mode. However, a significant limitation of TMA is the constrained signal bandwidth, which must be lower than the modulation frequency to avoid aliasing. This constraint can impede progress in wideband range-Doppler (RD) estimation. To address this problem, the paper proposes a TMA structure and signal processing method that integrates time, frequency, and time-frequency (TF) domains to extract information for RD estimation. The proposed methods effectively overcome the bandwidth limitation by utilizing TF filtering and data fusion techniques, thereby enhancing the performance of RD estimation in TMA. The simulation results validate the effectiveness of the proposed strategies.

In this letter, a novel covert communication strategy that utilizes a time modulated retrodirective array (TMRDA) is proposed to enhance communication covertness. Typically, beamforming (BF) is designed via employing cuckoo search (CS), in which the sidelobes are significantly suppressed. Then, the closed-form expression of covertness constraint is derived by considering the beam characteristic of TMRDA. On this basis, the block length and transmit power are further optimized to maximize the covert throughput. Our numerical results reveal the superiority of the proposed scheme over the existing covert communication strategies.