Terahertz (THz) offers the availability of huge bandwidth to provide unprecedented data rate for the sixth-generation mobile communication and beyond. Since the narrow beam would be transmitted in the terminals to address severe path loss, THz beam alignment has been a source of significant overhead. The Direction of Arrival (DoA) sensed from a low-frequency band communication system could help fast beam alignment of THz communication. However, it is inefficient since it wastes hardware sources and requires exchange information between the sub-6 GHz and THz systems. In this article, based on the spatial similarity of the intermediate frequency (IF) channel and THz channel, a THz communication system is designed by sensing the DoA of the leaky waves from IF ports of the classical superheterodyne communication structure to aid the THz beam alignment, in which the IF part is controlled by a switching network. It is fast and efficient, since the DoA is employed and no additional communication baseband is used. Compared to the conventional beam alignment methods, the proposed shows well performance on accuracy, reactiveness and overhead, especially in scenarios for limited channel measurement as well as massive multiple-input multiple-output which are regular in THz communication.

Terahertz (THz) massive MIMO with wideband hybrid precoding has been considered one of the crucial techniques to compensate for the high-path loss in 6G high-data-rate Internet of Things (IoT). However, the beam split in wideband hybrid precoding makes the beam of different subcarriers aiming at different directions, which results in only partial channel state information (CSI) from the users to the BS. The efficiency of the CSI-based terahertz (THz) wideband beamforming scheme which is more efficient than the hardware-based scheme in narrow-band would degrade severely. To address the degradation, in this article, we first propose a sensing-aided THz wideband hybrid precoding which restores the full CSI. Through sensing and deducing the angle-frequency information, we construct a channel-selecting matrix and inverse the full CSI from our complete channel dictionary. Moreover, in order to satisfy the multiuser access requirements in IoT, we also propose dynamic radio frequency (RF) chains and dynamic power allocation schemes to further enhance the performance in multiuser scenarios based on a new precoding perspective in which each RF chain serves only one user. This benefits from the highly sparse THz channel characteristic. The spectral efficiency and energy efficiency are employed to validate that the proposed is efficient. The numerical results demonstrate that our proposed sensing-aided wideband hybrid precoding scheme achieves similar performance to the optimal precoding and much better performance to the true time delay scheme and the full CSI-based scheme.

The Passive Keyless Entry and Start system (PKES) has become an essential element of vehicle systems since it allows owners to lock or unlock their properties without having to take out the keys. However, the system suffers from a potential and serious security problem because of a relay attack. This paper introduces dynamic biometrics to resolve such potential problems. Precisely, it opts for hand-gesture and proposes a Multi-Task Siamese Feature-pyramid network with Bidirectional Gated Recurrent Units (MTSFBet) against relay attack. MTSFBet is made up of a Dynamic Biometrics Extraction Module (DBEM) and Multi-Task Operation Module (MTOM). DBEM extracts trajectory and kinematic features from the gesture data of owners, whereas MTOM performs gesture classification and identity authentication using these features. Moreover, we designed a loss function for the identity authentication part. Eventually, based on the dataset collected by mobile devices, we constructed comparative experiments and ablation studies to demonstrate the effectiveness of the method. Our comprehensive model achieves an accuracy of 0.86 in gesture classification and an accuracy of 0.73 in identity authentication. The results showed that our MTSFBet significantly outperforms other comparison methods. The MTSFBet can also be used in any scenario associated with identity authentication based on hand gestures.

The beam split in the frequency domain seriously affects hybrid precoding performance in wideband terahertz (THz) massive multiple-input multiple-output (MIMO) systems. The receiver hardly catches full Channel State Information (CSI) of all subcarriers due to spatial angle diffusion caused by the beam split, which would decrease the efficiency of hybrid precoding. To address the decrease, sensing-aided hybrid precoding is proposed to deduce the frequency-angle information in this paper. A channel matrix inverting scheme which can regain full CSI from the frequency-angle information of partial CSI is modeled. A 300 GHz MIMO system with 15 GHz bandwidth is simulated to validate the proposed sensing-aided hybrid precoding. Spectral and energy efficiency are employed to characterize the performance of the systems. Compared with true-time-delayers (TTD) based and partial CSI based schemes with no sensing in the state of the art, the proposed sensing-aided scheme performs higher spectral and energy efficiency.