Accurate positioning is a prerequisite for Harmonized Communication and Sensing. Most existing fingerprint positioning methods require a large amount of data for training, which is a labor-intensive and time-consuming task. Consequently, the issue of few samples in positioning tasks is inevitable. To accurately position with a limited number of samples, a new few-shot positioning framework is proposed, named CK-GAT. Specifically, the framework initially extracts features from the limited labeled data through a meticulously designed neural network to construct high-dimensional Channel Knowledge (CK), which characterizes the features of the current environment. Subsequently, the Channel State Information (CSI) that need to be predicted are processed through the same neural network to extract features, which are then embedded into the CK. These features are enhanced by leveraging the environmental characteristics learned by Graph Attention Networks (GAT) to achieve precise positioning. Experimental results demonstrate that under the condition of limited labeled data, the proposed CK-GAT framework outperforms the current state-of-the-art and their semi-supervised variants, achieving an improvement in positioning accuracy by 0.85 m in outdoor scenarios and 0.19 m in indoor scenarios.

Delay-Doppler (DD) signal processing has emerged as a powerful tool for analyzing multipath and time-varying channel effects. Due to the inherent sparsity of the wireless channel in the DD domain, compressed sensing (CS) based techniques, such as orthogonal matching pursuit (OMP), are commonly used for channel estimation. However, many of these methods assume integer Doppler shifts, which can lead to performance degradation in the presence of fractional Doppler. In this paper, we propose a windowed dictionary design technique while we develop a delay-aware orthogonal matching pursuit (DA-OMP) algorithm that mitigates the impact of fractional Doppler shifts on DD domain channel estimation. First, we apply receiver windowing to reduce the correlation between the columns of our proposed dictionary matrix. Second, we introduce a delay-aware interference block to quantify the interference caused by fractional Doppler. This approach removes the need for a predetermined stopping criterion, which is typically based on the number of propagation paths, in conventional OMP algorithm. Our simulation results confirm the effective performance of our proposed DA-OMP algorithm using the proposed windowed dictionary in terms of normalized mean square error (NMSE) of the channel estimate. In particular, our proposed DA-OMP algorithm demonstrates substantial gains compared to standard OMP algorithm in terms of channel estimation NMSE with and without windowed dictionary.

The 6th generation mobile communication system (6G) will provide everything as a service (XaaS), where X includes communication, sensing, computing, artificial intelligence (AI), big data and security and more. Novel features such as sensing as a Service (SaaS) will contribute to further realising Internet of Everything (IoE). Integrated Sensing and Communication (ISAC) is identified as one of the six usage scenarios for 6G by the International Telecommunication Union Radiocommunication Sector (ITU-R), and the corresponding studies on the detailed technical performance requirements and evaluation methodologies have begun in 2024. Although ISAC has become a popular topic, there are no systematic performance requirements metrics and corresponding evaluation methodologies defined for SaaS in a mobile communication system, while conventional key performance indicators (KPI) for radar systems have been borrowed currently. Therefore, to fill this gap, this paper proposes SensCAP, a systematic CAPability performance metric composed of Sensing Capacity, Accuracy and Probability. The sensing capacity reflects the comprehensive sensing performance, which can be expressed as the number of targets that can be detected per unit area within unit time, given Sensing Quality of Service (QoS) requirements consisting of sensing accuracy and probability. Furthermore, the performance evaluation of the SensCAP is conducted through system simulation using proposed evaluation methodologies, and the KPI values are suggested as the guidelines for further study in ITU-R.

As a candidate technique to achieve sixth-generation wireless communication (6G), reconfigurable intelligent surface (RIS) has become popular in both academia and industry. For better exploration of the advantages of RIS, we compare the performances of RIS and network-controlled repeater (NCR) in 3GPP release-18. We first theoretically analyze the received signal power and signal-to-noise ratio performances for both RIS and NCR. Then, we simulate the reference signal received power and signal-to-interference-and-noise ratio performances at the system level for both RIS and NCR in the frequency range 1 and frequency range 2 bands. Finally, several insights on engineering applications are given based on the comparison between RIS and NCR.

Reconfigurable intelligent surface (RIS) is an emerging technique employing metasurface to reflect the signal from the source node to the destination node. By smartly reconfiguring the electromagnetic (EM) properties of the metasurface and adjusting the EM parameters of the reflected radio waves, RIS can turn the uncontrollable propagation environment into an artificially reconfigurable space, and thus, can significantly increase the communications capacity and improve the coverage of the system. In this paper, we investigate the far field channel in which the line-of-sight (LOS) propagation is dominant. We propose an antenna model that can characterize the radiation patterns of realistic RIS elements, and consider the signal power received from the two-hop path through RIS. System-level simulations of network performance under various scenarios and parameter configurations are performed, which show significant gain of RIS.

Electromagnetic (EM) side-channel analysis is a powerful attack for extracting secret information from cryptographic hardware implementations. Countermeasures have been proposed at the register-transfer level (RTL), layout level, and device level. However, existing EM radiation modeling and side-channel vulnerability mitigation methods do not consider the structural resilience of original designs, nor do they provide fine-grained security enhancements to those vulnerable submodules/components. These universal solutions may introduce unnecessary overheads on the circuit under protection and may not be optimized for individual designs. In this article, we propose a design/synthesis for side-channel security evaluation and optimization framework based on the${t}$-test evaluation results derived from RTL hardware implementations. While the framework apply to different side-channel leakage, we focus more on EM side channels. Supported by this framework, different RTL implementations of the same cryptographic algorithm will be evaluated for their side-channel resistance. In vulnerable implementations, submodules with the most significant side-channel leakages will be identified. Security design/synthesis rules will then be applied to these vulnerable submodules for security enhancements against side-channel attacks (SCAs). Experiments, including simulations and FPGA implementations on different AES designs, are performed to validate the effectiveness of the proposed framework as well as the security design/synthesis rules.

Fully homomorphic encryption (FHE) is a novel encryption method that can perform operations on encrypted data. The performance of applications based on FHE is still low due to the high computational complexity of operations on the ciphertext. This article combines the characteristics of FHE and the redundant encoding method to achieve faster radix-2 arithmetic operations in BGV-like schemes. First, a ciphertext integer addition with multiplicative depth two, namely, redundant carry-free addition (RCFA), is proposed by applying the carry-free feature of the redundant encoding method. This addition is$7.207\times $faster and uses 15.0% of the occupied memory at 512 bits compared with the nonredundant method. After utilizing the single-instruction–multiple-data (SIMD) technique, RCFA with SIMD further improves the efficiency by$3903\times $at 512 bits compared with the nonredundant SIMD method. Its ciphertext size and occupied memory are only 34.59% and 1.6% those of the nonredundant SIMD method. Second, to achieve efficient ciphertext multiplications, redundant multiplication (RM) of dual SIMD data (RMDS) and RM of SIMD and non-SIMD data (RMSNS) methods are proposed; they obtain speedups of$65.6\times $and$631.0\times $, respectively, at 32 bits compared with the nonredundant implementations. Finally, SHA-256 is implemented to validate the efficiency of the proposed arithmetic operations. Compared with the nonredundant SIMD method, this article obtains a speedup of$4.34\times $.

Visible light communication (VLC) multiple-input multiple-output (MIMO) technology is a promising technology in 6G. However, the existing capacity formulae for radio frequency (RF) cannot be directly used for VLC due to the constraints of transmitted signals and unique channel characteristics. In this paper, we make a comparison of different signal distribution. Firstly, we analyze the relationship between transmitted and received signals based on zonotopes model. Then the capacity gap between the truncated Gaussian distribution and uniform distribution is analyzed. Simulations show that the uniform distribution has a better performance than truncated Gaussian, which may promote new signal design for VLC.

Dynamic time division duplex (TDD) is one promising way to improve the spectrum efficiency of the wireless communication networks since flexible traffic adaptation can be achieved by dynamically changing uplink (UL) or downlink (DL) transmission direction. However, it also brings some new challenges because of the introduction of cross-link interference, including DL-to-UL interference (e.g., gNB-to-gNB interference) and UL-to-DL interference (UE-to-UE interference). Besides, fully dynamic TDD is promising for 5G, which makes the interference management more intractable. In this paper, we investigate the interference management schemes for 5G dynamic TDD and propose a new interference suppression schemes using advanced receivers, e.g., minimum mean square error interference rejection and cancellation (MMSE-IRC) receiver and enhanced MMSE-IRC (eMMSE-IRC) receiver. The analytic expressions of MMSE-IRC and eMMSE-IRC receiver for dynamic TDD interference suppression are given by theoretical analysis. Also, one interference measurement scheme is proposed to support the proposed interference suppression schemes. The simulation results confirm the performance gain of the proposed interference suppression schemes compared with the baseline minimum mean square error (MMSE) receiver and show promising performance gain of dynamic TDD.

Time division duplex (TDD) plays an important role in 5G systems because it employs an unpaired spectrum and offers channel reciprocity. However, employing TDD will lead to a long transmission latency due to the uplink/downlink transmission constraints. In this paper, we study the frame structure design for low latency communications in 5G TDD systems. We propose a frame structure design method that implements a shorter transmission time interval (TTI) and more switching points to allow lower latency in TDD systems. Analysis and evaluation results show that a shorter TTI and more switching points are not only beneficial in reducing user plane latency but also yield better performance in terms of user perceived throughput and user packet delay compared with current frame structure in LTE.

In this letter, we investigate an application of a generalized polar decomposition of the Mueller matrix for polarimetric synthetic aperture radar (Pol-SAR) classification. Six roll-invariant parameters (diattenuation, retardance, polarization power, depolarization anisotropy, depolarization power, and transmittance) are selected as features for the classification of scattering types. Experimental results using the AIRSAR data over Flevoland show that, for most field types, the D-R-AΔ- Δ-m00set provides the highest classification accuracy, followed by the D-R-PΔ-Δ-m00set which also provides better accuracy than the widely used H -α-(δ-γ)-A-span set. The proposed method would be valuable for Pol-SAR interpretation.