6G Wireless Communications in 7-24 GHz Band: Opportunities, Techniques, and Challenges

The sixth generation (6G) wireless communication nowadays is seeking a new spectrum to inherit the pros and discard the cons of sub-6 GHz, millimeter-wave (mmWave), and sub-terahertz (THz) bands. To this end, an upper mid-band, Frequency Range (FR) spanning from 7 GHz to 24 GHz, also known as FR3, has emerged as a focal point in 6G communications. Thus, as an inexorable prerequisite, a comprehensive investigation encompassing spectrum utilization and channel modeling is the first step to exploit potential applications and future prospects of using this FR in the 6G ecosystem. In this article, we provide FR3 deployment insights into emerging technologies including non-terrestrial network (NTN), massive multi-input multi-output (mMIMO), reconfigurable intelligent surface (RIS), and joint communications and sensing (JCAS). Furthermore, leveraging ray-tracing simulations, our investigation unveils the channel characteristics in FR3 are close to those in the sub-6 GHz band. The analysis of RIS-aided communication shows a higher spectral efficiency achieved in FR3 compared to other FRs when using the same RIS size. Finally, challenges and promising directions are discussed for FR3-based communication systems.Comment: 7 pages, 5 figures, 1 tabl

Probability of Line of Sight Evaluation in Urban Environments using 3D Simulator

The integration of Non-Terrestrial Networks (NTNs) into 6G networks is one of the most promising ways to achieve significant improvements in capacity, reliability, and global coverage. The design of NTN heavily relies on using channel models. In this paper, we propose two easy-to-use simulators for estimating the Line-of-Sight (LoS) probability $\mathbf{P_{LoS}}$ in a 3D urban environment. The first simulator is a 3D city simulator that employs simplified Ray Tracing (RT), while the second one is a lightweight geometry-based simulator that generates only the relevant buildings between users and Unmanned Aerial Vehicles (UAVs). Using these simulators, we assess the accuracy of existing models for $\mathbf{P_{LoS}}$ estimation and examine $\mathbf{P_{LoS}}$ for different UAV heights, user-UAV distances, and azimuth/elevation angles. We conclude that 1) existing models overestimate $\mathbf{P_{LoS}}$, resulting in overoptimistic NTN performance predictions, 2) nodes location (including azimuth and elevation angles) is an important factor influencing $\mathbf{P_{LoS}}$, however, this influence is not captured by the existing models.Comment: 6 pages, submitted to IEEE conferenc

Sensing with OFDM Waveform at mmWave Band based on Micro-Doppler Analysis

Joint communication and sensing (JCAS) technology has been regarded as one of the innovations in the 6G network. With the channel modeling proposed by the 3rd Generation Partnership Project (3GPP) TR 38.901, this paper investigates the sensing capability using the millimeter-wave (mmWave) band with an orthogonal frequency division multiplexing (OFDM) waveform. Based on micro-Doppler (MD) analysis, we present two case studies, i.e., fan speed detection and human activity recognition, to demonstrate the target modeling with micro-motions, backscattering signal construction, and MD signature extraction using an OFDM waveform at 28 GHz. Simulated signatures demonstrate distinct fan rotation or human motion, and waveform parameters that affect the MD signature extraction are analyzed. Simulation results draw the validity of the proposed modeling and simulation methods, which also aim to facilitate the generation of data sets for various JCAS applications

Multimodal Fish Feeding Intensity Assessment in Aquaculture

Fish feeding intensity assessment (FFIA) aims to evaluate the intensity change of fish appetite during the feeding process, which is vital in industrial aquaculture applications. The main challenges surrounding FFIA are two-fold. 1) robustness: existing work has mainly leveraged single-modality (e.g., vision, audio) methods, which have a high sensitivity to input noise. 2) efficiency: FFIA models are generally expected to be employed on devices. This presents a challenge in terms of computational efficiency. In this work, we first introduce an audio-visual dataset, called AV-FFIA. AV-FFIA consists of 27,000 labeled audio and video clips that capture different levels of fish feeding intensity. To our knowledge, AV-FFIA is the first large-scale multimodal dataset for FFIA research. Then, we introduce a multi-modal approach for FFIA by leveraging single-modality pre-trained models and modality-fusion methods, with benchmark studies on AV-FFIA. Our experimental results indicate that the multi-modal approach substantially outperforms the single-modality based approach, especially in noisy environments. While multimodal approaches provide a performance gain for FFIA, it inherently increase the computational cost. To overcome this issue, we further present a novel unified model, termed as U-FFIA. U-FFIA is a single model capable of processing audio, visual, or audio-visual modalities, by leveraging modality dropout during training and knowledge distillation from single-modality pre-trained models. We demonstrate that U-FFIA can achieve performance better than or on par with the state-of-the-art modality-specific FFIA models, with significantly lower computational overhead. Our proposed U-FFIA approach enables a more robust and efficient method for FFIA, with the potential to contribute to improved management practices and sustainability in aquaculture

Corrosion resistance of a magnesium hydroxide/stearic acid composite coating fabricated by vapor diffusion method on Mg-Li-Ca alloy

A composite coating of magnesium hydroxide/stearic acid on surface of Mg-1Li-1Ca alloy was prepared using vapor diffusion method to improve the corrosion resistance. The surface morphology and chemical composition of the films were characterized by high resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectrometer (FTIR) and X-ray diffraction analysis (XRD). Electrochemical experiments and immersion test were conducted to study corrosion resistance of the obtained composite coating.The formation and degradation mechanisms of the composite coating were proposed.The results show that the magnesium hydroxide coating has a petal-like structure and is well-adhered to the surface of Mg-1Li-1Ca alloy.The stearic acid coating does not change the petal-like structure of the magnesium hydroxide coating. However, the stearic acid can effectively prevent the aggressive medium penetrating into the internal coating due to its low surface energy and good hydrophobicity.The corrosion current density of the magnesium hydroxide/stearic acid (Mg (OH) 2/SA) composite coating (1.45 × 10–7A/cm2) is decreased by two orders of magnitude compared to that of the Mg-1Li-1Ca alloy substrate (2.70 × 10–5 A/cm2), leading to the enhanced corrosion resistance of magnesium alloy

Multi-Frequency Air-to-Ground Channel Measurements and Analysis for UAV Communication Systems

info:eu-repo/semantics/publishe