Orbital angular momentum (OAM) has attracted considerable attention as a novel solution for wireless communications because its orthogonal modes significantly increase the channel capacity without an additional frequency band. The joint multiplexing between OAM technologies and other modulation techniques has not been thoroughly investigated. In this paper, we first proposed the orthogonal frequency-division multiplexing-orbital angular momentum (OFDM-OAM) multiple-input-multiple-output (MIMO) system. The proposed OFDM-OAM MIMO based on discrete Fourier transformation (DFT) operations achieves a very high sum-rate and spectrum efficiency (SE). However, the expensive hardware and software overheads for transmitting and receiving OAM waves lead to an unexpected cost for the OFDM-OAM MIMO scheme. A time-switched OFDM-OAM (TOO) MIMO is then proposed to reduce the computational complexity. And the procedure of OAM generations and recoveries also explicitly been derived. The mathematical derivation shows that the proposed TOO MIMO system based on a simple switching sequence is suitable for small-scale and low-cost wireless broadband communications, and the simulation results demonstrate that the TOO MIMO scheme achieves a considerable SE and much less computational complexity than the OFDM-OAM MIMO scheme.

In the millimeter-wave (mm-Wave) multiuser-multiple-input multiple-output (MU-MIMO) system, the interferences among different users generally degrade the system performance. In the meantime, orbital angular momentum (OAM) or radio vortex communication suffers significant fading due to the nature of divergence radiation. In this contribution, we utilize the divergence and propose an OAM-based independent analog beam selection (OAM-IABS) as well as a sub-optimal beam search solution to address all the above challenges. Simulation results demonstrate the superiority of the proposed scheme.

The rapid development of artificial intelligence has significantly advanced the field of computer vision, particularly in image analysis and understanding. This paper provides a comprehensive review of the current state of the field, key technologies, and their applications across various real-world scenarios. It delves into the value of image analysis in critical areas such as personalized art, healthcare and medical image analysis, security monitoring and recognition technology, autonomous driving and traffic management, as well as industrial automation and quality control. This paper not only highlights the challenges and limitations, including dataset constraints, algorithm generalization, real-time computational costs, and privacy and ethical concerns, but also offers a forward-looking analysis of development trends such as interdisciplinary integration, weakly supervised and unsupervised learning, algorithm optimization and hardware advancements, and the protection of personal privacy and information. These insights provide a profound perspective on the future trajectory of computer vision and AI-driven image analysis.

This paper proposes a multi-coefficient estimation method for the dielectric parameters of rough materials and an effect level-based parameterization method for diffuse scattering models to characterize and model the diffuse scattering propagation at millimeter-wave frequencies. A series of diffuse scattering propagation measurements and simulations for rough materials have been performed at 40-50 GHz in a typical indoor scenario. Theoretical reflection coefficient, transmission coefficient, and scattering coefficient of rough materials, which are requisite for the proposed estimation method, are derived based on the Fresnel theoretical model and the Gaussian rough surface model. The directive model and double-lobe model are chosen and integrated with ray tracing tool to simulate the diffuse multipath propagation for rough materials based on effect level evaluation results. The optimal model parameters are obtained and various simulation results are compared and in particular, the estimated ranges of scattering coefficients agree well with the measured values. The investigations demonstrate that the proposed parameterization method is reliable and accurate for the diffuse scattering models and can be applied for the determination of model parameters from extensive materials measurement data, especially for millimeter-wave channel analysis and modeling.

As an emerging solution for line-of-sight (LOS) wireless communications, in air-to-ground (A2G) channels, the unmanned aerial vehicle (UAV), and allowing the dynamic and flexible network deployments enables the supplement or/and replacement of the terrestrial base stations (BSs). However, in conventional multiple-input-multiple-output (MIMO) systems, high-speed communications are significantly limited by channel crosstalks and spectrum scarcities. An orbit angular momentum (OAM) wireless network, allowing co-existence of multiple physical channels within the same frequency band, offers new degrees of freedom to address this dilemma. In this paper, we investigate the UAV-based A2G radio vortex wireless networks and study its channel model. Then we propose a branch and bound search-based mode selection (BBS-MS) scheme, which uses the spatial distribution characteristics of vortex beams to optimize the spectrum efficiency (SE). Theoretical derivations and numerical results demonstrate that our developed BBS-MS scheme can obtain the optimal performance, which outperforms conventional OAM-based MIMO systems. Also, it possesses a lower complexity compared with exhaustive searches.

Purpose – This study sets out to investigate the perceptions of e-buyers and e-lookers in Hainan, China on usability performance of China-based travel web sites, an emerging sector of the tourism industry in China. Design/methodology/approach – Data collection was conducted in Hainan, a province in Southern China, in December 2007. A structured questionnaire was used to collect the views of users on different usability dimensions and attributes on China-based travel web sites. Findings – Empirical findings indicated that respondents who only viewed China-based travel web sites had an average usability performance. More importantly, there was no significant difference between e-buyers and e-lookers. Research limitations/implications – The major limitations of the study are the non-random selection of respondents and that the respondents were from one province in China. Originality/value – With the views of 489 respondents, research findings should provide an overview for tourism practitioners to allocate their limited resources on e-business development appropriately.