Kronecker product-based codewords, constructed from 2D DFT bases, are fundamental to constructing Type I, Type II, and enhanced Type II codebooks in 5G New Radio (NR). While these codewords are conventionally interpreted as directed orthogonal beams, this paper reveals that a significant portion of these codebooks is associated with evanescent waves, rendering them redundant for practical array beamforming and channel representation. This redundancy is rigorously proven using mathematical and electromagnetic models and validated by full-waveform and system-level simulations. Leveraging this redundancy, we propose a method to compress these codebooks, typically reducing their size by 21.5%. This compression significantly decreases signaling and pilot overhead, enhancing the efficiency of channel state information feedback and beam training without adding algorithmic complexity. We also propose codebooks for irregular arrays that are compatible with existing NR feedback frameworks, potentially accelerating the standardization of irregular array deployment. Inspired by the revelation of codebook redundancy, we extend the discussions to the properties of near-field channel and classical Rayleigh channels, and offer practical suggestions for future standard designs.

Abstract Near-field technology is increasingly recognized due to its transformative potential in communication systems, establishing it as a critical enabler for sixth-generation (6G) telecommunication development. This paper presents a comprehensive survey of recent advancements in near-field technology research. First, we explore the near-field propagation fundamentals by detailing definitions, transmission characteristics, and performance analysis. Next, we investigate various near-field channel models—deterministic, stochastic, and electromagnetic information theory based models, and review the latest progress in near-field channel testing, highlighting practical performance and limitations. With evolving channel models, traditional mechanisms such as channel estimation, beamtraining, and codebook design require redesign and optimization to align with near-field propagation characteristics. We then introduce innovative beam designs enabled by near-field technologies, focusing on non-diffractive beams (such as Bessel and Airy) and orbital angular momentum (OAM) beams, addressing both hardware architectures and signal processing frameworks, showcasing their revolutionary potential in near-field communication systems. Additionally, we highlight progress in both engineering and standardization, covering the primary 6G spectrum allocation, enabling technologies for near-field propagation, and network deployment strategies. Finally, we conclude by identifying promising future research directions for near-field technology development that could significantly impact system design. This comprehensive review provides a detailed understanding of the current state and potential of near-field technologies.

The temperature and relative humidity (hereafter called humidity) in the indoor environment is closely related to the operation of its control system. The centralized control system, which has identical air inlets not only leads to uneven indoor temperatures and humidity but also highly controlled latency when interference occurs. To address this challenge and improve the precision and uniformity of temperatures and humidity in the indoor environment, we propose a distributed temperature and humidity control (DTHC) framework based on deep reinforcement learning (DRL). In this work, we use a constant temperature and humidity air-conditioning (CTHA) system for a museum as a case study to validate the optimization performance of the proposed controller. The state–action space, reward function, and DRL network structure are proposed. The air flow rate of multiple air inlets of CTHA is adjusted according to the feedback from the distributed temperature and humidity sensors. We develop a DRL-based computational fluid dynamics (CFD) experiment platform to evaluate the proposed mechanism. The experiment results show that our approach can improve the precision and uniformity of the temperature and humidity while enhancing the anti-interference capability of the control system. The adjustment time and energy consumed to reach the desired indoor air temperatures and humidity are reduced compared with rule-based methods.

The Virtual Reality (VR) user interface style allows natural hand and body motions to manipulate virtual objects in 3D envu-onments using one or more 3D input devices.This style is best suited to application areas where traditional two-dimensional styles fall short, such as scientific visualization, architectural visualization, and remote manipulation.Currently, the programming effort required to produce a VR application is too large, and many pitfalls must be avoided in the creation of successful VR programs.In this article we describe the Decoupled Simulation Model reality

The Virtual Reality user interface style allows the user to manipulate virtual objects in a 3D environment using 3D input devices. This style is best suited to application areas where traditional two dimensional styles fall short, but the current programming effort required to produce a VR application is somewhat large. We have built a toolkit called MR, which facilitates the development of VR applications. The toolkit provides support for distributed computing, head-mounted displays, room geometry, performance monitoring, hand input devices, and sound feedback. In this paper, the architecture of the toolkit is outlined, the programmer's view is described, and two simple applications are described.