With the increasing demand for internet of things (IoT) applications, especially for location-based services, how to locate passive mobile targets (MTs) with minimal beam adjustment has become a challenge. Resonant beam systems are considered promising IoT technologies with advantages such as beam self-alignment and energy concentration. However, resonant systems are difficult to apply to multi-user scenarios due to co-frequency interference. To establish a resonant system for multi-target localization, this paper designs an innovative resonant system architecture based on frequency division multiple access (FDMA), which enables a base station (BS) to establish connections with multiple mobile targets (MTs) with different carriers, and establishes a multi-channel cyclic model through a retro-directive array (RDA) to achieve one-to-many electromagnetic wave propagation and MTs direction of arrival (DOA) estimation through echo signals. Simulation results show that the proposed system supports resonant establishment between the BS and multiple MTs. This helps the BS maintain high DOA estimation accuracy when faced with multiple passive MTs, ensuring that the DOA error is less than 1° within a range of 5 m and 50° field of view, and the accuracy is higher than that of active beamforming localization systems under the same conditions.

Terahertz (THz) simultaneous wireless information and power transfer (SWIPT) is a promising technology for enabling ultra-high-rate and low-latency communications in massive battery-free Internet of Things (IoT) deployments for 6G networks. However, conventional THz systems rely on narrow directional beams that necessitate precise alignment, typically achieved through high-overhead beam scanning procedures, which fundamentally at odds with the energy constraints of battery-free IoT devices. In this paper, we propose a novel self-alignment architecture for THz SWIPT leveraging a reconfigurable intelligent surface (RIS) to eliminate complex beam scanning. By integrating phase conjugate circuits at both the base station and user equipment, the RIS facilitates a resonance-based bidirectional retroreflection mechanism, enabling the system to autonomously converge to an aligned state without manual intervention. We develop an analytical channel transfer model and a power cycle model to characterize the resonance-assisted beam alignment process and power transfer efficiency. Simulation results demonstrate that the RIS-enabled system achieves effective spatial power concentration with significant sidelobe suppression, leading to a communication capacity of 127.84 Gbit/s and a received power of 13.62 mW over a 2.2-meter link.

The pronounced signal attenuation characteristic of mmWave frequencies necessitates enhanced beam alignment techniques. Existing systems require scanning and steering procedures before beams can be aligned. This study introduces a novel resonant beam system (RBS) optimized for mmWave bands, featuring self-alignment capability. Utilizing retro-directive antenna arrays, our system achieves adaptive resonance, obviating the need for dedicated beam alignment. To address the interference issue typically confronted by the resonant structure, we incorporate a dual-frequency design that enables frequency division duplex (FDD) communication, alleviating interference. Intuitive analysis reveals that our proposed system can establish stable resonance within a microsecond (μs) scale of time. Preliminary assessments of the communication channel indicate that the system achieves maximum spectral efficiency of 4.8 bps/Hz while maintaining a bit error rate below 3.8 × 10−3in indoor environments.

With the rapid development of the internet of things (IoT), location-based services are becoming increasingly prominent in various aspects of social life, and accurate location information is crucial. However, RF-based indoor positioning solutions are severely limited in positioning accuracy due to signal transmission losses and directional difficulties, and optical indoor positioning methods require high propagation conditions. To achieve higher accuracy in indoor positioning, we utilize the principle of resonance to design a triangulation-based resonant beam positioning system (TRBPS) in the RF band. The proposed system employs phase-conjugation antenna arrays and resonance mechanism to achieve energy concentration and beam self-alignment, without requiring active signals from the target for positioning and complex beam control algorithms. Numerical evaluations indicate that TRBPS can achieve millimeter-level accuracy within a range of 3.6m without the need for additional embedded systems.

Due to power attenuation, improving transmission efficiency in the radio-frequency (RF) band remains a significant challenge, which hinders advancements in various fields of the Internet of Things (IoT), such as wireless power transfer (WPT) and wireless communication. Array design and retro-directive beamforming (RD-BF) techniques offer simple and effective ways to enhance transmission efficiency. However, when the target is an array or in the near field, the RD-BF system (RD-BFS) cannot radiate more energy to the target due to phase irregularities in the target region, resulting in challenges in achieving higher efficiency. To address this issue, we propose the RF-based resonant beam system (RF-RBS), which adaptively optimizes phase and power distribution between transmitting and receiving arrays by leveraging the resonance mechanism to achieve higher transmission efficiency. We analyze the system structure and develop an analytical model to evaluate power flow and resonance establishment. Numerical analysis demonstrates that the proposed RF-RBS achieves self-alignment without beam control and provides higher transmission efficiency compared to RD-BFS, with improvements of up to 16%. This self-alignment capability allows the system to effectively transfer power and information across varying distances and offsets. The numerical results indicate the capability to transmit watt-level power and achieve 21 bps/Hz of downlink spectral efficiency in indoor settings, highlighting the advantages of RF-RBS in information and power transfer for mobile applications.

The rapid expansion of the Internet of Things (IoT) necessitates robust solutions for charging and communicating with a multitude of devices, making simultaneous wireless information and power transfer (SWIPT) technology increasingly vital. However, existing methods can hardly provide high charging power, great channel capacity, and flexible mobility at the same time. This manuscript introduces a millimeter-wave resonant beam system for SWIPT (mmRB-SWIPT), leveraging retro-directive antenna arrays to enable automatic beam alignment and enhanced transmission efficiency without additional controls. A dual-frequency design allows the system to operate in a frequency-division duplex mode, thereby resolving the echo interference issues encountered in prior resonant beam systems. Analytical models are developed to evaluate the system’s viability and performance, with numerical analysis indicating the capability to transmit watt-level power and achieve 4.8 bps/Hz of spectral efficiency in indoor settings.

In the rapidly evolving field of the Internet of Things (IoT), simplifying infrastructure and deployment is highly competitive. This study introduces a novel approach using an individual-source resonant beam (RB) for passive 3-D positioning in IoT scenarios, excelling in efficient system design and signal utilization. The proposed solution simultaneously exploits the frequency structure and spatial distribution of RB to estimate position parameters, facilitating a compact design for both the base station (BS) and the mobile target (MT). The BS incorporates an individual-source RB transmitter, while the MT is equipped with a passive (electricity-free) reflector. Specifically, for extracting the distance information from RB, we develop theoretical models to illustrate the frequency attributes and associated structural variations of RB due to MT’s movement. Regarding angle estimation, we deduce the relationship between the RB field distribution and incident angles. We also conduct simulations to validate the entire positioning process. The results indicate the positioning accuracy can reach approximately 2 cm over a distance from 1.7 to 2.5 m. This technique sets a new benchmark for precise and efficient 3-D positioning, making it suitable for various IoT scenarios, such as smart homes, industrial automation, and asset tracking.

The rapid advancement of the next generation of communications and internet of things (IoT) technologies has made the provision of location-based services for diverse devices an increasingly pressing necessity. Localizing devices with/without intelligent computing abilities, including both active and passive devices is essential, especially in indoor scenarios. For traditional RF positioning systems, aligning transmission signals and dealing with signal interference in complex environments are inevitable challenges. Therefore, this paper proposed a new passive positioning system, the RF-band resonant beam positioning system (RF-RBPS), which achieves energy concentration and beam alignment by amplifying echoes between the base station (BS) and the passive target (PT), without the need for complex channel estimation and time-consuming beamforming and provides high-precision direction of arrival (DoA) estimation for battery-free targets using the resonant mechanism. The direction information of the PT is estimated using the multiple signal classification (MUSIC) algorithm at the end of BS. The feasibility of the proposed system is validated through theoretical analysis and simulations. Results indicate that the proposed RF-RBPS surpasses RF-band active positioning system (RF-APS) in precision, achieving millimeter-level precision at 2m within an elevation angle of 35°, and an error of less than 3cm at 2.5m within an elevation angle of 35°.

Both high-accuracy localization and power supply for mobile and Internet of Things (IoT) devices are demanding in the next-generation wireless networks. Recently, research on complete localization has been proposed, i.e., capturing the target’s location and identification (ID). However, the existing schemes face challenges, including: 1) improving positioning accuracy without the active emission of signals from the targets and 2) providing sufficient power for the targets to enable features such as ID. In this article, we present a simultaneous localization and power transfer (SLAPT) system relying on the resonant beam system (RBS), which can realize complete, passive, and high-accuracy positioning along with the capability of sufficient power supply. We first establish analytical models to illustrate the principles of power transfer to the target with an open-cavity laser, positioning the target, including Time-of-Flight (ToF) ranging and Angle-of-Arrival (AoA) estimation with the self-reproducing mode theory, wireless charging power conversion, and identifying the target using shutter modulation. Numerical results demonstrate that the proposed SLAPT system can achieve less than 1-cm positioning accuracy over 2-m distance in 16° Fields of View (FoVs) with 3-W wireless power supply. The proposed system allows passive and complete localization for the target without battery or power line in various IoT applications.

Locating mobile devices precisely in indoor scenarios is a challenging task because of the signal diffraction and reflection in complicated environments. One vital cause deteriorating the localization performance is the inevitable power dissipation along the propagation path of localization signals. In this paper, we propose a high-accuracy localization scheme based on the resonant beam system (RBS) and the binocular vision, i.e., binocular based resonant beam localization (BRBL). The BRBL system utilizes the energy-concentrated and self-aligned transmission of RBS to realize high-efficiency signal propagation and self-positioning for the mobile target (MT). The binocular method is combined with RBS to obtain the three-dimensional (3-D) coordinates of the MT for the first time. To exhibit the localization mechanism, we first elaborate on the binocular localization model, including the resonant beam transmission analysis and the geometric derivation of the binocular method with RBS. Then, we establish the power model of RBS, and the signal and noise models of beam spot imaging, respectively, to analyse the performance of the BRBL system. Finally, the results of numerical analysis and comparison show that BRBL balances system complexity and localization precision effectively, i.e., providing cm-level localization accuracy with its simplicity and ease of implementation.

Wireless charging for mobile Internet of Things (IoT) devices such as smartphones is extremely difficult. To reduce energy dissipation during wireless transmission in mobile scenarios, laser or narrow radio beams with sophisticated tracking control are typically required. However, reaching the necessary tracking accuracy and reliability is really difficult. In this article, inspired by the features of optical resonators and retroreflectors, we develop an experiment on a self-aligned resonant beam charging system for long-distance mobile power transfer. It exploits light resonances inside a double-retroreflector-based spatially separated laser resonator (SSLR), which eliminates the requirement for any kind of tracking control. Focal telecentric cat’s eye retroreflectors are employed here. The SSLR was investigated by both theoretical calculation and experiment. We also well assembled the transmitter and the receiver and demonstrated its application in mobile smartphone charging. The results show that above 5-W optical power (also obtained more than 0.6-W electrical power) transferring with negligible diffraction loss to a few-centimeter-size receiver is realized while the receiver moves arbitrarily within 2-m vertical distance and 6° field of view from the transmitter. The maximum horizontal moving range is up to ±18 cm. This wireless charging system empowers a smartphone in mobile operation with unlimited battery life without the need for a cable.

Optical wireless communications (OWC) utilizing infrared or visible light as the carrier attracts great attention in 6G research. Resonant beam communications (RBCom) is an OWC technology which simultaneously satisfies the needs of non-mechanical mobility and high signal-to-noise ratio (SNR). It has the self-alignment feature and therefore avoids positioning and pointing operations. However, RBCom undergoes echo interference. Here we propose an echo-interference-free RBCom system design based on second harmonic generation. The transmitter and the receiver constitute a spatially separated laser resonator, in which the retro-reflective resonant beam is formed and tracks the receiver automatically. This structure provides the channel with adaptive capability in beamforming and alignment, which is similar to the concept of intelligent reflecting surface (IRS) enhanced communications, but without hardware and software controllers. Besides, we establish an analytical model to evaluate the beam radius, the beam power, and the channel capacity. The results show that our system achieves longer distance and smaller beam diameter for the transmission beyond 10 Gbit/s, compared with the existing OWC technologies.