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.

With the explosive growth of the Internet of Things (IoT), simultaneous wireless information and power transfer (SWIPT) has emerged as a core solution for powering low-energy devices. To address the limitations of single-user adaptation and the high cost and power consumption caused by high local oscillator (LO) frequencies of up to 60 GHz, this paper proposes a low LO frequency resonant beam system (LLF-RBS) for multi-user self-aligning SWIPT. Our three-mixer phase conjugation (TMPC) circuit architecture reduces the requirement for key LO frequencies to the 28 and 32 GHz bands, representing an approximate 50% reduction. This architecture enables simultaneous phase conjugation, frequency translation, and information modulation within a low-cost hardware envelope. We theoretically prove that the system’s multi-user beamforming mechanism is physically equivalent to a power iteration algorithm, guaranteeing spontaneous convergence to the channel’s principal eigenmodes without explicit channel state information or digital beamforming control. Simulation results demonstrate that the LLF-RBS achieves adaptive self-alignment and watt-level power transfer for multiple users, attaining a downlink spectral efficiency of up to 21.4 bps/Hz.

Spatially distributed cavity (SDC) lasers are a promising technology for simultaneous light information and power transfer (SLIPT), offering benefits such as increased mobility and intrinsic safety, which are advantageous for various Internet of Things (IoT) devices. However, achieving beam transmission over meter-level long working distances presents significant challenges from cavity stability constraints, manufacturing/ assembly tolerances, and diffraction losses. This paper conducts a theoretical investigation of the fundamental restrictions limiting long-range resonant beam generation. We investigate cavity stability and beam characteristics, and propose a binary-search-based Monte Carlo simulation algorithm as well as a linear approximation algorithm to quantify the maximum acceptable tolerances for stable operation. Numerical results indicate that the stable region contracts sharply as distance increases. For fixed-component systems, an acceptable tolerance of 0.01 mm restricts the achievable transmission distance to less than 2 m. To address this limitation, we also prove the feasibility of long-range beam formation using precision adjustable elements, paving the way for advanced engineering applications. Experimental results verified this assumption, demonstrating that by tuning the stable region during assembly, the transmission distance could be extended to 2.8 m. This work provides essential theoretical insights and practical design guidelines for realizing stable, long-range SDC systems.

Direction of arrival (DOA) estimation technology offers a promising solution to address the sensing and positioning demands of Internet of Things (IoT) devices. Optical resonant beam systems (RBS), owing to their inherent characteristics of self-alignment, self-established energy focusing, and passive target sensing, make them naturally suited for DOA estimation in IoT scenarios. However, RBS suffer from limited angular resolution and a narrow field of view (FoV) in multi-target environments. To overcome these limitations, this paper proposes a high-resolution wide-field-of-view resonant beam DOA estimation system (RB-HWDOA). The RB-HWDOA integrates an optical spectrum-based DOA estimation algorithm (OSB-DOA), which leverages amplitude information in the two-dimensional Fourier spectrum of the resonant beam, overcoming the resolution limit imposed by the beam size in spatial-domain methods. Furthermore, we designed a telescope modulation (TM) structure to correct phase and direction mismatches, enabling a multi-Tx framework that focuses beams onto a common sensing module, thereby extending the effective FoV. Combined with the OSB-DOA algorithm, this design supports high-resolution DOA estimation for multiple targets simultaneously over a wide FoV. Simulation results show that OSB-DOA resolves angular separations down to 0.1◦ across multiple resonant beams, remains robust under noise, and the TM architecture enables multi-Tx integration for wide-FoV coverage, making RB-HWDOA a scalable and efficient solution for passive multi-target DOA estimation in complex IoT environments.

Sustainable energy supply and high-speed communications are two significant needs for the upcoming 6G applications. This paper introduces a self-aligning resonant beam system for simultaneous light information and power transfer (SLIPT), employing a novel coupled spatially distributed resonator (CSDR). The system utilizes a resonant beam for efficient power delivery and a second-harmonic beam for concurrent data transmission, inherently minimizing echo interference and enabling bidirectional communication. Through comprehensive analyses, we investigate the CSDR’s stable region, beam evolution, and power characteristics in relation to working distance and device parameters. Numerical simulations validate the CSDR-SLIPT system’s feasibility by identifying a stable beam waist location for achieving accurate mode-match coupling between two spatially distributed resonant cavities and demonstrating its operational range and efficient power delivery across varying distances. The research reveals the system’s benefits in terms of both safety and energy transmission efficiency. We also demonstrate the trade-off among the reflectivities of the cavity mirrors in the CSDR. Besides, an experiment was conducted to verified the feasibility of self-aligning beam generation and safety under the designed structure. These findings offer valuable design insights for resonant beam systems, advancing SLIPT with significant potential for remote device connectivity.

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.

Due to control limitations in the denoising process and the lack of training, zero-shot video editing methods often struggle to meet user instructions, resulting in generated videos that are visually unappealing and fail to fully satisfy expectations. To address this problem, we propose Align-A-Video, a video editing pipeline that incorporates human feedback through reward fine-tuning. Our approach consists of two key steps: 1) Deterministic Reward Fine-tuning. To reduce optimization costs for expected noise distributions, we propose a deterministic reward tuning strategy. This method improves tuning stability by increasing sample determinism, allowing the tuning process to be completed in minutes; 2) Feature Propagation Across Frames. We optimize a selected anchor frame and propagate its features to the remaining frames, improving both visual quality and semantic fidelity. This approach avoids temporal consistency degradation from reward optimization. Extensive qualitative and quantitative experiments confirm the effectiveness of using reward fine-tuning in Align-A-Video, significantly improving the overall quality of generated videos.

Resonant beam systems (RBS) have gained attention in optical wireless applications due to their unique self-alignment capability, enabling robust connections in mobile environments. However, RBS lacks physical layer encryption mechanisms, which poses security risks during identity authentication. This paper proposes a passive secure identity recognition (PSIR) system that directly embeds authentication features into the resonant beam’s physical characteristics. The proposed system utilizes a semi-reflective amplitude mask (SAM) to generate semi-reflective dark stripes (SDS) that induce nonlinear changes in the resonant beam modes at the Tx, facilitating secure transmission of identity information without explicit cryptographic protocols. Then, the convolutional neural networks (CNN) are employed for the classification of the resonant beam field, ensuring secure and accurate identity recognition. Simulation results demonstrate a nonlinear relationship between SDS and resonant beam modes, which cannot be distinctly displayed, thereby proving the security of the proposed PSIR system. Additionally, we trained an example model using a three-layer CNN. In a four-class classification task, the area under curve (AUC) value for each category was no less than 0.6, confirming the accuracy of the identity recognition.

As an essential aerial platform in Internet of Things (IoT) applications, UAV swarms require high-precision attitude estimation in GPS-limited and dynamic environments, which supports higher-level IoT functions such as smart logistics, disaster response, and environmental monitoring. However, most odometry-based pose estimation methods in dynamic scenarios without GPS encounter issues with cumulative errors over time. In this paper, we propose a method to reduce these cumulative errors by constraining the absolute positioning of Visual-Inertial Odometry (VIO) using relative poses obtained from multi-view landmark and Resonant-Beam (RBeam) sensors between UAVs. For synchronous moments, we estimate the 6 Degree-of-Freedom (DoF) relative pose using the Angle of Arrival and Time of Flight data from the RBeam, combined with nonlinear optimization. For asynchronous moments, a two-stage visual estimation method is introduced, combining multi-camera epipolar geometry for rotation recovery and depth reconstruction optimization for translation recovery, enabling the estimation of asynchronous relative poses. Finally, we design a global objective function based on a sliding window and factor graph, integrating RBeam, multi-view landmark, and VIO for absolute 6-DoF pose optimization of the UAV swarm. Simulation results demonstrate that optimizing with the addition of RBeam synchronous relative poses improves overall positioning accuracy by 32.94% compared to pure VIO. Incorporating both RBeam synchronous and visual asynchronous relative poses further enhances overall positioning accuracy by 37.65%. Additionally, the UAV’s attitude benefits from the rotational constraints provided by the RBeam, achieving over 30% improvement in the pitch and yaw directions.

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.

Simultaneous wireless information and power transfer (SWIPT) is considered a promising technology for the future of the internet of things (IoT), with significant potential to enable advancements in both smart living and smart production. As IoT devices often operate wirelessly using various types of radiation, such as radio frequency (RF), microwave, laser, etc, the topic of human-safe irradiance is getting increasingly important. The resonant beam system (RBS) exploits the self-aligning characteristics of spatially distributed laser resonators to simultaneously achieve high-power and high-capacity SWIPT. The self-protection RBS, equipped with an adaptive phase adjuster, further mitigates safety concerns by reducing the irradiance on the invasion object. However, the power optimization under safety restrictions of this system remains underexplored, leaving significant potential for further enhancement of its performance. In this paper, we establish a theoretical model of RBS with an adaptive phase adjuster, including the irradiance on the invading object. Furthermore, based on the proposed model, we construct an optimization framework using alternating optimization to refine the system parameters, which are equivalent reflectance of the output reflector, radius of the beam on the gain medium, and split ratio of the protective beam. Finally, the numerical results demonstrate that the system’s optical power output is enhanced by 19.91% while adhering to safety limits for the human skin of 1 W/cm2 in the standard “safety of laser products IEC 60825-1.”. As a SWIPT system, it can deliver an average of 5 W of electric power and achieve a spectral efficiency of 14.7 bps/Hz with 300 W input power over a distance of 9 m.

The Simultaneous Wireless Information and Power Transfer (SWIPT) technique heralds a new era for future Internet of Things (IoT) devices. Resonant Beam System (RBS) is emerging as a possible future for achieving long-range, high-power, and high-capacity SWIPT. However, ensuring human safety at higher power levels presents an unresolved issue. A novel approach to enhance safety utilizes self-mixing interference to minimize radiation exposure for invading objects. However, this design restricts the system to a predetermined position. Thus, the application of the system in mobile scenarios is still challenging. In this paper, we proposed an enhanced self-protection RBS with self-adaptive phase adjustment to support the mobility of the system. A phase adjuster is composed into the system which utilizes the linear Electro-optic effect (i.e. Pockels effect) to correct phase discrepancies. An Optical Phase-Locked Loop (OPLL) achieves self-adaptive functionality using its feedback loop. Based on the analytical model established in this paper, the proposed system does not compromise the safety of the original self-protection RBS but offers mobility. The SWIPT performance evaluations indicate a stable system output, with a spectral efficiency of approximately 13.77 bps/Hz and an electrical power output of 4.63 W over a distance of 6 m within a 5∘ field of view.

This two-part paper studies a point-to-point resonant beam communication (RBCom) system, where two separately deployed retroreflectors are adopted to generate the resonant beam between the transmitter and the receiver, and analyzes the transmission rate of the considered system under both the quasi-static and mobile scenarios. Part I of this paper focuses on the quasi-static scenario where the locations of the transmitter and the receiver are relatively fixed. Specifically, we propose a new information-bearing scheme which adopts a synchronization-based amplitude modulation method to mitigate the echo interference caused by the reflected resonant beam. With this scheme, we show that the quasi-static RBCom channel is equivalent to a Markov channel and can be further simplified as an amplitude-constrained additive white Gaussian noise channel. Moreover, we develop an algorithm that jointly employs the bisection and exhaustive search to maximize its capacity upper and lower bounds. Finally, numerical results validate our analysis. Part II of this paper discusses the performance of the RBCom system under the mobile scenario.

In the era of the Internet of everything (IoE) and the metaverse, there is a growing demand for high-accuracy indoor positioning for applications such as autonomous robots, virtual reality, and smartphones. This paper proposed a resonant beam phase-based passive localization (RBPPL) system optimized for high-precision indoor positioning in multi-access scenarios. By leveraging the self-alignment characteristic and integrating the analysis of resonant beam phase, angle of arrival (AoA) matching and binocular disparity method for 3D point coordinate acquisition, the RBPPL system achieves binocular passive multi-access 3D positioning with an error within 4 cm at a distance of 8 m. We present a novel multi-access AoA estimation method that overcomes the challenges of spot overlap in traditional CMOS-based angle analysis. We propose a telescope system to correct the phase and focus the propagation direction of optical resonant beam systems. Simulations demonstrate the system’s robustness and high accuracy. The proposed RBPPL system, optimized for multi-access scenarios, offers a promising solution for high-accuracy indoor positioning, supporting various IoE and metaverse applications. Future work will focus on real-world deployment and its potential in complex multi-access scenarios.

Motion planning at intersections is a challenging problem in autonomous driving due to the complicated interactions. The existing pipeline of "planning after predicting" is too conservative, can reduce traffic efficiency. Using game theory to model the non-cooperative coupling relationships between multiple vehicles can resolve the above problems, but such methods cannot guarantee safety without collision. This paper presents motion planning for autonomous driving with safe differential games based on Control Barrier Function (CBF), and also provides a safety-critical generalized Nash equilibrium seeking algorithm. We handle the hard CBF constraints through augmented Lagrangian multiplier method. Motivated by iterative Linear-Quadratic Game (iLQG) algorithm, we use the Taylor expansion method to approximate the model into an Linear-Quadratic (LQ) structure, and then incrementally solve this problem with an iterative feedback LQ game algorithm. Through Carla simulation and hardware testing, our results indicate that the algorithm can find a balance between safety and efficiency while maintaining real-time implementation performance.

Positioning and power transfer are crucial demands in the existing Internet of Things networks, where intracavity laser-based systems are proposed as a potential alternative for providing sufficient wireless power and high-accuracy positioning simultaneously. However, existing intracavity laser-based systems still face challenges in improving power transfer efficiency and system Field of View (FoV). This article proposes a joint sensing and power transfer (JSPT) system based on distributed coupled-cavity laser (DCCL) design. Power efficiency and FoV are enhanced owing to the external-cavity feedback in DCCL. The angle of arrival estimation based on the intrinsic self-alignment feature and polarization self-modulation ranging based on the self-mixing feature are achieved in the DCCL-based JSPT system. Moreover, we build analytical models for revealing the principle of DCCL and verifying the system performance relying on diffraction propagation-based beam field simulation and rate equation-based gain simulation. Numerical results demonstrate that DCCL-based JSPT achieves 4-W charging power and mm-level 3-D positioning within an FoV of ±40° and 2-m vertical distances, showing its capability for Internet of Things applications.

The relative localization (RL) of unmanned aerial vehicle (UAV) swarms has gained considerable traction within the realm of UAV formation control. However, most existing RL methods face the challenge of balancing accuracy and computational power in unknown environments. The Resonant Beam (RB) system, which features energy-concentrated and selfaligned transmission can be used for positioning with centimeterlevel accuracy. In this study, we improved the RB system through a double complementary metal-oxide-semiconductors (CMOS) design and proposed a corresponding calculation method to simultaneously obtain the relative position and relative attitude angle, making it adapt to RL problems of swarms. Building upon these advancements, we design a UAV system to solve the three-dimensional RL problems. For large-scale swarms and indirect RL situations, we propose an RB-featured direct-indirect link optimization algorithm considering dynamic correction to improve positioning accuracy and meet real-time requirements. The simulation results show that our root mean square error (RMSE) is within 4cm when the UAV reaches a maximum distance of 30m and is not adjacent to the baseline UAV. This represents a notable 24.2% improvement over the shortest path algorithm. Compared with using LiDAR only for RL, our method offers higher accuracy and achieves millisecond-level speed without requiring GPU computing power.

Free space optical (FSO) transmission has emerged as a key candidate technology for 6G to expand new spectrum and improve network capacity due to its advantages of large bandwidth, low-electromagnetic interference, and high-energy efficiency. Resonant beam operating in the infrared band utilizes spatially separated laser cavities to enable safe and mobile high-power energy and high-rate information transmission but is limited by Line-of-Sight (LoS) channel. In this article, we propose a reconfigurable intelligent surface (RIS) assisted resonant beam simultaneous wireless information and power transfer (SWIPT) system and establish an optical field propagation model to analyze the channel state information (CSI), in which LoS obstruction can be detected sensitively and non line-of-sight (NLoS) transmission can be realized by changing the phased of resonant beam in RIS. Numerical results demonstrate that, apart from the transmission distance, the NLoS performance depends on both the horizontal and vertical positions of RIS. The maximum NLoS energy efficiency can achieve 55% within a transfer distance of 10 m, a translation distance of ±4 mm, and rotation angle of ±50°.

Simultaneous lightwave information and power transfer (SLIPT) is increasingly vital in the burgeoning field of mobile Internet of Things (IoT) technologies. It offers a dual advantage: high-power wireless charging and high-rate data communication, essential for IoT devices. Resonant beam system, utilizing spatially separated laser resonators (SSLR), presents a promising solution. These systems enable the creation of resonant beams without necessitating beam steering devices or alignment/tracking processes, even when the receiver’s location changes. However, a critical challenge in deploying these systems within IoT scenario lies in their limited field of view (FoV) and coverage angle. In this paper, we present a design strategy for integrating concave mirrors with lenses in a cat’s-eye retroreflector configuration. This adjustment significantly enhances the FoV of the resonant beam SLIPT system, resulting in more efficient and broader system coverage. Through an analysis grounded in optical field propagation, we evaluate the FoV performance of the resonant beam SLIPT system. The numerical results show that with a retro-reflector dimension of 2.5 mm, our proposed system demonstrates the capability of conducting watt-level electrical power transfer, coupled with a communication capacity of approximately 10-bit/s/Hz under a 6.87° FoV. This substantial improvement in FoV not only addresses the current limitations but also provides new avenues for resonant beam SLIPT systems in a wide range of IoT applications.

To address challenges in outdoor multi-robot collaborative localization (MRCL) due to low GPS accuracy, we propose a system using three UGVs, each equipped with a shared camera and a laser rangefinder. Our trilateral localization algorithm combines least-squares matrix and gradient descent methods, resulting in an 80.4% improvement in accuracy compared to traditional methods. The system mitigates the limitations of GPS accuracy by utilizing accurate baseline measurements and optimizing the localization process. These advancements have potential applications in transportation, production, and logistics, enhancing MRCL performance in outdoor environments.

In industrial environments where pedestrians and vehicles closely interact, existing point positioning systems often yield inaccurate results by disregarding crucial vehicle information, such as shape and angles, thereby compromising effective early warning mechanisms. Moreover, existing positioning systems relying on visual or radar methodologies also have limitations due to environmental factors. To address these challenges, this article introduces a novel pedestrian and vehicle area positioning and warning system base on multiple ultrawideband (UWB) signals, offering detailed information about vehicle positioning, orientation, and shape. Employing multiple UWB tags alongside the two-way ranging (TWR) algorithm, this system models the vehicle’s positioning area and triggers alerts when the pedestrian-to-vehicle distance falls below a specified threshold derived from the shape and orientation data of the positioning area. Additionally, this work proposes a priori data for coordinate calibration, integrating extended Kalman filtering (EKF) and a dynamic threshold algorithm to seamlessly recalibrate the vehicle’s positioning in both stationary and mobile scenarios. Experimental results demonstrate that, compared with using original area data for positioning, the modified algorithm can reduce the positioning coordinate STD by 18.43%, and the vehicle body shake variance by 50.56%, while also achieving a 4.30% increase in success warning rate and a notable 33.35% decline in false warning rate.

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.

Simultaneous wireless information and power transfer (SWIPT) is regarded as the enabling technology for IoT, 5G and beyond, or even 6G. Resonant beam system (RBS) is a promising candidate to provide high-power, long-range, and intrinsically safe SWIPT. Yet ensuring human safety under high-power application scenarios is still challenging. In this paper, we propose a portable auto-protection (AP) scheme to enhance the safety of RBS. Leveraging self-mixing interference, the high-power resonant beam is automatically cut off as the low-power protective beam is obstructed by foreign objects, resulting in less radiation exposure to invading objects. The paper proposes a phase compensation scheme that resolves the contradiction between portability and interference-induced mode variation, allowing the receiver to be placed anywhere within the field of view. Moreover, by approximating the cavity to Fabry-Pérot interferometer, analytical models are established to reveal the safety-enhancement mechanism and evaluate the system performance. Numerical results demonstrate that the AP scheme will not significantly compromise the portability and SWIPT performance of RBS, as the average spectral efficiency and electric power are 13.55bps/Hz and 5.42W respectively, within 6m transmission distance.

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.

This two-part paper focuses on the system design and performance analysis for a point-to-point resonant beam communication (RBCom) system under both the quasi-static and mobile scenarios. Part I of this paper proposes a synchronization-based information transmission scheme and derives the capacity upper and lower bounds for the quasi-static channel case. In Part II, we address the mobile scenario, where the receiver is in relative motion to the transmitter, and derive a mobile RBCom channel model that jointly considers the Doppler effect, channel variation, and echo interference. With the obtained channel model, we prove that the channel gain of the mobile RBCom decreases as the number of transmitted frames increases, and thus show that the considered mobile RBCom terminates after the transmitter sends a certain number of frames without frequency compensation. By deriving an upper bound on the number of successfully transmitted frames, we formulate the throughput maximization problem for the considered mobile RBCom system, and solve it via a sequential parametric convex approximation (SPCA) method. Finally, simulation results validate the analysis of our proposed method in some typical scenarios.

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°.

Simultaneous lightwave information and power transfer (SLIPT) is a potential way to meet the demands of sustainable power supply and high-rate data transfer in next-generation networks. Although resonant beam-based SLIPT (RB-SLIPT) can realize high-power energy transfer, high-rate data transfer, human safety, and self-alignment simultaneously, mobile transmission channel (MTC) analysis under non-line-of-sight (NLOS) propagation has not been investigated. In this paper, we propose analytical models and simulation tools for reflector-assisted NLOS transmission of RB-SLIPT, where transmission loss and accurate beam field profile of NLOS MTC can be obtained with a receiver at arbitrary positions and attitude angles. We establish analytical models relying on full diffraction theory for beam propagation between tilted or off-axis planes. Then, we provide three numerical methods (i.e., NUFFT-based, cubic interpolation-based, and linear interpolation-based methods) in simulations. Moreover, to deal with the contradiction between limited computing memory and high sampling requirements for long-range transmission analysis, we propose a multi-hop sliding window approach, which can reduce the sampling number by a factor of thousands. Finally, numerical results demonstrate that RB-SLIPT can achieve 3W charging power and 10bit/s/Hz data rate over a 2m distance in NLOS scenarios.

Coupled with identification, 3D positioning can significantly enrich location-based services. Resonant beam (RB) is emerging as a promising solution to indoor positioning due to its self-aligning and energy-focused transmission. We propose a system for simultaneous localization and identification using RB as the individual medium. The base station (BS) employs a single-source RB, and each mobile target (MT) is equipped with a signal reflection module. For 3D localization, the BS estimates direction by analyzing RB’s spatial distribution and determines the distance from its frequency components. For identification, the passive MT captures the RB for power and reflects its identity (ID) to BS as spot flicker signals. To demonstrate the working principles, we have developed models for location estimation and ID recognition, as well as the power flow within the RB channel. In implementation, we incorporate a threshold regulation scheme for accurate image signal retrieval, along with an input power distribution model tailored for multi-access scenarios. Through simulating the entire process, we verify the system’s feasibility, including confirming the viability of ID recognition. We also evaluate localization performance, averaging ~ 1 cm at heights of 1.5 m ~ 2.5 m, showing promise for a wide range of potential applications.

To meet the growing demand for joint data and energy transmission, research on wireless information and power transfer is being promoted. The resonant beam enabled information and power transfer (RBIPT), which supports long-distance, high-power, and wide-bandwidth information and power transfer, has sparked widespread interest. The point-to-multipoint RBIPT system shows great promise for enabling simultaneous RBIPT for multiple receivers. However, the enabling system architecture has not been well studied in the literature, which is holding back the system implementation. To solve this problem, we propose a time division multiplexing RBIPT (TDM-RBIPT) system for multiple access, and constract a novel metric to evaluate the information and power transfer performance. We explore the TDM-RBIPT mechanism and design the architectures of the transmitter and the receiver. For the information transfer performance evaluation, we take system latency and throughput into consideration. We propose to estimate the system delay with the martingale theory by modeling the dynamic data processing procedures as Markovian processes with the markov chain monte carlo (MCMC) method. To evaluate the power transmission performance, we consider the transmitter’s power costs and the receivers’ power benefits. Numerical results reveal the effectiveness of the proposed TDM-RBIPT system and validate the accuracy of the proposed metric.

Simultaneous wireless information and power transfer (SWIPT) is a remarkable technology to support both the data and the energy transfer in the era of Internet of Things (IoT). In this article, we proposed a long-range optical wireless information and power transfer system utilizing retro-reflectors, a gain medium, a telescope internal modulator to form the resonant beam, achieving high-power and high-rate SWIPT. We adopt the transfer matrix, which can depict the beam modulated, resonator stability, transmission loss, and beam distribution. Then, we provide a model for energy harvesting and data receiving, which can evaluate the SWIPT performance. Numerical results illustrate that the proposed system can simultaneously supply 0–9 W electrical power and 18-bit/s/Hz spectral efficiency over 20-m distance.

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.

Simultaneous wireless information and power transfer (SWIPT) is a prospective technology that can handle the energy consumption and communication requirements in the Internet of Things. Resonant beam SWIPT (RB-SWIPT) scheme utilizes narrow optical beam as carrier and with spatially separated resonator structure, which can support high power and high rate SWIPT for mobile devices. However, the performance of original RB-SWIPT systems is limited by returning beam interference and transmission loss. In this paper, we propose a RB-SWIPT scheme for transmission-enhanced and anti-interference. The telescope internal modulator (TIM) and second harmonic generator (SHG) are adopted in the proposed system. The TIM can compress beams to reduce the transmission loss. The SHG can generate frequency-doubled beams to avoid interference. To evaluate the proposed system, we establish mathematical models to depict the beam transmission, energy conversion, electric power output and data receiving. Numerical results illustrate that the proposed system can achieve 18 bit/s/Hz spectral efficiency and deliver 8 W power over 100 m distance.

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.

The self-protection resonant beam system (RBS) is a promising long-range and high-power simultaneous wireless information and power transfer (SWIPT) scheme for energy-constrained Internet of Things (IoT) devices, which can achieve safe power and information transfer without mechanical control measures. In the system, a portion of the emitted resonant beam (RB) is reflected and refracted to form protective beams encircling the RB in 360° degrees. In this article, we propose an external object invasion model to evaluate the safety performance of self-protection RBS. With the invading of external object, the field propagation mode of the protective beam shifts, leading to the change of the pumping power threshold of the system, which controls the presence or absence of RB. The numerical results show that the maximal irradiance on invading object is around$0.5 \rm {W/cm^{2}}$at 2-$\rm {m}$transmission distance, with approximately 3-$\rm {W}$output electric power and 12-$\rm {bps/Hz}$spectral efficiency, which is less than the maximum permissible exposure (MPE) requirement for the human skin of$1 \rm {W/cm^{2}}$in the standard “safety of laser products IEC 60825-1.” As a result, the self-protection RBS can achieve high-range, high-power, and human-safe SWIPT.

Long-range, high-power wireless power transfer (WPT) and high-capacity communication can be achieved simultaneously in the resonant beam system (RBS), characterized with spatially separated transmitter and receiver. However, human safety in space transmission cannot be guaranteed if the transmitted power is above a certain level (e.g., several Watts). Thus, in this article, we propose a self-protection RBS, in which the protective beams embrace the energy-transfer resonant beam and are formed by the refracting part of the resonant beam emitted from the output reflector. If an external object comes across the protective beam whose power is very low, the protective beam transmission is cut off. Meanwhile, the resonant beam is interrupted due to the limit of excitation threshold. Then, we reveal the self-protection mechanism based on electromagnetic field propagation, self-mixing interference effect, and output power model. Afterward, we demonstrate that safe energy transfer can be realized by pumping gain medium with a pumping power that is greater than the threshold of the self-protection RBS and less than that of the unprotected RBS. Finally, the numerical results show that about 4.6-W electric power and 12.8 bps/Hz spectral efficiency can be transmitted at 2-m transmission distance safely in the self-protection RBS. Hence, the self-protection RBS provides a new way for safe simultaneous wireless information and power transfer (SWIPT) without mechanical control.

The resonant beam system (RBS) with double spherical retroreflectors presents a potential mobile simultaneous wireless information and power transfer (SWIPT) technology without any tracking control. However, the movement distance and performance are limited due to the effect of spherical aberration. To improve mobility performance in RBS, including movement distance and output power, we adopt an aspherical lens as the focusing mirror in a retroreflector. By shifting the beam phase distribution, the aspherical lens focuses all passing beams, particularly edge beams, on the focal mirror, enhancing energy concentration in the resonant cavity. The beam field propagation through cat’s-eye retroreflectors, gain medium, and air is studied for analyzing the transfer efficiency and output power, and we demonstrate that the axial movement distance in the aspherical resonator is about 7 m, which is more than twice as far away as the spherical resonator. Within a field of view of 3° at a distance of$1~\rm {m}$, the output power of the aspherical resonator is greater than that of the spherical resonator with the same movement angle, up to two times. The maximum output electric power and spectral efficiency are approximately$4~\rm {W}$and$12~\rm {bps/Hz}$, respectively.

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.

High communication speed and sufficient energy supply are the directions of technological development. Energy and information available anywhere and anytime have always been people’s good wishes. On this basis, the resonant beam system (RBS) has demonstrated its unique superiority in meeting the needs for energy and communication. The previous work has mostly focused on the analysis of charging performance of RBS and its steady-state characteristics. In order to analyze the communication performance of RBS more thoroughly, we propose a resonant beam charging and communication (RBCC) system and use the equivalent circuit analysis method to conduct transient analysis on it. The equivalent circuit reveals the dynamic establishment process of the resonant beam from scratch, which facilitates the analysis of the relaxation oscillation process and a deeper understanding of the energy transmission and communication performance. In addition, we explore the energy transmission and communication performance of the RBCC under different energy allocation strategies.

The increasing demands of power supply and data rate for mobile devices promote the research of simultaneous wireless information and power transfer (SWIPT). Optical SWIPT, as known as simultaneous light information and power transfer (SLIPT), has the potential for providing high-capacity communication and high-power wireless charging. However, SLIPT technologies based on light-emitting diodes have low efficiency due to energy dissipation over the air. Laser-based SLIPT technologies need strict positioning accuracy and scanning resolution, which may lead to the increase of costs and complexity. In this paper, we propose a mobile SLIPT scheme based on spatially separated laser resonator (SSLR) and intra-cavity second harmonic generation. The power and data are transferred via separated frequencies, while they share the same self-aligned resonant beam path, without the needs of receiver positioning and beam steering. We establish the analysis model of the resonant beam power and its second harmonic power. Numerical results show that the proposed system can achieve watt-level battery charging power and above 10-bit/s/Hz achievable rate at 6-m distance, which satisfies the requirements of most indoor mobile devices.

The demands for integrated communication and positioning (ICP) have been put forward in Internet of Things. However, the existing ICP systems either face challenges in trade-off between data rates and positioning accuracy or have difficulties in guaranteeing human safety while maintaining excellent performance. In this paper, we propose a monocular resonant beam-based ICP (RB-ICP) design for simultaneously realizing high-rate data transfer and high-accuracy localization while keeping the features as intrinsic safety. Utilizing the high-efficiency transmission channel of resonant beam system and the frequency-doubled beam design, we introduce the communication model without the echo interference issue. Then, we propose a distance estimation model using the phase-shift method with frequency-quadrupled beam design. Next, the angle of arrival estimation can be conducted relying on the energy-concentrated and self-alignment features of resonant beam. The simulation methods including centroid algorithm and signal conversion simulation in a photosensor along with the noise analysis are presented. In numerical analysis, we demonstrate that the positioning error can be less than 1cm and the achievable spectral efficiency can reach 16bit/s/Hz over 2m distance in 15° field of view (FoV). This proposed system enables simultaneous high-rate data transfer and high-accuracy receiver positioning for the applications such as augmented reality/virtual reality (AR/VR).

Optical wireless communication (OWC) meets the demands of the future six-generation mobile network (6G) as it operates at several hundreds of Terahertz and has the potential to enable data rate in the order of Tbps. However, most beam-steering OWC technologies require high-accuracy positioning and high-speed control. Resonant beam communication (RBCom), as one kind of non-positioning OWC technologies, has been proposed for high-rate mobile communications. The mobility of RBCom relies on its self-alignment characteristic where no positioning is required. In a previous study, an external-cavity second-harmonic-generation (SHG) RBCom system has been proposed for eliminating the echo interference inside the resonator. However, its energy conversion efficiency and complexity are of concern. In this paper, we propose an intra-cavity SHG RBCom system to simplify the system design and improve the energy conversion efficiency. We elaborate the system structure and establish an analytical model. Numerical results show that the energy consumption of the proposed intra-cavity design is reduced to reach the same level of channel capacity at the receiver compared with the external-cavity one.

High-power and high-rate simultaneous wireless information and power transfer (SWIPT) becomes more and more important with the development of Internet of Things technologies. Optical SWIPT, also known as simultaneous light information and power transfer (SLIPT), has unique advantages such as abundant spectrum resources and low propagation divergence, compared with radio-frequency (RF) SWIPT. However, optical SWIPT faces many challenges in beam steering and receiver positioning/tracking. Resonant beams generated by spatially separated laser resonators (SSLR) have many advantages, including high power, self-aligned mobility, and intrinsic safety. It has been proposed as the carrier of wireless charging and communication. Using resonant beams, mobile electronic devices can be remotely charged and supported with high-rate data transfer. In this paper, we propose a mobile optical SWIPT system based on asymmetric SSLR and present the system optimization procedure. We also determine the boundary of the charging power and communication rate, and discuss the trade-off between power transfer and information transfer. Numerical results show that both the charging power and the communication rate of the optimized asymmetric system are much higher than those of the symmetric system in the previous work.

Resonant beam communications (RBCom) is capable of providing wide bandwidth when using light as the carrier. Besides, the RBCom system possesses the characteristics of mobility, high signal-to-noise ratio (SNR), and multiplexing. Nevertheless, the channel of the RBCom system is distinct from other light communication technologies due to the echo interference issue. In this article, we reveal the mechanism of the echo interference and propose the method to eliminate the interference. Moreover, we present an exemplary design based on frequency shifting and optical filtering, along with its mathematic model and performance analysis. The numerical evaluation shows that the channel capacity is greater than 15 b/s/Hz.

Simultaneous lightwave information and power transfer (SLIPT) has been regarded as a promising technology to deal with the ever-growing energy consumption and data-rate demands in the Internet of Things. We propose a resonant beam based SLIPT (RB-SLIPT) system, which deals with the conflict of high deliverable power and mobile receiver positioning with the existing SLIPT schemes. At first, we establish a mobile transmission channel model and depict the energy distribution in the channel. Then, we present a practical design and evaluate the energy/data transfer performance within the moving range of the RB-SLIPT. Numerical evaluation demonstrates that the RB-SLIPT can deliver more than 4W charging power and enable 3Gb/s achievable data rate with the moving range of 20° field of view (FOV) over 3m distance. Thus, RB-SLIPT can enable simultaneous high deliverable power and high data rate in mobile scenarios without tracking control.

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.

Wireless energy transfer (WET) has recently emerged as an appealing solution for power supplying mobile/Internet of Things (IoT) devices. As an enabling WET technology, resonant beam charging (RBC) is well documented for its long-range, high-power, and safe “WiFi-like” mobile power supply. To provide high-quality wireless charging services for multiple users in a given region, we formulate a deployment problem of multiple RBC transmitters for balancing the charging fairness and quality of charging service. Based on the RBC transmitter's coverage model and receiver's charging/discharging model, a genetic algorithm (GA)-based scheme and a particle swarm optimization (PSO)-based scheme are put forth to resolve the above issue. Moreover, we present a scheduling method to evaluate the performance of the proposed algorithms. The numerical results corroborate that the optimized deployment schemes outperform uniform and random deployment in 10%-20% charging efficiency improvement.

The vision and requirements of the sixth generation (6G) mobile communication systems are expected to adopt freespace optical communication (FSO) and wireless power transfer (WPT). The laser-based WPT or wireless information transfer (WIT) usually faces the challenges of mobility and safety. We present a mobile and safe resonant beam communication (RBCom) system, which can realize high-rate simultaneous wireless information and power transfer (SWIPT). We propose an analytical model to depict its carrier beam and information transfer procedures. The numerical results show that RBCom can achieve more than 40 mW charging power and 1.6 Gbit/s channel capacity with orthogonal frequency division multiplexing (OFDM) scheme, which can be applied in future scenario where power and high-rate data are simultaneously desired.

The vision and requirements of the sixth generation (6G) mobile communication systems are expected to adopt free-space optical communication (FSO) and wireless power transfer (WPT). The laser-based WPT or wireless information transfer (WIT) usually faces the challenges of mobility and safety. We present here a mobile and safe resonant beam communication (RBCom) system, which can realize high-rate simultaneous wireless information and power transfer (SWIPT). We propose the analytical model to depict its SWIPT procedure. The numerical results show that RBCom can achieve 9 Gbit/s with 200 mW received optical power, which seems to connect the transmitter and the receiver with a mobile “wireless optical fiber”.

Resonant beam charging (RBC) is a promising wireless power transfer technology to provide long-range, high-power, mobile, and safe wireless power for the Internet of Things devices. The point-to-multipoint (PtMP) RBC system can charge multiple receivers simultaneously similar to WiFi communications. To guarantee the quality of charging service (QoCS) for each receiver and maximize the overall earning in the PtMP RBC service, we specify the charging pricing strategy and develop the high priority charge (HPC) scheduling algorithm to control the charging order and power allocation. Each receiver is assigned a priority, which is updated dynamically based on its state of charging (SOC) and specified charging power. The receivers with high priorities are scheduled to be charged in each time slot. We present the pseudo code of the HPC algorithm based on quantifying the receiver's SOC, discharging energy, and various relevant parameters. Relying on simulation analysis, we demonstrate that the HPC algorithm can achieve better QoCS and earning than the round-robin charge scheduling algorithm. Based on the performance evaluation, we illustrate that the methods to improve the PtMP RBC service are: 1) limiting the receiver number within a reasonable range and 2) prolonging the charging duration as long as possible. In summary, the HPC scheduling algorithm provides a practical strategy to maximize the earning of the PtMP RBC service with each receiver's QoCS guarantee.

Resonant beam charging (RBC) is the wireless power transfer (WPT) technology, which can provide high-power, long-distance, mobile, and safe wireless charging for Internet of Things (IoT) devices. Supporting multiple IoT devices charging simultaneously is a significant feature of the RBC system. To optimize the multiuser charging performance, the transmitting power should be scheduled for charging all IoT devices simultaneously. In order to keep all IoT devices working as long as possible for fairness, we propose the first access first charge (FAFC) scheduling algorithm. Then, we formulate the scheduling parameters quantitatively for algorithm implementation. Finally, we analyze the performance of FAFC scheduling algorithm considering the impacts of the receiver number, the transmitting power, and the charging time. Based on the analysis, we summarize the methods of improving the WPT performance for multiple IoT devices, which include limiting the receiver number, increasing the transmitting power, prolonging the charging time, and improving the single-user's charging efficiency. The FAFC scheduling algorithm design and analysis provide a fair WPT solution for the multiuser RBC system.

Power supply for Internet of Things (IoT) devices is one of the bottlenecks in IoT development. To provide perpetual power supply for IoT devices, resonant beam charging (RBC) is a promising safe, long-range, and high-power wireless power transfer solution. How long distance RBC can reach and how much power RBC can transfer? In this paper, we analyze the consistent and steady operational conditions of the RBC system, which determine the maximum power transmission distance. Then, we study the power transmission efficiency within the operational distance, which determines the deliverable power through the RBC energy transmission channel. Based on the theoretical model of the wireless energy transmission channel, we establish a testbed. According to the experimental measurement, we validate our theoretical model. The experiments verify that the output electrical power at the RBC receiver can be up to 2 W. The maximum energy transmission distance is 2.6 m. Both the experimental and theoretical performance of the RBC system are evaluated in terms of the transmission distance, the transmission efficiency, and the output electrical power. Our theoretical model and experimental testbed lead to the guidelines for the RBC system design and implementation in practice.

Resonant beam charging (RBC) can realize wireless power transfer (WPT) from a transmitter to multiple Internet of Things devices via resonant beams. The adaptive RBC (ARBC) can effectively improve its energy utilization. In order to support multiuser WPT in the ARBC system, we propose the time-division multiple access (TDMA) method and design the TDMA-based WPT scheduling algorithm. Our TDMA WPT method has the features of concurrently charging, continuous charging current, individual user power control, constant driving power, and flexible driving power control. The simulation shows that the TDMA scheduling algorithm has high efficiency, as the total charging time is roughly half (46.9% when charging 50 receivers) of that of the alternative scheduling algorithm. Furthermore, the TDMA for WPT inspires the ideas of enhancing the ARBC system, such as flow control and quality of service.

As a long-range high-power wireless power transfer (WPT) technology, resonant beam charging (RBC) can transmit watt-level power over long distance for the devices in the Internet of Things (IoT). Due to its open-loop architecture, RBC faces the challenge of providing dynamic current and voltage to optimize battery charging performance. In RBC, battery overcharge may cause energy waste, thermal effects, and even safety issues. On the other hand, battery undercharge may lead to charging time extension and significant battery capacity reduction. In this paper, we present an adaptive RBC (ARBC) system for battery charging optimization. Based on RBC, ARBC uses a feedback system to control the supplied power dynamically according to the battery preferred charging values. Moreover, in order to transform the received current and voltage to match the battery preferred charging values, ARBC adopts a dc-dc conversion circuit. Relying on the analytical models for RBC power transmission, we obtain the end-to-end power transfer relationship in the approximate linear closed-form of ARBC. Thus, the battery preferred charging power at the receiver can be mapped to the supplied power at the transmitter for feedback control. Numerical evaluation demonstrates that ARBC can save 61% battery charging energy and 53%-60% supplied energy compared with RBC. Furthermore, ARBC has high energy-saving gain over RBC when the WPT is unefficient. ARBC in WPT is similar to link adaption in wireless communications. Both of them play the important roles in their respective areas.

To enable electric vehicles (EVs) to access to the Internet of Intelligent Vehicles (IoIV), charging EVs wirelessly anytime and anywhere becomes an urgent need. The resonant beam charging (RBC) technology can provide high-power and long-range wireless energy for EVs. However, the RBC system is unefficient. To improve the RBC power transmission efficiency, the adaptive RBC (ARBC) technology was introduced. In this paper, after analyzing the modular model of the ARBC system, we obtain the closed-form formula of the end-to-end power transmission efficiency. Then, we prove that the optimal power transmission efficiency uniquely exists. Moreover, we analyze the relationships among the optimal power transmission efficiency, the source power, the output power, and the beam transmission efficiency, which provide the guidelines for the optimal ARBC system design and implementation. Hence, perpetual energy can be supplied to EVs in IoIV virtually.

Internet of Things (IoT) is powering up smart cities by connecting all kinds of electronic devices. The power supply problem of IoT devices constitutes a major challenge in current IoT development, due to the poor battery endurance as well as the troublesome cable deployment. The wireless power transfer (WPT) technology has recently emerged as a promising solution. Yet, existing WPT advances cannot support free and mobile charging like Wi-Fi communications. To this end, the concept of mobile energy transfer (MET) is proposed, which relies critically on a resonant beam charging (RBC) technology. The adaptive (A) RBC technology builds on RBC, but aims at improving the charging efficiency by charging devices at device preferred current and voltage levels adaptively. A mobile ARBC scheme is developed relying on an adaptive source power control. Extensive numerical simulations using a 1000-mAh Li-ion battery show that the mobile ARBC outperforms simple charging schemes, such as the constant power charging, the profile-adaptive charging, and the distance-adaptive charging in saving energy.

Wireless power transfer (WPT) is a promising solution to provide convenient and perpetual energy supplies to electronics. Traditional WPT technologies face the challenge of providing Watt-level power over meter-level distance for Internet of Things (IoT) and mobile devices, such as sensors, controllers, smart-phones, laptops, etc. Distributed laser charging (DLC), a new WPT alternative, has the potential to solve these problems and enable WPT with the similar experience as WiFi communications. In this paper, we present a multimodule DLC system model, in order to illustrate its physical fundamentals and mathematical formula. This analytical modeling enables the evaluation of power conversion or transmission for each individual module, considering the impacts of laser wavelength, transmission attenuation, and photovoltaic-cell (PV-cell) temperature. Based on the linear approximation of electricity-to-laser and laser-to-electricity power conversion validated by measurement and simulation, we derive the maximum power transmission efficiency in closed-form. Thus, we demonstrate the variation of the maximum power transmission efficiency depending on the supply power at the transmitter, laser wavelength, transmission distance, and PVcell temperature. Similar to the maximization of information transmission capacity in wireless information transfer (WIT), the maximization of the power transmission efficiency is equally important in WPT. Therefore, this paper not only provides the insight of DLC in theory, but also offers the guideline of DLC system design in practice.

Distributed laser charging (DLC) is a wireless power transfer technology for mobile electronics. Similar to traditional wireless charging systems, the DLC system can only provide constant power to charge a battery. However, Li-ion battery needs dynamic input current and voltage, thus power, in order to optimize battery charging performance. Therefore, neither power transmission efficiency nor battery charging performance can be optimized by the DLC system. We at first propose an adaptive DLC (ADLC) system to optimize wireless power transfer efficiency and battery charging performance. Then, we analyze ADLC's power conversion to depict the adaptation mechanism. Finally, we evaluate the ADLC's power conversion performance by simulation, which illustrates its efficiency improvement by saving at least 60.4% of energy, comparing with the fixed-power charging system.

Unlicensed LTE system holds high potential to effectively offload data/video traffic from the crowded licensed band. Previous effort of deploying LTE in the unlicensed band (e.g. license-assisted access LAA) relies on one or more LTE carriers in the licensed band, and may not be desired in certain scenarios. This paper studies a new technology of utilizing LTE directly in an unlicensed band, without any assistance from a licensed band, i.e. the stand-alone unlicensed LTE, for which we term SAiL. Various SAiL design considerations are discussed and several technologies are proposed to enable a success SAiL.

As a promising technique, cooperative relaying has attracted more and more attention from academia and industry recently. In this paper, we investigate the scheme of Decode-and-Forward Two-way Relaying (DF-TWR) relying on a cross-layer design, which combines adaptive Network-coded Modulation (NCM) at the physical layer and truncated Automatic Repeat reQuest (ARQ) at the data link layer. The relay node utilizes Network-Coded Quadrature amplitude modulation (NC-QAM) where NCM imposes only a modest signal-to-noise ratio (SNR) degradation on the single-link QAM performance. Additionally, we derive the achievable spectral efficiency in closed-form for transmission over Rayleigh fading channels. It is shown that this combination of adaptive NC-QAM and truncated ARQ substantially improves the system's throughput compared to the schemes operating without ARQ.

A cross-layer design is developed for quality-of-service (QoS) guaranteed traffic. The proposed design jointly exploits the error-correcting capability of the truncated automatic repeat request (ARQ) protocol at the data link layer and the adaptation ability of the adaptive modulation and coding (AMC) scheme at the physical layer to optimize the system performance. The queuing behavior induced by both the truncated ARQ protocol and the AMC scheme is analyzed with an embedded Markov chain. Analytical expressions for performance metrics such as packet loss rate, throughput and average packet delay are derived. Using these expressions, a constrained optimization problem is solved numerically to jointly determine the retry limit for the truncated ARQ protocol as well as the prescribed packet error rate for the AMC scheme so that the overall system throughput is maximized under the specified QoS constraints.

Scheduling plays an important role in providing quality of service (QoS) support for multimedia networks. We propose a cross-layer scheduler at the medium access control (MAC) layer for multiple connections with diverse QoS requirements, where each connection employs adaptive modulation and coding (AMC) scheme at the physical (PHY) layer. Each connection is assigned a priority, which is updated dynamically based on its channel and service quality; and the connection with the highest priority is scheduled each time. Our scheduler provides diverse QoS guarantees, uses the wireless bandwidth efficiently and enjoys flexibility, scalability and low implementation complexity. The performance of our scheduler is evaluated via simulations in the IEEE 802.16 standard setting.

Providing guaranteed quality-of-service (QoS) for multimedia applications over wireless fading channels is challenging. To this end, we develop a cross-layer design for multiuser scheduling at the data link layer, with each user employing adaptive modulation and coding (AMC) at the physical layer. By classifying users into: QoS-guaranteed and best-effort users, the proposed scheduler enables prescribed QoS guarantees and efficient bandwidth utilization simultaneously. Furthermore, our cross-layer scheduler enjoys low-complexity implementation and analysis, provides service isolation and scalability, decouples delay from dynamically-scheduled bandwidth, and is backward compatible with existing separate-layer designs. Accuracy of the performance analysis is verified by simulations and pertinent robustness issues are briefly discussed. Numerical examples illustrate the steady-state statistical performance for a single and multiple users, as well as the asymptotic behavior for a large number of users.

Assuming there are always sufficient data waiting to be transmitted, adaptive modulation and coding (AMC) schemes at the physical layer have been traditionally designed separately from higher layers. However, this assumption is not always valid when queuing effects are taken into account at the data link layer. In this paper, we analyze the joint effects of finite-length queuing and AMC for transmissions over wireless links. We present a general analytical procedure, and derive the packet loss rate, the average throughput, and the average spectral efficiency (ASE) of AMC. Guided by our performance analysis, we introduce a cross-layer design, which optimizes the target packet error rate of AMC at the physical layer, to minimize thpacket loss rate and maximize the average throughput, when combined with a finite-length queue at the data link layer. Numerical results illustrate the dependence of system performance on various parameters, and quantify the performance gain due to cross-layer optimization. Our focus is on the single user case, but we also discuss briefly possible applications to multiuser scenarios.

Providing guaranteed quality of service (QoS) with efficient bandwidth utilization over wireless fading channels is challenging. In this paper, we derive the throughput, the packet loss rate and the average delay of an end-to-end wireless link, where the transmitter relies on adaptive modulation and coding (AMC) at the physical layer while accounting for finite-length buffer effects at the data link layer. Guided by our cross-layer performance analysis, we develop a simple procedure to determine the minimal required bandwidth, which guarantees the prescribed QoS over the wireless link.

We study a wireless access system with adaptive modulation and coding (AMC) at the physical layer, finite-length queuing at the data link layer and a TCP protocol at the transport layer. We analyze the end-to-end TCP performance via a fixed-point procedure that effectively couples TCP with the AMC-based wireless link. Guided by the performance analysis, we present a simple cross-layer design, which optimizes the target packet error rate in AMC at the physical layer, so that the TCP throughput at the transport layer is maximized.

Wired-wireless multimedia networks require diverse quality-of-service (QoS) support. To this end, it is essential to rely on QoS metrics pertinent to wireless links. In this paper, we develop a cross-layer model for adaptive wireless links, which enables derivation of the desired QoS metrics analytically from the typical wireless parameters across the hardware-radio layer, the physical layer and the data link layer. We illustrate the advantages of our model: generality, simplicity, scalability and backward compatibility. Finally, we outline its applications to power control, TCP, UDP and bandwidth scheduling in wireless networks.

We developed a cross-layer design which combines adaptive modulation and coding at the physical layer with a truncated automatic repeat request protocol at the data link layer, in order to maximize spectral efficiency under prescribed delay and error performance constraints. We derive the achieved spectral efficiency in closed-form for transmissions over Nakagami-m block fading channels. Numerical results reveal that retransmissions at the data link layer relieve stringent error control requirements at the physical layer, and thereby enable considerable spectral efficiency gain. This gain is comparable with that offered by diversity, provided that the maximum number of transmissions per packet equals the diversity order. Diminishing returns on spectral efficiency, that result when increasing the maximum number of retransmissions, suggest that a small number of retransmissions offers a desirable delay-throughput tradeoff, in practice.

We consider the problem of embedded image transmission with feedback of channel state information (CSI) and retransmission request. Adaptive modulation is employed to improve the spectral efficiency. Constrained retransmission is employed to provide reliable packet transmission with limited delay. Performance analysis and numerical results over Nakagami block fading channels are provided for the transmission system with statistical or instantaneous CSI at the transmitter. The results show that CSI at the transmitter is very important for adaptive modulation/coding over fading channels.