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

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

Binocular Localization Using Resonant Beam

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 target. The binocular method is combined with RBS to obtain the three-dimensional (3-D) coordinates of the target 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 numerical results show an outstanding performance of centimeter level accuracy (i.e., $<5\mathrm{cm}$ in $0.4\mathrm{m}$ width and $0.4\mathrm{m}$ length effective range at $1\mathrm{m}$ vertical distance, $<13\mathrm{cm}$ in $0.6\mathrm{m}$ width and $0.6\mathrm{m}$ length effective range at $2\mathrm{m}$ vertical distance), which applies to indoor scenarios.

High-Power and High-Capacity Mobile Optical SWIPT

The increasing demands of power supply and data rate for mobile devices promote the research of simultaneous information and power transfer (SWIPT). Optical SWIPT, as known as simultaneous light information and power transfer (SLIPT), can provide high-capacity communication and high-power charging. However, light emitting diodes (LEDs)-based SLIPT technologies have low efficiency due to energy dissipation over the air. Laser-based SLIPT technologies face the challenge in mobility, as it needs accurate positioning, fast beam steering, and real-time tracking. In this paper, we propose a mobile SLIPT scheme based on spatially separated laser resonator (SSLR) and intra-cavity second harmonic generation (SHG). 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. We also evaluate the system performance on deliverable power and channel capacity. Numerical results show that the proposed system can achieve watt-level battery charging power and above 20-bit/s/Hz communication capacity over 8-m distance, which satisfies the requirements of most indoor mobile devices.

Mobile Wireless Power Transfer Using A Self-Aligned Resonant Beam

Wireless charging for a moving electronic device such as smartphone is extremely difficult. Owing to energy dissipation during wireless transmission, sophisticated tracking control is typically required for simultaneously efficient and remote energy transfer in mobile scenarios. However, reaching the necessary tracking accuracy and reliability is very hard or even impossible. Here, inspired by the structures of optical resonator and retroreflector, we develop a self-aligned light beam system for mobile energy transfer with simultaneous high efficiency and long distance by exploring radiative resonances inside a double-retroreflector cavity. This system eliminates the requirement for any tracking control. To reduce transmission loss in mobile scenarios, we combine the advantages of energy-concentration using an optical resonant beam and self-alignment using a double-retroreflector cavity. We demonstrate above 5-watt optical power transfer with nearly 100% efficiency to a few-centimeter-size receiver for charging a smartphone, which is moving arbitrarily in the range of 2-meter distance and 6-degree field of view from the transmitter. This charging system empowers a smartphone in mobile operation with unlimited battery life, where cable charging is no longer needed. We validate the simultaneous high efficiency and long distance of the mobile energy transfer system through theoretical analyses and systematic experiments.

Mobility-Enhanced Simultaneous Lightwave Information and Power Transfer

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 (IoT). We propose a resonant beam based SLIPT system (RB-SLIPT), 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 5 W charging power and enable 1.5 Gbit/s achievable data rate with the moving range of 20-degree field of view (FOV) over 3 m distance. Thus, RB-SLIPT can simultaneously provide high-power energy and high-rate data transfer, and mobile receiver positioning capability.

Lightweight Mask R-CNN for Long-Range Wireless Power Transfer Systems

Resonant Beam Charging (RBC) is a wireless charging technology which supports multi-watt power transfer over meter-level distance. The features of safety, mobility and simultaneous charging capability enable RBC to charge multiple mobile devices safely at the same time. To detect the devices that need to be charged, a Mask R-CNN based dection model is proposed in previous work. However, considering the constraints of the RBC system, it's not easy to apply Mask R-CNN in lightweight hardware-embedded devices because of its heavy model and huge computation. Thus, we propose a machine learning detection approach which provides a lighter and faster model based on traditional Mask R-CNN. The proposed approach makes the object detection much easier to be transplanted on mobile devices and reduce the burden of hardware computation. By adjusting the structure of the backbone and the head part of Mask R-CNN, we reduce the average detection time from $1.02\mbox{s}$ per image to $0.6132\mbox{s}$, and reduce the model size from $245\mbox{MB}$ to $47.1\mbox{MB}$. The improved model is much more suitable for the application in the RBC system.