Visible light communication (VLC) holds the promise of a high-speed wireless network for indoor applications and competes with 5G radio frequency (RF) system. Although the breakthrough of gallium nitride (GaN) based micro-light-emitting-diodes (micro-LEDs) increases the -3dB modulation bandwidth exceptionally from tens of MHz to hundreds of MHz, the light collected onto a fast photo receiver drops dramatically, which determines the signal to noise ratio (SNR) of VLC. To fully implement the practical high data-rate VLC link enabled by a GaN-based micro-LED, it requires focusing optics and a tracking system. In this paper, we demonstrate an active on-chip tracking system for VLC using a GaN-based micro-LED and none-return-to-zero on-off keying (NRZ-OOK). Using this novel technique, the field of view (FOV) was enlarged to 120° and data rates up to 600 Mbps at a bit error rate (BER) of 2.1×10 were achieved without manual focusing. This paper demonstrates the establishment of a VLC physical link that shows enhanced communication quality by orders of magnitude, making it optimized for practical communication applications.
Lithium-ion battery as an efficient, sustainable, and clean energy for electric vehicles (EVs) and smart devices becomes more popular with the worldwide demand for reduction of greenhouse gas emission. In all kinds of applications, an accurate real-time estimation for state of charge (SOC) of battery is necessary. Some conventional methods usually need to sample both battery currents and voltages. This article presents a novel SOC estimation algorithm without current detection. This algorithm just acquires the port voltages of cell to calculate the open-circuit voltage (OCV) which is related to SOC. By extracting a large number of battery voltages based on a step response, some important parameters that can track battery working process are determined. In order to verify the algorithm feasibility and accuracy, it has been tested on a commercial common field-programmable gate array (FPGA) in different application conditions. The algorithm accuracy is mainly limited by model accuracy and sampling sensor accuracy. The maximum error between ideal SOC and calculated SOC by this algorithm is within 4%, and the mean error is about 0.99%. So, this high-feasibility, accredited accuracy, easy integration, and low-cost solution has bright potential in smarter future.
Underwater wireless optical communications (UWOC) are considered an emerging high-speed wireless network for underwater applications and compete with underwater radio frequency (RF) communications and underwater acoustic communications (UAC). Even though the utilization of laser diodes (LDs) enhances the -3dB modulation bandwidth extraordinarily from a few tens of MHz to GHz, LDs have the features of high collimation and narrow spectrum. Without the point-to-point optical alignment, the performance of the LD-based UWOC system drops exponentially because the received optical power determines the signal-to-noise ratio (SNR) of the UWOC system. To achieve a high-performance and reliable UWOC link based on LDs requires focusing optics and an alignment system. In this paper, we demonstrated a CMOS monolithic photodetector with a built-in 2-dimensional light direction sensor for the UWOC link by using a 450 nm LD and none-return-to-zero on-off keying (NRZ-OOK) modulation method. Employing this innovative technique, the field of view (FOV) was enlarged to 120°, and data rates up to 110 Mb/s at a bit error rate (BER) of 2.3×10−10 were obtained. The establishment of a proposed UWOC physical link showed enhanced communication performance for more practical and robust wireless communication applications.
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