Mr. Shi Zhang Profile

Shi Zhang

at Tsinghua Univ.

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Publications (3)

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Proceedings Article | 24 November 2021 Paper

On BER performance for misaligned underwater wireless MISO laser links

Sen Du, Shi Zhang, Shuang Jin, Jinguo Quan, Yuhan Dong

Proceedings Volume 12066, 120661O (2021) https://doi.org/10.1117/12.2607167

KEYWORDS: Light sources, Receivers, Wireless communications, Scattering, Photons, Optical transfer functions, Optical alignment, Light scattering, Laser sources, Systems modeling

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Underwater wireless optical communication (UWOC) highly depends on the alignment between the receiver and transmitter in realization. In practice, the facts that laser sources have narrow divergence angles, water body suﬀers from ﬂuctuation, and precise positioning is very diﬃcult in the underwater environment bring great challenges to the link alignment as well as practical implementation. However, due to the intrinsic optical properties of seawater, photons will be scattered during the transmission process, resulting in the diﬀusion of light, which relaxes the requirements for strict alignment. Inspired by the uniform spatial distribution of the multi-source arrays with a close spacing, in this paper, we investigate the bit error rate (BER) performance of the multi-input single-output (MISO) laser links in the presence of receiver oﬀset. Based on a system model by considering scattering and absorption eﬀects and noises including background noise and blackbody radiation as well as OOK signaling and an ideal photon counter, we derived a closed-form expression of relationship among BER, transmit power, link range, receiver aperture and oﬀset distance, which is veriﬁed by Monte Carlo simulations. Numerical results suggest that, regardless of water types, linear light source arrays parallel to the oﬀset direction can improve the tolerance of receiver oﬀset with speciﬁc transmit power and link range for reliable communications. On this basis, we compared the anti-oﬀset performance in the case of diﬀerent inter-spacings of light source arrays such as dual-source and three-source schemes and also derived the optimal inter-spacing for light source to maximize the acceptable oﬀset distance with reliable communication for dual-source links.

Proceedings Article | 4 December 2020 Paper

Spatial channel model for underwater wireless optical communication links

Sen Du, Shi Zhang, Shuang Jin, Jinguo Quan, Yuhan Dong

Proceedings Volume 11617, 116173U (2020) https://doi.org/10.1117/12.2585523

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In order to evaluate the performance of underwater wireless optical communication (UWOC) systems, it is of significance to fully understand the impact of spatial diffusion of light beams. Meanwhile, simple and highly adaptable spatial channel modeling is also necessary and essential for performance evaluation and system design. In this paper, we focus on the spatial channel modeling and, in particular, quantify the photon spatial distributions for different water types, link distances, and transmitter/receiver characteristics. Via using the Gaussian distribution to complete the fitting, we have proposed a simple expression to describe the spatial irradiance distribution. The numerical results have shown that the proposed spatial channel model for UWOC systems agrees well with the Monte Carlo simulation results in terms of mean square error (MSE) with or below the order of 10⁻⁷ in both turbid coastal and harbor water and demonstrates a high adaptability to the link conditions. Furthermore, on this basis, we extend the study from single source to multi-source scenario and derive the corresponding expression of spatial channel model. Considering the integrity of closely spaced multi-source array, the multi-source model has been further simplified by two-dimensional Gaussian fitting.

Proceedings Article | 4 December 2020 Paper

A new method for calculating the precise electrical characteristics of quantum dot micro-LED

Keming Ma, Zixian Wei, Shi Zhang, Zhiyuan Cao, Lei Wang, Chien-Ju Chen, Meng-Chyi Wu, H. Fu, Yi Luo, Lai Wang, Yuhan Dong

Proceedings Volume 11617, 116173S (2020) https://doi.org/10.1117/12.2585520

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In this paper, we have fabricated and packaged a blue micro-LED with a diameter of 50-μm based on a single layer of InGaN QD micro-LED and present a new method to calculate the junction capacitance of micro-LEDs under forward voltage using the forward AC small-signal method. The results confirm that QD micro-LEDs, like commercial LEDs, show obvious negative capacitances at low frequencies and large voltages. The values of negative capacitance at high frequency and low voltage are so small and can be ignored, or there is no negative capacitance. We have also concluded the empirical expressions for negative capacitance, voltage, and frequency.

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