Mr. Zuhang Geng Profile

Zuhang Geng

at Tsinghua Univ.

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Proceedings Article | 24 November 2021 Paper

Generalized adaptively biased optical OFDM for optical wireless communications

Zuhang Geng, Fan Yang, Zhide Li, Yuhan Dong

Proceedings Volume 12066, 120661H (2021) https://doi.org/10.1117/12.2606984

KEYWORDS: Orthogonal frequency division multiplexing, Adaptive optics, Wireless communications, Berkelium, Receivers, Radio optics, Data communications, Telecommunications, Signal to noise ratio, Modulation

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Orthogonal frequency division multiplexing (OFDM) has been applied to optical wireless communication to achieve high data rates and wide bandwidth and solve the issues of inter-symbol interference (ISI). Due to the non-negative and real-valued characteristics of intensity modulation/direct detection (IM/DD) signaling for optical wireless communication systems, some optical OFDM schemes have been proposed to reach the requirements. Among these optical OFDM schemes, adaptively biased OFDM (ABO-OFDM) reserves 1/4 of the subcarriers and utilizes Hermitian symmetry to generate non-negative and real values after invert fast Fourier transformation (IFFT) and adding bias in time domain. In this paper, we extend the original ABO-OFDM scheme and proposed a generalized ABO-OFDM scheme in which 1/m subcarriers are reserved for any positive integer m. It is demonstrated that the bias added in time domain can be counteracted exactly in frequency domain, which means it has lower implementation complexity at the receiver than most of the other optical OFDM schemes. This generalized ABO-OFDM scheme has higher frequency efficiency and lower peak-to-average power ratio (PAPR) than asymmetrically clipped optical OFDM (ACO-OFDM) and higher power efficiency than direct current biased optical OFDM (DCO-OFDM). We also evaluate the impact of parameter m on system performance in terms of PAPR and bit error rate (BER). Consider the comparison with other optical OFDM schemes and the tradeoff above-mentioned, the generalized ABO-OFDM is a potential scheme to facilitate optical wireless communications with a flexible parameter m.

Proceedings Article | 4 December 2020 Paper

Channel estimation for OFDM-based underwater wireless optical communication systems

Yafei Ma, Zuhang Geng, Shuang Jin, Jinguo Quan, Yuhan Dong

Proceedings Volume 11617, 116173W (2020) https://doi.org/10.1117/12.2585526

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Underwater wireless optical communications (UWOC) could transmit data using blue or green light beams with high data rate and safety in a relatively short range. OFDM based UWOC systems are able to further increase data rate, however, highly dependent on the accuracy of channel estimation. In this paper, we consider the channel estimation problem for OFDM based UWOC systems. We firstly apply Monte Carlo simulation to obtain the channel impulse response (CIR) of UWOC links under different conditions to facilitate the design of the subsequent OFDM systems. Secondly, we evaluate the pilot-based least squares (LS), and two types discrete Fourier transform (DFT) channel estimation methods and compare their performance. Numerical results have suggested that the temporal pulse spread strongly degrades the performance of the channel estimation. These two DFT methods especially DFT channel estimation with noise threshold method achieved the best performance among these prior works. While for the signal-to-noise ratio (SNR) less than 10 dB, the performance of DFT with noise threshold method is still poor. To solve this problem, we propose a new channel estimation approach of DFT with adaptive noise threshold (DFT-ANT) which adaptively adjusts the noise threshold based on SNR, and analyze its complexity and normalized mean square error (NMSE) performance in underwater environment. Numerical results have validated the proposed approach which outperforms existing channel estimation methods especial DFT with noise threshold method in terms of accuracy for various water types.

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