A Novel Threshold Scheme for Reducing Spatial Intersymbol Interference in Vehicular Visible Light Communication Based on Image Sensors

LEDs can be used to communicate under the premise of satisfying illumination, which lays the groundwork for visible light communication (VLC). The application of outdoor VLC has drawn more attention, especially the application of vehicle-to-vehicle (V2V) which can significantly improve traffic safety and information transmission efficiency. The image sensor has the characteristics of spatial separation, easily realizes MIMO, and does not need to be strictly aligned with the transmitter, so it is especially suitable for vehicular VLC. However, because of the diffuseness of LED and the small pixel size of the image sensor, it is easy to produce the blooming effects and interfering among symbols. When decoding at the receiving terminal, it will judge the status Off of LEDs to be the status On. By analysing the blooming effects caused by surrounding LEDs, a novel threshold scheme is proposed in this paper according to the probability distribution of the sum of the optical power of the LED itself and after interference. Experiments show that the proposed method has advantages in improving BER compared with the expected threshold method and the average method, especially with long-distance communication (70 m), and the BER has been improved by 57% and 39%, respectively.

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An ANN-Based Adaptive Predistorter for LED Nonlinearity in Indoor Visible Light Communications

Electronics ◽

10.3390/electronics10080948 ◽

2021 ◽

Vol 10 (8) ◽

pp. 948

Author(s):

Jenn-Kaie Lain ◽

Yan-He Chen

Keyword(s):

Visible Light ◽

Light Emitting Diode ◽

Optical Power ◽

Visible Light Communication ◽

Universal Function ◽

Visible Light Communications ◽

Least Mean Square ◽

Training Sequences ◽

Led Nonlinearity ◽

Electrical Source

By modulating the optical power of the light-emitting diode (LED) in accordance with the electrical source and using a photodetector to convert the corresponding optical variation back into electrical signals, visible light communication (VLC) has been developed to achieve lighting and communications simultaneously, and is now considered one of the promising technologies for handling the continuing increases in data demands, especially indoors, for next generation wireless broadband systems. During the process of electrical-to-optical conversion using LEDs in VLC, however, signal distortion occurs due to LED nonlinearity, resulting in VLC system performance degradation. Artificial neural networks (ANNs) are thought to be capable of achieving universal function approximation, which was the motivation for introducing ANN predistortion to compensate for LED nonlinearity in this paper. Without using additional training sequences, the related parameters in the proposed ANN predistorter can be adaptively updated, using a feedback replica of the original electrical source, to track the LED time-variant characteristics due to temperature variation and aging. Computer simulations and experimental implementation were carried out to evaluate and validate the performance of the proposed ANN predistorter against existing adaptive predistorter schemes, such as the normalized least mean square predistorter and the Chebyshev polynomial predistorter.

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