| Visible light communication is a wireless communication technology that uses the visible light emitted by the LED light source as the information carrier and the free space within the illumination range as the transmission medium.However,since visible light communication needs to meet the requirements of communication and lighting at the same time,it is necessary to perform certain dimming processing on the transmitted signal.The main idea of the digital dimming method is to adjust the duty cycle of the digital signal it transmits to achieve a balanced distribution of "0" and "1" elements.There will be a problem of chromaticity shift that affects the lighting quality,and the digital dimming technology is very suitable for the fast on-off characteristics of LEDs.In the digital dimming technology,the coding technology can flexibly adjust the duty cycle of the digital signal without changing the structure of the transmitter and receiver.The run-length limit(RLL)coding is due to its uniformity The distribution characteristics of "0" and "1" have been suggested by the IEEE in the related patents of visible light communication,and the improved channel code after the cascade can also improve the error performance of the communication system.The improved channel code techniques currently used in visible light communication include RS codes,Turbo codes and LDPC codes.As an emerging channel code technology,Polar codes is the only channel code technology that has been mathematically proven to reach the Shannon limit in B-DMC channels,and has been applied to 5G communications.However,the application of Polar codes in visible light communication is still in its infancy and has great research value and room for improvement.This paper takes this as a starting point,and conducts further research on the coding and decoding technology of Polar codes for dimming in visible light communication.This paper firstly introduces the domestic and foreign status of visible light communication and Polar codes,and expounds the domestic and foreign research status of Polar codes in visible light communication.After that,the basic principle and system structure of visible light communication for indoor environment are expounded,and its channel model is modeled and analyzed.Then the channel polarization principle,information bit selection method and decoding algorithm of Polar codes are researched and analyzed in detail,and several commonly used information bit selection methods and decoding algorithms are given.And its performance under indoor visible light communication is simulated and analyzed.Based on the research and analysis of visible light communication and Polar codes,a cascaded Polar-RLL codes coding method suitable for dimming control is proposed.After cascade coding,the dimming value of 50% duty cycle is satisfied,and the system can pass In order to achieve a wider range of dimming values by the insertion of Polar codes frozen bit punching and compensation symbols,the article gives the recommended range of dimming values and corresponding parameter settings,and conducts a variety of dimming values with the same type of scheme.And the simulation analysis of code length,this method is better than the same type of scheme.Finally,in order to solve the iterative decoding problem of concatenated coding,a concatenated polar-RLL codes joint optimization decoding method based on the Polar codes SCAN decoding algorithm is proposed,and the scatter EXIT graph is used in the simulation analysis to determine the decoding convergence.Threshold,which gives the performance under different iterations,the performance difference with the same type,and the theoretical computational complexity. |
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