Research On Joint Fast Blind Likelihood Detection Algorithms In Visible Light Communication

Visible light communication is a communication technology that uses the beam of illumination to transmit information.It has a wide bandwidth and high transmission rate.What's more,VLC not only conforms to the concept of green transportation and fast travel in intelligent transportation,but also meets the needs of contemporary communication.Therefore,it is a necessary technology for the future development of civilized cities.However,due to the complex outdoor environment,the LED traffic light will be affected by atmospheric turbulence during transmission,resulting in attenuation of the optical pulse energy and shortened communication distance.At the same time,other light sources such as sunlight will also generate strong background radiation at the receiving end,causing the bit error rate to rise.Therefore,this paper aims to analyze the influence of atmospheric turbulence and background light on LED traffic light communication system based on pulse modulation technology,atmospheric turbulence theory and background light theory to improve the quality of system communication.Then to study measures to reduce turbulence and background light.The main work of this paper is as follows:Firstly,we introduced the components of outdoor visible light communication.It includes an optical signal transmitting end,a turbulent and background optical channel,and a receiving end.We described the factors affecting the visible light communication system,including weather conditions,turbulence and background light.What's more,we also introduce the trend of LED light pulse in turbulent and background light environment.Then,we use random phase screen to simulate atmospheric turbulence,and use blackbody radiation function to simulate the background noise generated by sunlight at the receiving end.Secondly,we introduced the basic principles of fixed threshold detection,mean detection and traditional blind likelihood detection in detail.In addition,we had proposed an improved blind likelihood detection algorithm.This algorithm combines the PPM frame header of the transmitting end and implements the method of frame detection grouping and constrained search at the receiving end,which not only avoids the flat phenomenon,reduces the complexity,but also reduces the pair.The dependence of the channel statistical characteristics eliminates the noise value close to the signal value and suppresses the effects of atmospheric turbulence and background light,thereby improving the detection accuracy.Finally,the effectiveness of the algorithm is verified by simulation.The simulation results show that the algorithm effectively solves the plate problem and reduces the complexity.When the turbulence intensity,background light intensity,transmission distance and luminous intensity change,compared with other detection algorithms,the improved algorithm has the lowest system error rate,and is more suitable for outdoor visible light communication and improves system performance.Thirdly,we introduced the principle of the power inversion algorithm and the receiving model of uniform line array.We established a visible light communication system between LED traffic lights and vehicles under strong background light,and introduced the power inversion algorithm into the system to suppress the influence of strong background light.We analyzed and compared the effects of the number of receivers and the intensity of the background light on the power inversion algorithm.We also analyzed and compared the bit error rate of the system under different signal-to-interference ratios.The simulation results show that the power inversion algorithm can suppress the strong background light by finding the optimal weights,which makes the receiver array produce deep nulling in the direction of strong background light and keep the gain constant in the direction of signal.When the number of array elements is 3,the power inversion algorithm can generate a deep null in the direction of strong background light,the gain in the signal direction is almost constant,and the cost is the lowest,which is favorable for promotion.When the signal-to-interference ratio is less than-15,the system error rate is always at 10^-4,enabling high-quality transmission.Finally,the experimental platform of the LED traffic light communication system based on PPM modulation is built by FPGA in the outdoor turbulent environment.The improved blind likelihood detection algorithm and the mean detection algorithm are used to recover the signals.We compared the bit error rate of the two detection algorithms at different distances.The experimental results show that the improved blind likelihood detection algorithm has better suppression of turbulence.