Research On Equalization Technology And FPGA Implementation In Visible Light Communication

Visible light communication technology,as a new type of wireless communication technology,has become a research hotspot in the field of communication because of its advantages of green environmental protection and no spectrum authentication.At the same time,people have put forward higher requirements for the communication distance and communication rate in visible light communication.However,the limited bandwidth of LEDs severely restricts the improvement of the communication rate.In addition to improving the components in the communication system,using complex high-order modulation,equalization is the most essential technique aimed at the non-ideal transmission characteristic of the channel.By compensating the channel,optimizing the overall transmission characteristic of the system,the communication rate can be improved.Therefore,equalization technology has high research value and research significance in visible light communication.Based on this,this paper focuses on the equalization technology in visible light communication,and through theoretical analysis and simulation,completed the adaptive equalizer design and FPGA implementation suitable for the visible light communication system.The main research contents of this paper are as follows:(1)Research the channel model and equalization principle in visible light communication.We analyzed the key components of the visible light communication channel:LED and a photoelectric receiver.And mainly focused on the frequency response model of the LED,which is the main reason for the narrow bandwidth of the channel in visible light communication.Besides,we measured the channel model in actual visible light communication through experiments,which can be equivalent to a low communication channel.Finally,we analyzed the causes of inter-symbol interference in a digital baseband transmission system with a limited frequency band,and the principle of the equalizer to eliminate inter-symbol interference.(2)Research the adaptive equalization algorithm in visible light communication.We analyzed the principle of adaptive equalization.Based on the introduction of the Wiener filter and the steepest descent method,we proved the existence of the Wiener solution and derive the Wiener solution.Also,we introduced the equalizer with two structures of linear horizontal and decision feedback.In the linear horizontal equalizer,we discuss the LMS algorithm,RLS algorithm and the improved algorithm of LMS.At the same time,we acquire the OOK signal in the actual visible light communication system,take Matlab offline simulation with different equalization structures and equalization,and compare the advantages and disadvantages of several algorithms.Finally,we determine an equalizer design scheme suitable for this system and obtain Optimal parameters under this algorithm.(3)Research the theory of the blind equalization algorithm in visible light communication.We analyze the principle of blind equalization,the process of Bussgang-type blind equalization and three typical applications.And further,demonstrate the constant modulus equalization(CMA)algorithm which is most widely used.Besides,we verified the applicability of the blind equalization algorithm in this system through Matlab simulation.At the same time,we also analyze the improvement of the performance of the variable step algorithm in blind equalization.(4)Complete FPGA design of adaptive equalizer in visible light communication.Based on the above equalizer design,we designed and implemented the adaptive equalizer in FPGA.And we proved the correctness of the FPGA design with offline data simulation according to the existing conditions.The simulation results show that the 50Mbps OOK signal is transmitted in visible light communication,and the bit error rate can be reduced to 8 × 10-4 through the adaptive equalizer.