Research On Duplex Visible Communication System Based On DSP

In recent years,with the continuous development of technology and the popularity of various wireless digital terminals,people have put forward higher and higher requirements for the transmission rate and capacity of wireless communication systems.After decades of development,traditional radio frequency communication technology has entered the 5G era.With the continuous improvement of communication rate,the shortage of radio spectrum resources and the increasingly high cost of base station construction have increasingly become an important factor limiting its development.Visible band,because of its huge potential communication capacity and the wide application of LED lighting equipment,has attracted widespread attention of researchers.As a supplementary means of radio frequency communication in the field of short-distance communication,visible light communication?VLC?technology has its unique advantages in many fields such as intelligent lighting,intelligent transportation,indoor positioning and photon payment,and has become a hot research direction.In this paper,we design and implement a duplex visible communication system based on DSP and OFDM?Orthogonal Frequency Division Multiplexing?by studying the relevant theory of visible communication.The specific work of this paper is as follows:At first this paper introduce the key technology principle of visible light communication system.Then the structure and modulation characteristics of LED light source are analyzed,and the principle of OFDM technology is expounded.Then we study QAM?Quadrature Amplitude Modulation?modulation technology and channel estimation technology,and further give the basic flow chart of visible optical communication system based on OFDM technology.Secondly,the hardware circuit of visible light communication system is designed and implemented,including the minimum system of DSP28335,transmitter module,receiver module and human-computer interaction module.The transmitter module is mainly composed of DA conversion circuit,DC bias circuit and LED drive circuit.The receiver circuit includes photoelectric detection module,single-ended differential circuit and AD acquisition circuit.Then,we introduce the software design and implementation of visible light communication system.We introduces the working mode and interface of this system,and designs the physical data frame structure based on OFDM system model.Then the design and debugging of QAM modulation/demodulation module,IFFT/FFT algorithm module and channel estimation algorithm module are given.Finally,the duplex visible communication system based on OFDM is tested and analyzed,including transmission distance,transmission rate,bit error rate and system stability of the system.The test results indicate that with 16QAM modulation mode,the transmission distance of the system is about 1.0 m,the communication rate can reach 1.9 Mbps,the bit error rate is less than 10^-3,and the whole system can work steadily in 5 hours.Under the normal working conditions,the system can send and receive text information accurately.