Research On Visible Light Communication System Based On OFDM

With the wide spread and popularization of light-emitting diodes,visible light communication technology emerges as the times require.Traditional radio frequency communication technology is facing many challenges,such as the increasing shortage of communication spectrum resources,the high transmission power which leads to too much energy loss and insufficient security.With the increasing demand for the transmission capacity and transmission rate of wireless communication system in modern society,the challenges it faces are also growing.Visible light communication technology,as a new wireless communication technology,works in the visible band.It has abundant spectrum resources and has not been developed at present.It also has great potential to use existing power line networks and LED devices to reduce development costs with the available large-scale construction of visible light communication network.Orthogonal frequency division multiplexing?OFDM?is a multi-carrier modulation technology,which has been widely used in visible light communication systems in recent years.OFDM technology can effectively reduce the interference between sub-channels caused by signal multipath transmission.Compared with other modulation methods,this technology can also use the system frequency band more effectively and improve the data transmission capability of the whole communication system.In this paper,a point-to-point single-ended visible communication system based on DSP and OFDM technology is designed and implemented by studying the theory of visible light communication.The work of this paper is as follows:Firstly,this paper introduces the key principle of visible light communication technology,expounds the principle of OFDM technology,and compares the difference between DC biased orthogonal frequency division multiplexing?DCO-OFDM?system and asymmetrically-clipped optical OFDM?ACO-OFDM?system.Combining with the design requirements of this system,DCO-OFDM is adopted as the modulation mode of this paper.Then,based on the implementation principle of the OFDM technology,the hardware implementation of the transmitter and receiver of the visible light communication system is designed,including processor circuit,digital-to-analogue?DA?conversion circuit,LED driver circuit,photoelectric conversion circuit,amplifier module and analogue-to-digital?AD?acquisition circuit,and the implementation principle of each part is introduced in detail.Then,the software design of the system is given,and the implementation principles of Quadrature Amplitude Modulation?QAM?module,Fast Fourier Transformation/Inverse Fast Fourier Transformation?FFT/IFFT?module and channel estimation module used in the system are mainly introduced.Finally,the hardware and software of the system are integrated,and the performance of the whole system is tested.The key indicators of the system,such as bit error rate,transmission distance and transmission rate,are tested respectively.The experimental results show that the system can successfully realize point-to-point single-end communication.The system has a maximum communication rate of 266Kbps and a maximum communication distance of 1.3 m with a bit error rate of 10^-3.