Research On Adaptive Receiving Method Of Visible Light Communication System

Visible light communication technology has the advantages of sufficient bandwidth resources,no electromagnetic pollution,etc.It can be used as light source for communication while for illumination.It can alleviate the pressure of radio frequency communication,realize indoor high-speed safe Internet access.It can be used to implement accurate position and navigation.The applications are also extended to intelligent home,intelligent transportation and Internet of things and other fields.The communication range of the visible light communication system is limited to the illumination coverage of the white LED.Since the transmission energy of the light signal attenuates with the increase of distance.Light intensity varies with the change of the client's location.If a receiver with fixed gain is used,the signal intensity varies greatly within the illumination range,which lead to saturation or loss of received signals,thus seriously degrade the communication performance.In order to solve the problem induced by a fixed gain,an adaptive receiver for visible light communication is realized.The gain is adjusted automatically in light of the variation of light intensity.The method leads to a relatively stable output.The theoretical bandwidth of the designed adaptive receiver is 30 MHz.For a constant transmit power of LED,when the receiver is positioned 1.65 m from the light source,the variation of the amplitude is insignificant for communication in illumination zone if the receiver has a longitudinal movement in a range of-0.15m~0.45 m or lateral shift in a range of ±0.85 m.In order to enhance the anti-interference ability of visible light communication system,an OFDM(orthogonal frequency division multiplexing)modulation-demodulation algorithm based on FPGA is studied.Multipath interference effect is degraded effectively based on the algorithm.