Research On Pre-equalization Technology Of Transmitter Signal In Wireless Optical Communication System

Wireless optical communication is a communication mode with light wave as carrier.Compared with traditional radio communication technology,it is widely used in various fields because of its fast transmission rate,large system capacity,strong anti-interference ability and good confidentiality.Wireless optical communication is mainly divided into laser communication and short-range wireless optical communication.This thesis mainly studies the short-range wireless optical communication,using LED?light-emitting diode?as the light source for data transmission.In wireless optical communication system,the attenuation of the response of the light source is more significant as the frequency of the signal is higher,it is more difficult to modulate the high frequency signal,thus affecting the stability and effectiveness of the signal in the transmission process.In order to solve the problem of attenuation of light source in high frequency response,a cascade amplifier pre-equalization method is designed to act on the transmitter of wireless optical communication system.This method uses the small signal model of transistor amplifier circuit to set the parameters of all kinds of circuit devices.It could compensates the attenuation of the high frequency signal transmitted by the source non-linearly and improves the modulation performance of the wireless optical communication system.This method makes the equalizer have greater attenuation of the low frequency transmission characteristic of the source and stronger compensation effect of the high frequency by cascade mode.This thesis analyze the cascade amplify pre-equalization method theoretically,and the pre-equalization circuit is designed according to the frequency response characteristics of the selected light source.In order to verify the improvement of signal transmission performance of wireless optical communication system by cascade amplify pre-equalization method,it is important to build a wireless optical communication system to test the pre-equalization circuit effect.In the process of building the system,the bias circuit,driving circuit and signal processing circuit of the receiver are designed and manufactured.Experiments show that the pre-equalization circuit not only broadens the frequency response range of the light source,but also suppresses low frequency interference,expands the 3 dB bandwidth of the wireless optical communication system from 12 MHz to 235MHz.When the transmission distance is 30 cm,the data transmission rate under the OOK?On-Off Keying?modulation mode is 555 Mbit/s,and the error rate is1.7×10^-5.The data transmission rate is 490Mbit/s at the farthest transmission distance of 80 cm and the error rate is3.2×10^-4.The experimental results show that the cascade amplify pre-equalization method can increase the 3dB modulation bandwidth of the wireless optical communication system by an order of magnitude.It can compensate the attenuation of the response of the light source when transmitting high frequency signal and improve the transmission performance of wireless optical communication system.