Research On Hybrid Modulation And Demodulation Technology Of Optical Wireless Communication

Optical wireless communication(OWC)is a communication technology that uses laser signals to transmit information in space.OWC has many advantages,such as high rate,high capacity,high security,no electromagnetic interference,free of frequency permission,etc.It can be used as the main means of communication between satellites in space,as well as provide high-speed and reliable data transmission in atmosphere environment.It is an important part of future communication network.Atmospheric turbulence is the greatest challenge for OWC system to transmit data in atmospheric environment.The intensity scintillation effect caused by turbulence will seriously affect the performance of signal transmission.As one of the key technologies in OWC system research,modulation and demodulation technology can effectively suppress the impact of atmospheric turbulence and improve the transmission performance of the system.Since the development of OWC modulation and demodulation technology,there have been various modulation methods based on amplitude,frequency,time,phase and polarization.However,traditional single modulation has its own advantages and disadvantages,and it is difficult to meet the needs of bandwidth,power and error performance at the same time.In order to improve the performance of OWC system in an all-round way,In order to improve the performance of OWC system in all aspects,combining several modulation methods to produce the multi dimensional hybrid modulation gradually become a research hotspot.Firstly,this paper expounds the significance and current situation of OWC and its modulation and demodulation technology,and demonstrates the importance of research on modulation technology.Secondly,the background knowledge of OWC system and atmospheric turbulence channel is introduced,which provides a basis for the establishment of the whole system model.Then the performance of various traditional modulation technologies is studied and analyzed,and the modulation and demodulation technology based on Inverse Manchester Code(IMC)is introduced.The main work of this paper includes:(1)A multi-dimensional hybrid modulation and demodulation technology called polarization multiplexing inverse manchester quardrature phase shift keying is proposed,which is based on IMC codes and combined with polarization switching,polarization multiplexing and quadrature phase modulation(QPSK).The scheme of modulation and demodulation is given,and the system model of transmitter and receiver of OWC system is designed;(2)The bandwidth efficiency of PM-IMC-QPSK is analyzed theoretically,and the BER of the system in M?alaga atmospheric turbulence channel is deduced.Then the theoretical derivation results are numerically simulated and compared with the traditional multi-pulse position modulation(MPPM)and a hybrid modulation method QAM-MPPM under different turbulence intensities;(3)based on the proposed modulation scheme and Multiple-Input Multiple-Output(MIMO)technology,the BER performance of MIMO-IMC system is theoretically deduced and simulated.The Theoretical derivation and simulation results show that the proposed PM-IMC-QPSK modulation and demodulation scheme has both high bandwidth efficiency and excellent BER performance,and can effectively deal with the atmospheric turbulence effect.At the same time,it can further weaken the interference caused by atmospheric turbulence and improve the overall performance of the system after combining MIMO technology.