Research On Optical To Radio Communication System In Complex Electromagnetic Environment

In modern communication systems,optical communication has presented an unparalleled advantage.For a long time in the future,society will step into a huge capacity and ultra-high-speed optical communication era.Among them,the radio spectrum is related to political,economic,military and other aspects.It has become an important strategic resource of the country.However,in the current shortage of low-band spectrum resources,the communication system encounters radiation when it completes its mandated tasks,or The distribution of the power and time of the conducted electromagnetic emission level in different frequency bands is complex and variable.In such a complex electromagnetic environment,higher requirements are placed on the quality of communication signal transmission.Moreover,the dispersion and nonlinear effects can greatly affect the quality of signal transmission during transmission.Therefore,it has an efficient transmission system with high energy utilization and high spectrum utilization,which can compress the wireless transmission spectrum to the maximum extent and achieve high efficiency.An effective way of communication,which has direct economic benefits and important strategic significance.In view of the above situation and problems,this paper adopts ROF technology and combines passive optical network which has the advantages of low cost,transparent service and easy maintenance.the generation mode of millimeter wave is analyzed and studied,which is one of the key technologies in ROF system.In order to reduce the dependence of fiber dispersion on optical transmission and realize large-capacity and long-distance transmission,this paper deeply studies the basic principle of lithium niobate-Mach-Zehnder modulator and deduces the formula,combining with optical binary code pattern.In order to improve the spectrum utilization,the theoretical analysis of phase shift keying modulation and demodulation is carried out.The ROF system based on 8PSK and16PSK modulation is designed by optisystem simulation software.The influence of two modulation techniques on the transmission quality of the system is studied.The specific work is as follows:Firstly,in the background of complex electromagnetic environment,the traditional NRZ modulation format is taken as a reference,and a new optical dual binary modulation format is proposed.The transmission performance of the two modulation formats is analyzed by eyediagram and photoelectric spectrogram.The experimental results show that the bandwidth of the optical signal modulated by LDF-ODB is narrower,mainly concentrated near the central frequency?193.07 THz?,and its bandwidth utilization is high,but its bit error rate is about4.14e^-8.The bandwidth utilization of the optical signal modulated by NRZ is low,but its bit error rate is lower than that of LDF-ODB modulation,about 7.24e^-11.The use of single mode optical fiber,fork,optical amplifier,photodiode and other devices in the system model makes the cost of the system equipment lower,the dispersion tolerance higher,the spectral efficiency higher,and the Anti-nonlinear effect higher.It provides two modulation schemes for users to access the PON system flexibly.Then,according to the characteristics of MPSK modulation with high frequency band utilization,taking octal phase shift keying?8PSK?and hexadecimal phase shift keying?16PSK?modulation as examples,an odd sideband ROF suppression system based on Mach-Zehnder modulator is designed.and the spectrum,constellation and bit error rate curves of the two modulated signals are compared under different optical signal-to-noise ratio?OSNR?conditions.The analysis shows that the transmission performance of the 8PSK signal is better than the 16PSK signal.The transmission performance of the two modulated signals under the 15GHz and 20GHz RF signals is also discussed.By analyzing the constellation diagram and error code characteristics of the received signal,it is proved that compared with16PSK signal,8PSK signal reduces the frequency of modulated signal,saves the spectrum resources better,enlarges the communication capacity and achieves stable transmission.Finally,a full duplex optical wireless communication?ROF?link scheme is designed for dispersion and nonlinearity.The downlink of the system uses 8PSK and 16PSK to modulate and demodulate.The control variable method is used to control the value of optical signal-to-noise ratio?OSNR?and transmission distance.The advantages and disadvantages of the two modulation modes and the transmission performance of the system are analyzed by observing the differences between the spectrograms and BER curves of the two signals.In order to further reduce system cost and optimize resource allocation,the unmodulated optical signal in downlink is used as carrier signal of upstream baseband signal,which is transmitted back to central station after DPSK modulation.