Research On Transmission Theory And Key Technologies Of 6G Photonic Terahertz Wireless Communication

With the promotion and evolution of the fifth generation（5G）and future mobile communication technology,the demand for data communication traffic is increasing day by day,people’s demand for ultra-high data rate and ultra-low delay of communication is increasing day by day,and consumers’ demand for service quality is getting higher and higher.Applications such as virtual reality（VR）,augmented reality（AR）,cloud computing and Internet of Things（IoT）are also putting higher demands on real-time communication rates to some extent.Traditional low-frequency communication has gradually failed to meet the urgent demand of exponential explosive growth of information.Ultra-wideband photonic terahertz wireless communication can meet the dual demand of communication bandwidth and mobility for future communication networks.Terahertz communication frequency band is the main application frequency band of the sixth generation and future mobile communication technology.Exploring the theory and key technologies of ultrawideband photonic terahertz wireless transmission with large capacity and high spectral efficiency has become an important topic in the field of optical communication.In this paper,the ultra-wideband photonic terahertz wireless transmission theory and key technologies are deeply studied,and the structure and algorithm of generating photonic terahertz signal are improved and optimized to obtain high-quality terahertz signal.Multi-frequency terahertz communication system is studied,and phase precoding and amplitude precoding are used.The fusion probability shaping and geometric shaping coding techniques for terahertz signals are studied.The main work and innovations of this paper are as follows:1.An optical multi-carrier source generation method based on phase modulator cascade is proposed,and the generation of 400-ghz terahertz signal is realized by pushpull Mach Zdell modulator.The scheme using alternative light source multicarrier signal source and the local oscillator laser source,through the push-pull Mach zendell modulator gain QPSK/16QAM modulation signal,and then generate terahertz wave signals,to avoid the two free operating way of laser heterodyne beat frequency offset and phase noise problem,reduce the complexity of the receiver digital signal processing.The ortho-phase shift keying/16-orthogonal amplitude modulation signals were successfully transmitted by back-to-back and 10 km standard single-mode fiber respectively,and the calculated bit error rates were all lower than the 7%hard decision forward error correction threshold of 3.8×10^-3.The scheme has the advantages of simple structure,stable signal frequency and improved system performance.2.An optical multi-carrier source generation method based on intensity modulator is proposed,and 390 GHz terahertz signal generation is realized by using in-phase orthogonal modulator.The optical frequency comb generated by The Mach Zender intensity modulator is used as the optical multi-carrier source,and two beams（order-7 and order+6）are selected as the local oscillator laser source and signal laser source,and 2 Gbaud/3 Gbaud 16QAM signals are loaded in the in-phase orthogonal modulator.Finally,the 390 GHz terahertz signal is generated by beat frequency in single carrier photodiode.2 Gbaud 16QAM terahertz wave signals are successfully transmitted by back-to-back and 10 km standard single-mode fiber respectively,and the measured bit error rate reaches 7%hard decision forward error correction threshold below 3.8×E-3.In addition,the relationship between the bit error rate of 3 Gbaud 16QAM terahertz signal and the transmission distance of optical fiber is also studied.3.A frequency locked phase locked flat optical multi-carrier generation method based on cascaded external modulated laser and phase modulator is proposed to realize multifrequency orthogonal frequency division multiplexing terahertz wireless transmission.In order to solve the problem of frequency instability of terahertz signal generated by using multiple freely operating laser schemes,a cascade of external modulated laser and phase modulator is used as optical multi-carrier source instead of signal laser source and local oscillator source,which has the characteristics of frequency and phase locking.Several optical frequency comb lines are selected as signal laser sources to load the multi-carrier signal,and the vector microwave signal driving the optical intensity modulator is precoded by digital signal processing technology,including amplitude and phase.An appropriate optical frequency comb line is selected as the local oscillator laser source,and no signal is loaded.The corresponding optical carrier and optical local oscillator enter the corresponding UTC-PD heterodyne beat frequency to generate fourchannel OFDM terahertz signals at 350GHz,400GHz,450GHz and 500GHz,respectively.The transmission is then carried out in a wireless link.The signals were recovered in the receiver respectively,and the bit error rates of the four signals were all lower than the hard decision threshold of 3.8×e^-3.