High-speed Photonic Terahertz Wireless Communication System Assisted By Probabilistic Shaping

With the rapid development of Internet applications,global data traffic has shown an exponential growth,and ultra-high-speed wireless communication becomes a research frontier.Due to the limitation of bandwidth,microwave or millimeter wavebased wireless faces the difficulty in achieving ultra-high wireless speed beyond 100Gbit/s.Compared to the microwave and millimeter wave,the terahertz(THz)band features much larger available bandwidth,and hence it has a very promising potential in next generation ultra-high-speed wireless.Typically,THz wireless systems can be divided into electronics or photonics-based.Between them,the photonic terahertz wireless communication systems can achieve higher data rates because of larger bandwidth supported by photonic devices.However,the typically low photo-electronic conversion efficiency severely limits the achievable THz power and hence the wireless transmission distance.To solve this problem,we propose the probabilistic shaping(PS)assisted photonic terahertz wireless communication technique,with a purpose to improve THz communication bit-energy.This thesis firstly introduces the basic elements in a photonic terahertz wireless communication system,the methods of terahertz signal generation and detection,as well as their advantages and disadvantages.Then the link budget is calculated based on the key devices in a photonic terahertz wireless link,such as an uni-traveling carrier photodiode(UTC-PD)and a Schottky mixer,so as to estimate the capacity of such a system,providing theoretical knowledge.Subsequently,we present the principle of PS and derive the shaping gain in an additive white Gaussian noise(AWGN)channel model from the perspective of information theory.We simulate the mutual information of shaped signals,and confirms that the PS signals is closer to the Shannon limit than the uniformly distributed signals,when the system signal noise ratio(SNR)is low.Finally,we conduct photonic terahertz wireless communication experiments operating in the 350 GHz band in the lab.In the experiment,20 Gbaud 16-QAM signals are successfully transmitted over a 4.5 m wireless link with an improved system sensitivity assisted by the PS.Besides that,a PS-16QAM-OFDM signal is transmitted over a 2 m wireless link without a THz lens at the transmitter side,with a rate of up to 122.5 Gbit/s.We hope this work can provide a solution for extending the THz transmission distance,and pave a way to further increase the capacity of a photonic terahertz wireless communication system.