Research Of 5G-Oriented Millimeter-Wave Radio-Over-Fiber Systems' Structure Design And Its Performance

With the explosive growth of network traffic,the existing communication system has been unable to meet the demands of people in all aspects.In view of the problem which is urgent to be solved,the relevant 5G-oriented technologies have been developing continuously and have made a great breakthrough.In these relevant technologies,the communication method using millimeter wave?MMW?as carrier is the most straightforward and effective way to realize the high capacity of 5G communication system owing to the high frequency and wide bandwidth of MMW.Besides,MMW has significant effects on the large scale MIMO array antenna due to its various advantages.However,MMW has large transmission loss in the air.So,the MMW's coverage ability to the remote areas is poor.To solve this problem as well as meet the requirement of 5G communication system network architecture,as the most suitable solution,MMW radio-over-fiber?MMW-RoF?communication system based on external modulators has become a hot research spot in the field of 5G communication technologies.In the MMW-RoF communication systems based on external modulators,a certain frequency interval of coherent optical carriers are generated in the transmitter,after the optical fiber transmission and the heterodyning beating effect of photonic detector in the receiver,the system can generate a certain frequency MMW signal.Due to the methods of coherent optical carriers'generation and baseband data modulation are various,there is a big difference in the quality of the generated MMW based on different method.Furthermore,the price of optical devices is expensive.So,in the research of MMW-RoF communication systems based on external modulators,how to use the simple structure of the system to economically produce high-quality MMW has become a problem that researchers must solve.In this paper,we first research the relevant techniques of MMW generation and the anti-dispersion ability of the different modulation methods of base-band data.Then,the MMW generation technique based on LiNbO₃ Mach-Zehnder modulator?LN-MZM?and the opticl single side-band?OSSB?modulationare employed in our researches.On the basis of these work mentioned above,two MMW-RoF communication systems are proposed.In the first system,the coherent optical carriers are generated by dual parallel Mach-Zehnder modulator?DP-MZM?.Then,the LN-MZM is employed to realize the OSSB modulation of the coherent optical carriers.The system can generate two MMWs simultaneously.The frequency multiplexing amount of the generated MMWs are three and five times the frequency of the local oscillator?LO?.The performances of MMWs are tested by digital simulation.The results show that the signal quality is good.The proposed system is simple-structured and easy to be implemented.Owing the identical transmission path of optical signals,there are no unnecessary polarization state difference and time delay between optical signals at different wavelengths.In addition,from the point of view of improving the economic efficiency,this scheme has certain research value.Considering the cross interface of the optical signals in the output of the first system's LN-MZM,we propose a new MMW generation system based on optical path separation.The proposed system utilizes cascaded LN-MZMs to generate coherent optical carriers and realize OSSB modulation based on optical path separation.Two MMWs can also be generated simultaneously,the frequency multiplexing amount of the generated MMWs are six and eight times the frequency of the LO,which is larger than that of the first system.The performances of MMWs are tested by digital simulation.The results show that the signal quality is good.In addition,the system 2 is optimized in the progress of research,which resulting in a better insertion loss balance between two different optical paths.By reducing the number of MMW,the system 2 will have the ability of transmitting high bit rate base-band data.The results of digital simulation show that the millimeter wave signal has good performances.