Research On The Generation Mrthod Of Radio Over Fiber Signal

As the information industry has developed rapidly over the past two decades,new services including high-quality Internet Protocol Television(IPTV),virtual reality(VR)video calling and cloud computing have also sprung up.In order to meet the needs of users,the state proposed some strategies such as "Broadband China" and "Smart City".Thus,the development of efficient access network(RAN)technology has become one of the most essential parts of advancing the overall digitalization process.Due to its wider bandwidth,lower loss and stronger resistance to electromagnetic interference,radio over fiber(ROF)technology is regarded as the development direction of current and even the next generation wireless access network.However,ROF still needs to overcome a mass of technical hurdles as a new technology.For instance,the cost of installation and maintenance in the ROF system is high while the frequency band utilization rate is low.The study of modulation technology of optical carrier radio frequency signal with large capacity,high stability and high flexibility has become a research hotspot in order to furtherly promote the development of ROF.Based on the traditional ROF system signal modulation and generation technology,the dissertation focuses on the generation,modulation and crosstalk suppression methods of optical carrier millimeter-wave signals.Three different ROF signal generation schemes are proposed to realize low-cost and large-capacity ROF signal generation and transmission.The main work and innovations of the dissertation are as follows:(1).A scheme for generating dual independent sideband(ISB)vector millimeter-wave(mm-wave)signals based on one single inphase/quadrature(I/Q)modulator is proposed.In the proposed scheme,software defined optics(SDO)technology is used to generate two independent ISB vector millimeter-wave signals by one I/Q modulator.The two ISB vector mm-wave signals have different carrier frequencies and vector modulation formats.A dual ISB signal carrying 3 8GHz 16QAM vector modulated signal and 40GHz QPSK vector modulated signal is generated in the experiment,and the BER-free transmission of this signal is achieved in an ROF link containing 10km standard single-mode fiber(SSMF)and 0.5m wireless channel.The results show that:when the input power is greater than-10.5dBm,the bit error rate(BER)of the 38GHz 16QAM signal can reach the hard-decision-forward error correction coding(HD-FEC).When the input power is greater than-8.7dBm,the BER of the 40GHz QPSK signal can reach HD-FEC.(2)This dissertation analyzes the causes of crosstalk in dual ISB system,and proposes three schemes to alleviate crosstalk damage in dual ISB system:frequency separation crosstalk suppression scheme,phase matching crosstalk suppression scheme,and crosstalk compensation scheme based on the multiple-input multiple-output(MIMO)equalization algorithm.The effectiveness of the proposed scheme is experimentally demonstrated.After using the frequency separation crosstalk suppression scheme,the 4Gbaud 30GHz 16QAM signal and 4Gbaud 38GHz QPSK signal sets have a lower overall BER than the 4Gbaud 30GHz 16QAM signal and QPSK signal sets.The phase-matching crosstalk suppression scheme can improve the receiving sensitivity by 4.3dB when the BER of 36GHz QPSK signal is 1×10-3,and the receiving sensitivity can be improved by 2.2dB when the BER of 36GHz 16QAM signal is 1 × 10-2.The crosstalk compensation scheme using MIMO equalization algorithm can improve the receiving sensitivity by 36GHz.When the BER of QPSK signal is 1×10-3,the receiving sensitivity can be increased by 3.7dB,and when the BER of 36GHz 16QAM signal is 1 × 10-2,the receiving sensitivity can be increased by 1.9dB.Meanwhile,the MIMO equalization algorithm module can be used together with the phase matching crosstalk suppression scheme and the frequency separation crosstalk suppression scheme to further improve the performance of the dual ISB system.(3)This dissertation proposed a scheme for generating wideband single sideband(SSB)vector millimeter wave signal by a single push-pull Mach-Zendel modulator(MZM).In the proposed scheme,SDO technology is used to generate a wideband single sideband modulated signal.The wideband single sideband modulated signal includes one unvector modulated negative frequency signal component and one vector modulated positive frequency signal component.In the experiment,a 1 Gbaud 40GHz 16QAM wideband SSB millimeter-wave signal and a 4Gbaud 40 GHz QPSK wideband SSB millimeter-wave signal are generated using an MZM with a bandwidth of 30GHz.The experimental study shows that:after 10km single-mode fiber(SMF-28)transmission,the BER of the QPSK signal can reach HD-FEC when the received optical signal power is greater than-11.8 dBm.And the BER of the 16 QAM signal can reach HD-FEC when the received optical signal power is larger than9.6 dBm.(4)In this dissertation,a new scheme based on polarization operation is proposed to generate an optical carrier RF signal with a 4-pulse amplitude(PAM4)modulation format.In this scheme,a polarization modulator combined with two intensity modulators(IMs)is used to generate PAM4 millimeter-wave signals through polarization operation of polarization controller(PC)and polarizer.The scheme is able to avoid the use of expensive digital-to-analog converters(DACs),thus reducing costs.The generation of 9.07 GHz PAM4 signal and its transmission in 80 km SMF-28 were experimentally realized.The experimental results show that the BER of the generated PAM4 signal is less than HD-FEC when the received optical power is larger than-8.3dBm,and the signal has good tolerance to transmission impairment.