Research On Key Technologies Of B5G Mobile Fronthaul Based On Analog Radio Over Fiber

With the development of new communication services such as cloud computing,automatic driving,and the Internet of things,the International Telecommunication Union（ITU）has defined three main use cases for fifth genaration（5G）mobile communication including enhanced mobile broadband（e MBB）,ultra-reliable and low-latency communications（URLLC）,and massive machine-type communications（m MTC）.This requires higher bandwidth,lower latency and more connections for the mobile fronthaul link connecting the baseband processing unit（BBU）and the remote radio unit（RRU）.Although the most widely used digital radio over fiber（D-Ro F）technology based on a common public radio interface（CPRI）has the advantage of high signal fidelity,its low spectral efficiency makes it unable to support large-scale capacity upgrading.Mobile fronthaul based on analog radio over fiber（A-Ro F）has the advantages of high spectral efficiency,low latency,and simple structure of remote base stations.It is considered to be the most potential solution for5G and beyond 5G（B5G）mobile communication network.Considering the different characteristics of the Sub-6 GHz and millimeter-wave frequency bands of 5G and B5G mobile communications,two research goals have been proposed in this dissertation,namely:low cost and high linearity integrated four-channel radio frequency（RF）optical transceiver module for Sub-6 GHz,and generation and transmission of multi co-frequency millimeter-wave signals on a single optical carrier for the millimeter-wave frequency bands.The specific research contents and results are as follows:（1）The low loss optical coupling scheme is proposed,the broadband impedance matching of RF link is realized,and an integrated four-channel RF optical transceiver module with the size of 58 mm×46 mm×20 mm is successfully fabricated.The third-order spurious-free dynamic range（SFDR3）of the four channels of the designed optical transceiver in the frequency range of 2-12 GHz is above 93.46 d B·Hz^2/3.Moreover,the experimental results show that the module could support the mobile fronthaul of the 4×600Mbps 64-ary quadrature amplitude modulation-orthogonal frequency division multiplexing（64QAM-OFDM）signal at 2-12 GHz and the 5.801Gbps 16QAM-OFDM signal at Sub-6GHz.（2）The causes of crosstalk between symmetrical sideband signals caused by IQ amplitude imbalance,IQ delay difference and finite extinction ratio of the electro-optic modulator are analyzed,and a scheme to eliminate the crosstalk at the transmitter is proposed.This scheme can improve the sideband suppression ratio of optical single-sideband modulation based on Dual-Drive Mach Zehnder modulator（DDMZM）from less than 8 d B to more than 30 d B.Enabled by this scheme,the error vector magnitude（EVM）values of two 8 Gbps 16QAM signals with the carrier frequency of 14 GHz over 50 km standard single-mode fiber（SSMF）transmission are less than 10%.An asymmetric double sideband modulation scheme based on an optical IQ modulator is proposed.In this scheme,32 GHz millimeter-wave signals can be obtained at the receiver with the help of self-heterodyne coherent detection technology by using RF signals with the carrier frequencies of 12 GHz and 20 GHz at the transmitter.Two 3.2 Gbps 16QAM signals with the carrier frequency of32 GHz are successfully transmitted over 25.5 km SSMF,and the EVM values of both signals are less than 12.5%without any digital compensation algorithm at the receiver.（3）With the help of self-heterodyne coherent detection technology,the generation and transmission of four independent millimeter-wave signals on a single carrier are successfully realized.The MZM is connected in parallel with the dual-polarization IQ modulator,and the four low-frequency RF signals are successfully up-converted to the same frequency high-frequency millimeter wave signals.The experiments show that four 1.6 GBaud 16QAM millimeter-wave signals with the carrier frequency of 30 GHz could be generated at the receiver by using four independent 1.6 GBaud 16QAM signals with the carrier frequency of10 GHz and a single-tone signal with the carrier frequency of 20 GHz at the transmitter.Moreover,the sampling rate of the digital to analog converter at the transmitter can be as low as 24 Gsa/s.Meanwhile,the scheme does not need to use any digital compensation algorithm at the receiver.This scheme can improve the capacity and spectral efficiency of mobile fronthaul on a single carrier,effectively reducing the cost and complexity of the B5G mobile fronthaul system.