Research On Theory And Key Techniques In Millimeter-wave Over Fiber Based On Digital Signal Processing

Mobile communication has been developed rapidly in the past 20 years, it has brought a great impact on people's life style, work style and social politics, economy and so on. In order to support the rapid development of mobile communications, a large number of spectrum resourced are needed, the millimeter wave (mm-wave) band has a huge bandwidth, it can be used in future wireless communications and space communications to provide large capacity service. However, the millimeter wave signal has a great loss in free space transmission due to the high frequency, which seriously affects the transmission distance. Aiming at the problem of millimeter wave transmission distance limited, the radio over fiber (RoF) technology based on the millimeter wave radio frequency remote arises at the historic moment. At the receiver end of RoF system, coherent detection can be adopted to realize the linear detection of optical signal, digital signal processing (DSP) can be adopted to compensate the transmission impairments of the signal. In the process of signal transmission, if a section of optical fiber is break or cannot reach, wireless millimeter wave transmission can be used to instead of optical fiber transmission in this section, and that is the optical fiber wireless integrated system.On the basis of the existing research of domestic and foreign scholars, this paper conducts intensive research on high-order vector millimeter wave generation technique based on external modulator in RoF, carrier phase estimation (CPE)algorithm in coherent optical communication and optical fiber wireless integrated system, achieving high-order vector millimeter wave generation technique based on a single phase modulator (PM), optimizing computation complexity of CPE algorithm,proposing the implementation scheme of high frequency spectral efficiency and low cost optical fiber wireless integrated system.1. The thesis proposes and experimentally demonstrates a method to generate photonic frequency-doubling 16-quadrature-amplitude-modulation (16QAM) vector millimeter-wave signal by using phase modulator with precoding technique. Aiming at the problem of low spectral efficiency of millimeter-wave signal with quadrature phase shift keying (QPSK) modulation, relatively small optical signal to noise ratio(OSNR) and weak stability based on Mach-Zehnder Modulator (MZM), the thesis proposes and experimentally demonstrate a method to generate photonic frequency-doubling 16QAM vector millimeter-wave signal by using a single phase modulator with amplitude and phase precoding technique. The PM is driven by a 2-Gbaud 16QAM modulated precoded vector signal at 20GHz. The generated optical radio frequency signal at 40GHz is single-mode fiber transmitted over 22-km distance,and after heterodyne beating in a single-ended photodiode (PD), 40-GHz electrical vector mm-wave signal displaying regular 16QAM modulation can be generated with a bit-error-ratio (BER) less than the hard-decision forward-error-correction (HD-FEC)threshold of 3.8×10-3. This is the first time to demonstrate high-order QAM vector mm-wave signal generation based on a single PM.2. The thesis proposes a two stage CPE algorithm based on improved QPSK partition algorithm. Aiming at the problem of high computational complexity of existing blind phase search (BPS) algorithm, the thesis proposes a two stage CPE algorithm based on improved QPSK partition algorithm, the first stage of the algorithm which is based on traditional P3 algorithm is used to realize rough estimate,the second stage of the algorithm which is based on proposed improved QSPK partition algorithm is used to compensate the residual phase noise. The simulation results show that the performance of this algorithm is similar to that of BPS algorithm,but the computational complexity is about 13 times lower than that of the BPS algorithm.3. The thesis proposes and experimentally a Q-band seamlessly integrated fiber-wireless system based on 16QAM modulation and coherent detection. Aiming at the problem of low spectral of optical fiber wireless integrated system based on QPSK modulation, the thesis proposes and experimentally a Q-band seamlessly integrated fiber-wireless system based on 16QAM modulation, where 80Gb/s polarization multiplexing (PM) 16QAM is transmitted over 50-km single-mode fiber-28 (SMF-28)wire link, 0.5-m 2x2 multiple-input multiple-output(MIMO) wireless link, and another 50-km SMF-28 wire link at last. Conventional multi-modulus-algorithm(MMA) equalization is introduced at the receiver to realize polarization demultiplexing and minimize crosstalk between two polarizations. For the first time,the thesis realizes the fiber-wireless integration signal transmission with high-order modulation (16QAM) and polarization multiplexing (PM) at Q-band, spectrum efficiency is raised from 2bit/s/Hz (QPSK) to 8bit/s/Hz (PM-16QAM).4. The thesis propose and experimentally demonstrate a wireless fiber integration system at the W band which adopting a directly modulated laser (DML) for E/O conversion at the receiver. Aiming at the problem of high cost of receiver base station(BS) due to the use of MZM and PM for E/O conversion, the thesis propose and experimentally demonstrate a wireless fiber integration system at the W band which adopting a DML for E/O conversion at the receiver. At the receiver, a DML is used to realize E/O conversion. The received 85 GHz wireless millimeter-wave signal is first down-converted into a 10 GHz electrical intermediate-frequency (IF) signal to overcome the insufficient bandwidth of the subsequent DML. By using this scheme,the thesis transmit a 10 Gb/s 16 QAM signal over a 10 m wireless link, and then deliver it over a 2 km single-mode fiber-28 (SMF-28) wire link with a bit error ratio that is less than the HD-FEC threshold of 3.8×10-3. Experimental results show that the DML can be used for the E/O conversion of a 16QAM signal.