| With the rapid development of broadband wireless access and improvement of user experience, low-frequency band is too crowded to meet the demand for bandwidth. The basic principles of information theory tell us that using electromagnetic waves to transmit information, the higher the frequency, the greater the available bandwidth. Therefore, researchers have never given up exploring the high-frequency band. Microwave photonics as a new cross-disciplinary, integrating the advantages of optical communication and wireless communication, is considered as an option with much potential to meet the requirements of both high bandwidth of transmission link and convenience of wireless access. In the past few years, there has been an increasing effort in researching new microwave photonics techniques for different applications, including photonic generation, processing, control and distribution of microwave and millimeter-wave (mm-wave) signals, optically controlled phased array antennas, and radio over fiber (ROF) systems. Microwave photonic link has overcome the electronic bottleneck found in traditional microwave systems since the introduction of optical technologies, and has wide application prospects in the fields of high-speed broadband wireless access, radar and satellite communications, electronic warfare, sensor networks, instrumentation testing, astronomical detection, and biomedical.These works are supported by the National Basic Research Program of China (973 Program). The dissertation focuses on key technologies in microwave photonic signal processing and ROF system. The main work and innovations of the dissertation are as follows:(1) Two Criteria for ROF Link with Vector Signal Transmission.With the increasing congestion of frequency resources, the higher order vector signal with high spectral efficiency is still viewed as the preferred solution for ROF link. Generally there are three conventional modulation modes in microwave photonic link, double-sideband (DSB), single-sideband (SSB), and double-sideband carrier suppression (DSB-CS). However, not all of them can be choices for vector signal transmission. Meanwhile, chromatic dispersion (CD) has always been a significant impairment in long fiber link, as well as for ROF link with vector signal transmission.In this section, we demonstrate the theory of three traditional modulation modes and CD impact for ROF link with vector signal transmission. Two criteria for ROF link with vector signal transmission are proposed, which has guiding significance for ROF link design, system architecture, and information transmission.(2) Compensation of Chromatic-Dispersion for Full-Duplex ROF Link with Vector Signal Transmission using Frequency Tripling.In this section, we improve the traditional ROF link with SSB modulation, and a ROF link in line with the two criteria of vector signal transmission is proposed. It is necessary to take CD into account for ROF system architecture. CD causes each spectral component to experience different phase shifts, and produce a phase difference between the two beat signals, which results in a constellation rotation (CR) of the composite vector signal and bring trouble to subsequent transmission, demodulation, and digital signal processing. Therefore, frequency tripling modulation (FTM) and symmetry theory are proposed to compensate such CD induced CR, and a full-duplex ROF link with vector signal transmission using FTM is accomplished accordingly.Generally speaking, the CD impact factor for a ROF link depends closely on the fiber-link distance, modulation frequency, and the fiber dispersion parameter, which means it is not easy for a single schedule of CD compensation to fit all ROF systems with different kinds of fibers or fiber lengths. However, our method of CD compensation has nothing to do with the fiber dispersion parameter or fiber length, and all we need is just appropriate allocation of the bandwidth, which greatly expands the range of applications for ROF links. To the best of our knowledge, this is the first time. Meanwhile, our schedule can fit different ROF system is not in the cost of extra equipment or complex structure, in the contrast, our plan makes the whole ROF link significantly cost-effective. Moreover, central station is greatly simplified since only one local oscillator is needed for both the generation of an optical millimeter-wave signal and the carrier of downlink signal.(3) Compensation of Chromatic-Dispersion for Full-Duplex ROF Link with Vector Signal Transmission using an Optical Phase Shifter.In the previous section, FTM and symmetry theory is proposed to compensate CD induced CR, and the method of CD compensation has nothing to do with the fiber dispersion parameter or fiber length, which can fit different ROF systems. However, it still needs appropriate allocation of bandwidth to satisfy the symmetry theory. Then, what does more generalized CD compensation scheme look like?In this section, we improve the previous CD compensation method by further studying the theory of modulation and CD impact in ROF link, instead of following the symmetry theory. Meanwhile, A full-duplex ROF system with vector signal transmission using an optical phase shifter (OPS) is proposed, and CD induced CR is entirely overcome thanks to our method.(4) Full-Duplex ROF Link with Seamless Convergence and High-Speed Broadband Wireless Access.In the previous section, the ROF systems can only handle one radio-frequency band at a time regardless of what kind of CD compensation technologies are adopted. Generally speaking, mm-wave with different band has different propagation characteristic, which restricts the scope of single-band ROF systems. However, there is no doubt that applications can be extremely expanded if ROF systems are able to handle multiple radio-frequency bands at a time.In this section, combining the advantages of Wi-Fi band and V-band (57GHz-64GHz), a full-duplex ROF link with seamless convergence and high-speed broadband wireless access is proposed, and information can flexibly switch between the two bands.
|
PDF Full Text Request