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Study On Optical Millimeter Wave Generation In Radio Over Fiber System

Posted on:2009-05-20Degree:MasterType:Thesis
Country:ChinaCandidate:C HuangFull Text:PDF
GTID:2178360242490868Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
The radio-over-fiber (ROF) system, which brings together the agility of wireless access and the huge capability and low cost of fiber, will play an important role in the future broadband wireless access services . High quality optical millimeter (mm)-wave generation is a key technique to realize low cost and high transmission performance in the ROF systems. In the thesis, the technique of mm-wave generation in ROF system are mainly discussed, and three schemes of mm-wave generation are proposed and realized:The principle and transmission performance of the mm-waves generated by different modulation schemes have been discussed. The chromatic dispersion(CD) will limit the transmission distance of mm-wave if all sidebands of the optical mm-wave carries the baseband signal. So, two schemes of optical mm-wave generation using one external modulator has been proposed, and the transmission performance of the mm-waves have been analyzed. One scheme is using a phase modulator to generate a double sidebands signal by subsidiary carrier modulation (SCM), the first-order sidebands which are to generate the mm-wave are separated by an optical filter at base station. This modulation scheme is simple and has been demonstrated experimentally, the power penalty after transmission over 20-km 2.5Gbps NRZ is smaller than 0.2 dBm. Another scheme is using a dual-arm LiNbO3 Mach–Zehnder interferometer modulator to generate mm-wave by optical carrier suppression (OCS). The mm-wave generated by this scheme can immune the fiber dispersion with small modulation depth, and the transmission performance is same as OCS modulation with big modulation depth.In addition ,orthogonal frequency division multiplexing (OFDM) can combat RF microwave multipath fading in wireless communication , and also can combat CD and polarization mode Dispersion (PMD) in optical communication. The OFDM-ROF system will combine the advantages of OFDM and ROF. Based on this advisement, we have also proposed a scheme of optical mm-wave generation in ROF based on OFDM. The principle and dispersion performance of OFDM mm-wave generated by OCS is analyzed with theoretics and simulation. Although the subsidiary carriers of OFDM signal have different phase shift caused by fiber dispersion, the OFDM receiver can realize channel equalization. And the downlink signal can be received exactly.
Keywords/Search Tags:optical communication, radio–over-fiber (ROF), millimiter wave, dispersion, phase modulator (PM), intensity modulator, Orthogonal Frequency Division Multiplexing (OFDM), optical carrier suppression (OCS)
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