| With the rapid development of the communications industry, the demand for broadband communications services is becoming increasingly. Wireless communication link is acclaimed due to it can achieve flexible access for user terminals. But by now, narrow band wireless communication technology cannot meet the requirement of broad band in future communication, and the low frequency radio spectrum they use is very crowded. Millimeter wave (mm-wave) technology can realize greater transmission capacity and higher data transfer rates, but high loss and line-of-sight propagation make broadband millimeter wave communication system complex and costly. RoF, the integration of optical and wireless technologies, is a promising technique to resolve the issues and therefore provides a way to increase capacity and coverage as well as to reduce the system costs. ROF has the advantages of low loss, large available bandwidth, immune to electromagnetic interference, easy to install and maintain. Recent years, optical mm-wave generation becomes a key technology in the field of ROF, the frequency multiplication technology can reduce the system cost effectively and improve the performance at the same time. But the problem of date mismatch between wireless and fiber exist in high bit rate and high capacity system. W-band(75-110GHz) mm-wave can provide35GHz bandwidth, and is at the atmospheric attenuation window. It is easy to realize gigabit-class wireless access rate. So it is expected to solve the problem of date mismatch between wireless and fiber.In this paper, firstly, we overview the features, application, research status and development of RoF technology, and introduce the features of WDM-PON technology briefly. Secondly, we analyze the generation of optical millimeter-wave signal, especially the external modulation technology. And compare the difference between double sideband modulation (DSB), single sideband modulation (SSB) and optical carrier suppression (OCS). Clarify the advantage of using Mach-Zehnder modulator nonlinear effects to generate optical millimeter wave signal. Thirdly, based on the ROF technology, we put forward a full-duplex radio-over-fiber (RoF) link providing multiband wireless accesses. In this system, in the downlink, second order sideband are generated in central station by using a LN-MZM, data is modulated on the positive second order sideband, and a phase shifter is induced in the negative second order sideband. After transmitting along the fiber, base station realize the multiplex millimeter wave signal generation. In the uplink, the upstream signal is carried by the optical carrier abstracted from the downlink signal. We build a simulation link, and verify the performance of this system by observe the eye diagram and BER curves. Fourthly, we combine the WDM-PON with W band ROF technology, propose a novel broadband mm-wave RoF access network based on optical local oscillator broadcasting and wavelength conversion. By using the for-wave mixing in semiconductor optical amplifiers produce W-band ROF signal. The upstream signal is modulated on the carrier abstracted from downstream signal. Baseband modulation upstream signals multiplexed at remote node unit and transmit to central station. Realize the W-band full-duplex broadband mm-wave RoF link. Lastly, a conclusion and prospect of this paper are given in the fifth chapter. |
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