Study On Link Model Of Full-duplex Radio Over Fiber

With the increasing requirements of high speed and large capacity wireless communication, a new technology named radio over fiber (ROF), which is a kind of wireless access technology, can efficiently combine the advantages of optical fiber communication and wireless communication and get the rapid development in the recent years. This dissertation focuses on the scheme of link model of full-duplex ROF. The main works are listed as below:1. The basic principles of millimeter wave generation technology are introduced. The external modulation method and optical heterodyne method were analyzed and discussed. In addition, the dispersion, the nonlinear of optical fiber and the linewidth of the light source, which have distinct influence on the transmission of optical signal, are also discussed, especially the walk-off effect caused by the dispersion in optical fiber.2. A new full-duplex radio over fiber link model is proposed. For the down link, two Mach-Zehnders modulator cascaded are employed to generate sextupling-frequency millimeter wave; the single side-band modulation is used to overcome the walk-off effect, thereby the transmission distance is effectively improved. In the meanwhile, the first order sideband is employed as the carrier of uplink baseband signal and thus the requirement of additional laser source is eliminated. Furthermore, self-homodyning demodulation method is adopted to avoid the need of local oscillators, thereby the cost of system is reduced. Numerical result shows that the proposed full duplex model can produce60GHz millimeter wave by only using10GHz modulated signal. The transmission distance for down link can reach to250km and that for the up link is more than300km.3. A new full-duplex radio over fiber link model based on optical heterodyne method is proposed. The Quadrature Amplitude Modulation, which is a popular modulation format is applied to the full-duplex ROF system, greatly improve the spectrum efficiency. In the meanwhile, due to the improvement of spectrum efficiency, the symbol rate of signal will be reduced under a certain communication rate, thus the effects of dispersion of signal would be weakened. Self-homodyning demodulation method is adopted to avoid using optical phase-locked loop to reduce the effects of laser phase irrelevance. By using QAM signal modulation on one of the optical sidebands, the walk-off effect can be efficiently reduced due to the existence of dispersion in the fiber. The dispersion effect can deflect the constellation graph and thus affect the demodulation performance. It can be found that there is a linear relationship between fiber transmission distance and the deflection angle. Though setting a calibration phase at the receiving end, the offset of constellation diagram can be calibrated. The transmission distance for down link can reach to40km and that for the up link is60km.