The Design Of Dispersion Tolerant OFDM-RoF System Based On Multiple Modulators

Radio-over-fiber(RoF)is a kind of technique integrating the optical communication and the wireless communication.As a feasible scheme to exploit the millimeter-wave(MMW)spectrum resource,RoF realized the long distance transmission of MMW signal by using optical fiber to connect the central station(CS)and the base station(BS).However,there are lots of optical harmonics with different frequency transmitted together over the optical fiber and they influenced each other,the chromatic dispersion was born.The chromatic dispersion reduces the power of MMW signal and distorts the symbols of baseband signal,which attenuated the transmission performance of ROF system severely.Many structures had been proposed to overcome the chromatic dispersion effect,but most of the structures are limited to different factors,such as the cost of transmitter,poor modulation efficiency or low MMW signal power.The multiple modulators structure is employed in this paper to generate MMW signal.The RoF system based on multiple modulators structure has several advantages such as simple transmitter mechanism,high MMW power,multiple frequency MMW signals generated in the same system,etc.According to the similarity between chromatic dispersion effect and multipath effect in the wireless communication system,it is conceivable that introduced orthogonal frequency division multiplexing(OFDM)technique can overcome the inter symbol interference(ISI)in RoF system.A multiple modulators structure based OFDM-RoF system is proposed and demonstrated in this paper,the transmission performance is also analyzed and discussed in detail.The mathematical model of multiple modulators structure based RoF system is introduced in the chapter 2,the three characteristics compared with conventional RoF system have been summarized and analyzed.The key technologies of OFDM have been discussed in chapter 3 in order to explain that OFDM how to overcome ISI.And the mathematical derivation of chromatic dispersion affecting on RoF system is given in the chapter 4.we found that the chromatic dispersion effect causes the power periodic fading effect and the ISI effect.The compensation schemes also proposed after a deeper mathematical derivation.In the chapter 5,the multiple modulators structure based OFDM-RoF system is built by employing Optisystem and Matlab simulation.After overcoming the power periodic fading effect and the ISI caused by chromatic dispersion,the transmission performance of RoF system is obviously increased,the long distance transmission of high frequency MMW signal in RoF system is realized.