Design Of Radio Over Fiber For Wireless Access Network

With the rapid development of communication industry,many emerging services come into our lives, which lead to the increasing demand for bandwidth and bring a serious challenge to the existing wireless communication system. ROF is one of the most promising way to solve this problem while combining the bandwidth benefits of the optical communication and the mobile benefits of the wireless communications. On the other hand, we can also improve the carrier frequency and explore unused millimeter-wave band, which can evade the congested frequency band and increase the communication bandwidth simultaneously. In this way, we can also break the bandwidth bottleneck. So it is easy to realize gigabit-class wireless access rate.In this paper, we first make an overview of the origin, research background, advantages,application fields and research status of RoF system. Then, the basic structure of RoF system and the different modulation schemes such as direct and external modulation are analyzed in detail. The generation mechanism of phase modulator and intensity modulator is deduced, and the realization principle of double sideband modulation single sideband modulation and carrier suppression modulation is described. At the same time,for the frequency conversion in the RoF system, the up-conversion of the signal is realized by the optical heterodyne method and the OEO, and the received signal is down-converted by envelope detection.(1) A frequency-tunable wireless access scheme based on optoelectronic oscillating(OEO) technology is proposed and experimentally demonstrated. By using this scheme, the frequency of the transmitted wireless signals can be tuned through adjusting the wavelength of the input light. 1.25 Gbit/s OOK signals with the carrier frequency of 8-14.5 GHz are generated and transmitted through a radio over fiber (RoF) link. Envelop detecting technique is employed in the receiver to support the down-conversion and demodulation. Electrical local oscillators (LO) are not required in the transmitter and receiver end, which simplifies the system structure and lower the cost.(2) Due to the poor wireless condition in the long tunnels, conventional communication technique cannot meet the high-quality communication demands of the passengers. A full-duplex radio over fiber system employing WDM-PON (Wavelength Division Multiplex-Passive Optical Network) with optical subcarrier reuse for the tunnel communication is proposed and experimentally demonstrated. By combining the WDM and DAS (Distributed Antenna System) techniques, a wireless access network can be achieved to provide different wireless services through optical channels. Moreover, the transmission bandwidth can be increased by using this proposed scheme which can also suppress the signal degradation under the scenario of tunnel transmission. The optical generation and transmission of electrical 16/64QAM vector signals at 24 GHz are demonstrated in proof-of-concept experiments.(3) Combining the multi-carrier technology with RoF technology, the OFDM-RoF link is simulated using the optisystem 14 software. Then, based on the commercial 4G VoLTE system, we set up the VoLTE-RoF demonstration verification platform experimently, realizing the long-distance transmission of the voice and video signal.