Research On Multi-service Transmission System Based On Radio Over Fiber

With the appearance of some new high-speed and real-time services,such as interactive applications in recent years,the bigger bandwidth and the better performance of the communication system are needed under a big data condition.Thanks to large bandwidth and low loss of optical fiber communications,and the flexible access of wireless communications,radio over fiber?RoF?technology has become one hot topic for high-speed and large-capacity data transmission.Meanwhile,the transmission frequency and efficiency could also be further enhanced through novel designs of the RoF links and systems.As a result,the RoF system supporting multi-service is demonstrated,which would make some contributions to large-capacity transmission in theory.The corresponding research has an important significance in the practical applications as well.In this paper,we firstly make an overview of the system structure of the RoF technology and its development process.The research progress in the capacity improvement and structural simplification at home and abroad is also introduced.Subsequently,we analyze the research status of multi-service Ro F system.Finally,the typical modulation technologies to signal generation and processing in RoF system are analyzed theoretically in details.In particular,the multi-service access system is designed and demonstrated experimentally.Based on the theory above,this paper is organized as following:?1?The topology of the multi-service RoF system is design,and the transmission structure as well as the keying technologies is summarized.At the same time,the frequency band characteristics which must be available to reduce the interference between the services is analyzed in a unidirectional transmission.?2?A bidirectional RoF transmission system based on frequency-quadruped vector signal and wavelength reuse technique is proposed and experimentally demonstrated.For the downlink transmission,a stimulated Brillouin scattering-assisted narrow-band optical notch filter and a Sagnac loop are employed to generate a frequency-quadrupled vector signal directly in optical domain.At the base station,the unmodulated sideband of the downlink signal is filtered out by a polarizer and reused as the uplink optical carrier to achieve wavelength reuse.In the experiment,a quadrature phase shift keying?QPSK?signal centered at 24 GHz is generated by frequency beating.The system performance is evaluated by transmitting a 400 Mbit/s downlink QPSK signal at 8 GHz and a 400 Mbit/s baseband on-off keying?OOK?signal as uplink over a 6.15-km fiber link.The BER reaches 10^-5,and the eye diagrams and constellation diagrams indicate the bi-directional simultaneous system has an excellent transmission performance.?3?A real-time multi-service RoF system based on directly-modulated optical link is established.The experiment verifies the simultaneous transmission performance of an OFDM signal at 4GHz and an OOK signal at 10GHz.The length of fiber link is 10km,and the bit rate achieves 1Gbit/s.The BER curves are also measured,wherein both of them could reach 10^-5.The measured eye diagrams and constellation diagrams are quite well.Furthermore,a real-time RoF transmission of HDTV service is completed.According to the static link experiment,another real-time service experiment is demonstrated experimentally,involving VoLTE and HDTV signals simultaneously.These two services are respectively corresponding to the modulation formats of OFDM and OOK.In this experiment,after a2-km fiber link,the HDTV display is clear over another 1.5-m wireless channel,without delay frame,and the Vo LTE signal covers an 8-m distance,the voice calls are smooth.