| The fifth generation mobile communication(5G)is mainly driven by the requirements of ultra-high spectrum efficiency,low latency,and high energy efficiency in the future applications such as Internet of Things(IoT),Gigabit-level wireless connectivity,and Tactile Internet.Due to the filter-bank multicarrier(FBMC)can overcome the disadvantages of synchronization and large carrier side lobe that exist in the Orthogonal Frequency Division Multiplexing(OFDM),it has been selected as the physical layer candidate scheme of the long-term evolution(LTE)and IMT-2020.At the same time,since the 5G needs to support diverse scenarios and machine-typecommunication which require large system throughput and massive connections,nonorthogonal multiple access(NOMA)is an appropriate technology that can be applied to the above scenarios.Radio over Fiber(RoF)is a key network access technology of the fifth generation mobile Internet.It can be used as a "transparent" technical solution to achieve a large-capacity low-cost wireless signal joint processing network which is reliable,easy-to-maintain maintenance and management.The new air interface technology and RoF technology are hot topics in 5G research.The parameters in the 5GRoF system will affect the signal transmission,which will affect the design and application of the 5G system.In order to provide some references for the application of the new air interface physical layer in 5G-RoF system,in this thesis,FBMC and NOMA applied in 5G RoF optical transmission are investigated.The theoretical models are established and the transmission performance is analyzed.Finally,system performance enhancement methods are studied.The main work in this thesis are as follows:The basic structure of the RoF system and the characteristics of optical modulator and optical fiber transmission link are analyzed.Based on the basic principles of FBMC,a verification platform of FBMC-Ro F optical transmission system is designed and built.The theoretical model of 5G-RoF system based on FBMC is established.The optical characteristics of fiber-optic link which play a role as the carrier of wireless signal transmission in RoF system are analyzed,and the influence of fiber nonlinearity on the transmission of FBMC wireless signal is analyzed.The research results indicate that the dispersion in the optical fiber will affect the transmission of wireless signals.At the same time,the effects of changing the wireless carrier frequency and the transmission rate on the system performance are analyzed.Finally,the analysis of the influence of the change of optical launch power on the system performance are deeply studied.A centralized feedback-based pre-equalization mechanism and a method of using dispersion compensating fiber to resist frequency selective fading are studied.In the centralized pre-equalization,preambles acting as training symbols are transmitted to the user equipment.At the user equipment ends,those training symbols are feedback to the transmission end.Feedbacks from multiple users will be used to estimate the channel and pre-equalize the signals.In the scheme of apply dispersion-compensating fiber,the dispersion-compensating fiber is used as a component of the RoF fiber transmission link to compensate the chromatic dispersion in the single-mode fiber.The research results show that the two schemes can effectively compensate for the damage to the high frequency part of signal caused by the frequency selective attenuation loss which due to the fiber-optic dispersion.Based on the basic principles of NOMA,a verification platform of NOMA-RoF optical transmission system is designed and built.The theoretical model of 5G-RoF system based on NOMA is established.The influences of power allocation,modulation format and optical fiber transmission distance on system performance in power domain non-orthogonal multiple access are investigated.Then,the effects of non-linearity in signal modulator and the change of optical power on system performance are deeply studied.The research results indicate that there are different optimal power allocation values for different modulation formats;the optimal performance can be guaranteed by properly setting the modulator parameters and the optical power. |
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