The Design Of Distributed Antenna System Based On RoF

With the development of mobile communication technology,the rapid growth in the number of smart mobile devices leads to a surge in wireless data traffic.Therefore,a high speed,large capacity and long distance design scheme is urgently sought for optical wireless converged access network in academia and industry.The RoF technique combines the feature of highly mobile and flexible in wireless communication and the advantages of low loss,large capacity and high reliability in the optical fiber communication,which provides an effective solution to the efficient and flexible deployment of access networks and meets the development trend of optical wireless hybrid access.Simultaneously,as one of the key technologies for the 5th generation wireless systems,the distributed antenna system greatly shortens the distance between the base stations and users compared with conventional centralized system.Moreover,it can efficiently improve the spectral utilization,energy efficiency and deployment flexibility,and reduce costs.This thesis focus on the practical application of RoF-DAS in the access networks implementation,and the main work are shown as follows.(1)Firstly,a design scheme of radio-over-fiber distributed antenna system is proposed.Key modules and parameter indicators in proposed system architecture are demonstrated,including modified MAC frame based on IEEE.802.3 protocol,optical switches array,RoF network based on star topology and colorless RAU based on RSOA.Using the address code of the MAC frame,address identification and flexible control of signal transmission and reception for each RAU would be achieved.(2)How to optimize the performance of point-to-point RoF links is a urgent problem.In the second part,we study the modulation/demodulation of a one-bit sigma delta modulator and its application in proposed system.An analog RF signal is converted into digital serial bit stream after sigma delta modulation before electro-optical conversion.Compared with conventional AROF(analog radio-over-fiber)link,it is highly immune to attenuation and distortion during signal transmission over fiber.(3)To improve the energy efficiency of proposed system,beamforming technology based on OCPAA(Optically Controlled Phased Array Antenna)is studied.Firstly,OTTDLA(Optical True Time Delay Line Array)based on optical switches is designed,optical switches are utilized to select delay lines we need to control the phase of RF signal on an optical carrier,which completes the beamforming of PAA(Phased-Array Antennas)in different directions.(4)According to the structure of RoF-DAS designed by us,wireless positioning mechanism based on TDM-TDOA technology is proposed.Firstly,combining distributed antenna polling mechanism with TDOA technology,parameters collection and calculation are completed.These parameters are combined with classical positioning algorithms(Chan Algorithm,Chan Assisted Taylor Algorithm)to calculate the position of terminals in system coverage.Meanwhile,we have done some simulations to analyze the system positioning accuracy in terms of different algorithms and PAA amounts.Secondly,application of health information collection is achieved based on RoF-DAS architecture.Sensor data is collected by Zigbee end devices,which is transmitted to the coordinator by the RoF link.Finally,it is received by PC and displayed on the host computer.