The Design of Distributed Antenna System Based on RoF

云昊

季伟

硕士

山东大学

光无线融合接入网;;RoF-DAS;;Sigma Delta调制/解调;;光控相控阵;;波束赋形;;无线定位

随着移动通信技术的发展,智能移动设备数量的快速增长导致流量数据的激增,因此寻求一种高速率、大容量、长距离的光无线融合接入网的设计方案,成为学术界与工业界的研究重点之一。光载射频技术(Radio-over-Fiber,RoF)融合了无线通信移动性与灵活性强的特点以及光纤通信低损耗、大带宽、高可靠性等优势,为接入网高效而灵活的部署提供了有效的解决方案,符合光无线融合接入的发展趋势。同时,分布式天线系统作为5G移动通信网络的关键技术,相较于传统的集中式基站,进一步拉近了用户与基站间的距离,提升了通信网络的频谱利用率、能量效率以及部署的灵活性,并降低了布设成本。本文主要对基于RoF的分布式天线系统(Distributed Antenna System,RoF-DAS)在接入网中的实际应用展开研究,主要的工作如下:(1)本文首先提出了一种基于RoF的分布式天线系统设计方案,介绍了系统架构中的关键模块及参数指标,包括:基于IEEE 802.3协议改进的MAC(Medium Access Control)帧结构、光开关阵列、基于星型拓扑结构的光纤分配网络、基于反射式半导体光放大器(Reflective Semiconductor Optical Amplifier,RSOA)的无色化远端天线单元(Remote Antenna Unit,RAU)。利用MAC帧中的地址码实现了对各分布式阵列天线的地址标识以及信号收发的灵活控制。(2)针对RoF链路优化的问题,本文研究了一位Sigma Delta调制器的调制/解调原理以及在系统中的应用。该调制器可以在电光转换前将射频模拟信号转换成数字脉冲,相较于传统的光载射频模拟链路,有效克服了信号在光纤传输过程中的衰减与失真。(3)为了进一步提升系统的能量效率,本文研究了基于光控相控阵的波束赋形技术。设计了基于光开关切换的光延时线阵列结构,利用光开关对阵列中的延时线进行切换,控制光载射频信号的相位,进而实现阵列天线在不同方向上的波束指向。(4)根据已设计的RoF-DAS系统架构,本文提出了一种基于TDM-TDOA(Time Division Multiplexing-Time Difference of Arrival)技术的无线定位机制。基于系统的分布式天线轮询机制结合TDOA技术,完成定位参数的采集和计算,并利用现有的无线定位算法(Chan算法、Chan与Taylor协同算法)实现了对系统覆盖范围内终端的位置计算,同时,研究了 TDOA测量值引入的误差在不同的阵列天线数量以及定位算法下对系统定位精度的影响。其次,设计了基于RoF的分布式天线组网架构并实现了健康信息采集业务的承载,以ZigBee终端作为底层传感数据采集设备,利用RoF链路将传感数据上传至ZigBee协调器,最终通过串口被PC端上位机接收并实时呈现。

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.