Research And Implementation Of CPRI Protocol In Multimode Optical Fiber Distribution System Based On FPGA

In order to meet the requirement of deep coverage of different types of wireless signals in the service area and to solve the problem of difficult management and maintenance in the construction of traditional networks,the communication operators introduced a multi-mode optical fiber distribution system.The multimode optical fiber distribution system consists of three parts:access unit,expansion unit and remote unit.Due to the lack of a unified interface standard,the connection of each unit will become difficult.In order to solve this problem,the CPRI protocol specification proposed by Common Public Radio Interface(CPRI)is adopted in the multi-mode optical fiber distribution system.According to this specification,the CPRI interface module is designed.The CPRI interface module will be used for the connection and data transmission between the various units of the system.Therefore,CPRI protocol specification is the key to realize interconnection of each unit in multimode optical fiber distribution system.Firstly,this paper studies the composition and content of CPRI protocol,and points out the current development of CPRI protocol.Then,according to the composition of CPRI protocol,the contents of each part are introduced in detail.Then the overall structure of the multimode optical fiber distribution system and the system composition of the remote unit are analyzed.The software and hardware resources needed to design and implement the CPRI interface module are introduced.This paper focuses on the design and implementation of CPRI interface module in remote unit by using hardware description language Verilog and FPGA chip.Based on the analysis and research of CPRI protocol,and combined with the system requirements,a feasible design scheme of CPRI interface module is proposed.The design scheme divides the CPRI interface module into three parts:the instant clock part,the physical layer design and the data link layer design.The clock part is composed of external clock generating circuit and internal clock of the FPGA.The physical layer consists of scrambling module,buffer module and high-speed serial transceiver module.The data link layer consists of superframe synchronization detection module,framing and decoding module,HDLC module,link management module and reset management module.Each sub-module will give detailed functions and specific implementation methods in the design.Finally,on the actual product equipment,the designed CPRI interface module is verified and tested,and the correctness of the connection design is verified by grabbing the signal waveform transmitted on the CPRI interface module by the integrated logic analyzer.The test proves that the CPRI interface module designed by FPGA has the characteristics of easy upgrade,flexible configuration,convenient implementation and low cost,and has good application value.