The Design And Implementation Of GPON OLT Transmitter Circuit

With the growing need of access bandwidth from consumers, present bandwidth becomes insufficient for the future demands. As a representative of the next generation broadband access technologies, FTTx is an effect way to break the bottleneck of access and becomes the ultimate form of"last mile"in the future. GPON, i.e. Gigabit-capable Passive Optical Network, is the latest broadband access standard for passive optical network based on ITU-T G.984.x. GPON is a point-to -point fiber access technology which has the advantages of wide bandwidth, high efficiency, large coverage range and abundant user ports etc. Therefore, GPON is regarded as one of the best solutions to implement FTTx and to solve the problem of broadband access by experts in the communication industry. At present, the core technologies of GPON are in the hand of foreign firms and research institutes. Otherwise, some interflow has been realized on certain levels in domestic research, but there are still large spaces to be improved in functions and performances especially for the core technology: chip design.GPON system consists of OLT (Optical Line Terminal), ODN (Optical Distribution Network) and ONU/ONT (Optical Network Unit / Optical Network Terminal). As the startinging point of the entire GPON system, OLT transmitter is an important part of GPON system, affecting performance of the whole system. Research and development in this dessertation focus on hardware (RTL) design of the GPON OLT transmitter circuit.On the basis of analyses and research on ITU-TG.984.x Standard related to GPON, GPON structures and working principles including grobal structure, functional models, hierarchical model and protocol stack are introduced in this dessertation. Combined with G.984.2 protocol, some criterions on physical medium layer of GPON are briefly introduced. Finally the grobal design scheme of the GPON system was established.According to the specifications of the G.984 series standard, the designed structure of GPON OLT transmitter circuit is given in this dessertation, emphasizing the detailed analyses on main modules including asynchronous FIFO module, GEM framing module, PCBd module, GTC framing module, AES encrypting module, FEC coding module, scrambler module, CRC check module and initialization module. Schemes of every module are designed, and hardware description language Verilog HDL is used to complete RTL design. Simulations are issued on RTL design of modules and the results show that the design meets the demands of G.984 series standard.At last, FPGA system verification platform are introduced in this dessertation. RTL design of OLT transmitter circuit was verified by using FPGA prototype on this platform, and the verification results meet the demands of the design. Combined debug scheme of entire GPON system including OLT transmitter, OLT receiver, ONU transmitter and ONU receiver are also given based on this platform.