Ofdm-based Broadband Network Testing Technology Research

This paper mainly discusses the principles of OFDM(Orthogonal Frequency Division Multiplexing) and the application in the field of ADSL(Asymmetrical Digital Subscriber Loop) broad band accessing. The technology of DMT(Discrete Multiple Tones) ,channel decode and complicated course control are deeply studied. The paper demonstrates the macro project design of ADSL signal acquisition card. The card can pick-up the ADSL signal from one POS(Phone Old System) subscriber without influence of the user's Internet surf and phone call. Finally it will send the ATM cell which are demodulated and decoded from original signal to PC via Ethernet. It will provide more dependable test data for the diagnosis of failure in the ADSL line. The hardware design of ADSL signal acquisition card is given in the paper. To meet the whole performance of system and macro design of the system, modularizing design is utilized. The pieces of high performance chip such as AFE(Analog Forward End) and Ethernet controller are used. Especially, FPGA is used as the core operation device in the system. Take advantage of its powerful and flexible performance capabilities, the complicated information processing and course control are both achieved. It makes the design more simple , less resources and lower price by the utilize of FPGA.Three kind of channel encode/decode technologies are researched which are TCM(Trellis Coded Modulation) and Viterbi decode, Reed-Solomn encode/decode and CRC(Cyclic Redundancy Check).The arithmetic for FPGA hardware are given, together with software simulations.Finally,The paper settles the problems of three kind of synchronization in the ADSL system(sample synchronization, ADSL frame synchronization and superframe synchronization).