The Design Of Baseband OFDM Modem Based On FPGA

With the development of wireless communication, the transmission speed of communication system is being paid more and more attention. More and More governments and companies began to focus on how to communicate efficiently, high-speedily and safely.OFDM (Orthogonal Frequency Division Multiplexing) is a high-speed transaction technology which can defeat ICI (Inter-Channel Interference) and ISI (Inter-symbol Interference), so it makes OFDM more and more popular. OFDM transmits high-speed data through many sub-carriers which are parallel and have lower transmission frequency. All the sub-carriers are orthogonal, so their frequency spectrum can overlap each other. This can not only decrease ISI, but also increase frequency spectrum utilization. Because of all above, OFDM has become a popular research subject and the first choice in 4G mobile communication technology.In this paper, we introduce the basic theory and operating principles of OFDM. Then we analyze the related key technologies of OFDM modem and point out the advantages over other kinds of technologies. Fix point data format with 16 bits is designed for the system after full analysis of the structure of OFDM. Modules in modulator and demodulator are designed and implemented, including serial/parallel conversion, QPSK mapping/demapping, insert/remove pilot, IFFT/FFT, insert/remove CP and so on. A new FFT algorithm using pipleline, pingpong operation to coordinate speed and resource occupation is presented in this paper.The design is based on the chip of ALTERA's CycloneII EP2C20F484C7N. Verilog HDL is used as a tool in Quartus II and Modelsim in the design. Simulation waves are also given out. Finally, the feasibility of this design is proved by using the output data of the modulator as the input data of the demodulator.