The Research On OFDM Modem Realization

Orthogonal Frequency Division Multiplex (OFDM) is a new technology that transmits data in at a high speed on wireless channel. It belongs to multi-carriers modulating technology, and its most remarkable character is the high-speed transmitting ability as well as the excellent resistibility to interface of signal interval and decline of channel selectivity. Broadcast standards, DVB2T of Europe and ISDB2T for instance and HIPER/2 in wireless LAN standard, have adopted OFDM technology.The key technology of OFDM is Fast Fourier Transform Algorithm (FFT). Because of the large amount of the carrier wave to be modulate, the number of points to be calculated in FFT increases accordingly. So it can't be satisfied with traditional method and technology of electronic system design. The quick development of FPGA makes realization of OFDM possible. It operates fast, has flexible inner design, has multiplication unit which can be designed freely and has some memory units. All can be done in one chip.The OFDM modem in this design applies the XC3S400 chip that belongs to Spartan-3 series made by Xilinx to realize the OFDM modulation and demodulation in transmission system and receiving system. In transmission system, the original signal is modulated to OFDM signal after be coded in DPSK. And in receiving system, the modulated OFDM signal is synchronized and demodulated. The OFDM is modulated according to the signal parameter in DAB system. The paper introduces the theory and design of OFDM modem which include the hardware part and software part. This design has wide practicability and can be applies to the new generation of the digital audio and video system, HDTV and so on.