Design And Implementation Of OFDM Baseband System On FPGA

OFDM(Orthogonal frequency division multiplexing) modulation has high spectrum efficiency and the ability to cope with the frequency selective fading caused by channel multi-path effect. And it has become the key technique in physical layer of the 4th generation mobile communication and WLAN(Wireless Local Area Network) systems. FPGA(Field Programmable Gate Array) contains a large number of ALUs(Arithmetic Logic Unit), IP(Intellectual Property) cores and the ability of ISP(In System Programmability) and has been widely applied in the implementation of communication systems, especially in the prototype verification phase. Implementing the reconfigurable communication systems in concept of SDR(Software Defined Radio) on FPGA has become one of the development directions. In this paper, an OFDM baseband system referring to IEEE 802.11 a is designed and implemented on FPGA. The main work is as follow. Firstly, the coding techniques of OFDM based system are researched and implemented including scrambling and descrambling, convolutional coding and Viterbi decoding, blocking interleaving and de-interleaving. Secondly, the performance of common digital modulation is analyzed and the 16 QAM is implemented. Thirdly, the OFDM modulation and demodulation is implemented, including pilot insertion, OFDM modulation/demodulation based on FFT(Fast Fourier Transform), and CP(Cyclic Prefix) adding. Fourthly, the OFDM symbol synchronization algorithms based on CP and PN(Pseudo-Noise) preamble are analyzed and implemented. In this paper, the performance of the algorithm based on PN is proved to be much better than the CP based one. The OFDM baseband system in this paper is developed in QuartusⅡwith Verilog HDL.