The Research Of OFDM Baseband System Based On FPGA

In recent years, OFDM (Orthogonal Frequency Division Multiplexing) technology is researched widely. According to this new technology, many protocols are put forward. WiMax(Wireless Metropolitan Area Networks) represents air interface of the wireless communication system that content IEEE 802.16, the IEEE established the standard air interface of PHY, that's 802.16d. This protocol prescribe data is communicated by burst model. The way of modulation is OFDM, which has many advantages such as its high speed, low cost and so on. As a commerce standard, it has been generalized extensively.This paper mainly concentrates on the PHY of IEEE 802.16d and its realization on the FPGA Virtex pro II manufactured by the XILINX corporation.Firstly, the basic principle and the key technology are discussed. The baseband simulation link is built according to the physical flow of IEEE 802.16d OFDM system. Software like MATLAB and SIMULINK are used to find the differences between the case of with CP and without CP and the BER performance when the number of Rayleigh multi-pass is different. Because of the complexity of the synchronization algorithm and channel estimation algorithm, some other way must be created to reduce the calculation quantity so that the FPGA realization is possible. After analyzing several algorithms, a new way is found that is not only simple but also effective. The conclusion that the LS algorithm is the best one in the channel estimation in FPGA is also got easily.Secondly, the FPGA realization of transmitter and receiver is also completed in this paper. In order to raise the frequency of the system, the pipeline structure is used. In the design, the way of programming Verilog and use IP core is combined to save the resource. After some simplify on its structure, the new algorithm is realized without doing the difficult division in the field of complex number. Software flat ISE 9.2i and Modelsim 6.0c are used to design, synthesis and simulation. The results got from FPGA and data from MATLAB are compared carefully and no difference is found, which indicate that the sixteen bit data in FPGA can insure the accuracy.Finally, the RS-232 is used to check this system, which knows whether this system really works.