| Orthogonal Frequency Division Multiplexing (OFDM) is a kind of digital modulation technology of multi-carriers, which has many characteristics, such as higher spectrum efficiency, stronger ability of anti-multi-path interference and lower cost. It is suitable for the demand of the wireless communications in high speed, broad band and mobility, and will become the pivotal modulation and transmission technology of the next generation wireless communications (4G) . An introduction to the concepts of wireless communications, channel characteristics, wireless local area network (WLAN) and mufti-carriers technology is given at first. The emphases are put on the researches on the key technology of realizing OFDM, the combination, of OFDM and mufti-input multi-output (MIMO) and the application in WLAN system. The main researches and results are the following:(1) The key technology of realizing OFDM. The technologies including the modulation and demodulation of sub-carriers, the circular prefix, the channel estimation and the option of the system parameters are discussed.(2) MIMO-OFDM technology. Combining MIMO with OFDM, the MIMO-OFDM technology has superiority in increasing system capacity and dependability. Taking the space time code technology as an example, the system structure of MIMO-OFDM is researched.(3)The application of OFDM in the WLAN system. Applying OFDM to the WLAN physical layer, there are many kinds of encoding and modulating modes. Such systems can support multi-speed transmission mode, have higher transfer speed and spectrum efficiency, and have better system performance. As an example, the system structure of IEEE 802.11a WLAN is discussed.(4) The research on the dynamic simulation of OFDM system. With the Simulink Toolbox of MATLAB software, the simulation model of the baseband OFDM system is built, the BER performance under different conditions are compared and analyzed, and the simulation results provide a valuable theoretic reference to practical systems.
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