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DM towards slowing the pace of practice . Because the OFDM subcarriers are orthogonal to each individual , the use of FFT to achieve this modulation, but in practice , the time complexity of the Fourier transform device , the transmitter and receiver oscillator stability and linearity requirements of the RF power amplifier and other factors OFDM technology implementation. In the 1980s , MCM get a breakthrough , LSI technology to promote the implementation of the FFT , OFDM Modem and gradually enter the high-speed digital mobile communications field. 1990s , OFDM began to be widely used in Europe and Australia, the broadcast channel broadband data communications , digital audio broadcasting (DAB), high-definition digital television (HDTV) and wireless LAN (WLAN) and other fields. [ 1 ]

The fourth generation mobile communication system programs to OFDM (orthogonal frequency division multiplexing ) as the core technology to provide value-added services , it is in the field of application of broadband has great potential . Compared with the third generation mobile communication systems , using a variety of new technologies, OFDM has a higher spectrum efficiency and good anti-multipath interference, it not only can increase the system capacity , and more importantly, it can better meet multimedia communication requirements , which will include voice, data , video and other multimedia services through large amounts of information with high quality broadband channel sent . [ 2 ]

Ie, orthogonal frequency division multiplexing OFDM is a multicarrier modulation technique. And the traditional single- carrier system , OFDM system, each subcarrier channel spectrum overlap , so it has a high spectral efficiency , the spectral efficiency than single carrier nearly doubled. Meanwhile , OFDM through the string and conversion , reducing the impact on the system of the radio channel , enhanced anti-multipath and frequency selective fading capability simplifies channel equalization . You can also inserts a guard interval between OFDM symbols so that the guard interval is greater than the maximum delay spread of the wireless channel that can maximize the elimination of multipath caused by the inter-symbol interference (ISI), Thus , OFDM transmission technology as an efficient deep attention, and gradually become more standard key technologies , such as digital audio broadcasting DAB, digital Video Broadcasting DVB, wireless local area network , digital TV DTV and fourth-generation mobile communications.

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