| As the rapid progress of Internet, data services have grown up fast, and all these have brought new taste of the wireless networks. But nowadays wireless systems, such as 3G, WLAN, have some defects in respect of speed, cost, range and mobility. So the mobile broadband wireless access (MBWA) has got more and more attention.The mobility provided by the transmission of speech and data without the need of a cable connection has lead to the wide integration of mobile telephones and computers in every day's life. With the increase in transmission speed and quality, provided by these techniques new interesting services, e.g. video telephony or the ubiquitous usage of the Internet can be provided to the mobile user. However, the benefit of mobility adds a certain cost to the system. Unlike cable connections, wireless systems suffer from a high variance of the delay and the attenuation of the transmitted signals. This effect varies over time and frequency and rises with the data-rate. In order to assure the fault-tolerant transmission, while providing high data rates Orthogonal Frequency Division Multiplexing (OFDM) has been developed. With OFDM the spectrum is separated into small sub-bands, the so-called sub-carriers, which are placed in order to assure a high utilization of the given bandwidth.OFDM technology has gained much attention these years for its excellent behavior in spectrum utilization, parallel data processing, anti-interfere, etc. And OFDM has been listed as one of the candidate technologies of the next generation communication system. When the signal based on OFDM transmits through the wireless channel, it undergoes the frequency selective loss, and different sub-carriers of one... |
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