Research On Synchronization Technology Of OFDM Wireless Communications System

Orthogonal frequency division multiplexing (OFDM) is a special form of Multicarrier modulation, where a single data stream is transmitted over a number of lower rate subcarriers. The basic idea of OFDM is to divide the available spectrum into several orthogonal subchannels (subcarriers). By making all subchannels narrowband, they experience almost flat fading, which can almost eliminate inter-symbol interference. And that the frequency response of the subchannels is overlapping and orthogonal help OFDM obtain a high spectral efficiency. Because of the robustness against frequency selective fading and high spectral efficiency OFDM is considered as the enabling technology for transmitting data at extremely high rates over time-dispersive radio channels.However, one of the arguments against OFDM system is that OFDM is highly sensitive to synchronization errors, in particular to the frequency errors. How to obtain correct OFDM symbol timing and carrier frequency efficiently is highly critical to OFDM systems. OFDM systems need the subcarriers to be strictly orthogonal or the carrier frequency errors will bring serious inter-carrier interface which will reduce the performance of the system greatly. At the transmitter OFDM system modulates data onto the subcarriers using IFFT and demodulates the data from the subcarriers by FFT at the receiver. So how to get the correct FFT widows position is im-portant to the OFDM system performance. In digital OFDM receiver, the received continuous-time signal is sampled at instants determined by the receiver clock. The effect of a clock frequency offset is twofold. First, the useful signal component is rotated and attenuated and second the...