The Research On The OFDM Communication System's Channel Estimating And Synchroization

Orthogonal frequency division multiplexing modulation uses many parallel sub-carriers, which transmit low-speed data, to realize high-speed communication. Because it's various advantages in lessening the severe effects of inter-symbol interference, OFDM is suitable for high-speed data transmission in wireless channel. The next generation wireless mobile communication system is expected to provide ubiquitous, high-quality, and high-rate mobile multimedia transmission. Due to OFDM's advantages such as high spectral utilization rate, simple hardware implement and specially the ability to oppose the frequency-selective decline and narrowband interference, it is highly recommended in the next generation of mobile communication. It is hot-point problem of current mobile communication research.This thesis introduces the history and current situation of OFDM technology at first, then narrates the basic principle of OFDM including OFDM's basic structure, time domain and frequent domain characteristics, etc. To make OFDM system's principle more clear, the typical figures of each part of OFDM are drawn. Furthermore, the advantages and key technologies of the OFDM system are presented. OFDM system is very sensitive to the synchronous errors of carrier frequency. In order to reduce the influence of frequency offset in OFDM system, it needs to estimate and compensate it. This paper reasearches on the advantages/disadvantages and the applying situation of the Maximum Likelihood Estimation (MLE), void-carries, pilot-frequency, and simulates to test its performance. What's more, the improved algorithm of time synchronization for a kind of OFDM symbol is proposed. This method can overcome the faults of required great sample data using the multi-symbol algorithm and shorten the time of time-capture. And the method deduces and puts forward the new related function used in decision. This paper builds a kind of the OFDM time offset estimation in the multi-path. This estimation can till work effectively even in the heavy multi-situation. Finally, this estimation performance is validated by simulation. Orthogonal Frequency Division Multiplexing; Channel estimation;...