Study And Realization Of Channel Estiamtion Technology For OFDM System With Fading Channels

Nowadays, to meet all kinds of demands, crafts have been used in more occasions, such as forest fire prevention, marine survey, and so on. But data communication capacity of the occasions is enormous. And the environment is more complicated. So the traditional communication mode is difficult to fit with present demand. So the new transmission data link based on the OFDM technology is studied to resolve the bottleneck of data transfer rate. OFDM technology having the advantages of high spectrum efficiency, strong anti-interference capability and using IDFT/DFT to realize modulation and demodulation, has been the core of most promising technology in the new generation of wireless mobile communication system. OFDM system is very sensitive to frequency offset, but the poor propagation environment of wireless channel leads to amplitude and phase distortion of the transmission signals, and limit transmit speed of them. Therefore reliable channel estimation is the key issue to achieve high-speed data communication for OFDM system.At First, this paper analyses the transmission characteristics of wireless channel, and focuses on the characteristics of aeronautical channel. It discusses aircrafts should adopt different channel parameters in different flight states, and propose the method of modeling aeronautical channel. At the next, this paper analyses he realization principle and anti-jamming mechanism of OFDM technology, and studies various channel estimation algorithms and their performance in OFDM system. Aiming at the channel estimation methods based on the pilot, the paper research some inserted methods of Pilot including Block Pilot, Comb-type Pilot, and Scattered Pilot. In addition, the channel estimation algorithms is analyzed such as LS, MMSE, SVD, domain transformation, and so on. As the inserted Pilot algorithms Wiener filter algorithm, linear interpolation, Gaussian interpolation, Cubic interpolation are described and compared. After studying in-depth of inserted methods of pilot and the channel estimation based on the pilot, a two-dimensional pilot based on mob-type Pilot and Scattered Pilot is proposed for OFDM system, and uses the insert method to estimate channel character. Simulation result indicates that MMSE having better performance is too complicated to be realized, SVD is easier than MMSE, but its performance becomes worse with increased signal-to-noise ratio. The LS algorithm has been proved lower 2-4dB contrasted with the MMSE. But the LS algorithm is simple and easy to implement. So LS estimation algorithm based pilot, and combined with equalization algorithm are adopted to realize on FPGA. At last, the paper introduces the hardware platform of data link, and analyzes design of receiver and transmitter in data link base-band, including analysing scheme, selecting chip, designing circuit.The module combining channel LS estimation based on pilot with equalization algorithm is added to the base-band processing module in the OFDM system. By testing the module, the results indicate that the receiving data of various modulation after equalized are ideal, which meet the actual system design requirements. Finally, the hardware platform for data transmission conforms with design standard of software defined radio. Therefore, according to different demand of systems, it is required to change software design rather than to change hardware platform.