Channel Estimation For Narrow Band Cofdm System And Its Implementation

To be a high-speed data transmission technique,orthogonal frequency division multiplexing(OFDM) has been widely used in wireless communication systems. Due to its capability to combat multi-path fading, in mobile communication systems,a dynamical estimation is necessary since the channel is frequency-selective and time-varying. The project employs the channel encoder method by cascading the RS encoder and convolution encoder. Through the interleave process, the capability of correcting normal channel error was guaranteed. Besides, this project increase the length of the outside interleave to 34 bytes. Because of that, 272 continuous errors can be corrected. It can decrease the error through channel estimation and equalization according to the received signal; thus, decrease the pressure of channel correcting. Therefore, channel estimation is very important to the performance in high-quality video transmission system.Firstly, this dissertation introduces the OFDM theory and the coder OFDM system; analyze the function and parameters setting of each module, given the design process of digital upconverter briefly.Secondly, the dissertation discuss the multi-path fading of wireless channel, compare the performance of DQPSK and QPSK, analyze pilot-based channel estimation, design the discrete pilot insert pattern according to the time-varying and frequency selective characters of the channel, compare the performance of several interpolation algorithms, improve the IDFT/DFT interpolation method, and the simulation result was given.Thirdly, through the analysis of the pilot-based channel estimation principle, design the channel estimation method by doing linear interpolation in time and second-order interpolation in frequency. Through the simulation platform of the channel model, analyze the symbol error rate and the distribution of constellation points, which prove that the scheme in this dissertation can be implemented effectively.Lastly, each module of channel estimation was implemented in FPGA according to the theory. Each module was tested and verified through the simulation in modelsim. Through debugging in FPGA, the performance of channel estimation was verified finally.