Study Of Channel Estimation Algorithm In OFDM System Based On IEEE802.11a And Realization On FPGA

OFDM technology is an effective way for the high-speed data stream transmission,whose strong anti-interference ability and high spectral efficiency can meet people’s urgentrequirement on high-speed wireless transmission, therefore, the application of OFDMtechnology has been paid more and more attention. However, the OFDM system is verysensitive to frequency offset, and the distortion of the amplitude and phase of thetransmitting signal may occur in a poor wireless channel environment which will affect thecommunication quality of the OFDM system. Therefore, the channel estimation technologyof OFDM system is one of the key technologies to ensure that the data transmission fasterand reliable.This thesis describes the basic principle of OFDM technology and IEEE802.11aprotocol specification. The transmission characteristics of the wireless channel and thechannel estimation algorithm for OFDM systems are researched in the thesis, and theperformance of LS algorithm, MMSE algorithm and SVD algorithm based on the trainingsequence and linear interpolation, second-order interpolation, Cubic interpolation, DFTinterpolation, DCT interpolation based on pilot are analyzed via simulation. The thesisBuilds a system simulation model of channel equalization and demapping under the Matlabenvironment based on IEEE802.11a. According to the frame structure of IEEE802.11aprotocol and the characteristics of the indoor wireless channel, the LS channel estimationalgorithm based on the average is utilized and whose superiority is verified by the simulationdiagram of the mean square error and bit error rate. Finally, the thesis carry out the hardwaredesign for LS channel estimation based on the average and equalization part combinningwith Matlab simulation using Spartan-3E development board of Xilinx as hardware platformand Verilog HDL language as programming language. The whole design including: themodule of long training sequence extraction, the channel estimation module, the energycalculation module, the channel equalization module. According to analyzing the results offunctional simulation and hardware simulation of each module, a conclusion can be obtainedthat they have the same simulation results, which can prove the channel estimation andequalization is correctly implemented on the FPGA. Because the simulation result of channelequalization can not directly reflect the correctness of the equalization result, therefore, onthis basis, the hardware design of demapping part is added to this thesis. By observing theoutput data of demapping, it can be found that the hardware simulation, the Matlabsimulation and the functional simulation have the same results; this can verify the correctness of the hardware implementation of demapping module and the output results of channelestimation and equalization. Get the channel estimation and equalization module anddemapping module to be co-simulation tested, the results show that on-line test results onFPGA are consistent with the functional simulation results. The simulation results show thatthe channel estimation and equalization module and the demapping module can be used as asub-module of the whole OFDM baseband processing receiver, calibrating the amplitude andphase change of the data caused by the wireless channel and do demapping for the correcteddata realtime and continuous.