| It is imperative to carry out related research on new generation of civil aviation ground-to-air broadband data link to satisfy the ever-expanding needs of air passenger communications in future ground-to-air communication system.LTE(Long Term Evolution)aviation ground-to-air broadband system,which is based on OFDM technology,gains more and more attentions depending on its better utilization of spectrum,capability of anti-multipath and support of access to high-speed terminals.Channel estimation is a necessity for coherent demodulation,which is really important for LTE aviation ground-air broadband system,especially in face of scarce spectrum resource,large delay spread and large frequency shift under high-speed movement of the aircraft,so it's urgent to propose a new channel estimation algorithm to solve the above problems.Therefore,in consideration of the damage of the orthogonality of subcarriers and abnormal transmission of singal,which is due to the large delay spread and large doppler shift,this thesis combined the sparsity of aeronautical channel and studied the application of Compressed Sensing theory to channel estimation in LTE aviation ground-to-air broadband,considering transmitting characteristics of ground-to-air channel comprehensively,and constructed a frame suitable for channel estimation of LTE aviation ground-to-air broadband system instead of the traditional orthogonal basis acting as the measurement matrix to improve the performance of channel estimation and utilization of spectrum resource,which is furthermore,providing the support and foundation of physical layer transmission technology for the development of LTE aviation ground-to-air broadband system.The main contents of this thesis are as follows:(1)Instead of the partial Fourier transform matrix as measurement matrix in the traditional sparse channel estimation,this thesis introduced the concept of frame,which is suited to aeronautical LTE air-ground broadband communication system,put doppler shift into this frame to make compensation for aeronautical channel at the receiver,combined the redundancy characteristics of the frame to increase the number of sampling points of channel in delay-doppler domain and enhance the sparse representation of channel,and finally overcomed the defects of orthogonal base employed in traditional channel estimation under the environment with large delay spread and large frequency shift.This implement can provide the support and foundation of tramsmitition technologies of physical layer for the future development of LTE aviation air-ground broadband communication system.(2)The performance of traditional algorithm of channel estimation :LS,LMMSE algorithm,traditional algorithm of sparse channel estimation and sparse channel estimation based on frame construction proposed in this thesis were compared and analyzed in BER(Bit Error Rate),MSE(Mean Square Error),reconstruction error,distribution of Constellation diagram and running complexity,etc;Analyzed the impact of pilot number,pilot patterns,doppler shift and maximum delay spread to the performance of BER and MSE.The simulation results show that the performance of the improved algorithm proposed in this thesis is better than that of the traditional channel estimation algorithm in the BER and MSE on the premise of the same pilot pattern,which performs 5d B improvement in BER and MSE and reduces the number of pilots largely;It performs nearly same when the number of pilot is more than 8 times of the sparsity and performs quite well when the number of pilot is between 4 to 8 times of sparsity;The performance of random pilot is better than that of uniform pilot,such as comb pilots;The improved algorithm performs better when the doppler shift and maximum delay spread is smaller.These results can serve as guidelines for channel estimation and equalization research in LTE aviation ground-to-air broadband system,which can also promote the application and deployment of LTE aviation ground-to-air broadband system furthermore. |
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