Optimization Of Channel Estimation Algorithm For OFDM Systems And Multi-user Transmission Scheme Design

Orthogonal Frequency Division Multiplexing(OFDM)technology is one of the widely used technologies in contemporary mobile communication systems,which can effectively combat the effects of multipath fading and delay dispersion and provide higher symbols transmission rate and frequency band utilization.However,due to the complexity and time variability of the channel,the deterioration of the channel estimation performance will lead to a decrease in the performance of the receiving end.Existing OFDM channel estimation algorithms often ignore engineering application scenarios and implementation complexity for performance reasons.In order to meet the demand of large capacity and adapt to the application scenario where multiple users transmit data at the same frequency at the same time,a set of multi-user transmission receiving end detection system is designed.Based on this,this paper addresses the problem of noise interference in the Least Square channel estimation(LS)algorithm in the frequency domain.Design an algorithm based on Discrete Fourier Transform(DFT)and threshold-based pre-estimation denoising,using a hardware platform and Field Programmable Gate Array(FPGA)to verify the feasibility of the algorithm engineering implementation and performance.Aiming at the problem that the minimum mean squared error(MMSE)algorithm is too complex,a low complexity Linear Minimum Mean Squared Error(LMMSE)algorithm is designed by using leading auxiliary data.The platform verifies the performance of the algorithm.Finally,a joint preamble and pilot channel estimation algorithm is designed to improve the sensitivity performance of the receiver.Then,using the characteristics of channel sparsity in OFDM system,a signal estimation algorithm based on preamble modified adaptive orthogonal matching tracking compressed sensing is designed.Based on the previous compressed sensing channel estimation algorithm,this algorithm optimizes the input signal in the compressed sensing signal reconstruction algorithm and improves the accuracy of channel estimation.At the same time,for an unknown channel sparsity scenario,an adaptive channel sparsity estimation algorithm is proposed to achieve the same channel estimation accuracy under the unknown sparsity channel scenario as the known sparsity scenario.Finally,for the problem that the orthogonal multiple access technology cannot meet the system capacity of multiple users,the non-orthogonal technology based on the power domain is designed for the scenario of two users transmitting on the same frequency.Optimize the design of synchronization,channel estimation and demodulation for the process of Serial Interference Cancellation(SIC)at the receiving end to ensure the correct reception of each users information.Based on the feasibility of the hardware platform verification scheme,engineering tests show that the reception of two users information is accurately completed within a suitable transmission distance.