Research On Channel Technology Of MIMO-OFDM System

As the key part of MIMO(Multiple Input and Multiple Output)-OFDM(Orthogonal Frequency Division Multiplexing)system,Channel technology determines the quality of communication systems,and has great research value and significance.Therefore,this paper studied three aspects of MIMO-OFDM system:channel modeling,channel estimation and channel security capacity.Firstly,this paper established a MIMO channel model based on Jakes simulator with 2 by 2 Antenna constellation.Secondly,to avoid direct-current(DC)offset on the performance of channel estimation in MIMO-OFDM systems,this paper proposed a new SLS channel estimation based on zero correlation zone(ZCZ)superimposed training sequence.The main idea of the new approach is:use the good balance and related areas of ZCZ superimposed training to remove the affects for the performance of channel estimation.Thirdly,to reduce large computation complexity of the traditional MMSE(Minimum Mean Square Error)channel estimation method,we proposed an improved low complexity MMSE method.The advantages of the improved method in reducing computation complexity are as flowing:A)The new training sequence has good orthogonality,which can reduce the matrix inversion.So,it can greatly reduce computation complexity;B)The elements of the new training sequence in frequency domain are purely real or purely imaginary,which are simple and can thus simplify the calculation;C)Then the singular value decomposition algorithm is used to further reduce the computational complexity.Simulation results show that the improved MMSE method can not only keep good performance of MSE,but also greatly reduce computational complexity.Fourthly,for the security of system,the channel security capacity of the system which has the eavesdropper was studied.Based on Gaussian broadcast channel,this paper analyzes and verifies the changes of the channel secrecy capacity of the system with eavesdropper by the means of function derivation and simulation.The results show that under certain circumstances,the secrecy capacity will increase with the increasing of signal fading factor,signal to noise power ratio and the noise power radio between main channel and wiretap channel.Therefore,this thesis is significant in guiding MIMO-OFDM system channel technology research.