The Research On Predistortion Behavior Model Of Power Amplifier In Mimo System

To meet the needs of high-speed and high-capacity mobile communication,multiple-input multiple-output(MIMO)technique has been widely used in the current fifth generation(5G)mobile communication systems.However,while the application of this technique doubles the system capacity and spectrum utilization,due to the close distance between its radio frequency(RF)channels,it may even be integrated on the same chipset,which is easy to produce crosstalk between channels,and the crosstalk will introduce new nonlinear distortion through the power amplifiers and deteriorate the performance of the communication system.It will also bring new challenges to the linearization technique of the system.Thus,it is of great practical significance to study a linearization method that can compensate for crosstalk and amplifiers nonlinearity at the same time.In this thesis,low-complexity digital predistortion model is proposed for the problems of increasing the number of model basis functions due to the crosstalk in MIMO scenarios and excessive hardware complexity during calculation.The main work is as follows:1.In this thesis,a modified crossover digital predistortion model based on magnitude-selective affine function(M-CMSA)is proposed for MIMO systems,which can ensure the accuracy the model and reduce the hardware complexity.The M-CMSA model converts the high-order nonlinear term in CODPD into the linear function,which avoids the calculation of multiple complex number multiplication;At the same time,the improved segmentation method is used to extract model coefficients,which can effectively reduce the matrix size in the calculation process,simplify the inverse process of matrix transposition,and reduce the hardware complexity further.The performance of the model is verified on a 2 × 2 MIMO platform.For two 60MHz three carrier LTE signals,when-20dB nonlinear crosstalk is introduced.The experimental results show that the M-CMSA model has similar performance with the control item CODPD model,but the hardware complexity can be reduced by about 70%.Using M-CMSA model to compensate the nonlinearity of power amplifier in MIMO system can achieve higher model accuracy and better linearization performance under the premise of low hardware complexity.2.An improved digital predistortion model(Quasi-Parallel Hammerstein,QPH)based on Hammerstein model is proposed for MIMO systems.The model is composed of nonlinear module and filtering module,which can reduce the number of coefficients and reduce complexity significantly.An iterative identification method is adopted to solve the coefficients of the QPH model,which converges quickly and gets the coefficient solutions accurate.The experimental results show that the adjacent channel power ratio(ACPR)of the QPH model is more similar to the 2×2PH model than the CODPD model,the A-CODPD model and the curtailed C-DPD model for the two channel three carrier 60MHz LTE signals,but the number of the proposed model coefficients is reduced by more than 73%compared with the 2x2PH model;For two dual-carrier 40MHz LTE signals,the QPH model can achieve a linearization effect similar to the 2×2PH model with a much smaller number of coffients than the 2×2PH model.The digital predistortion model suitable for MIMO systems proposed in this thesis can reduce the consumption of hardware resources while ensuring model accuracy,and has a broad application prospect in MIMO mobile communication system.