Research On Satellite Communication Downlink Beamforming Technology Based On Convex Optimization

With the advantages of wide coverage,long transmission distance,safety and reliability,satellite communication will play an increasingly important role in the field of mobile communication in the future.The spaceborne beamforming(BF)technology can effectively improve the spectral efficiency and communication capacity of satellite communication system by jointly processing the signals transmitted or received by multiple antenna units,so it has been widely used in satellite communication system.This thesis uses convex optimization tools to study the BF scheme of multibeam satellite communication downlink,as follows:1.A secure BF scheme based on the criterion of security rate maximization and limited satellite transmission power is proposed.Specifically,when the eavesdropper's location is accurately known,a BF scheme based on the generalized Rayleigh quotient is proposed.When the eavesdropper's approximate location is known,an iterative robust BF scheme is proposed by using Cauchy-Schwarz inequality,Charnes-Cooper method and semi-definite relaxation method.The computer simulation results show that the two proposed BF schemes have obvious advantages in improving the security performance of satellite communications compared with the traditional schemes.2.A secure BF scheme based on the criterion of security energy efficiency maximization is proposed under the condition of limited security rate and total satellite transmit power.When the location of the eavesdropper is accurately known,first fix the transmission power,and use the Charnes-Cooper method to convert the problem to a convex problem,and then use the golden section method to perform a one-dimensional search on the transmission power to obtain the optimal solution and BF vector.When the system only obtains the approximate location of the eavesdropper,a nested iterative algorithm combining fractional planning,penalty function,and Difference of Convex(DC)programming is proposed to complete the robust BF design.The computer simulation results show that the two proposed BF schemes can significantly improve the safety performance of the system.3.A BF scheme based on multi-objective optimization is proposed,which not only guarantees the fairness of resource allocation among multiple users,but also takes into account spectrum efficiency and energy efficiency.First,the trade-off between spectral efficiency and energy efficiency under the utility function is modeled as a multi-objective optimization problem(MOP).Then,the weighted sum method is used to transform the multi-objective optimization problem into a single-objective optimization problem.The maximum value of the spectral efficiency under the utility function is obtained by using the Cyclic Coordinate Ascent(CCA)method,and then the maximum spectral efficiency is substituted into the single objective optimization problem,and the Pareto optimal set and the corresponding BF weight vector of the original multi-objective optimization problem are obtained by using the cycle coordinate ascending method again.Finally,computer simulation verifies the effectiveness and superiority of the proposed BF scheme.