Coding Design And Optimization Of Satellite-to-Ground Wireless Communications

In recent years,multibeam satellite communications have attracted the interest of the industry and academia with its high spectrum efficiency and high energy efficiency(EE).Considering that future wireless networks will need to support a rapidly increasing data flow and provide stable and reliable network coverage in remote areas,multibeam satellite communications can make flexible and efficient use of available resources to meet the needs of future wireless networks.In order to solve the problem of spectrum scarcity,technologies such as multiple-input multiple-output(MIMO),large frequency reuse factor,and precoding have been used in multibeam satellite communications to enhance system performance.This work mainly studies the coding design and optimization of satellite-to-ground wireless communications(SGWC)based on multibeam satellite to improve system capacity and EE.In order to reduce the bit error rate of SGWC,the application of space frequency coding technology in narrowband single satellite dual polarization(SSDP),dual satellite single polarization(DSSP)and dual satellite dual polarization(DSDP)systems is studied in this work.Specifically,the Alamouti space-frequency coding scheme based on 2×2 MIMO-orthogonal frequency division multiplexing(MIMO-OFDM)is applied to the SSDP system and DSSP system,while the G4 space-frequency coding scheme based on 4 × 4 MIMOOFDM is applied to the DSDP system.In order to improve the multiuser sum rate of SGWC,the problem of user grouping under the unicast scenario to maximize the sum rate is studied in this work,and how to divide users into multiple groups with the same number of satellite beams is considered.According to power and channel correlation,users are selected one by one and put into the group to maximize the sum rate of the group where the user belongs,until the group sum rate no longer increases or the number of remaining users is zero.As a comparison,the situation removing the restrictions that the group sum rate no longer increases in the above iteration stop conditions is considered in this work,so that all users can be assigned to a group to obtain SGWC services.In order to optimize the EE of SGWC,the satellite precoding technologies in the unicast scenario and the unicast joint multicast scenario are studied in this work,in which the total power and the quality of service are constrained without loss of generality.In fact,the EE maximization problem is a fractional programming(FP)one,which can not be solved directly.For unicast scenarios,an EE optimization algorithm based on quadratic transformation(QT)is presented in this work.By implementing QT,the numerator and denominator of the EE expression are decoupled;then the numerator and denominator of the signal-to-interference-and-noise ratio(SINR)expression are decoupled by using QT again.Therefore,the original non-convex problem is transformed into a convex optimization one that can be solved iteratively.For unicast joint multicast scenarios,an EE optimization algorithm based on minimum mean square error(MMSE)is presented in this work.First,the original problem is transformed into a concave-convex FP one by using the equivalence between MMSE and SINR.And then the concave-convex FP problem is transformed into a convex one by using the first-order Taylor lower bound approximation and Charnes-Cooper transform.Therefore,the joint optimization of the tranmitter precoding and the receiver merge is realized.Finally,the effectiveness of the above algorithm is verified by simulation.