Joint Optimization Transmission Of Energy Efficiency And Spectral Efficiency For Multi-beam Satellite Communication System

In the integrated ground-air-space-sea for the future mobile communication systems,satellite communications(SATCOM)network has been taken as an important supplement and extension of terrestrial communication network.In order to provide broadband interactive data traffic,satellite is currently implementing a multi-beam radiation pattern.Full frequency reuse is used in SATCOM to utilize the spectral resources more efficiently,which also leads to severe inter-beam interference.The beamforming,as an effective interference mitigation technique,has been widely concerned by researchers.In addition,due to the focus on the energyefficient network,energy efficiency(EE)has become a key performance metric in the design of SATCOM transmission schemes.Motivated by these considerations,we investigate the joint optimization transmission of EE and spectral efficiency(SE)for multi-beam SATCOM in this thesis.Firstly,we study robust energy-efficient multigroup multicast transmission in multi-beam SATCOM.Specifically,we consider the beamforming design towards two different targets.The first target is to minimize the total power while guaranteeing that the EE of each group is above a prescribed threshold.To solve this problem,we first adopt a closed-form tight approximation for the ergodic rate.Then the semidefinite relaxation(SDR)and the concave-convex procedure(CCCP)are utilized to transform the difference of concave(DC)programming into a convex problem.Finally,based on the ranks of the optimal solutions,the eigenvalue decomposition or the Gaussian randomization approach is invoked to generate the final feasible solutions.The second target is to maximize the minimal EE of all groups under the total power constraint.To solve this nonconvex fractional programming problem,we first approximate this problem by the SDR and then convert the nonconvex constraints to convex ones by applying the bisection search and the CCCP.Numerical results validate that the ergodic rate approximation has high accuracy,and demonstrate that the proposed robust algorithms significantly outperform the conventional ones,especially for the cases with large channel phase error variances.Secondly,we investigate EE and SE tradeoff for multigroup multicast transmission in multi-beam SATCOM.The tradeoff between EE and SE provides a new perspective for the transmit design in SATCOM,i.e.,one can jointly optimize the system EE and SE of the SATCOM system.In addition,jointly considering that it is challenging to obtain accurate channel state information at the transmitter,we study the tradeoff between EE and SE for the robust beamforming in multi-beam SATCOM.Specifically,with the quality of service and total power constraints taken into account,we study the robust beamforming aimed at maximizing the resource efficiency,which is defined as the weighted sum of the system EE and SE,to achieve the tradeoff between EE and SE with more flexibility.To solve this problem,we first approximate the ergodic user rate and ergodic signal-to-interference-plus-noise ratio,both with closed forms.Then,SDR is applied to tackle the optimization of beamforming vectors via relaxing the rank constraints.To handle the sum of fractions involved in the optimization objective,a nested iterative algorithm exploiting the quadratic transformation and majorization-minimization(MM)algorithm is proposed.Finally,the eigenvalue decomposition is utilized to obtain the beamformers.Simulation results indicate the effectivity of our proposed algorithm in achieving the EE-SE tradeoff and illustrate the superiority of the robust approach compared with the conventional baselines.Finally,we study robust beamforming for non-orthogonal multicast and unicast(NOMU)transmission in multi-beam SATCOM.We model the multi-beam SATCOM system with NOMU transmission,where satellite simultaneously transmits unicast and multicast signals to multiple users.To be specific,we investigate joint optimization for EE and SE in NOMU system.First of all,the resource efficiency metric is used to transform the multi-objective optimization problem into resource efficiency maximization problem which is a single objective optimization problem.Then the approximate ergodic rates and SDR are adopted to simplify the problem formulation.Since there is DC programming expression in the numerator of the fraction which is in the objective function,MM algorithm is exploited to transform this numerator into a concave function.Then,the quadratic transformation is used to transform the sum-of-ratios programming into a standard convex problem.Accordingly,a nested iterative algorithm applying MM algorithm and quadratic transformation is proposed.Simulation results illustrate the performance gain of the NOMU transmission algorithm compared with the conventional one,which indicates that the NOMU technique plays a significant role in enhancing SE of SATCOM system.