Multi-beam Coordinated Transmission For Satellite Mobile Communications

Due to the high throughput demand of future satellite mobile communication systems,the multi-beam architecture has been generally adopted in the satellite mobile communication systems to provide services to users in the wide coverage area.In the multi-beam satellite mobile communication systems with full frequency reuse,inter-beam interference(IBI)has become the major obstacle for increasing the overall system throughput.To reduce IBI and achieve the advantages of multi-beam coverage,the channel between multiple beams on the satellite side and multiple users at the earth can be regarded as a multiple-input multiple-output(MIMO)channel for multi-beam coordinated transmission.We investigate multi-beam coordinated transmission for satellite mobile communication systems in this thesis.Firstly,the multi-user downlink multi-beam joint precoding is investigated.We investigate the multi-user regularized zero forcing(RZF)precoding for the single satellite scenario.Simulation result shows that,the proposed approach can offer better gains especially with smaller reuse factors compared with the conventional approach.For coexisting multi-beam satellite mobile communication systems,despite mitigating the IBI in every single satellite,adjacent satellite interference(ASI)still needs to be handled.We firstly introduce the system model with inter-satellite cooperation or coordination.Combined with the multi-satellite multi-user RZF precoding,we then propose a user scheduling method with the goal of maximizing the system sum rate.Numerical results demonstrate the advantage of the proposed approach over the traditional approach in terms of sum rate.Moreover,we propose a low complexity frequency coloring algorithm for coexisting multi-beam satellite mobile communication systems.Secondly,we investigate multicast downlink multi-beam joint precoding.To mitigate the effect of imperfect channel state information(CSI)due to the long propagation delay,we propose average signal to interference plus noise ratio(SINR)maximization and outage-based robust multigroup multicast precoding.We first investigate robust multigroup multicast precoding that maximizes the minimum average SINR under the per beam power constraints.We show the relationship between the robust max-min fair problem and the robust power minimization problem with partial CSI.Motivated by this,we propose a precoder for the robust power minimization problem,in which the semidefinite relaxation and Gaussian randomization are adopted.Then,we investigate an outage-based multigroup multicast optimization problem under the criterion of minimizing per beam transmission power while guaranteeing that the probability of each user's achievable SINR larger than a given threshold.By developing an approximation method to transform the computationally infeasible probabilistic constraints into a tractable form,we then propose a low complexity precoder based on the semidefinite relaxation approach.Moreover,we investigate user clustering which only requires partial CSI and derive the condition for user clustering to maximize the approximated average SINR,and we obtain that the users with high dependent estimated channel vectors should be merged into the same cluster.Motivated by this user clustering condition,we further propose a low complexity user clustering algorithm.Simulation results demonstrate that both of the proposed robust approaches can provide substantial performance gains over the conventional approach.