Research On Physical-layer Multicasting In High Throughput Satellite Communication Systems

Besides the advantages of satellite communication,such as the large coverage and the insensitivity to communication distance,High Throughput Satellite(HTS)communication systems have high throughput and low communication cost which make up for the deficiencies of traditional satellite communication.Recently,HTS communication has experienced rapid development,expanded application area and high communication demands.Commonly used transmission modes,such as unicasting and broadcasting,are inefficient to handle services with multicast feature for HTS communication.It is necessary to adopt high efficient transmission techniques to improve capacity of the system.Thanks to the multi-beam architecture implemented by multi-beam antennas,HTS systems usually adopt a four-color frequency reuse scheme among the beams and achieve a high frequency reuse factor to obtain high throughput.However,the four-color frequency reuse scheme is not able to make use of the available bandwidth.Full frequency reuse schemes can make full use of the available bandwidth to accommodate more users than before and implement flexible frequency scheduling among beams.With full frequency reuse,the feeds of several beams can cooperate to make targeted point to multi-point physical-layer transmission for multiple users with one radio resource according to user channel state,which can save the radio resources of the system.Nevertheless,there are only few studies of physical-layer multicasting in HTS communication systems,which only involve the multicasting in multiplex frame transmission to increase the efficiency of each frame.Thus,the advantages of physical-layer multicast transmission have not been made full use of in HTS communication systems.This thesis studies the physical-layer multicast transmission in HTS communication systems with full frequency reuse.Considering the characteristics of HTS communication,user scheduling and precoding according to user channel state information(CSI)are adopted to improve the performance of physical-layer multicasting in different application scenarios.The research contents and objectives can be specified as follows.First,models of physical-layer multicasting in different application scenarios are analyzed since current HTS systems fail to make full use of the physical-layer multicast transmission.Currently,research on multicasting in HTS systems only involves the multiplex frame transmission.Besides this,physical-layer multicast transmission can benefit various types of services.Thus,it is important to determine the application scenarios of multicast transmission in HTS communication systems.The multicast transmission of multicast services and multiplex frame transmission are analyzed and the corresponding transmission models are generalized.It is determined that user scheduling and precoding can be adopted to improve the performance of physical-layer multicasting.The above work acts as a basis for the follow-up work.Second,for multicast services,subgrouping-based multicast transmission is proposed to increase the spectral efficiency and corresponding user grouping algorithms are put forth.The number of users in each multicast group may be large on account of the large service area of HTS.The spectral efficiency of the multicast transmission may be low to guarantee that all the users can successfully receive the data.Thus,the purpose of the study is to improve the low spectral efficiency caused by the large number of users.Multicasting in multiple beams and a single beam are investigated,respectively.For the former case,the users are grouped according to user CSI to improve the spectral efficiency by dividing the users into subgroups,and two user grouping algorithms with low complexity are proposed.For the latter case,a layer-based transmission scheme which can provide differentiated services for users is proposed to improve the spectral efficiency of some users.Third,considering the long transmission delay and the stability of channel state,user scheduling and precoding algorithms with low complexity are investigated for the multiplex frame transmission in multiple beams to improve the performance of multicast transmission.To deal with the co-frequency interference caused by full frequency reuse,user scheduling and precoding can be adopted,respectively.Few studies have taken the characteristics of HTS communication into consideration during the algorithm design of physical-layer multicasting.Considering the long transmission delay of satellite communication,algorithms with high complexity may further increase processing delay.Additionally,since the channel magnitude does not vary significantly in fixed HTS communication,user CSI can be utilized for user scheduling and precoding,and the transmission should guarantee the fairness among users.The user scheduling is decoupled into two subproblems to reduce the complexity.User scheduling algorithms are designed aiming at guaranteeing fairness among users.The precoding is obtained by solving the precoding direction vector and power allocation problems.The concept of signal to leakage and noise ratio is utilized to reduce the complexity by setting up an optimization problem to obtain each precoding vector.The power allocation problem has the objective of maximizing the minimum fairness to guarantee fairness among users.