The Performance Analysis Of Space Information Transmission Based On Satellite Cooperation

As the rapid development of satellite communications,the space communication based on satellite cooperative communications has been a complementary system for terrestrial communications,which makes it be able to meet the requirements of the space exploration and the integration communication in the furure.Space communications always have bad performance caused by asymmetrical data transmission and special channel condition,where the asymmetrical data transmission is resulted by the reason that each communication node in the space communication lies in different geographic location.In addition,the bad weather conditions and the obstruction in surrounding environment make the channel in space communications be special.Hence,aiming at the above problems in the space communication,this paper analyzes the system performance of spaces communications based on satellite cooperative communications.First,in order to solve the asymmetrical data transmission in space communications based on satellite cooperative communications,this paper proposes a novel scheme by combining hierarchical modulation and network coding called HM-NC.In the proposed scheme,under the condition of two sources-one relay-one destination the channel between satellite and ground node is model as shadowing-Rice fading,then that between ground nodes is described as Rayleigh distribution.In the following,the satellite relay received the asymmetrical data form two sources and dealt with them by HM-NC.According to the transmission of each node,we derive the expressions of BER,throughput and access probability by adopting HM-NC,traditional scheme and Opportunistic User Selection?OUS?scheme.The simulation results show HM-NC can reduce BER and improve the throughput performance.Second,aiming at the issue that the space communications based on Ka-band satellite communications are suffered influence from the weather and surrounding environment,this paper proposes a new two-state and three-order channel model,namely rain-average shadowing and clear-average shadowing.As for each state,the shadowing is divided into three orders according to the influence level of the shadowing,that is infrequent light shadowing,average shadowing and frequent heavy shadowing.Futhermore,based on the two-state and three-order channel model,an adaptive transmission scheme is proposed.First,we choose seven modulation and coding schemes which are commonly used in space communications.Second,in case of the Bit Error Rate?BER?threshold is10^-6,then this paper designs the adaptive transmission scheme by simulating the BER,computing the Signal Noise Ratio?SNR?threshold and deciding the Modulation and Coding Scheme?MCS?respectively for two-state and three-order channel conditon in Ka-band space communications.At last,simulation results demonstrate the adaptive transmission scheme cam improve the system throughput and spectral efficiency.