Research On Relay Cooperative Communication Technology For High Speed Railway Mobile Communication Systems

The construction of high-speed railways has been developing rapidly recently.Railway transportation becomes a major mode of transportation gradually in all countries,because it has been relatively less affected by objective conditions and un-control factors.The highly operation speed of the railway has greatly facilitated to people's travel and reduced the time of train operations.The continuous improving train speed has brought convenience to people,meanwhile it has also increased much higher requirements for high-speed railway mobile communication systems.The user of train has many series to deal and need high-rate transmission of data for mobile communications.Lower data transmission rates,shortage of frequency resources and higher dropped calls have become an important problem confronting high-speed railway communications system.The user signal quality as well as the performance of the transmission link experiences severe loss due to wireless channel fading and propagation loss.In order to improve the quality at receiver side,spatial diversity is realized by means of cooperation technology based on the characteristics of uncorrelated channel.Compared with public moving scenes,the characters of user distribution range under HSR scenarios is distributed along the track and not random.In this thesis,the cooperative relay MRN is deployed on the top of the train,and the cooperative transmission between the relay MRNs is used to improve the communication performance from the base station side to the user terminal.The main research is divided into three parts: the reasonable distance of deployment relay MRN,the channel selection basis of cooperation relay MRN and the performance analysis of cooperative scheme based on statistics.Firstly,the reasonable distance of deployment relay MRN is studied.The cooperative transmission model formed by deploying the relay MRN in the high-speed railway scene becomes more complicated than the traditional railway mobile communication system.Considering the path loss under the high-speed railway scenario during signal transmission and in the case of fixed train length,the optimal spacing of deployed relay MRNs is analyzed.Secondly,when relay MRN is established in the cooperative communication model,the two-hop cooperative communication transmission link formed by the relay MRN under the high-speed railway scenario is affected not only by the backhaul link under rice fading channel but also by the access link rayleigh fading channel.It is necessary to study their respective impacts on the two-hop link to determine the basis for the selection of cooperative relay MRNs.The study show that when the two-hop link exist the backhaul link under rice fading channel and the access link rayleigh fading channel,the rice fading channel has a great influence on the two-hop link from the base station side to the user terminal.so,the cooperation selection scheme of relay MRN is based on the condition of the rice fading channel.Finally,the selection scheme of relay MRN based on statistical principles is proposed.The bit error rate performance and system throughput of the proposed relay cooperative scheme are analyzed and the simulation results are verified.The study of bit error rate performance is divided into two cases that considering the channel conditions of the access link and without considering the channel condition of the access link.The simulation results show that the cooperation scheme of this thesis can improve the bit error rate and system throughput at the receiver compared with the direct transmission.With the number of cooperative relay MRNs increasing,the bit error rate and system throughput performance are significantly improved.When the access link channel condition is better,the improvement effect is more obvious.