Research On Multicarrier Transmission Technique For Troposcatter Communication Systems

The troposcatter communication,which has the advantages of long single-hop communication distance,high obstacle-climbing ability and superior reliability,turns to be one of the main means of communications in future information system operations.The high reliability and large capacity are required in the troposcatter communication systems to transmit the command information and guidance data.Then,it is an important problem in military communication that to enhance the capacity of the troposcatter communication in different environment.After analyzing the architecture of troposcatter communication systems,the troposcatter channel characteristics and the method of anti-multipath interference are researched.In order to improve the communication capacity,the MIMO and OFDM/OQAM technology are introduced in order to reduce the influence of the time-varying and multipath property.The main content and findings are shown as follows:1.The basic network framework,including the foundational communication network,early-warning detective network,guiding & tracking network,is built.The functional component and topological structure of the communication network are analyzed,then the networking technology of troposcatter communication is researched.The principle and work mode of troposcatter communication systems are researched,according to the functional requirement of troposcatter communication.2.The statistics properties of the troposcatter channel,including slow fading,fast fading fading and the transmission loss,are analyzed.On this basis,the TDL channel mode is established.The channel testing projects are conducted,including signal changes with frequency,antenna azimuth and elevation.The changes of the signal in twenty four hours are also tested.Then the multipath time delay is researched,and the anti-multipath fading methods in troposcatter communication system are studied.The diversity and combining techniques of troposcatter communication are simulated and analyzed emphasically.The simulation shows that this technology is able to improve the troposcatter communication performance.3.The troposcatter communication system based on OQAM/OFDM is designed.The fast implementation method is proposed.Analysis and simulation results show that the technology can improve the troposcatter communication performance.For scattered pilot channel estimation in OQAM/OFDM systems,this paper proposes an iterative aided pilot channel estimation method,which can achieve better channel estimation performance without increasing pilot consumption and auxiliary pilot power.The compress sensing technology is applied to scattered pilot channel estimation,which effectively avoids the error caused by interpolation in traditional channel estimation methods and reduces the system pilot overhead.For blockpilot channel estimation,an iterative LMMSE method is proposed,which can achieve better performance without covariance matrix information of the channel.4.The MIMO technology is applied,and the MIMO-OQAM/OFDM technology is researched from two aspects of spatial multiplexing and spatial diversity.As for spatial diversity,the traditional Alamouti codes can not be directly applied to OQAM/OFDM systems.In this paper,a block-based coding method is proposed to overcome the influence of imaginary part interference on the orthogonality of Alamouti codes.As a result,the performance of the system can be improved effectively.In terms of MIMO-OQAM/OFDM systems,the channel estimation methods based on pairs of pilots and interference approximation methods are studied.Aiming at the problems existing in traditional frequency domain IAM channel estimation methods,the time domain channel estimation method based on block preamble is proposed.With this method,the error platform phenomenon caused by the frequency domain channel estimation method can be avoided as the channel delay spread is large.At the same time,this method uses fewer pilots,and can effectively improve the spectrum utilization of the system.