Research On New Genergation Mobile Satellite Communication System

With the continuous development of mobile satellite communication technology, the demand for satellite communications in both military and civilian users keeps on rising. Establishing a broadband satellite communication system with high transmission rate, wide coverage, short time delay and high flexibility has become the development trend in the future. OFDM system has become an alternative technical solution for the new generation satellite communication systems due to its simple implementation, bandwidth flexible configuration and high spectrumefficiency. However, comparing with terrestrial traditional mobile communication network, satellite communication has properties of large coverage, without being limited by the geographical and natural conditions, long communication distance and limited power, etc. Therefore, simply following the existing OFDM related technique will reduce the satellite system working efficiency or even cannot run normally.Random access technique, as the first interaction step between terminals and the communication network affects whether the whole process of communication system can work smoothly. And it is one of the key research problems of the satellite communication system. Therefore, research on random access technology which is suitable for the new generation satellite communication system is a technical challenge faced by constructing this system. This thesis adopts the new generation of mobile satellite communication system as the research object, and has a detailed research on the random access technology under this specificscenario. The main research results are shown as follows:(1) For the new generation of mobile satellite communication system, this thesis adopts the design idea of ZC sequence. Considering about the satellite communication properties of the large round-trip delay difference within one beam and the wide coverage of the beam, this thesis proposes two kinds of random access signal format design schemes. One adopts the classical random access signal format design scheme and designs a new format which is suitable for the new generation of satellite mobilecommunication system. This design scheme can basically meet the big difference of round-trip delay under normal random access process. The other scheme is based on delay pre-compensation. Before the access sequences are transmitted, the mobile terminal estimates the transmission delay roughly and compensates the delay, which makes the transmitted signals within one beam are synchronized with the beam center and arrive at the satellite receiver at the same time. This scheme can reduce the influence of large terminal round-trip delay within the same beam, save the time/frequency resources of the systems and guarantee a higher access performance.(2) In allusion to the problem of lower single satellite location accuracy for the satellite communication system, this thesis puts forward an enhanced satellite terminals autonomous cooperative positioning algorithm based on Kalman filter according to the new generation of mobile satellite communication system terminal cooperation mechanism. It utilizes the measurement of RSSI of the unpositioning mobile terminals within one spot beam to gain the parameters of satellites and the beam center and the parameter set under the cooperative condition. And then conduct least-squared rough estimation and Kalman filter quadratic optimization to determine the precise coordinates of the terminals. This algorithm can realize more preciseterminal positioning under the scenario of single satellite. Moreover, the proposed solution can reduce the positioning error range by increasing the collaboration terminals, which can improve the stability of localization.(3) In order to reduce the impacts on satellite communication system timing advanced estimation caused by the large Doppler frequency shift, this thesis proposes a lower complexity DFT spectrum analysis timing advanced estimation algorithm based on symmetric ZC sequences. This algorithm adopts the original ZC sequence and its conjugate sequence as the transmittedpreamble signal, and conducts multiplication and DFT operation with ZC and the conjugate of ZC sequence respectively at the receiver. And then make subtraction between these two parts of the signals to eliminate the Doppler frequency shift. This algorithm can improve the timing advanced estimation accuracy of high dynamic Doppler frequency shift without any additional time/frequency resources.(4) Evaluate the performance of the new generation of satellite communication systems and build a system simulation platform with the systemcharacteristics involving many key technologies. Simulate and analyze the performance of the new generation of mobile satellite communication system proposed by ITU. And provide the theoretical basis and data support for further research of the system. Finally submit a new generation of mobile satellite communication system assessment report to ITU as the assessment team of China.