Research On LTE Adaptation For Satellite Mobile Communication

The Satellite Mobile Communication System has the advantages of wide coverage, high-quality outdoor channel and strong invulnerability, which is widely used in the construction of communication networks in remote areas, disaster relief emergency communications, military communications and other fields. With the development of the terrestrial mobile communications standards, many domestic and international research institutions have carried out extensive research to the next-generation satellite system mobile communication system and its key technologies based on LTE system since 2011. In China’s 12 th Five-Year Plan, it is drawn up to build the test network of our own satellite mobile communication system based on LTE(Long Term Evolution). Currently, the research to improve the adaptability of LTE system to the satellite environment becomes a key point in this field. This dissertation takes the integration of LTE and satellite mobile communications as a starting point, and focus on the adaptability improvement of downlink joint transmission technology, uplink timing synchronization and SIP session control protocol in GEO satellite. The main work is shown as follows:1. With the analysis of the key technical issues in the integration of satellite mobile communications and LTE, this dissertation describes detailly the MIMO technology, OFDM technology and the improved adaptability of protocol standards, and respectively analyses the system composition, load allocation and protocol of the satellite LTE system. By researching the propagation characteristics of satellite mobile communication channel model of wireless channel with studying three classic, the analytical expression of satellite LTE channel capacity is given combined with ground research of MIMO channel, to establish the theoretical foundation of this performance analysis.2. In view of the same frequency network in GEO satellite LTE system, the problem of random narrowband co-channel interference is serous, which is due to the user data randomly distributed in the subcarrier. To solve this problem, a cell model with frequency reuse in GEO satellite mobile communication system with the same frequency network is proposed. By analysing the joint transmission technology adaptation in existing multi-beam satellite downlink of the model, this dissertation puts out a kind of downlink transmission method based on BD(Block-Diagonalization) pre-coding algorithm, which is based on Lutz mobile satellite communication channel model. Theoretical analysis and simulation results show that the proposed method allows the user to obtain 0.8 ~ 1.8 bps/Hz channel capacity gain in the beam edge region and lower computational complexity.3. As the timing error in large satellite delay will destroy OFDM symbol orthogonality, the analysis of traditional satellite timing synchronization technology is discussed. Then drawing on the existing delay error estimation methods of mobile communication systems,an uplink timing synchronization optimization method based on LMS estimated is proposed, which is compensated by closed-loop control. The simulation results show that the proposed method can ensure the uplink timing synchronization accuracy to meet the requirements of the LTE standard synchronization in satellite environment, which reduces the loss of transmission rate 9% compared with the existing methods.4. Considering the large delay in session setup process when using the SIP protocol session control mechanism in terrestrial LTE system, a model of P2 P covering layer satellite overlay network based on DHT structure with P2 PSIP technology is proposed, which takes the structure characteristics of the SkyTerra satellite system communication system as a reference. With the adaptability improvement of the existing mechanisms, a kind of P2 PSIP session control mechanism suitable for GEO satellites is introduced. The simulation results with OPNET software show that the proposed session control mechanism can effectively reduce the number of signaling through the gateway station in the process of session establishment, thus reducing the session setup delay.