Research On Key Technologies Of Satellite Communication Terminals For Maritime Buoys

With the increasing frequency of global ocean exploration,the data rate of data relay communication based on satellite communication from deep sea to land is getting increasingly higher.The satellite communication terminal needs to transmit the monitoring data acquired by underwater load to the shore-based station in real time under the harsh dynamic environment of ocean.The current data rate less than 10 kbps can no longer meet the transmission needs of observation data such as images and videos.At the same time,the satellite communication terminal is faced with the difficulty of satellite tracking under the complex sea conditions.The traditional "SOTM(satcom on the move)" can not meet the demand of rapid satellite tracking under high dynamic conditions.Therefore,it is of great significance to explore the high-rate satellite communication terminal system and satellite fast acquisition and tracking technology for China's Marine exploration.This paper mainly carries out research on the key technologies applied to of highrate satellite communication terminals of martime buoys,including the technologies of high sensitivity and low-IF receiver,fast integrated navigation,high-precision satellite carrier's closed-loop tracking,fast acquisition of spread spectrum signal and so on.The main work and innovation points are as follows:1.Research on high-rate satellite relay communication technology for martime buoys.Firstly,aiming at the high-rate communication demand of martime buoys and considering the satellite communication link resources,communication system and link budget,the Light and miniaturization satellite communication terminals are designed based on China's relay satellite and Tian Tong-1 satellite link resources respectively.The terminal realizes high-rate data transmission with data rates at 2 Mbps from maritime buoy to airborne satellite and ground station firstly in China.Secondly,in order to realize the lightweight and miniaturization of the terminal,a high sensitivity low-IF receiver based on zero-IF structure is proposed.The receiver receives spread spectrum signal featuring the bandwidth of 6 MHz and the sensitivity of-118 d Bm.Finally,the terminal adopts the variable bit rate technology based on adaptive sea conditions and TDM(time division multiplexing)retransmission mechanism based on large capacity storage to eliminate the potential data loss caused by the deterioration of signal-to-noise ratio or even interruption of the link under complex sea conditions,thus ensuring the reliability of the maritime satellite communication link.2.A low-cost,high-precision and rapid integrated navigation tracking scheme assisted by carrier closed-loop tracking is proposed.Under sea condition with level 4,the terminal can steadily track satellite signals,which solves the problem of rapidly establishing large loop communication link between satellite and terminal.The tightly integrated GNSS/SINS(Global Navigation Satellite System and Inertial Navigation System)Navigation System using redundancy parameter error of pseudo-range and pseudo-range rate to do closed-loop correction on their respective system error.The navigation precision,anti-jamming capability and dynamic performance are all superior to the loose integrated navigation system used by the traditional "SOTM".The terminal conducts closed-loop cone scan tracking according to the signal strength of satellite carrier,which further improves the tracking accuracy of satellite communication terminal to 2° and reduces the tracking response speed to 20 ms,and is superior to beacon step tracking adopted by traditional "SOTM"3.A four-channel parallel acquisition algorithm combining partial matched filters and fast Fourier transform(PMF-FFT)is proposed to rapidly capture satellite spread spectrum carrier signal and provide the signal strength value for satellite signal closedloop tracking.Compared with the traditional pseudo-code FFT algorithm,the new algorithm reduces the maximum acquisition time to 26.5% and the maximum computation amount to 46.9%.It also improves about 4 times in the frequency resolution and 1.6 d B in the receiving sensitivity compared to PMF-FFT algorithm.The parallel PMF-FFT algorithm greatly reduces scallop loss,thus ensuring acquisition sensitivity.The parallel PMF-FFT algorithm is suitable for tracking of satellite signal rapidly and stably by the violently shaken antenna within 20 ms under level-4 sea state.4.The research of communication,tracking algorithm,satellite communication terminal function and performance verification and analysis system has been completed.Among them,the algorithm verification platform uses a set of FPGA hardware circuit to realize the parallel high-speed processing of baseband signal modulation and demodulation,encoding and decoding,framing and unframing,phased array beam control,large capacity storage control and other functions.The processing environment based on ARM architecture system is adopted to realize efficient processing of compact integrated navigation algorithm,network protocol and other functions.The highintegration algorithm verification platform ensures the convenience of testing and debugging.Secondly,a portable test system is designed and developed to quickly detect the key characteristics of S-band maritime satellite communication terminals in performance debugging,system joint test and test site.Finally,based on the test results of the satellite communication terminal's large loop communication at sea,the data of the lake and sea tests are analyzed,which lays a foundation for the optimization of the terminal system.The satellite communication terminal studied in this paper breaks through the lowcost,high-precision,rapid acquisition and tracking technology,and supports the maritime buoys or other marine carriers to realize the application of 2 Mbps high-rate and real-time data communication with the shore-basedstation,which is of great significance in the field of military and civilian applications.