The Closed-loop Tracking Study Of Satellite Mobile Communication Systems

Array antenna satellite mobile communication system is a wireless multi-access communication system, which communicates with spread spectrum technology beam forming technology. It makes multi-user data transmission at the same time come true. Array antenna technology is a new technology applies to mobile satellite communications, Array antenna for mobile satellite communications technology is a new technology, it can reduce the impact of multipath effects, channel interference, maximizing the utilization of spectrum resources, using DBF (digital beam forming) technology in SDMA (space division multiplexing address)mode. Spread spectrum technology plays a huge role in anti-jamming and antenna-array’s spatial filtering, and it can ameliorate the long transmission distance, poor channel environment, multipath effects and other issues in mobile satellite transmission. Based on previous theoretical studies, we proposed a closed-loop tracking algorithm with three-dimensional (space-time-frequency) federated search, which combines CDMA (code division multiplexing address), SDMA, and frequency search. Algorithm complexity is reduced and computational efficiency increases under guaranteeing CDMA and SDMA technology’s superiority circumstance. The main point of the paper work and innovation show below:1. Improving the system design, proposing closed-loop tracking technology. This technique not only to achieve the user’s real-time point, but to capture the real-time spread spectrum signal and to transport data from the moving target by a certain algorithm, on the basis of hardware implementation. So the focus of tracking is the data transmission is not interrupted.2. Two kinds of closed-loop tracking structure were designed. First structure is completing DBF before dispreading and demodulation; second structure is PN-code synchronization, carrier synchronization and DBF complete together. In regard of the two structures, we study the traditional DBF technology and DOA technology, and simulate some algorithm applying to the structures. Considering realizability, computational complexity, we proposed a closed-loop tracking algorithm with three-dimensional (space-time-frequency) federated search algorithm, which applies LMS (least mean square)algorithm into the second structure.3. Composing the three-dimensional federated search algorithm’s hardware logic and simulating it in ModelSim software. From the result, receiver can correctly complete PN code acquisition and beam forming when the SNR (Signal to Noise Ratio) is less than-30dB. Considering the performance, the algorithm is worse than theoretical threshold for3dB in SNR index.4. Building a wired hardware system test-platform, which includes satellite analog circuit board, DBF receiver board, CPCI chassis and so on. We can study the receiver’s signal data using SignalTap Ⅱ software by regulating the sending-signal’s SNR from satellite analog circuit board. From the results of the entire module’s work and hardware system testing, the validity of the algorithm, the correctness of the logic and the rationality of the system design are proved.