【作者】 龚晓春；

【导师】 徐国栋；

【作者基本信息】 哈尔滨工业大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 本学位论文以国家安全重大基础研究973项目——“微型航天器新概念、新机理研究”为背景,对分布式微型航天器DMSS (Distribtute Micro Spacecraft System)的星间时钟同步问题进行深入研究。对分布式微型航天器系统而言,星间定时同步关系是非常关键的。分布式微型航天器要求多颗微小卫星编队或者组网共同完成协同观测和信息交换等空间任务,星间时钟同步是保障这些空间任务正常执行的基础。目前系统研究星间时钟同步问题的文献较少,本文针对分布式微型航天器的星间时钟同步问题提出了全面的解决方法,包括微小型星间相对定时同步工具、GPS (Global Positioning System)定时同步技术、星间链路通信协议和星间链路时钟同步四个研究部分,对影响同步的各种因素予以分析,指出改善同步精度的措施,为实现高精度的星间时钟同步提供实践和理论上的基础。在分析国外现有星间相对状态测量设备的基础上,提出微小型的星间相对定时同步设备——微型核同步系统。根据星间精确交换时间信息的原理,结合星间射频通信技术和星载电子系统微型化技术,本文提出星间相对定时同步设备的框架结构,包括信号处理、射频收发和GPS接收单元,并进行软、硬件的协同设计与验证工作。本文采用COTS (Commercial off-the-shelf)技术来实现同步系统的原理样机,采用紧凑灵活的电路结构取代原有星间通信工具的分系统、多单元的电路结构。通过搭建测试平台,本文对该同步系统样机的功能模块进行有效性和可行性的验证。在分析GPS授时技术的基础上,提出适用于分布式微型航天器的高精度星间定时同步方法。为改善星间定时同步精度,本文分析GPS伪距差分技术和星座几何因子优化方法,研究同步系统振荡源频率稳定度对定时同步精度的影响。通过分析振荡源的频率误差特性和测量方法,本文选择温度补偿晶体振荡器作为星间定时同步设备的振荡源,并提出为振荡源建立准确的星上时钟偏差模型的方法。在该时钟偏差模型的基础上,本文结合卡尔曼滤波器对GPS定时解算数据进行信号处理,仿真验证卫星间钟面差估计精度的改善情况。在分析现有星间通信协议、星间链路拓扑和多址接入方式的基础上,本文提出支持星间链路时钟同步服务的通信协议。本文分析了CCSDS Proximity-1协议的数据链路层和物理层规范,讨论该协议提供的定时服务方法。通过研究主从星结构的星间链路拓扑,本文提出自动主星选举方法。在多址接入的研究中,本文对IEEE 802.11的MAC层协议进行分析,重点分析支持时限服务的点协调功能PCF(Point Coordination Function),并结合星间链路时钟同步服务提出改善接入等待时间的方法。通过比较传统的双向时间比对法和分布式计算机系统的时钟同步法,本文提出引入概率时钟同步思想到星间时钟同步领域中,以解决缺乏GPS信号等外部时间基准信号的分布式微型航天器的定时同步问题。本文首先采用几何法分析概率时钟同步方法的内在涵义,提出改进的星间链路概率时钟同步法。该方法以星间链路的上、下行信号传输延迟时间差为出发点进行分析以改善同步精度,并用贝叶斯估计对在轨运行的DMSS星间钟面差进行计算并校时。结合微型核同步系统样机传输延迟分布的实验结果,本文推导了该方法的读时钟误差、同步成功概率以及同步精度的表达式。更多还原

【Abstract】 Supported by the Major State Basic Research Development Program of China (973 Program)—“Study of new concept, new mechanism of micro-spacecraft”, inter-satellite onboard clock synchronization methods for Distributed Micro Spacecraft System (DMSS) are deeply studied in this paper.As for DMSS, inter-satellite onboard timing and clock synchronization are critical. DMSS requires many micro-satellites to constitute formation flying system or satellite network to perform a common space task, like coordinated observation or information exchange etc., there inter-satellite timing and synchronization information play an essential role for ensuring the correctness of these space tasks. Up to now, few papers are concerned with timing and synchronization for DMSS. This paper proposes a framework of solution for DMSS clock synchronization problem systematically, which includes research of micro inter-satellite relative timing and synchronization tool, Global Positioning System (GPS) timing method, inter-satellite communication protocol and inter-satellite clock synchronization method. This paper analyzes various factors which influence timing precision, and proposes solutions of improving the precision, thus it provides both practical and theoretical foundation for high precision of inter-satellite timing and clock synchronization. Based on the analysis of current abroad inter-satellite relative state measurement equipment, this paper proposes micro inter-satellite relative timing and clock synchronization equipment, General Cell Synchronization System.Based on principle of inter-satellite time information exchange, binding inter-satellite radio frequency (RF) communication technology and onboard micro electronic system technology, this paper proposes the architecture of inter-satellite synchronization system, which involves signal processing unit, RF transceiver and GPS receiver, and realizes software/hardware co-design and validation for this synchronization system. This paper develops a demonstration system with Commercial off-the-shelf (COTS) technology, which has compact circuit architecture instead of multiple modules architecture used by traditional RF communication tools. By building testbed, this paper confirms validity and feasibility of this demonstration system’s functional modules.Based on analysis of GPS time transfer technology, this paper proposes a set of reasonable high precision inter-satellite timing scheme for DMSS. To improve inter-satellite timing precision, this paper analyzes GPS pesudorange difference method and GPS satellites selection optimization method, and influence of receiver oscillator’s frequency stability on inter-satellite timing and synchronization precision. By analyzing error characteristics and measurement method of oscillator, this paper chooses temperature compensate crystal oscillator (TCXO) as clock source of inter-satellite relative clock synchronization system, and proposes to build accurate clock bias model for the clock source. Based on the clock bias model, this paper applies Kalman filter to process observed GPS timing data to validate the improvement of relative timing precision among satellites.Based on research of present inter-satellite communication protocols, inter-satellite link topologies and multiple access methods, this paper proposes appropriate inter-satellite link protocol to support timing and synchronization service among satellites. This paper analyzes criterions of data link layer and physical layer of CCSDS Proximity-1, and discusses its timing correlation method. By investigating master/slave topology, this paper proposes automatic master satellite seletion method. On investigation of multiple access technologies, this paper analyzes MAC protocol of IEEE 802.11, especially Point Coordination Function (PCF), and proposes methods to decrease average access waiting time, considering inter-satellite clock synchronization service.By comparing traditional two-way time comparison method with clock synchronization method in distributed computer system, this paper proposes to introduce probabilistic synchronization idea to inter-satellite synchronization field, so as to solve the inter-satellite onboard clock synchronization problem when DMSS is devoid of external time reference signal, like GPS signal. This paper analyzes inherent meaning of probabilistic clock synchronization with geometry method, and then it proposes an improved inter-satellite probabilistic onboard clock synchronization method. The method starts with difference between uplink and downlink signal delay to analyze how to increase timing precision, and applies Bayesian approach to compute satellite clock bias so as to calibrate it when DMSS is on orbit flying. Based on experimental results obtained from measuring signal transmission delay distribution with the demonstration system of General Cell Synchronization System, this paper systematically deduces arithmetical expression of clock reading error, probability of success synchronization and timing precision of the method.更多还原