【作者】 叶萍；

【导师】 战兴群；

【作者基本信息】 上海交通大学 ， 导航、制导与控制， 2011， 博士

【摘要】 21世纪是信息技术高速发展的时代,牵引并依赖于信息技术的精确制导技术也将进一步加速发展。20世纪末发展成熟的精确制导技术在21世纪将发展成为实用化技术。目前,低成本导航与制导技术是发展实用化精确制导技术的首要内容。MEMS IMU/GNSS组合导航系统具有成本低、体积小、重量轻、功耗低等优点,因此在汽车定位、精细农用机械车辆导航、林区防火的无人机、精确制导武器、卫星探测等方面具有非常重要的应用价值。受2008年上海航天技术研究院科研基金的资助,本文作者开展了高动态GNSS/INS组合导航快速初始对准技术的研究,并对组合导航系统进行了设计。结合新一代组合制导系统的研制现状和发展趋势,为进一步提高GNSS动态性能、抗干扰能力以及其和MEMS IMU集成的组合系统定位能力,本文进行了更深入的MEMS IMU/GNSS组合导航技术研究。由于载体对象的高动态特点,其上装载的GNSS接收机在捕获信号和跟踪定位上面临很大的挑战,因此致使GNSS/INS组合系统的定位效果受到严重影响。本论文以MEMS IMU/GNSS超紧组合为研究目标,并以MEMS IMU环路辅助的GNSS/INS紧组合技术为研究重点,深入研究了MEMS IMU辅助的GNSS信号捕获、MEMS IMU辅助的GNSS信号跟踪、MEMS IMU辅助的GNSS/INS紧组合导航定位算法和基于矢量跟踪结构的GNSS/INS超紧组合算法,旨在改善MEMS IMU/GNSS组合导航系统在卫星信号衰减场合中的性能。主要的研究思路和工作体现在以下五个方面:1.调研分析国内外GNSS/INS组合导航技术以及基于MEMS的GNSS/INS组合制导系统的服役现状,结合课题的技术需求和工程可实现性,确定MEMS惯性器件环路辅助的GNSS/INS紧组合研究内容和基于矢量跟踪结构的GNSS/MEMS INS组合研究方案。2.针对高动态运动所带来的GNSS信号捕获时间变长的问题,从机理上分析IMU速度辅助GNSS接收机的信号捕获方法和流程,建立衡量信号捕获性能的指标,着重研究MEMS IMU辅助时影响捕获性能的载体多普勒误差和由其导致的捕获搜索区间,定量评估比较GNSS接收机在MEMS IMU辅助前后的捕获性能,开展捕获实验。3.在信号跟踪误差和抗干扰指标计算的研究基础之上,设计适用于高动态的纯GNSS和IMU辅助的GNSS环路结构、鉴相器类型和环路参数,研究环路带宽门限和最优带宽的设计问题,评估比较MEMS IMU辅助前后接收机的动态跟踪性能和抗干扰性能,开展跟踪实验。4.研究组合导航系统的定位性能和系统实现。建立MEMS IMU环路辅助的GNSS/INS紧组合导航物理实现结构,从系统可观性分析的角度设计基于单通道的全维组合滤波器,进而研究降维滤波算法;构建仿真系统和仿真场景实验,验证算法的有效性,全面评估系统的导航精度;着重分析组合导航系统实现的两个时间同步问题,即组合导航Kalman滤波器中MEMS IMU和GNSS量测数据之间的同步,以及由MEMS IMU获取的GNSS环路控制信息和GNSS基带信号之间的数据同步,提出解决方案,研制基于FPGA的时间同步系统,并进行地面验证。5.为进一步提高系统的动态性能和抗干扰能力,在GNSS接收机矢量跟踪技术的基础上,研究基于矢量跟踪结构的MEMS IMU/GNSS超紧组合导航技术,分析超紧组合导航结构和系统配置,研究基于定常加速度模型的超紧组合算法和滤波器设计,提出机载一体化MEMS IMU/GNSS超紧组合系统的设计方案。本文的关键技术和创新性主要体现在以下四个方面:1.构建了MEMS IMU环路辅助GNSS接收机捕获和跟踪性能的评估方法,从而确定了GNSS接收机经MEMS IMU辅助前后的捕获时间、信号跟踪门限、带宽门限和前端抗干扰能力,为满足高动态应用环境需求的MEMS IMU辅助的接收机环路参数和结构设计提供依据,对工程样机的研制具有重要的参考价值。2.设计了一种适用于高动态的MEMS IMU辅助GNSS接收机的环路结构(IMU辅助的三阶PLL和PLL辅助的二阶DLL),提出了带宽门限的迭代求解方法,确定了接收机带宽设计范围,从而使接收机可以在要求的载噪比变换范围内稳定跟踪信号,为接收机环路参数的设计提供了便捷、有效的方法。3.提出了一种基于双通道星间差分的降维滤波算法,抵消了组合导航滤波器状态变量中接收机钟差和钟漂的影响,不仅减小了微处理器计算负荷、提高了效率,而且在卫星信号状况良好和较差的环境中都可以确保良好的定位精度,对于组合系统工程化发展具有实际应用价值。4.提出了一种基于递推Kalman滤波方法的软件同步方案,解决了MEMS IMU获取的GNSS环路控制信息和GNSS基带信号之间的数据同步问题,从而解决了超紧组合技术中的关键问题,对于超紧组合导航系统的开发具有建设性的意义。本文的研究结论主要有以下五点:1.MEMS IMU辅助接收机环路时,接收机在冷启动下捕获时间缩短30%,在温启动下缩短96%,在热启动下重捕能力提高40%。温启动模式下,惯性辅助对接收机捕获性能的提高最显著。因此,MEMS IMU辅助的捕获技术在民用方面也具有广阔的应用前景。基于MAX2769 GNSS软件接收机平台捕获实验,结果反映接收机冷启动时捕获效率提高了33.8%,验证了评估结论。2.为满足10g/s加加速度的高动态应用环境,高动态接收机在环路结构方面需采用三阶PLL环路和PLL辅助的二阶DLL,在鉴相器选型方面需采用二象限反正切型PLL鉴相器和开方后归一化型DLL鉴相器。3.在10g/s加加速度的高动态应用环境中,经MEMS IMU辅助后,GNSS接收机三阶PLL的带宽门限由18 Hz降低到1Hz,信号跟踪门限由28dB-Hz降低到21dB-Hz,接收机整体抗干扰性能提高7.4dB。4.基于星间差分的降维滤波算法和全维滤波算法具有同等的导航性能,其中卫星信号良好时3D位置误差(MRS)约为7m,3D速度误差为0.2 m/s。在微处理器的浮点运算能力上,采用降维滤波算法后,一个滤波周期内的浮点计算时间由0.6MFLOPS缩短到0.4MFLOPS,其复杂度降低了31.1%,提高了滤波器的运算效率。5.经地面实验验证,论文研制的基于FPGA的时间同步系统实现了MEMS IMU传感器测量数据与GNSS接收机时间的精确同步,其中同步精度可达600us,满足大多中等精度GNSS/INS组合系统的同步测量要求。更多还原

【Abstract】 The 21st century is the era of rapid development of information, and precision-guided technology which depends on information will further accelerate the development. In the new century, the late 20th century developed precision-guided technology will become a practical technology. At the present, low-cost navigation and guidance technology is the primary aspect to develop the practical precision guidance technology. The high points of MEMS IMU/GNSS, low-cost, low-size, low-weight and low power consumption, wholly meet the requirements for wide application fields, such as vehicle positioning, fine farm machinery navigation, UAV for forest fire, precision guided munitions and satellite detection. Preliminary research on rapid GNSS/INS alignment technology was funded by the Shanghai Academy of Spaceflight Technology in 2008. On the basis of the preliminary background research of navigation and guided system, this dissertation would give attention to new GNSS/INS technology with ultratight coupling or deep integration so as to enhance GNSS tracking, anti-jamming and positioning. Considering modern target’s characteristic with high dynamic, the ability of GNSS receiver to acquire and track signal is challenged, and thus GNSS/INS integrated navigation capability is badly affected. The objective of this dissertation is to introduce modern IMU to the GNSS receiver’s tracking loops, to analyze GNSS receiver’s improvements in acquisition, tracking and anti-jamming, and to design realizable MEMS IMU/GNSS tight integration with IMU-aided receiver tracking loops and characterize its navigation performance in signal-attenuated applications. Furthermore, the dissertation would like to explore an ultratight coupling navigation system with supreme reliability and integrity to improve system performance and survivability. The primary research contributions and roadmap are summarized as follows:1. Collection and summary of all the related literatures and previous works. With this information, and taking into account the technique requirements and project limits, MEMS IMU/GNSS tight integration with IMU-aided receiver tracking loops and ultratight coupling are chosen to be researched. 2. To investigate MEMS IMU-aided GNSS receiver acquisition technology. The acquisition capability index including mean acquisition time and signal detection index is developed. Several main factors influencing the acquisition performance with IMU assistance are analyzed. Based on MEMS IMU-aided Doppler accuracy and almanac-based Doppler accuracy in different receiver startup modes, MEMS IMU-aided acquisition time is quantitatively determined and compared with standard GNSS capability, and acquisition experiments are conducted.3. To implement MEMS IMU-aided GNSS receiver tracking technology. Based on the analysis of DLL and PLL total tracking errors, the structure and implementation of both high dynamic GNSS receiver and MEMS IMU-aided GNSS receiver are provided, and the design of both optimal bandwidth and bandwidth threshold is given. According to the designed MEMS IMU-aided GNSS receiver tracking loops, the tracking and anti-jamming capability are assessed and compared with designed high dynamic GNSS capability, and tracking experiments are implemented.4. To develop MEMS IMU/GNSS integrated navigation technology with IMU-aided GNSS receiver tracking loops. The dissertation designed an EKF-based tightly integrated navigation algorithm trough observability analysis and proposes a reduced navigation algorithm by differencing across satellites. A high-credibility simulation platform of navigation system is constructed for verifying the autonomous navigation accuracy in various signal-attnuated scenarios. In addition, this dissertation draws attention to two time synchronization issues in the implementation of MEMS IMU-aided GNSS/IMU navigation system, and each synchronization scheme is given.A flexible low-cost time synchronizer with FPGA is developed, and vehicle experiments are conducted.5. To investigate MEMS IMU/GNSS ultratight integration navigation technology based on vector tracking structure in order to imporove the performance of dynamics and anti-jamming. Based on vector-based tracking structure of GNSS receiver, the reduced-dimension filter algorithm by differencing across satellites is designed for integrated navigation filter. Consequently, the schematic design of an ultratight MEMS IMU/GNSS receiver is tentatively proposed.The key technology and innovations in the research focus on the following points:1. The assessment method on IMU-aided acquisition, tracking and anti-jamming capability is built. The results of GNSS improvements on acquisition time, signal tracking threshold, bandwidth threshold and RF anti-jamming are displayed. The assessment results and method make contributions to both loop design and prototype development of high dynamic IMU-aided receiver.2. An IMU-aided third-order PLL structure and PLL-aided second-order DLL structure is proposed to satisfy the high dynamic requirement with 10g/s jitter. An iteration-based bandwidth threshold resolution is proposed to make the receiver stably track the GNSS signal in required carrier-noise-ratio environments.3. A novel algorithm based on the differencing pseudorange measurements and Doppler measurements across satellites is proposed so as to eliminate the clock components including receiver clock bias and clock drift. The computational efficiency is improved, and good positioning performance can be kept in various signal-attnuated applications.4. A synchronization software scheme based on recursion Kalman is proposed to synchronize the IMU-aided NCO information and GNSS baseband measurements, and make contributions to MEMS IMU/GNSS ultratight system development.The reseach conclusions are summarized as follows:1. With the aid of MEMS IMU, the acquisition capability in cold start and warm start are improved 30% and 96% respectively, and the reacquisition capability in hot start is enhanced 40%. The remarkable enhancenment in warm start shows wide prospect of IMU-aided acquisition technique in civil applications. According to the test of MAX2769-based GNSS SDR, the acquisition capability is examined.2. In the design of high dynamic GNSS receiver, third-order PLL and PLL-aided second-order DLL can meet the high dynamic requirement with 10g/s jitter.3. With the aid of MEMS IMU, the bandwidth threshold of GNSS third-order PLL is reduced from 18Hz to 1Hz, the signal tracking threshold is reduced from 28dB-Hz to 21dB-Hz, and the mean anti-jamming performance is improved by 7.4dB.4. The MRS errors of position and velocity, estimated by proposed navigation algorithm based on differencing across satellites, are 7m and 0.2m/s respectively. Compared with the traditional navigation algorithm, the computational efficiency is enhanced by 31.1%.5. The field van test result of the low-cost time synchronizer demonstrate that the synchronizer with FPGA developed in the research can achieve an accuracy of around 600 us between MEMS IMU and GNSS receiver.更多还原