卫星导航系统电离层闪烁检测与弱化关键技术研究
发布时间：2018-08-24 07:51
【摘要】：空间电离层引起的信号延迟和闪烁导致的信号异常变化,是影响卫星导航系统建设最为棘手的误差之一,也是影响系统连续性和可靠性的重要因素。如何估计并修正电离层延迟带来的测量误差、削弱电离层闪烁的影响,确保系统的稳定运行和用户的使用性能,是卫星导航系统建设中的重大难题,因此研究电离层背景下的导航信号接收技术,具有重要的工程价值和战略意义。在这一背景下,论文开展了以下几个方面的研究工作:(1)针对传统的利用多频测量值估计电离层延迟的方法,不能应用于单频接收机的问题,结合下一代卫星导航信号采用BOC调制、具有分裂谱的特点,研究提出了基于BOC调制双边带信号模型的电离层延迟估计算法。该算法利用傅里叶级数展开推导了上下边带标称频率处码相位延迟量和载波相位超前量的表达式,以及估计载波频率0f处电离层延迟及其变化量的方法,并通过平滑算法进一步提高了估计的精度,仿真结果表明,该方法可有效提高电离层延迟量的估计精度,以BOC(10,5)、BOC(14,2)、BOC(15,2.5)为例,此方法的最优估计精度较高,分别能达到1.26m、0.90m和0.84m,远远高于现有单频Klobuchar模型的估计精度。这使得下一代BOC信号的单频接收机具有了准确估计电离层延迟的能力。(2)针对传统的电离层闪烁检测方法需要积累一段时间观测数据、实时性较低的问题,提出了基于码环NCO调整量的电离层闪烁检测算法。由于电离层闪烁引发信号功率快速衰减时,码环NCO的调整量将会超出正常分布的范围,并出现与电离层闪烁规律相近的波动,该算法根据这一特征,通过码环NCO调整量的变化,检测是否发生电离层闪烁,并粗略估计电离层闪烁的强弱。仿真结果表明,这种方法采用毫秒量级的检测间隔,在较短时间内可进行多次检测,检测概率显著提升,相对于单次检测,多次检测的检测概率在弱闪烁条件下提升了4倍,在强闪烁条件下检测概率提升了8~10倍;该方法以码环NCO控制字调整量作为判决量,可以实现电离层闪烁在10s内的准确检测,相对于传统的事后统计分析,该方法可以极大提升电离层闪烁检测的实时性。(3)针对电离层闪烁会造成卫星导航信号快速衰落、严重时导致失锁,影响监测接收机等系统设备的连续性和稳定性的问题,首次提出了基于阵列处理技术减轻电离层闪烁影响的方法。阵列天线接收在指定方向形成高增益波束,提高该方向卫星信号的载噪比,可减轻电离层闪烁对接收机的不利影响。由于电离层闪烁在短时间内(ms量级)是强相关的,而阵元间的传播时延在亚纳秒量级,阵列处理过程可视为分段稳定的过程,文中给出了存在电离层闪烁条件下的阵列信号处理模型,进一步分析表明对于不存在干扰的情形,基于最大信干噪比准则得到的权值与空域匹配滤波器的权值相同,且最大增益方向信噪比提升与阵元个数N成正比。此外还提出了基于可用率的电离层闪烁影响减弱评估方法,定义了电离层闪烁情况下的可用率指标,分别采用单天线软件接收机和阵列接收机对实际采集的电离层闪烁数据进行了仿真分析,结果表明:4元天线阵接收信号载噪比比单天线提高约6d B,7元天线阵接收信号载噪比比单天线提高约8d B,验证了采用天线阵可以提高电离层闪烁情况下的接收信号载噪比,进而降低电离层闪烁对信号接收的影响;在载噪比门限33d BHz情况下,在电离层闪烁较小(闪烁指数S4=0.2)时,接收信号载噪比及可用率受影响较小;在电离层闪烁较严重(闪烁指数S4=1.2)时,接收信号载噪比及可用率将显著下降,而采用天线阵波束形成技术可以显著改善接收信号载噪比,可用率可改善39%,验证了天线阵波束形成对电离层闪烁影响的改善效果。(4)针对传统基于星历参数的卫星来波方向估计方法精度差的问题,提出了一种相关前空间相关的波束跟踪改进算法。现有的相关后空间相关跟踪算法存在码剥离的资源消耗与阵元个数呈正比的缺点,文中提出了一种将空间相关环节置于码剥离模块之前,使得不论阵元个数是多少,都只需要三组码剥离模块,随着阵元个数的增加,这种处理的优势会更加明显。在阵列与卫星信号的相对来波方向慢变时且码环和载波环稳定跟踪的条件下,本文提出的算法与相关后波束跟踪算法是等价的,文中在数学上给出了严格证明。进一步的仿真分析表明,新算法可以实现波束的快速准确收敛,对卫星来波方向实现高精度估计,且载噪比提升约6d B,从而实现信号来波方向的稳定跟踪和信号功率增强,有效降低电离层闪烁的影响,也可进一步推广至各类弱信号导航下的应用。(5)针对在评估电离层闪烁对几何精度因子和系统可用性影响方面,缺乏定量分析和统计方法的问题,提出了基于空时二维的电离层闪烁影响评估方法,研究了以GDOP值恶化因子、可用性等级、闪烁影响恶劣函数等作为参量的评估准则,有效评估了电离层闪烁对几何精度因子和系统可用性的影响。相对于分析GDOP的绝对值变化,采用GDOP值恶化因子的评估方法,能更直观地反映出电离层闪烁前后GDOP值的相对变化。基于闪烁影响恶劣函数以及空时二维的可用性评估可知,电离层闪烁影响是一种区域效应,一般集中在闪烁中心所对应的投影区域,影响系统可用性的量级在4210~10--,不会对卫星导航系统造成较大范围的影响。论文研究成果已应用于我国北斗卫星导航系统的总体论证以及地面设备研制等项目中。
[Abstract]:Signal anomaly caused by ionospheric delay and scintillation is one of the most difficult errors affecting the construction of satellite navigation system, and also an important factor affecting the continuity and reliability of the system. Operational performance and user performance are important problems in the construction of satellite navigation system. Therefore, it is of great engineering value and strategic significance to study the reception technology of navigation signal in ionospheric background. The method of layer delay can not be applied to single-frequency receiver. Considering that the next generation satellite navigation signals are modulated by BOC and have the characteristics of splitting spectrum, an algorithm of ionospheric delay estimation based on BOC modulated bilateral-band signal model is proposed. The expressions of delay and carrier phase lead, and the method of estimating ionospheric delay and its variation at carrier frequency 0f are given. The estimation accuracy is further improved by smoothing algorithm. The simulation results show that the method can effectively improve the estimation accuracy of ionospheric delay. Taking BOC (10,5), BOC (14,2) and BOC (15,2.5) as examples, this method can improve the estimation accuracy of ionospheric delay. The optimal estimation accuracy is 1.26m, 0.90M and 0.84m, respectively, which is much higher than that of the existing single-frequency Klobuchar model. This makes the single-frequency receiver of the next generation BOC signal have the ability to accurately estimate the ionospheric delay. (2) The traditional ionospheric scintillation detection methods need to accumulate some time observation data, real-time performance. A new ionospheric scintillation detection algorithm based on the adjustment of code-loop NCO is proposed to detect the ionospheric scintillation. When the ionospheric scintillation causes the signal power to decay rapidly, the adjustment of code-loop NCO will exceed the normal distribution and the fluctuation of the ionospheric scintillation will occur. According to this characteristic, the algorithm changes the adjustment of code-loop NCO. The simulation results show that this method can detect many times in a short time by using the detection interval of milliseconds, and the detection probability is significantly increased. Compared with single detection, the detection probability of multiple detection is increased by four times under weak flicker condition, and the detection probability of multiple detection is enhanced under strong flicker condition. The detection probability of ionospheric scintillation is increased by 8-10 times under the condition of scintillation. The method can detect the ionospheric scintillation accurately within 10 seconds by using NCO control word adjustment as the decision variable. Compared with the traditional post-event statistical analysis, this method can greatly improve the real-time performance of ionospheric scintillation detection. (3) For ionospheric scintillation will cause satellite navigation information. A method based on array processing technology to reduce the ionospheric scintillation effect is proposed for the first time. The array antenna receives a high gain beam in the specified direction, and improves the carrier-to-noise ratio of the satellite signal in this direction, which can reduce the ionospheric scintillation effect. The disadvantage of scintillation on the receiver is that the ionospheric scintillation is strongly correlated in a short time (ms order) and the propagation delay between the elements is in sub-nanosecond order. The array processing can be regarded as a piecewise stable process. A signal processing model of the array in the presence of ionospheric scintillation is presented. Further analysis shows that the array is non-existent. In the case of interference, the weights based on the criterion of maximum signal-to-interference-to-noise ratio are the same as those of space-domain matched filters, and the enhancement of maximum gain-to-direction signal-to-noise ratio is proportional to the number of elements N. In addition, an assessment method of ionospheric scintillation mitigation based on availability is proposed, and the availability index in the case of ionospheric scintillation is defined. The results show that the carrier-to-noise ratio of the received signal of the 4-element antenna array is 6 d B higher than that of the single antenna, and the carrier-to-noise ratio of the received signal of the 7-element antenna array is about 8 d B higher than that of the single antenna. It is verified that the ionospheric scintillation can be improved by using the antenna array. The carrier-to-noise ratio (CNR) of the received signal in the case of small ionospheric scintillation (scintillation index S4 = 0.2) is less affected when the CNR threshold is 33d BHz; the CNR and availability of the received signal are less affected when the scintillation index S4 = 1.2 is serious (scintillation index S4 = 1.2). The effect of antenna array beamforming on ionospheric scintillation is validated. (4) To solve the problem of poor accuracy of traditional ephemeris-based satellite DOA estimation methods, a correlation front space is proposed. The existing correlated post-spatial correlation tracking algorithm has the disadvantage that the resource consumption of code stripping is directly proportional to the number of array elements. In this paper, a new method is proposed to put the spatial correlation link before the code stripping module, so that no matter how many array elements are, only three groups of code stripping modules are needed. When the relative direction of the array and the satellite signal is slowly changing and the code loop and the carrier loop are stable, the algorithm proposed in this paper is equivalent to the correlated post-beam tracking algorithm, which is proved mathematically rigorously. Further simulation analysis shows that the new algorithm can be realized. The fast and accurate convergence of beam can estimate the direction of arrival of satellite with high accuracy, and the carrier-to-noise ratio can be increased by 6 d B, so that the stable tracking of the direction of arrival of signal and the enhancement of signal power can be realized, and the influence of ionospheric scintillation can be effectively reduced. It can also be further extended to the application of weak signal navigation. (5) Aiming at the evaluation of ionospheric scintillation pairs. In the aspect of geometric accuracy factor and system availability, the problem of lacking quantitative analysis and statistical method is presented. A method of evaluating ionospheric scintillation impact based on space-time two-dimensional is proposed. The evaluation criteria with deterioration factor of GDOP value, usability level and bad function of scintillation effect as parameters are studied. The ionospheric scintillation effect on geometry is effectively evaluated. Compared with the absolute value of GDOP, the relative change of GDOP value before and after ionospheric scintillation can be reflected more intuitively by the evaluation method of GDOP value deterioration factor. The results of this paper have been applied to the general demonstration of Beidou satellite navigation system and the development of ground equipment in China.
【学位授予单位】：国防科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN967.1
本文编号：2200129
[Abstract]:Signal anomaly caused by ionospheric delay and scintillation is one of the most difficult errors affecting the construction of satellite navigation system, and also an important factor affecting the continuity and reliability of the system. Operational performance and user performance are important problems in the construction of satellite navigation system. Therefore, it is of great engineering value and strategic significance to study the reception technology of navigation signal in ionospheric background. The method of layer delay can not be applied to single-frequency receiver. Considering that the next generation satellite navigation signals are modulated by BOC and have the characteristics of splitting spectrum, an algorithm of ionospheric delay estimation based on BOC modulated bilateral-band signal model is proposed. The expressions of delay and carrier phase lead, and the method of estimating ionospheric delay and its variation at carrier frequency 0f are given. The estimation accuracy is further improved by smoothing algorithm. The simulation results show that the method can effectively improve the estimation accuracy of ionospheric delay. Taking BOC (10,5), BOC (14,2) and BOC (15,2.5) as examples, this method can improve the estimation accuracy of ionospheric delay. The optimal estimation accuracy is 1.26m, 0.90M and 0.84m, respectively, which is much higher than that of the existing single-frequency Klobuchar model. This makes the single-frequency receiver of the next generation BOC signal have the ability to accurately estimate the ionospheric delay. (2) The traditional ionospheric scintillation detection methods need to accumulate some time observation data, real-time performance. A new ionospheric scintillation detection algorithm based on the adjustment of code-loop NCO is proposed to detect the ionospheric scintillation. When the ionospheric scintillation causes the signal power to decay rapidly, the adjustment of code-loop NCO will exceed the normal distribution and the fluctuation of the ionospheric scintillation will occur. According to this characteristic, the algorithm changes the adjustment of code-loop NCO. The simulation results show that this method can detect many times in a short time by using the detection interval of milliseconds, and the detection probability is significantly increased. Compared with single detection, the detection probability of multiple detection is increased by four times under weak flicker condition, and the detection probability of multiple detection is enhanced under strong flicker condition. The detection probability of ionospheric scintillation is increased by 8-10 times under the condition of scintillation. The method can detect the ionospheric scintillation accurately within 10 seconds by using NCO control word adjustment as the decision variable. Compared with the traditional post-event statistical analysis, this method can greatly improve the real-time performance of ionospheric scintillation detection. (3) For ionospheric scintillation will cause satellite navigation information. A method based on array processing technology to reduce the ionospheric scintillation effect is proposed for the first time. The array antenna receives a high gain beam in the specified direction, and improves the carrier-to-noise ratio of the satellite signal in this direction, which can reduce the ionospheric scintillation effect. The disadvantage of scintillation on the receiver is that the ionospheric scintillation is strongly correlated in a short time (ms order) and the propagation delay between the elements is in sub-nanosecond order. The array processing can be regarded as a piecewise stable process. A signal processing model of the array in the presence of ionospheric scintillation is presented. Further analysis shows that the array is non-existent. In the case of interference, the weights based on the criterion of maximum signal-to-interference-to-noise ratio are the same as those of space-domain matched filters, and the enhancement of maximum gain-to-direction signal-to-noise ratio is proportional to the number of elements N. In addition, an assessment method of ionospheric scintillation mitigation based on availability is proposed, and the availability index in the case of ionospheric scintillation is defined. The results show that the carrier-to-noise ratio of the received signal of the 4-element antenna array is 6 d B higher than that of the single antenna, and the carrier-to-noise ratio of the received signal of the 7-element antenna array is about 8 d B higher than that of the single antenna. It is verified that the ionospheric scintillation can be improved by using the antenna array. The carrier-to-noise ratio (CNR) of the received signal in the case of small ionospheric scintillation (scintillation index S4 = 0.2) is less affected when the CNR threshold is 33d BHz; the CNR and availability of the received signal are less affected when the scintillation index S4 = 1.2 is serious (scintillation index S4 = 1.2). The effect of antenna array beamforming on ionospheric scintillation is validated. (4) To solve the problem of poor accuracy of traditional ephemeris-based satellite DOA estimation methods, a correlation front space is proposed. The existing correlated post-spatial correlation tracking algorithm has the disadvantage that the resource consumption of code stripping is directly proportional to the number of array elements. In this paper, a new method is proposed to put the spatial correlation link before the code stripping module, so that no matter how many array elements are, only three groups of code stripping modules are needed. When the relative direction of the array and the satellite signal is slowly changing and the code loop and the carrier loop are stable, the algorithm proposed in this paper is equivalent to the correlated post-beam tracking algorithm, which is proved mathematically rigorously. Further simulation analysis shows that the new algorithm can be realized. The fast and accurate convergence of beam can estimate the direction of arrival of satellite with high accuracy, and the carrier-to-noise ratio can be increased by 6 d B, so that the stable tracking of the direction of arrival of signal and the enhancement of signal power can be realized, and the influence of ionospheric scintillation can be effectively reduced. It can also be further extended to the application of weak signal navigation. (5) Aiming at the evaluation of ionospheric scintillation pairs. In the aspect of geometric accuracy factor and system availability, the problem of lacking quantitative analysis and statistical method is presented. A method of evaluating ionospheric scintillation impact based on space-time two-dimensional is proposed. The evaluation criteria with deterioration factor of GDOP value, usability level and bad function of scintillation effect as parameters are studied. The ionospheric scintillation effect on geometry is effectively evaluated. Compared with the absolute value of GDOP, the relative change of GDOP value before and after ionospheric scintillation can be reflected more intuitively by the evaluation method of GDOP value deterioration factor. The results of this paper have been applied to the general demonstration of Beidou satellite navigation system and the development of ground equipment in China.
【学位授予单位】：国防科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN967.1
【参考文献】
相关期刊论文 前1条
1 王晓明;殷耀国;杨自明;;全球导航卫星系统的现代化进展[J];全球定位系统;2006年04期
，本文编号：2200129
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