GPS中频信号仿真与微弱信号捕获、跟踪方法研究
摘要
近年来,以GPS为代表的卫星导航产品越来越多的进入人们的生活,然而普通的GPS接收机在高楼密集、树荫遮挡、室内等环境中定位的可用性与可靠性下降。因为在这些区域GPS信号受到障碍物遮挡、多径效应等影响,衰减严重,导致信号功率低于-150 dBm,而普通GPS接收机的灵敏度仅为-130 dBm。因此如何提高GPS接收机的灵敏度成为当前迫切需要解决的问题。
研究发现,GPS信号捕获与跟踪模块的灵敏度决定了GPS接收机在弱信号环境中的性能,因此研究能够捕获、跟踪微弱信号的算法就成为提高接收机灵敏度的关键。GPS信号仿真器可以有效仿真受到各种干扰的微弱GPS信号,是捕获、跟踪算法研究与验证的基础。
因此,本文的工作包括:仿真器设计,弱信号捕获、跟踪算法研究三方面:
1、在对GPS信号结构、特性以及主要干扰源进行分析的基础上,利用数学模型仿真受干扰的微弱GPS中频信号,完成GPS中频信号仿真器设计。仿真器能够有效仿真受到多普勒效应,多径干扰、热噪声影响的GPS L1载波中频信号。
2、在弱信号捕获算法设计中,为提高捕获灵敏度,本文首先采用相干积分与非相干积分结合的方式消除了数据码长度对相干积分增益的影响,其次采用差分相干积分减小非相干积分中的平方衰耗。为提高信号捕获速度和精度,本文利用FFT工具进行伪码捕获、2次载波频率捕获,代替传统的顺序搜索法,FFT法,提高了捕获速度与精度。
3、在弱信号跟踪环设计中,针对传统非线性PLL环易受噪声干扰的缺点,本文提出一种简化模型的自适应卡尔曼、扩展卡尔曼载波跟踪环代替传统的PLL环。设计中,对状态方程模型进行了简化,并采用基于协方差修正等方法优化环路,提高了环路稳定性和精度。
仿真实验表明:
仿真信号的频域、功率、自相关特性与实际信号相符。相干-非相干算法、差分相干算法能捕获载噪比为25 dB/Hz微弱信号,其中码捕获、频率捕获精度分别达到2.5Hz,0.2码元。卡尔曼、扩展卡尔曼跟踪算法能够有效跟踪到载噪比分别为26 dB/Hz、24 dB/Hz的微弱信号。
GPS receiver has been widely used. However, the reliability and accuracy of general GPS receiver suffers from limitations indoors or in urban canyons. In these perturbed signal environments, the signal strength is less than -150dBm and the general receiver only has a sensitivity of -130dBm. So improving the sensitivity of GPS receiver becomes the problem that should be addressed.
Signal acquisition and tracking is critical for a GPS receiver to function in perturbed signal environments. The design of weak signals acquisition and tracking algorithm has become the key to achieve high sensitivity. GPS signal simulator which can be used to simulate GPS signal and interference, is the foundation of algorithm verification. Above all, this thesis includes three parts.
1. GPS IF signal simulator design. Based on the analyzing of GPS signal and errors, the GPS L1 carrier interfered by multipath effects and white noise are simulated based on mathematical models. A user interface is designed for GPS IF signal simulator.
2. Weak signal acquisition. In order to enhance the acquisition sensitivity, firstly, the coherent-noncoherent integration was adopted to eliminate the restrictions on coherent integration gain. Secondly, the differential coherent integration, which allows a 1.5 dB SNR improvement in processing loss as compared to noncoherent methods, is proposed. At last, the FFT based code and carrier acquisition algorithm is implemented to improve the acquisition speed and accuracy instead of the traditional method.
3. Weak GPS signal tracking. Traditional non-linear PLL is vulnerable to noise interference. In this thesis, the simplified adaptive kalman, EKF based weak signal carrier phase tracking loop are proposed. The tracking loop model has been simplified and optimized by covariance medication and adaptive algorithm.
The simulation shows that:
The characteristics of simulation signals are consistent with the real one. The noncoherent integration, differential integration acquisition algorithm can acquire the weak signal at the CNR of 25dB/Hz with the frequency, code accuracy of 2.5Hz and 0.2 code. Kalman, EKF tracking algorithm can effectively track weak signal at the CNR of26,24dB/Hz.
研究发现,GPS信号捕获与跟踪模块的灵敏度决定了GPS接收机在弱信号环境中的性能,因此研究能够捕获、跟踪微弱信号的算法就成为提高接收机灵敏度的关键。GPS信号仿真器可以有效仿真受到各种干扰的微弱GPS信号,是捕获、跟踪算法研究与验证的基础。
因此,本文的工作包括:仿真器设计,弱信号捕获、跟踪算法研究三方面:
1、在对GPS信号结构、特性以及主要干扰源进行分析的基础上,利用数学模型仿真受干扰的微弱GPS中频信号,完成GPS中频信号仿真器设计。仿真器能够有效仿真受到多普勒效应,多径干扰、热噪声影响的GPS L1载波中频信号。
2、在弱信号捕获算法设计中,为提高捕获灵敏度,本文首先采用相干积分与非相干积分结合的方式消除了数据码长度对相干积分增益的影响,其次采用差分相干积分减小非相干积分中的平方衰耗。为提高信号捕获速度和精度,本文利用FFT工具进行伪码捕获、2次载波频率捕获,代替传统的顺序搜索法,FFT法,提高了捕获速度与精度。
3、在弱信号跟踪环设计中,针对传统非线性PLL环易受噪声干扰的缺点,本文提出一种简化模型的自适应卡尔曼、扩展卡尔曼载波跟踪环代替传统的PLL环。设计中,对状态方程模型进行了简化,并采用基于协方差修正等方法优化环路,提高了环路稳定性和精度。
仿真实验表明:
仿真信号的频域、功率、自相关特性与实际信号相符。相干-非相干算法、差分相干算法能捕获载噪比为25 dB/Hz微弱信号,其中码捕获、频率捕获精度分别达到2.5Hz,0.2码元。卡尔曼、扩展卡尔曼跟踪算法能够有效跟踪到载噪比分别为26 dB/Hz、24 dB/Hz的微弱信号。
GPS receiver has been widely used. However, the reliability and accuracy of general GPS receiver suffers from limitations indoors or in urban canyons. In these perturbed signal environments, the signal strength is less than -150dBm and the general receiver only has a sensitivity of -130dBm. So improving the sensitivity of GPS receiver becomes the problem that should be addressed.
Signal acquisition and tracking is critical for a GPS receiver to function in perturbed signal environments. The design of weak signals acquisition and tracking algorithm has become the key to achieve high sensitivity. GPS signal simulator which can be used to simulate GPS signal and interference, is the foundation of algorithm verification. Above all, this thesis includes three parts.
1. GPS IF signal simulator design. Based on the analyzing of GPS signal and errors, the GPS L1 carrier interfered by multipath effects and white noise are simulated based on mathematical models. A user interface is designed for GPS IF signal simulator.
2. Weak signal acquisition. In order to enhance the acquisition sensitivity, firstly, the coherent-noncoherent integration was adopted to eliminate the restrictions on coherent integration gain. Secondly, the differential coherent integration, which allows a 1.5 dB SNR improvement in processing loss as compared to noncoherent methods, is proposed. At last, the FFT based code and carrier acquisition algorithm is implemented to improve the acquisition speed and accuracy instead of the traditional method.
3. Weak GPS signal tracking. Traditional non-linear PLL is vulnerable to noise interference. In this thesis, the simplified adaptive kalman, EKF based weak signal carrier phase tracking loop are proposed. The tracking loop model has been simplified and optimized by covariance medication and adaptive algorithm.
The simulation shows that:
The characteristics of simulation signals are consistent with the real one. The noncoherent integration, differential integration acquisition algorithm can acquire the weak signal at the CNR of 25dB/Hz with the frequency, code accuracy of 2.5Hz and 0.2 code. Kalman, EKF tracking algorithm can effectively track weak signal at the CNR of26,24dB/Hz.
引文
[1]Sameet Mangesh Deshpande.Study of Interference Effects on GPS Signal Acquisition[Dissertation].Calgary University.2004.1,30-44,71-79
[2]Elliott D.Kaplan and Christopher J.Hegarty著.寇艳红译.GPS原理与应用.第二版.北京.电子工业出版社.2007.110-220
[3]James Bao-yen Tsui.Fundamentals of Global Positioning System Receivers A Software Approach" A John Wiley & Sons Inc.2004.34-40,120-150,160-169,224-270
[4]皮亦呜,张婧,蔡吕听.GPS信号的差分相关捕获算法研究.全球定位系统2006.4 1-4
[5]Mohammad H.Zarrabizadeh and Elvino S.Sousa.A Differentially Coherent PN Code Acquisition Receiver for CDMA Systems.IEEE Transactions on communications.Vol.45,NO.11,1997.1456-1465
[6]Oh-Soon Shin and Kwang Bok.Differentially Coherent Combining for Double-Dwell Code Acquisition in DS-CDMA Systems.IEEE Transactions on communications.Vol.51,No.7,2003.1046-1050
[7]Andreas.Schemid and A.Neubauer.Performance Evaluation of Differential Correlation for Single Shot Measurement Positioning.Proceedings of ION GNSS 2004.Long beach,CA.Sep,2004.1998-2009
[8]巴晓辉,李金海,陈杰.不需辅助信息的室内GP S信号捕获算法.电子技术应用.2006(6).130-132
[9]Nesreen I.Ziedan and James L.Garrison.Unaided Acquisition of Weak GPS Signals Using Circular Correlation or Double-Block Zero Padding.IEEE Position Location and Navigation Symposium 2004.Apr 2004.461-470
[10]Mark L.Psiaki and Hee Jung Extended Kalman Filter Methods for Tracking Weak GPS Signals.Proceedings of ION GPS 2002.Portland,OR.Sep,2002.24-27
[11]Mark L.Psiaki.Smoother-Based GPS Signal Tracking in a Software Receiver.Proceedings of ION GPS 2002.Salt Lake City,UT.Sept,2002.2900-2913
[12]张婧 基于非线性滤波的GPS微弱信号处理的研究[学位论文].上海.上海交通大学2007.25-26,47-63
[13]刘荟萃,许晓勇,王飞雪.扩频测距系统中多径信号伪码跟踪误差分析及消除技术.全球定位系统2005.6.34-38
[14]Richard D.J.The multipath estimating delay lock loop.Proceedings of IEEE Second International Symposium on Spread Spectrum Techniques and Applications.Yokohama,Japan.Nov-Dec,1992 39-42
[15]Richard D.J.van Nee and Jaap Siereveld.The Multipath Estimating Delay Lock Loop:Approaching Theoretical Accuracy Limits.Proceedings of IEEE Position,Location and Navigation Symposium.1994.Las Vegas,NV,USA.Apr,1994.246-251
[16]Matilde Sanchez-Fernandez.Performance Analysis and Parameter Optimization of DLL and MEDLL in Fading Multipath Environments for Next Generation Navigation Receivers.IEEE Transactions on Consumer Electronics,Vol.53,No.4,2007.246-251
[17]刘基余.GPS卫星导航定位原理与方法.北京.科学出版社.2003.118-152
[18]LeiDong.IF GPS Signal Simulator Development and Verification[Dissertation].Calgary University.2003.25-46
[19]ICD200C(2000).GPS Interface Control Document,ARINC Research Corporation.NAVSTAR GPS Space Segment / Navigation User Interfaces,IRN-200C-004.
[20]Luo,N.Precise Relative Positioning of Multiple Moving Platforms Using GPS Carrier Phase Observables[Dissertation].Calgary University.2001
[21]王智.高动态多普勒条件下的扩频接收技术研究[学位论文].上海.上海交通大学.2007.31-42
[22]Wei Yu.Selected GPS Receiver Enhancements for Weak Signal Acquisition and Tracking[Dissertation].Calgary University.2007.41-45,75-100
[23]Sanjeet Singh.Comparison of Assisted GPS and High Sensitivity GPS in Weak Signal Conditions[Dissertation].Calgary University.2006.13-32
[24]成骤,谢式千,潘承毅.概率论与数理统计(第三版).北京.高等教育出盘社2000
[25]沈用欢等.实用数学手册.北京.科学出版社2001
[26]http://mathwodd.wolfram.com/
[27]John G.Proakis著.张力军等译.数字通信(第四版).北京.电子工业出版社.
[28]李玉红,寇艳红,张其善.微弱GPS信号捕获算法研究.遥测遥控.2005,7
[29]刘海涛.高灵敏度GPS_Galileo双模导航接收机的研究与开发[学位论文].长沙.国防科学技术大学.2006.23-45
[30]陈后金等.数字信号处理.北京.高等教育出版社.2004.92-127
[31]田日才.扩频通信.北京.清华大学出版社.2006.57-83
[32]Peter Rinder Nicolaj Bertelsen.Design of a signal frequency GPS Software Receiver[Dissertation].Aalborg University.2004.25-42
[33]Nyunook Kim.Interference Effects on GPS Receivers in Weak Signal Environments[Dissertation].Calgary University.2006.9-30
[34]Ping Lian.Improving Tracking Performance of PLL in High Dynamic Applications[Dissertation].Calgary University.2004.43-57
[35]Brown,R.G.and P.Y.C.Hwang.Introduction to Random Signal and Applied Kalman Filtering.second edition.John Wiley & Sons,Inc.second edition 1992
[36]秦永元,张洪钺,汪叔华.卡尔曼滤波与组合导航原理.西北工业出版社.1998
[37]Loebis D,Sutton R,Chudley J,et al.Adaptive tuning of a Kalman filter via fuzzy logic for an intelligent AUV navigation system Control Engineering Practice.Vol.12,NO.12,2004
[38]卞鸿魏等.组合导航系统新息自适应卡尔曼滤波算法.上海交通大学学报.2006.40(6).1000-1003
[39]曾翠娟等.GPS动态定位的自适应卡尔曼滤波算法研究.导航.2006.3(1).39-49
[40]Sage A P,Husa G W.Adaptive Filtering with Unknown Prior Statistics,Proceedings of Joint Automatic Control Conference,1969,760-769
[41]张道松.非线性系统滤波及其在制导中的应用研究[学位论文].哈尔滨工业大学.2006.10-24
[42]吕伟,王艳东.Sage-Husa自适应卡尔曼滤波算法在SINS初始对准中的应用研究.战术导弹控制技术2005.(3).52-55
[43]沈云峰,朱海,莫军,宋裕农.简化的Sage-Husa自适应滤波算法在组合导航中的应用及仿真.青岛大学学报.2001.16(1).44-50
[44]刘广军,吴晓平,郭品.Sage滤波器的发散问题解决.全球定位系统.2002.27(1).6-9
[45]郭福成,李宗华,孙仲康.无源定位跟踪中修正协方差扩展卡尔曼滤波算法.电子与信息学报.2004.26(6).917-921
[46]冯鹏,邹世开.卡尔曼滤波器UD分解滤波算法的改进.遥测控制.2005.26(1).10-14
[47]隋树林等.基于UD-EKF自主光学导航方法仿真.系统仿真学报.2007.19(3).482-485
[2]Elliott D.Kaplan and Christopher J.Hegarty著.寇艳红译.GPS原理与应用.第二版.北京.电子工业出版社.2007.110-220
[3]James Bao-yen Tsui.Fundamentals of Global Positioning System Receivers A Software Approach" A John Wiley & Sons Inc.2004.34-40,120-150,160-169,224-270
[4]皮亦呜,张婧,蔡吕听.GPS信号的差分相关捕获算法研究.全球定位系统2006.4 1-4
[5]Mohammad H.Zarrabizadeh and Elvino S.Sousa.A Differentially Coherent PN Code Acquisition Receiver for CDMA Systems.IEEE Transactions on communications.Vol.45,NO.11,1997.1456-1465
[6]Oh-Soon Shin and Kwang Bok.Differentially Coherent Combining for Double-Dwell Code Acquisition in DS-CDMA Systems.IEEE Transactions on communications.Vol.51,No.7,2003.1046-1050
[7]Andreas.Schemid and A.Neubauer.Performance Evaluation of Differential Correlation for Single Shot Measurement Positioning.Proceedings of ION GNSS 2004.Long beach,CA.Sep,2004.1998-2009
[8]巴晓辉,李金海,陈杰.不需辅助信息的室内GP S信号捕获算法.电子技术应用.2006(6).130-132
[9]Nesreen I.Ziedan and James L.Garrison.Unaided Acquisition of Weak GPS Signals Using Circular Correlation or Double-Block Zero Padding.IEEE Position Location and Navigation Symposium 2004.Apr 2004.461-470
[10]Mark L.Psiaki and Hee Jung Extended Kalman Filter Methods for Tracking Weak GPS Signals.Proceedings of ION GPS 2002.Portland,OR.Sep,2002.24-27
[11]Mark L.Psiaki.Smoother-Based GPS Signal Tracking in a Software Receiver.Proceedings of ION GPS 2002.Salt Lake City,UT.Sept,2002.2900-2913
[12]张婧 基于非线性滤波的GPS微弱信号处理的研究[学位论文].上海.上海交通大学2007.25-26,47-63
[13]刘荟萃,许晓勇,王飞雪.扩频测距系统中多径信号伪码跟踪误差分析及消除技术.全球定位系统2005.6.34-38
[14]Richard D.J.The multipath estimating delay lock loop.Proceedings of IEEE Second International Symposium on Spread Spectrum Techniques and Applications.Yokohama,Japan.Nov-Dec,1992 39-42
[15]Richard D.J.van Nee and Jaap Siereveld.The Multipath Estimating Delay Lock Loop:Approaching Theoretical Accuracy Limits.Proceedings of IEEE Position,Location and Navigation Symposium.1994.Las Vegas,NV,USA.Apr,1994.246-251
[16]Matilde Sanchez-Fernandez.Performance Analysis and Parameter Optimization of DLL and MEDLL in Fading Multipath Environments for Next Generation Navigation Receivers.IEEE Transactions on Consumer Electronics,Vol.53,No.4,2007.246-251
[17]刘基余.GPS卫星导航定位原理与方法.北京.科学出版社.2003.118-152
[18]LeiDong.IF GPS Signal Simulator Development and Verification[Dissertation].Calgary University.2003.25-46
[19]ICD200C(2000).GPS Interface Control Document,ARINC Research Corporation.NAVSTAR GPS Space Segment / Navigation User Interfaces,IRN-200C-004.
[20]Luo,N.Precise Relative Positioning of Multiple Moving Platforms Using GPS Carrier Phase Observables[Dissertation].Calgary University.2001
[21]王智.高动态多普勒条件下的扩频接收技术研究[学位论文].上海.上海交通大学.2007.31-42
[22]Wei Yu.Selected GPS Receiver Enhancements for Weak Signal Acquisition and Tracking[Dissertation].Calgary University.2007.41-45,75-100
[23]Sanjeet Singh.Comparison of Assisted GPS and High Sensitivity GPS in Weak Signal Conditions[Dissertation].Calgary University.2006.13-32
[24]成骤,谢式千,潘承毅.概率论与数理统计(第三版).北京.高等教育出盘社2000
[25]沈用欢等.实用数学手册.北京.科学出版社2001
[26]http://mathwodd.wolfram.com/
[27]John G.Proakis著.张力军等译.数字通信(第四版).北京.电子工业出版社.
[28]李玉红,寇艳红,张其善.微弱GPS信号捕获算法研究.遥测遥控.2005,7
[29]刘海涛.高灵敏度GPS_Galileo双模导航接收机的研究与开发[学位论文].长沙.国防科学技术大学.2006.23-45
[30]陈后金等.数字信号处理.北京.高等教育出版社.2004.92-127
[31]田日才.扩频通信.北京.清华大学出版社.2006.57-83
[32]Peter Rinder Nicolaj Bertelsen.Design of a signal frequency GPS Software Receiver[Dissertation].Aalborg University.2004.25-42
[33]Nyunook Kim.Interference Effects on GPS Receivers in Weak Signal Environments[Dissertation].Calgary University.2006.9-30
[34]Ping Lian.Improving Tracking Performance of PLL in High Dynamic Applications[Dissertation].Calgary University.2004.43-57
[35]Brown,R.G.and P.Y.C.Hwang.Introduction to Random Signal and Applied Kalman Filtering.second edition.John Wiley & Sons,Inc.second edition 1992
[36]秦永元,张洪钺,汪叔华.卡尔曼滤波与组合导航原理.西北工业出版社.1998
[37]Loebis D,Sutton R,Chudley J,et al.Adaptive tuning of a Kalman filter via fuzzy logic for an intelligent AUV navigation system Control Engineering Practice.Vol.12,NO.12,2004
[38]卞鸿魏等.组合导航系统新息自适应卡尔曼滤波算法.上海交通大学学报.2006.40(6).1000-1003
[39]曾翠娟等.GPS动态定位的自适应卡尔曼滤波算法研究.导航.2006.3(1).39-49
[40]Sage A P,Husa G W.Adaptive Filtering with Unknown Prior Statistics,Proceedings of Joint Automatic Control Conference,1969,760-769
[41]张道松.非线性系统滤波及其在制导中的应用研究[学位论文].哈尔滨工业大学.2006.10-24
[42]吕伟,王艳东.Sage-Husa自适应卡尔曼滤波算法在SINS初始对准中的应用研究.战术导弹控制技术2005.(3).52-55
[43]沈云峰,朱海,莫军,宋裕农.简化的Sage-Husa自适应滤波算法在组合导航中的应用及仿真.青岛大学学报.2001.16(1).44-50
[44]刘广军,吴晓平,郭品.Sage滤波器的发散问题解决.全球定位系统.2002.27(1).6-9
[45]郭福成,李宗华,孙仲康.无源定位跟踪中修正协方差扩展卡尔曼滤波算法.电子与信息学报.2004.26(6).917-921
[46]冯鹏,邹世开.卡尔曼滤波器UD分解滤波算法的改进.遥测控制.2005.26(1).10-14
[47]隋树林等.基于UD-EKF自主光学导航方法仿真.系统仿真学报.2007.19(3).482-485