The Characteristics Of PN Code Correlation And Its Applications Under High Dynamics

In the satellite navigation receiver, there is not only carrier frequency offset but also code frequency offset between the received and the local signals when the host vehicle is in high dynamic motion. The precious studies mostly aimed at carrier frequency offset, while there were very few systemic theoretical studies on the influences of code frequency offset. There is still large space for improving the efficiencies and performance in the designing of high dynamic receivers. Moreover, the influence of satellites' motion on the metering precision of pseudo range in high precision receivers with the precision demand of 0.5ns is yet not neglectable when the host vehicle is static. Based on these two applications, this thesis focuses on the influence of code frequency offset. It contains four sections:In sectionⅠ, the correlation function of PN codes under dynamic conditions is studied. Under dynamic conditions code frequency offset makes the code correlation function deformed. The precious study was limited to first-order dynamic, i.e., constant code frequency offset and the integration time interval during which the chip slipping due to code frequency offset is less than one chip. And mostly the numerical calculation method was used, except that Unjeng Cheng derived the expressions of correlation function and its mean value.In the thesis, first the PN code correlation function, its mean and variance are derived by the method of summing chip by chip, with the correlation time interval extended to arbitrary length and the dynamic condition extended to the case of second-order, i.e., constant code frequency offset rate. And also the upper bound of variance is given. This method is accurate. But its shortcoming of very complicated expression disables it from being used to analyze the characteristic of PN code correlation and guide the analyses and devising of code synchronization. So we present a method which is referred to as stationary random process integrating. The PN code correlation function and its mean with arbitrary integration time interval under first-order and second-order dynamic are derived and verified by simulations. The characteristics of PN code correlation function under first-order and second-order dynamic are analyzed. The result shows that under dynamic conditions the code correlation function is no longer triangular and three dynamic effects of main-lobe spreading, correlation peak shifting and decreasing take place, and moreover the code correlation function loses its symmetry under second-order dynamic. By comparison between second-order and first-order dynamic based on the peak value loss expressions it is concluded that the second-order dynamic factor code frequency offset rate can induce loss or gain in the order of dB, and the conditions when second-order dynamic can be simplified to first-order dynamic and the method how to decision are given. Compared with the method of summing chip by chip, the method of stationary random process integrating is simpler and more practical. And its precision is high when the PN code period length L >>1. In sectionⅡ, the influences of high dynamic on acquisition are investigated. The precious study focused on the influence of carrier frequency offset on acquisition. The influence of code frequency offset has been seldom analyzed, and the theoretical study with both carrier and code frequency offset taking into account has not been seen in the literature. In this thesis the PN code correlation function with both constant carrier and code frequency offset and also carrier Doppler-code Doppler joint loss are derived. The study shows that ignoring the code frequency offset will induce errors in the order of dB or 10dB. Based on it the IF integration time of the common acquisition system called segment correlation-video integration is optimized, the comparison study shows that optimizing with the code frequency offset ignored brings little performance loss, so the IF integration time can be optimized according to the carrier frequency offset only.In sectionⅢ, the code phase metering methods for code acquisition and tracking under dynamic conditions are investigated. Based on the expressions for code correlation function under dynamic conditions, the phase metering methods and their errors for code acquisition and tracking under first-order and second-order dynamic are studied. Two code phase metering methods for code acquisition under dynamic, two code phase metering methods for first-order dynamic tracking and three code phase metering methods for second-order dynamic tracking are proposed. The presented metering methods for code acquisition can almost remove the common-used method's error of the order of 10ns to 100ns, so that can reduce the burden of code tracking circuit. And the presented code phase metering methods for code acquisition can almost remove the common-used method's error of the order of 0.001m～0.1m, so that can improve the precision of PN code ranging.In sectionⅣ, the dynamic delay effect in positioning solution under high dynamic is studied. It is pointed out that when the transmitter is moving, there is a delay effect in the reflection of the observed pseudo range on the transmitter motion state. In the telemetry and tracking integrated system with inverse GPS principle, the dynamic delay effect of pseudo range can induce positioning error in the order of m. The revising method is to align the transmitting time of the observed pseudo range at all the observation stations.The thesis provides with theoretical guidance for the analysis and designing of dynamic spread spectrum code synchronization, and provides with methods for (a) high precision PN code ranging under dynamic conditions and (b) pseudo range observation in the positive positioning systems in order to avoid the dynamic delay errors.