| Precise spread spectrum ranging directly determines the performance of satellite navigation and positioning,satellite TT&C and orbit determination,etc.However,no matter in the civilian or military fields,intentional and unintentional interference are inevitable,and it is a severe challenge to the precise spread spectrum ranging.Both interference signal and anti-interference measure can affect ranging performance,even lead to function failure of a ranging system.Reliability and precision become the focus of modern applications of the spread spectrum ranging.Hence,the basic question of this thesis is how to realize the precise spread spectrum ranging in the presence of interference.Focused on the problem,this thesis studied four key technical problems,while the main contribution and novelty are list as follows:1.To analyze and evaluate the ranging performance in the presence of continuous wave interference(CWI),a quantitative calculation and evaluation method of ranging error is proposed,based on the continuous frequency spectrum of spread spectrum signal.The non-ideal random property of pseudo-random noise codes,the pulse modulation shape and the limited intergrtion time are taken into account,and a refined signal frequency spectrum model is constructed.The static and dynamic ranging error induced by CWI are derived,then ranging error envelope,sensitive region and sensitive bandwidth are defined to quantitatively evaluate the ranging performance under CWI.2.To analyze and evaluate the ranging performance in the presence of narrow band interference(NBI),a quantitative calculation and evaluation method of anti-NBI performance is proposed.Both system stability and ranging accuracy are considered,and performance evaluation metrics with and without interference are provided.The interference margin of ranging system is defined,it represents the largest interference to signal power ratio that to make sure a ranging system keep stable and satisfy the accuracy requirement.Meanwhile,the margin reference factor is extracted to quantitative describe the weight relationship between stability and precision under certain application scenarios.it explicitly indicates restrictive factors of anti-interference performance,then the calculation of interference margin is greatly simplified.3.To solve the problem of interference detection and identification based on notch filter,a method based on a two-stage adaptive IIR notch filter is proposed.It can judge the existence of interference,and estimate the interference frequency.By means of optimizing the adaptive gradient algorithm,the estimation accuracy and detection sensitivity of interference parameters are improved.With typical parameters,the detection sensitivity of CWI is improved by about 2.6 d B,up to-12.8 d B,while these of double CWI and NBI are up to-8.5 d B and-4.1 d B,respectively.Then,a two-stage notch filter is designed to identify the three kinds of interference,and it is the essential prerequisite for the anti-interference design of spread spectrum ranging system.4.To design the interference suppression and the anti-interference measure of ranging system,an interference suppression method based on a heterodyne tunable LP-FIR notch filter is proposed.Combined with the previously designed interference detection and identification method,the anti-interference of ranging system is realized.In the interference suppression method,a Hilbert filter,a one-stage heterodyne modulation and a LP-FIR notch filter are used to suppress CWI and NBI at different frequencies.The method is simple,flexible and easy to realize,while the impact of anti-interference measure on ranging accuracy can be reduced significantly,and the ranging accuracy close to CRLB can be obtained.All the research results above are confirmed to be effective and practical with theoretical analyses and experimental verifications.They are of great theoretical and practical significance to the design of precise spread spectrum ranging system in a complex electromagnetic interference environment. |
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