High Precision Receiving And Multipath Mitigation Techniques For Modern Satellite Navigation Signals

Modernized satellite navigation systems use plenty of new techniques,especially widely applied binary offset carrier?BOC?signals,to improve the spectrum utility,positioning accuracy,multipath mitigation and anti-interference performances etc.However,the new techniques also introduce some new problems and challenges for receiver design.The multi-peaks of BOC signal self-correlation function will introduce tracking bias and degrade the positioning accuracy.The BOC signals with wide bandwidth needs high sampling frequency and computational complexity,which limit the receiver design with low-power consumption and miniaturization.In order to resolve these problems,this paper researched on the high-precision unambiguous receiving and multipath mitigation techniques,which proposed the following progresses and innovations:1)Double estimator?DE?algorithm and double phase estimator?DPE?algorithm widely researched and used can track the BOC signals without ambiguity.Although DE and DPE algorithms are respectively suitable for different situations,both have the same tracking structure and the different tracking signal-to-noise ratio?SNR?loss.I proposed a general tracking structure based on double tracking loops,and designed the optimal subcarrier waveform with different modulation parameters and bandwidth under the minimum tracking SNR loss principle.With respect to DE and DPE algorithms,the proposed algorithm can improve 0.4dB and 0.5dB SNR under the bandwidth limited condition.2)By combining the code and subcarrier phase estimation,DE algorithm can obtain the unambiguous high-precision pseudo-range measurement.However,the traditional combining method is unstable for high-order BOC signal or under multipath conditions.We proposed a subcarrier ambiguity detection and solution algorithm with velocity vector projection.The high-precision velocity estimation is used to monitor the subcarrier pseudo-range measurement change.When the big change is detected,the velocity is also used to predict the user position to resolve the ambiguity quickly.With respect to the traditional method,the proposed algorithm can improve the pseudo-range estimation robustness for high-order BOC signal or under multi-path condition,for BOC?15,2.5?signals with carrier-to-noise ratio C/N₀=30dB,the average false-alarm probability is reduced 260 times.3)The traditional matched filter and DE algorithms for tracking high-order BOC signals required much computational complexity.In order to decrease the complexity,we proposed a coherent combining algorithm with dual sidebands of BOC signals.The algorithm based on the precise dual-sideband model of high-order BOC signal,and used the linear relationship of subcarrier phase and differential of dual sideband carrier phase.With respect to DE algorithm,for high-order BOC signal,the proposed method can reduce 90%computational complexity with less than 0.5dB SNR loss.4)There are two type waveforms of code correlation reference waveform?CCRW?technique for BOC signals:the first type generates the reference waveform at the baseband BOC signal change edge;and the second one at the pseudo-noise?PN?code edge.Both of them do not have an effective trade-off of tracking accuracy and multipath mitigation.We proposed a waveform generated at the edge of subcarrier,and derived the optimal base waveform with maximum multipath mitigation.This waveform is a non-linear transform of baseband BOC signals,which can reduce 37.4%multipath error envelope area with respect to the first type waveform and about 80%mean square deviation of thermal noise with respect to the second type one.5)The QStrobe multipath mitigation algorithm for high-order BOC signal has a narrow convergence area,which is not robust for the high-dynamic receiver design.I proposed a multipath mitigation algorithm with multi-region discriminator.The algorithm used an open-loop Kalman filter to estimate the tracking error.According to the estimation,the QBOC and QStrobe discriminators are switched in real-time,which can expand the convergence region to[-1,1]code.At the same time,the optimal principle of QStrobe algorithm was changed,which can improve 57%and 51%the multipath error envelope area of BOC?15,2.5?and BOC?14,2?respectively.6)The traditional unambiguous CCRW techniques are designed separately with different BOC?m,n?signals,which are not the general method and not the optimal waveform at most time.I proposed a general unambiguous waveform design algorithm using the minimum wave iteration for all BOC?m,n?signals.With respect to traditional algorithms,the proposed algorithm can obtain the optimal waveform with different principles such as the best multipath mitigation performance,the minimum thermal noise error or the largest convergence region.At the same time,the quantization levels,and the minimum pulse width can also be fixed with the algorithm.At last,I summarized the research achievements and planned the next step works.Some of the proposed algorithms in the paper have been used in the multi-system monitor receiver design for ground stations of BeiDou satellite navigation systems of China.