| Various types (P code, C code, etc.) of observations generated by Multi-GNSS (GPS, GLONASS, Galileo, BDS, etc.) in multi-frequency (at least trip-frequency) are the major feature of the modern GNSS. Nowerdays, special combinations are utilized corresponding to different purpose under different environment for high accuracy GNSS applications, e.g., the inter-frequency, inter-type linear combinations as well as inter-stations, inter-satellites, inter-epochs differencial combinations, and gradually developed the data processing model and high accuracy navigation service based on dual-frequency observations.Concerning the modernization of GPS and GLONASS, together with the new GNSS systems, Galileo and especially BDS, which is the first constellation with full consistency of three carriers ensured for all satellites, as wll as the constructions of various continuous operation reference systems (CORS), the GNSS data processing technology, mathmetical model, products definition and the software in its current stage is not full meet the demand of multi-frequency GNSS applications. However, within the GNSS community all over the world, including IGS, there has not proposed a systematic solution up to now. As a result, in-depth study on multi-frequency GNSS high accuracy data processing and the development of correspongding sofeware is not only the trend of GNSS community, but also plays a key faction for the expansion of BDS applications internationally. Consquently, this dissertation aism at a generalized-processing algorithm which is navigation system independent and carrier number unrelated.Take the above goals into consideration, in this dissertation; we began with the investation of the physical and geometry models that involoved with satellite navigation signal generating, broadcasting and processing seperatlly. Follow on, a new GNSS adjustment system is proposed in which the original zero-deference, un-combined signals are processed directly. With the new observation formule, a strong emphasis is given on several key questions, including:regularization of datum deficiency for the bias and clock parameters; ionosphere delay parametlizatoin with temporal and spatial constrains; UPD separation as well as ambiguity resolution. Based on those theoretical studies, Multi-frequency GNSS processing system has been designed and developed independently to access the full capabilities of the multi-GNSS frequencies and signals. Finally, this novel model is demonstrated in terms of flexibility and reliablity with network data processing as well as single station data processing with GPS and BDS observations. Main contents and contributions of this dissertation include:1. With the zero difference un-combinationed signal, a generalized-positioning model that the navigation system independent and the carrier number unrelated is promoted, which is suitable for both single-and multi-sites data processing. For the synchronization of different signals, uncalibrated signal delays (USD) are more generally defined to compensate the signal specific offsets in code and phase signals respectively.2. Based on the analysis of the algebraic structures, this generalized-positioning model is further refined with the minimum constrains to regularize the datum deficiency of the observation equation system. To guarantee the flexibility of our promoted solution, the typical treatment methods which are regarded as ionosphere-free and geometry-free combination for satellite clock estimatin as well as differencial code bias and ionosphere delay modeling, respectivally, are studied in depth.3. From our investigation on the stochastic characteristics of the ionospheric delay over a station, it cannot be precisely represented by either a deterministic model in the form of a low-order polynomial or a stochastic process for each satellite, because of its strong irregular spatial and temporal variations. Therefore, a novel approach is developed accordingly in which the deterministic representation is further refined by a stochastic process for each satellite with an empirical model for its power density. Furthermore, ionospheric delay corrections from a constructed model using GNSS data are also included as pseudo-observations for a better solution. A large data set collected is processed with the new approach and several commonly adopted approaches for validation, the improvement for single frequency in North, East and Up direction are47.8%,53.7%and52.5%respectivally, while for dual frequency the improvement is16.5%,13.9%and l6.8%respectivally. The ionosphere modeling experiments are also carried out with both CMONOC and provincial CORS stations, which shows an improvement of50.3%and70.7%with respect of GIM.4. Through comprehensive and in-depth study of ambiguity resolution based on double differenece and single difference, this paper promoted the UPD generation and ambiguity resolution based on the zero difference un-combinationed observations. Results based on data of CMONOC network covered show that the accuracy of our ambiguity-fixed PPP improved about5.6%,8.6%and11%in the East, North and Up components respectively than ambiguity-float PPP.5. With this new model, uncalibrated signal delays (USD) and ionospheric delays are derived for both GPS and BeiDou with a large dada set. Numerical results demonstrate that, with a limited number of stations, the uncalibrated code delays and uncalibrated phase delays are determinate and evaluated. Extra experiments concerning the performance of this novel model in point positioning with mixed-frequencies of mixed-constellations is analyzed, in which the USD parameters are fixed with our generated values. The results are evaluated in terms of both positioning accuracy and convergence time. |
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