Research Of GPS Raim On Harsh Conditions

With the wide application of GPS in the field of civil aviation, the special needs of the aviation navigation such as precision, high security and high reliability has placed enormous demands on the integrity monitoring capabilities of the navigation system, to enhance the research of GPS integrity monitoring, timely and effective detection and exclusion of the satellite fault has extremely important practical significance. This thesis introduces the RAIM algorithm, analysis the impact about the change of tiny pseudorange bias and little visible satellites of GPS on the RAIM, propose an improved RAIM algorithm, designe and realize a simulation system of the satellite navigation integrity monitoring to verify the algorithm.Firstly, the development and the current situation of GPS integrity monitoring especially the RAIM algorithm has been introduced, including principles and models of least square residual method of RAIM, then analysis the limitation and improvement of conventional RAIM algorithm combinated with GPS system and special demand of aircraft entering stage.Secondly, according to conventional RAIM failed when tiny pseudorange bias occurrence, analysis the reason and resaerch the changes of pseudorange residuals statistical law, propose improved RAIM algorithm based on fuzzy parameter adaptive adjusted though fuzzy inference system, describe the mathematical models and basic principles, do the comparison simulation experiment combined with the tiny slow-varying pseudorange bias and tiny sudden pseudorange bias. Simulation results prove that the improved RAIM algorithm can detect satellite faults with the tiny pseudorange bias changes and ensure the PMD and PFA of RAIM, reduce the fault detection time significantly and enhance the continuity, security, reliability of navigation greatly.Then, the RAIM algorithm aiding of INS and clock bias has been proposed because the conventional RAIM couldn’t excluse the fault satellite when the number of visible GPS satellites is less than six. Elaborat the characteristics of the integrated GPS/INS navigation system with the tightly integrated and loose integrated model, do the experiment with the the nonlinear tightly integrated navigation simulation system, which test feasibility of the RAIM algorithm aiding of INS and clock bias and verify the effectiveness of improved RAIM algorithm in the aiding RAIM conditions.Finally, a simulation system of satellite navigation integrity monitoring based on data processing, availability judgment, fault detection, fault exclusion, positioning and the results showing modules, simulation Verification has been passed by conventional RAIM, improved RAIM and RAIM aiding of INS and clock bias with the simulation system, which has a good interface, can easily port to expand and provides a good simulation platform for exploration and research RAIM algorithm.The contribution of study in this thesis is to provide approaches for key techniques of RAIM such as tiny pseudorange bias, little visible GPS satellites and some other hash conditions of GPS. The results can be applied in further study on implementation of receiver terminal software integration and engineering practice.