Instantaneous Gps Signal Simulation And Navigation Algorithms

In normal situations where continuous Global Position System (GPS) signals can be received, the position and velocity measurement of the GPS receiver are accomplished by continuous tracking of GPS signals with PLL/FLL and DLL to get the navigation data. However, GPS receivers can receive only incontinuous or partial GPS signals in some circumstances, such as indoors, urban areas with lots of buildings, signals reflected by objects in ocean, signals received by the single antenna of rotating projectile, or partial signals by turning off GPS receivers regularly to save limited power, and so on. It's still an open issue how to measure velocity and calculate location of GPS receivers with partial GPS signals.To address above issues, this dissertation presents researches on the simulation method of GPS partial intermediate frequency (IF) signal and the development of a software-based IF GPS signal simulation system. Based on signals outputted from the simulation system, methods of positioning and velocity measurement with partial GPS signal are further researched. The innovative results from this dissertation are as follows:(1) The simulation of GPS IF signal. A mathematical signal model is built to express the digitized IF GPS signal as a function of various errors during propagation, such as satellite clock error, ephemeris error, ionosphere error, and troposphere error etc, which make the simulated signals are more approximate to GPS signals in real environments. It can simulate the process of frequency down-conversion, sampling and quantization. For high dynamic rotating projectile with attitude changing with time, the algorithm of calculating the Doppler frequency shift of the GPS signal is given. In addition, With the GPS receiver's antenna radiation pattern, a simulation method for visible GPS satellites forecast and signal magnitude modulation is also proposed. Based on above model and algorithms, the mechanism of estimating GPS satellite signal status is given in detail and a simulation system is developed. Compared to the conventional RF GPS simulator, this simulation system avoids the uncertainty brought by the method of RF GPS signal generation. Moreover, it can model error sources that affect the pseudo-range precision and tracking performance, and therefore is more suitable for theoretic algorithm research.(2) Key technologies of positioning with partial GPS signals. Key technologies of positioning with partial GPS signals are researched in depth, including the method of getting navigation data, extracting code phase, as well as signal transmitting time recovery, etc. A method that refines the code phase with the optimized shortening the search step length and curve fitting methods is proposed, and a graph that expresses the relation between the precision of the code phase and the length of the partial signal in different SNR are obtained with the Monte Carlo simulation method. The feasibility of the positioning method with partial GPS signals is verified with the modified iterative Least Square method.(3) Velocity measurement with partial GPS signals. The classical and modern spectral estimation theories are applied to GPS velocity measurement. After comparative study, a Periodogram-based velocity measurement method is proposed, and simulation is performed to verify that the velocity can be measured with this method and the precision of the velocity is adequate to meet user's demands in certain scenarios.(4) Based on the positioning technologies with partial GPS signal as researched above, the design of a spinning projectile GPS receiver solution with single antenna is proposed. Kalman filter theory is applied to smooth the positioning results that are calculated with periodic and partial GPS signals, and the forecast function of Kalman filer is used to estimate and process the exceptional measurements, which highly improves the navigation precision.The research results as represented in this dissertation have not only theoretical value for the research of navigation methods with partial GPS signals, but also practical significance in development and application of spinning projectile GPS receiver with single antenna. Further research and work will be continued along these directions.