چكيده به لاتين
Abstract:
Global Satellite Navigation Systems (GNSS) are considered among the essential technologies of today world. The Global Positioning System (GPS), which is widely used in military and civilian domains, is the most common navigation system.
Today, acquisition of Global Positioning System (GPS) signals is difficult in weak signal environments due to the significant reduction in signal-to-noise ratio, the presence of code Doppler phenomenon and the navigation bit sign transition. Post-correlation techniques are utilized to solve these problems. Despite the advantages of these techniques, they suffer from the code Doppler and the navigation bit sign transition. The first problem changes the real phase code that is causes the different correlation maximum not to fall into the same code phase. The second problem reduces the correlation function amplitude. As a result, the both of them reduce the detection probability in the out of detector.
In this thesis, an improved semi-bit differential acquisition method has been presented that can improve the code Doppler and the bit sign transition in post-correlation techniques. To evaluate the provided method, the simulations were performed on three real datasets. The results show that the amount of required input SNR to detect at least four satellites in the proposed method is -48.3 dB, but in traditional differential and non-coherent methods are -20 dB and -9 dB, respectively.
Keywords: GPS, Acquisition, Weak Signal, Differential, Coherent, Non-Coherent.
