Weak GPS Signal Acquisition Research Articles

Acquisition of weak GPS signals using wavelet-based de-noising methods

Various factors cause GPS signals to be weakened in their path from satellites to receiver. This phenomenon leads to some problems in the normal stages of the positioning process, including acquisition stage. The wavelet transform is one of the tools that have been employed in several methods to improve receiver’s sensitivity in confronting weak GPS signals. Choosing an appropriate threshold plays a key role in the performance of this de-noising method. This study presents two methods for selecting an appropriate threshold. In the first method, the threshold is determined based on the statistical information extracted from the signal. On the other hand, the threshold in the second method is determined by type II fuzzy sets. The results show that employment of these two methods increases SNR gain as well as the range of acquirable SNR which makes signals acquisition with minimum post-correlation SNR of in a GPS receiver possible.

SAW based convolver for GPS signal acquisition module

Aiming at acquiring navigation signal with weak strength at large speed in challenging environment, SAW convolver is employed to implement partial correlation in weak strength and high dynamic GPS signal acquisition. After introducing principle of GPS signal acquisition, difficulty in acquiring GPS signal in special environments, for example indoor, urban street and woods, is analyzed in detail. The suitability of SAW device in acquiring challenging GPS signal is discussed about. A novel GPS receiver structure based on SAW device is proposed. In final, simulation is performed to testify effectiveness of this new structure.

Urban environment solutions to GPS signal near-far effect

Our aim at improving GPS receivers' availability in an urban environment, weak GPS signal acquisition becomes one key issue in satellite navigation signal processing. In special signal propagation environments, such as indoors, urban crayons, and woods, various factors such as signal propagation power loss, amplitude attenuation, and phase, time, and frequency delay distortions produce at the signal receiving end, what is now known in the literature as, the GPS signal near-far effect, which results in severe degradation of the GPS signal acquisition performance. To mitigate the near-far effect, we focus on four main factors, which are the signal strength attenuation; the Doppler frequency distortion; carrier phase uncertainty; and multi-path distribution because a proper optimization of these factors appears to improve the acquisition performance effectively.