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 $-6.5\mathrm{d}\mathrm{B}$ in a GPS receiver possible.

各种因素导致GPS信号从卫星到接收器的路径减弱。这种现象在定位过程的正常阶段（包括获取阶段）会导致一些问题。小波变换是已在多种方法中采用的工具之一，可用来提高接收机在面对微弱的GPS信号时的灵敏度。选择合适的阈值在这种降噪方法的性能中起着关键作用。这项研究提出了两种选择合适阈值的方法。在第一种方法中，基于从信号中提取的统计信息来确定阈值。另一方面，第二种方法中的阈值由II型模糊集确定。$-6.5\mathrm{d}\mathrm{乙}$ 在GPS接收器中。