In recent years, researches on the weak GPS signal acquisition have
attracted a lot of attentions to provide an accurate position in indoor
environment. It has been studied that GPS signal acquisition process
needs a longer integration time for conventional FFT acquisition method
under the weak signal condition. However, the maximum data length for
the coherent integration time method is limited by the navigation data bit
transition effect. In fact, the GNSS weak signal may be “transient” in the
receiver, with duration generally shorter than the observation interval; it therefore can be defined as non-stationary signal. Consequently, this paper presents a signal analysis technique for GPS signal based on the Empirical Mode Decomposition (EMD). The EMD process decomposed any
complicated data into a finite and often small number of Intrinsic Mode
Function (IMF) components and a residual trend. The general features of
the IMF components are described along with the ability to combine IMF
components and the residual to form low frequency or high frequency filters.This paper takes the characteristics of the EMD as a filter to reduce the noise prior to the signal acquisition process. As a result, the weak signal can be further acquired by focusing on the filtered GPS signals.In this paper, the analytical background of the EMD is introduced and its effectiveness is experimentally evaluated using the GPS raw
Intermediate Frequency (IF) signals which are collected by a software GPS
receiver. The results demonstrate that EMD-based GPS signal acquisition
method is adequate on capturing transient events such as the weak signal
under the indoor environment.