## 4 Experiments and Discussion
### Performance Analysis of the Resampling Strategy  
With emphasis on effects of the proposed strategy on signal acquisition, we execute the resampling strategy and the conventional algorithm (without the resampling strategy) on all datasets. Experimental results are discussed in terms of acquisition effectiveness, sensitivity, computation and time cost. Figure 5 presents the characteristics of the received broadband signal in the frequency and time domains, as well as the amplitude distribution of the received signal in Dataset 1. By applying the bandpass filter to the received broadband signal, the power of the side lobe signals was filtered out and the main lobe signal was retained, as shown in Figure 6. The bandwidth and intermediate frequency of the main lobe signal were the same as that of the received broadband signal, \(B_{d}=2.046\) MHz and \(f_{\rm{IF}}=7.4\) MHz. Besides, the sampling frequency of the main lobe signal was the conventional one, \(f_{s}=53\) MHz. Applying the resampling strategy to the main lobe signal, the resampled signal was obtained, as presented in Figure 7. Specially, the resampled signal had the same bandwidth of the main lobe signal, while the intermediate frequency changed from \(f_{IF}=7.4\) MHz to \(f_{dIF}=1.43\) MHz. Meanwhile, as a result of the resampling strategy, the sampling frequency was greatly reduced from the conventional one \(f_{s}=53\) MHz to \(f_{ds}=5.97\) MHz, to reduce the data size of the resampled sequences used in FFT, IFFT, and correlation calculation. Here, circular correlation time of signal acquisition was fixed as \(L_{x}=20\) ms. \begin{table}
\begin{tabular}{c c c c c} \hline
**Dataset No.** & **1** & **2** & **3** & **4** \\ \hline Data Type & 8-bit Real Data & 8-bit Real Data & 8-bit Real Data & 8-bit Complex Data \\ Intermediate Frequency (MHz) & 7.4 & 7.4 & 7.6 & \(-0.02\) \\ Conventional Sampling Frequency (MHz) & 53 & 53 & 79.25 & 4 \\ \hline \end{tabular}
\end{table} 
Table 1: The main parameters of GNSS signals used in the experiments. Figure 5: The received broadband signal of Dataset 1 in the frequency and time domains, and the amplitude distribution. The bandwidth of the main lobe signal is 2.046 MHz and the intermediate frequency is 7.4 MHz. Figure 6: The main lobe signal filtered from the received broadband signal of Dataset 1 in the frequency domain. The bandwidth of the main lobe signal is 2.046 MHz, the intermediate frequency is 7.4 MHz and the sampling frequency is 53 MHz. Figure 7: The resampled signal by applying the resampling strategy to the main lobe signal of Dataset 1 in the frequency domain. The bandwidth of the resampled signal is 2.046 MHz, the intermediate frequency is 1.43 MHz and the sampling frequency is 5.97 MHz. The acquisition results of Dataset 1 are listed in Table 2. There were 7 satellites (\(PRN\) 5, 6, 12, 17, 24, 25, and 29) acquired successfully. It also has proved the capability of the proposed strategy to adapt to the signals with different carrier-to-noise ratios. Comparing experimental results of the resampling strategy and the conventional method (without the resampling strategy), it can be found that the two algorithms demonstrated almost the same acquisition performances, including acquired satellites, carrier frequency, Doppler frequency shift, and code phase offset. There is no obvious loss of acquisition performance for the resampling strategy. In addition, it is remarkable that the correlation magnitude of each acquired satellite decreased to about 10% as a result of the resampling strategy, shown in the bold columns in Table 2. This can be qualitatively attributed to the reduced-size samples for circular correlation by the resampling strategy, see Equation (10). Moreover, the correlation ratio of signal acquisition reflects the relationship of the satellite signal and local PRN replica, acting as the acquisition threshold in this paper.