# An Efficient Digital Channelized Receiver for Low SNR and Wideband Chirp Signals Detection
## 3 Results and Discussion
### Simulation Experiments  
The system parameters and prototype filter parameters are shown in Table 2. The overlapping channel division method is adopted, and the channel overlap factor is 0.3. The filter structure is a non-critical sampling structure based on WOLA. The oversampling factor is 1.6, determined by the channel overlap factor. Figure 7 shows the realized magnitude response for filter banks. The number of output channels is \(K/2\). As shown in Figure 7, it is clear that there is no blind zone for the signal interception in the receive bandwidth. In addition, oversampling ensures no aliasing of the signal spectrum within the channel. For the purpose of demonstration, the input signal parameters are shown in Table 3. The input signal for simulation includes three chirp signals. The first two chirp signals fall within the channel, and the third is distributed across the channel. The SNR for all three signals is 0 dB. The signal processing is shown below. \begin{table}
\begin{tabular}{c c c} \hline  & **Parameter Type** & **Parameter Value** \\ \hline \multirow{3}{*}{System parameters} & Sampling Rate (\(f_{s}\)) & 1200 MHz \\  & Channel number & 32 \\  & Decimation number & 20 \\ \hline \multirow{3}{*}{Filter parameters} & Passband frequency & 19.5 MHz \\  & Stopband frequency & 28.5 MHz \\ \cline{1-1}  & Filter order & 256 \\ \hline \end{tabular}
\end{table} 
Table 2: System parameters and prototype filter parameters. Figure 7: The magnitude frequency response of filter banks. (Different color lines indicate the frequency response of the bandpass filter for different channels). The WOLA channelization results are shown in Figure 8. For convenience, only the amplitude response of the first 16 channels is shown. Based on the adaptive detection threshold and the instantaneous magnitude, the correct channels are identified as 2, 3, 5, 6, and 7. The IFM of the correct channels are shown in Figures 9 and 10. Figures 9 and 10 show that the original IFM is sensitive to noise and has poor frequency estimation accuracy when the SNR is low. After processing by the local flat mean algorithm, the frequency estimation accuracy improves significantly. The frequency estimation results for the correct channels are as follows  
\[ \begin{cases}f_{BW2}=19.95\;\text{MHz},f_{CF2}=2.81\;\text{MHz}\\ f_{BW3}=19.68\;\text{MHz},f_{CF3}=-5.08\;\text{MHz}\\ f_{BW5}=35.74\;\text{MHz},f_{CF5}=3.27\;\text{MHz}\\ f_{BW6}=41.64\;\text{MHz},f_{CF6}=0.12\;\text{MHz}\\ f_{BW7}=33.06\;\text{MHz},f_{CF7}=-6.27\;\text{MHz}\\ \end{cases}  \tag{25}\]  
Figure 8: The WOLA channelization results. (The blue line indicates the instantaneous amplitude of the signal in the channel, and the red dashed line indicates the detection threshold). \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter Type** & **Signal 1** & **Signal 2** & **Signal 3** \\ \hline Modulation type & Chirp & Chirp & Chirp \\ SNR & 0 dB & 0 dB & 0 dB \\ Bandwidth & 20 MHz & 20 MHz & 100 MHz \\ Center frequency & 40 MHz & 70 MHz & 185 MHz \\ Pulse width & 5 \(\upmu\)s & 5 \(\upmu\)s & 20 \(\upmu\)s \\ \hline \end{tabular}
\end{table} 
Table 3: Input signal parameters. Introduce the the channel centre frequency to obtain the start and end frequencies of the signal in the channel. The results can be expressed as  
\[ \begin{cases}f_{st2}=30.34\text{ MHz},f_{sp2}=50.29\text{ MHz}\\ f_{st3}=60.08\text{ MHz},f_{sp3}=79.76\text{ MHz}\\ f_{st5}=135.40\text{ MHz},f_{sp5}=171.14\text{ MHz}\\ f_{st6}=166.80\text{ MHz},f_{sp6}=208.44\text{ MHz}\\ f_{st7}=202.20\text{ MHz},f_{sp7}=235.26\text{ MHz}\\ \end{cases}  \tag{26}\]  
Channel arbitration is then completed based on the IFM results. The results show that the intercepted mixed pulse stream consists of three separate signals. The signals within channels 5, 6, and 7 belong to the same signal. The estimation results of signal parameters are shown in Table 4. Simulations show that the proposed receiver architecture is reliable for low SNR chirp signal interception with high parameter estimation accuracy.