# High-Resolution Through-the-Wall Radar Imaging with Exploitation of Target Structure
## 4 Results
### Simulated Dataset  
Simulations were performed for a monostatic radar with a 77-element monostatic ULA. The spacing between elements is set as 1.9 cm. Each element transmits a stepped-frequency signal and receives the target returns. The transmitted wave consists of 200 equally spaced frequency steps and covers the 1 GHz to 3 GHz. The detailed parameters are given in Table 2. The middle of the antenna array is regarded as the original point. The front wall is 2.44 meters away from the antenna array, but it is not considered in the scenario for simplicity. The locations of the two side walls are around \(\pm 1.83\) m crossrange, whereas the location of the back wall, parallel to the antenna array, is 6.37 m downrange. The scattering coefficient of the direct path is determined according to \(\mathcal{N}(0,1)\). In addition, the signal amplitudes of the received returns decrease as the distance increases. A target occupying \(Q=8\) contiguous pixels is considered, as shown in Figure 3a. The received signal includes a total of \(K=4\) paths, consisting of the direct echo as well as indirect paths reflected on the surfaces of the three walls. To simulate the real scenario, the measurements with an SNR of 0 dB plus additive Gaussian noise are employed for simulations. When using the classical BP method, all available data are used; however, only a quarter of all frequencies are chosen at random for the CS-based imaging. We first present the reconstructed image using the BP algorithm in Figure 3b in which three ghosts exist due to the three indirect paths from three interior walls, respectively. It is evident that the BP-based algorithm is unable to properly rebuild the scenario and distinguish the true target from the ghosts. The reconstruction result contains a much higher amount of clutter. In addition, the resolution of the BP algorithm is 0.75 m owing to the 2 GHz band. Constrained by the Rayleigh boundary, the exact shape of the target is hard to obtain. In these CS-based approaches, it is observed that these ghosts from multipath propagations can be effectively alleviated due to the exploitation of group sparsity structure, as depicted in Figure 3b-f. The reconstruction result using the BOMP method is provided in Figure 3c, and it is clear that several fake pixels are located around the real positions, even though the true sparsity number is used in advance. Figure 3d depicts the imaging result based on the BSBL method. It can be found that the reconstruction result is similar to the ground truth, whereas some spurious isolated pixels occur because of the target structure being neglected. Figure 3e gives the reconstructed result using the overlapping group CS algorithm. It is clear that the overlapping group CS algorithm can reconstruct and capture the target shape, whereas it leads to some fake pixels around the real locations owing to the inappropriate overlapping partition. Figure 3f suggests that the proposed method can successfully reconstruct the target with a continuously clustered structure and effectively suppress the separated and false targets by enforcing the clustered prior. The improvements of the proposed method are also verified by the NMSE values, which are, respectively, 1.13 in the BOMP method, 0.78 in the BSBL method, 0.82 in the overlapping GS method, and 0.58 in the proposed algorithm. In addition, we also provide the executive \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Value** \\ \hline Initial frequency & 1 GHz \\ Cut-off frequency & 3 GHz \\ Bandwidth & 2 GHz \\ Number of steps & 500 \\ Step frequency & 10 MHz \\ Number of elements & 77 \\ Element interval & 1.9 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. time comparisons among these methods, as shown in Table 3. It is observed that the BOMP method has the smallest runtime, and the runtime is less than 1 s, because the used iteration number of this method is exactly the sparsity number. The executive time in the proposed method is comparable to that in the BSBL method.