# LEO-Based Satellite Constellation for Moving Target Detection
## 4 Discussion  
A novel multi-source fusion detection method based on LEO satellites has been introduced in this paper. The application of pre-compensation, clutter suppression and multi-source fusion detection processes demonstrates the efficiency of our study in moving target detection process.  
Considering that LEO-based satellite constellation is confronted with the non-coincidence problem with regard of multi-source echoes. That is, the target focusing positions with different LEO satellites do not coincide at one cell in DFR domain as a result of the high-speed motion platform, which can be solved by constructing the pre-compensation function based on the antenna beam directivity. From Figure 5, one can see that the target energy can be focused on the same cell in DFR domain after multi-source fusion process, which further verifies the effectiveness of our pre-compensation theory.  
For the DFR-based clutter suppression strategy, the size of the DFR cell is designed by deducing its upper and lower limits according to the multi-station configuration. In this way, both the clutter suppression effectiveness and the multi-station fusion efficiency are taken into consideration. For the DFR cell where the target is located, the corresponding clutter echo can be suppressed more than 30 dB through reasonably setting the maximum value of DFR cell, as indicated in Figure 7a,b. In Figure 8, the target echo fusion problem caused by high-speed motion platform can be greatly alleviated by selecting the minimum value of the DFR cell.  
Further, the enhanced CFAR detection strategy based on the exponential weighted likelihood measurement can be carried out by transforming the fused data from range coordinate to Cartesian coordinate, which essentially reduces the false alarm probability caused by the echo fusion related to different range loops in multi-station configuration. For the first step, the echo fusion process is performed through employing the coordinate system transformation operation, and the echoes with multiple satellites are focused on the same cell, as demonstrated in Figure 9, which verifies the effectiveness of the fusion strategy. In step 2, the weight distribution of the contrast between the sliding window center and the edge region, as shown in Figure 10a, is introduced to decrease the target diffusion energy and reduce the false alarm probability. On this basis, the exponential weighted likelihood ratio is modeled in step 3 to construct the multi-source fusion detection factor, which is indicated in Figure 10b. In step 4, the second-order statistic is deduced to achieve the CFAR threshold. One can see from Figure 11 that the proposed LRWB detection method could further improve the detection performance. Besides the self-transmitting and self-receiving operation mode, the LRWB-detection method is available for other operation modes. The reasons are chiefly as follows, for different configurations, the echoes with multiple satellites can be combined in the Cartesian coordinate based on the projection relationship, where the target signals corresponding to different satellites are presented as distinct iso-range lines.  
Compared with the recent work (LRB detection method) [4], the proposed method achieves a significant multi-source fusion detection performance based on LEO constellation, which is verified from the experimental results.