# Efficient Multipath Clutter Cancellation for UAV Monitoring Using DAB Satellite-Based PBR
## 5 Simulation  
The same DAB illuminator in the above section was simulated with seven targets, the parameters of which are listed in Table 2, to further evaluate the performance of moving clutter rejection. The clutter region covers the first 41 range bins, for which the clutter-to  
Figure 4: Suppression performance of different ECA versions. noise ratio (CNR) decreases linearly from 70 dB to 0 dB. An exponential power spectrum density (PSD) was used to model the fluctuation of clutters caused by moving scatter [40]:  
\[P(f_{d})=r\delta(f_{d})+(1-r)\frac{\beta\lambda}{2}e^{\beta\lambda|f_{d}|}, \tag{34}\]  
where the stationary component is represented by the delta function \(\delta(f_{d})\) multiplied with the power proportion factor \(r\), while the moving clutters' statistic characteristic is dependent on the radar wavelength \(\lambda\) and the shape factor \(\beta\) determined by the wind speed. The above parameters were settled as \(r=0.9\) and \(\beta\lambda=14\) for all clutter cells. The simulation was performed via Julia [41] on a desktop with Intel (R) Core (TM) i5-9600 KF CPU at 3.7 GHz, and all ECA versions were implemented with the same parameters in Section 4.2, except for \(K=51\). Both ECA-C/LF were realized with precompression, and ECA with a Doppler extension ranging from \(-2\) Hz to \(2\) Hz in steps of \(1\) Hz was also simulated. A 1000-point Taylor window with a maximum sidelobe level of 35 dB was applied to decrease the energy leakage alongside the Doppler domain, leading to an extra SNR loss of about 0.92 dB. The 2D-CCFs, normalized according to the noise power, are compared in Figure 5, for which the consistent noise distribution verifies the rational approximation introduced in (23). The limited suppression of standard ECA without Doppler extension is verified by the strong residual in Figure 4(b), although its influence on detection is mitigated to some extent by the Taylor window. On the contrary, all other versions can form a wider notch around the zero Doppler, leading to better robustness when dealing with moving clutters. Notice that some performance regression caused by ECA-CF's discontinuity can be found at the notch's edge in Figure 4(f) around the 0 th range bin, for which the residual power has the same level as noise and is thus negligible in this example. The mentioned flexibility of ECA-C/LF can be comprehended with the triangular rejection area in Figure 4(i), which is formed by a set of low-pass filters with linearly decreasing bandwidth. Since the clutter intensity usually decays with the increasing bistatic delay, similar processing can preserve the distant targets with low speed while removing the close clutter thoroughly. The Doppler slice of target three is shown in Figure 6 with its zoomed-in view to better indicate the influence of ECA-B's Doppler ambiguity, where the periodic modulations are marked with arrows and the peak values at the target Doppler demonstrate the different retention of low-speed targets well. Although ECA with a Doppler extension has the highest output SNR, a Doppler offset of about 0.18 Hz could be found in the zoomed-in view, which has no effect on target detection but makes the Doppler estimation unbiased. A denser Doppler extension with a smaller step size can overcome this problem at the cost of extra SNR loss and computational burden. In order to better compare the performance of different ECA versions, their time cost together with the third target's SNR after suppression are measured and listed in Table 3, where the influence of Doppler ambiguity is also summarized. It can be found that the extra loss caused by ECA-LF, ECA-CF, ECA-S, and ECA-B is 0.45 dB, 1.11 dB, 5.95 dB, and 11.46 dB, respectively, for which the consistency with Figure 4 verifies the analysis in Section 4.2. Other than that, although ECA with Doppler extension performs best on target retention, its processing cost is far more than the other algorithms and thus impractical for real-time processing.