## 5 Simulations and Performance Analyses
### Comparison with the Exiting Methods
Therefore, it is concluded from the third experiment that the proposed joint optimization approach can provide satisfactory cancellation capability and detection performance in the presence of ICM-MP fluctuation and off-grid issues. In the fourth experiment, we compare the performance of the proposed joint optimization algorithm with other existing methods in different ICM-MP scenarios. First, we consider three ICM-MP scenarios, namely no ICM-MP fluctuation, that is, \(\sigma_{2,p}=0\), \(\sigma_{2,p}=0.8\), and \(\sigma_{2,p}=1.6\). In the simulation, the MDR of three MP signals is \(-20\) dB, and the remaining simulation parameters are the same as in the third experiment. Figure 7 presents the SINR loss performance against the normalized Doppler frequency in different ICM-MP scenarios. From the simulation results, it is found that SRA, LSA, and the proposed algorithm outperform STAP regardless of the presence or absence of the ICM-MP fluctuation. Moreover, the SINR loss performance of SRA suffers a lot in these three cases. The reason is that the presence of ICM-MP fluctuations and off-grid problems disturbs the MP clutter estimation in SRA, leading to a severe SINR performance loss. Moreover, the SINR loss performance of LSA changes obviously with respect to ICM-MP fluctuations. Especially as the velocity standard deviation \(\sigma_{2,p}\) increases, the performance of LSA becomes worse. This is because the accuracy of the selected atoms and estimated profile in LSA is sensitive to the ICM-MP fluctuation. Conversely, the proposed joint optimization algorithm always features acceptable SINR loss performance, whether the ICM-MP fluctuation is present or not. In Figure 8, we present the corresponding detection results of the proposed joint optimization approach and the other three methods. The results illustrate that STAP yields substandard detection performance, and SRA no longer performs properly even in the absence of CIM-MP fluctuation. Additionally, as \(\sigma_{2,v}\) increases, the detection performance of LSA improves. However, the proposed algorithm still provides satisfactory detection performance. Figure 6: Target detection performance versus range cell for different methods. Then, we make a quantitative comparison between the proposed algorithm, SRA, and LSA with different ICM-MP fluctuations, i.e., \(\sigma_{2,v}=0.2\), \(0.6\), \(1.0\), \(1.4\), and \(1.8\). The SINR loss value at the target Doppler frequency considering different \(\sigma_{2,v}\) is listed in Table 3. It is clear that the proposed joint optimization method can cope with the off-grid issues and is robust to the ICM-MP fluctuation. In the fifth experiment, the SINR loss performances of different approaches with different MDR values are discussed. Figure 9 presents the SINR loss performances of different algorithms. In the simulation, we consider three MP signals having the same MDR values and set the MDR values as \(-22\) dB and \(-17\) dB, respectively. Other simulation parameters are the same as the third experiment. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\sigma_{2,v}\) & \(0.2\) & \(0.6\) & \(1.0\) & \(1.4\) & \(1.8\) \\ \hline SRA (dB) & \(-5.046\) & \(-5.032\) & \(-5.097\) & \(-5.104\) & \(-5.096\) \\ LSA (dB) & \(-4.451\) & \(-4.827\) & \(-5.115\) & \(-5.481\) & \(-5.668\) \\ Proposed algorithm (dB) & \(-4.278\) & \(-4.321\) & \(-4.318\) & \(-4.432\) & \(-4.417\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The SINR loss value at the target Doppler frequency with different \(\sigma_{2,v}\). Figure 7: Impacts of ICM-MP fluctuation on SINR loss performance of the proposed algorithm and the existing methods. (**a**) \(\sigma_{2,v}=0\); (**b**) \(\sigma_{2,v}=0.8\); (**c**) \(\sigma_{2,v}=1.6\). It is seen from Figure 9 that the SINR loss performances of STAP and LSA vary obviously with MDR, and the SINR loss performance deteriorates with an increasing MDR value. The reason is that the high MDR causes deep nulls in the MP clutter area for STAP and residual MP clutter in profile estimation for LSA.