# Co-Channel Interference Suppression for LTE Passive Radar Based on Spatial Feature Cognition
## 4 Simulation Analysis
We find from the demodulation results that the signal at \(1^{\circ}\) is a multipath version of the signal at \(-45^{\circ}\). We then use the ECA-B algorithm to suppress the interference signal with the purified signal at \(-45\) degrees as the reference signal. After that, the cross-correlation result is shown in Figure 11b. It can be seen that the peaks caused by the DMI from the BS-IoO have vanished. This shows that the DMI was cancelled adequately. However, the target is still not detectable. This is because of the presence of the co-channel interference. The INR estimated is larger than the predefined threshold, i.e., \(5\) dB in this simulation. The above cancellation loop is repeated in the following. Figure 12 shows the spatial spectrum reconstruction result at cancellation loop 2. Because the DMI from the BS-IoO was cancelled at cancellation loop 1 above, the interference signals indicated by the peaks in Figure 12a correspond to the CCBSs. Similarly, we extract two peaks from Figure 12a with the largest amplitudes, from which the DOAs of the two corresponding interference signals are estimated as \(-30\) and \(20\) degrees. Next, we use the beamforming and purification techniques to get the clean versions of the reference signals  
Figure 10: The cross-correlation results after interference suppression by the traditional method, (**a**) spatial-time (**b**) time-spatial. at \(-30\) and \(20\) degrees. ECA-B is then performed with the reference signals obtained to suppress the interferences. The cross-correlation result at this step is shown in Figure 11(b). It can be seen that the target is still not detectable, because the interference residual is still large and the INR of the interference residual estimated is still larger than \(5\) dB. Therefore, the cancellation loop needs to repeat again. Figure 13 shows the spatial spectrum reconstruction result at cancellation loop 3. We extract the two apparent peaks in the figure to estimate the DOAs of the two corresponding interference signals, which are \(-67\) and \(69\) degrees, respectively. Next, the beamforming and purifying techniques are used to get the clean versions of the interference signals at the two DOAs, and ECA-B is performed to suppress the corresponding interference. The cross-correlation result at this step is shown in Figure 11(b). The target is still not detectable and the INR of the interference residual estimated is larger than \(5\) dB. The cancellation loop needs to be repeated once more. The spatial spectrum reconstruction result at cancellation loop 4 for the remaining signal is shown in Figure 14. It can be seen that there is one apparent peak. We extract this peak to estimate the DOA of the corresponding interference signal, which is \(-19\) degrees. Next the beamforming and purifying techniques are used to get the clean versions of the interference signals at this DOA, and ECA-B is performed to suppress the corresponding interference. The cross-correlation result at this step is shown in Figure 11(b). It can be seen that the target is clearly seen in the range Doppler surface. The INR of the interference residual estimated is smaller than the predefined threshold, and the cancellation loop terminates. Figure 11: Cross correlating result at cancellation loop 3, (**a**) spatial spectrum reconstruction results, (**b**) cross-correlation results. Figure 12: Cross-correlating result at cancellation loop 2, (**a**) spatial spectrum reconstruction results, (**b**) cross-correlation results. In the following, we investigate the influence of the antenna array size on the suppression performance of the proposed method. We set one BS-IoO and six CCBSs. Fifteen DMI from the BS-IoO are simulated and five multipath signals for each CCBS are simulated. The direct signal to noise ratio of the BS-IoO at the radar receiver is set to 50 dB. The SNRs of the other interference signals are randomly simulated 12 dB smaller than the BS-IoO direct signal. One target is simulated with an SNR of \(-25\) dB.