In through-the-wall radar imaging (TWRI), wall returns are often stronger than target returns, which make the targets behind walls invisible in the radar image. Spatial filtering that relies on the removal of the spatial zero-frequency components is a useful way for wall-clutter mitigation. Unfortunately, it applies to through-the-wall radar (TWR) with synthetic aperture array only. In this paper, a method based on spatial signature is proposed to suppress the wall-clutter in multi-input and multi-output (MIMO) TWRI. Firstly, the traditional spatial filtering method is discussed, as well as the reasons for the inapplicability for MIMO TWR. Secondly, the wall and target spatial signatures based on MIMO array are analyzed, respectively. The results indicate that the former has stability and symmetry, whereas the latter not. Thirdly, according to the above differences, a new method, symmetry subtraction, is applied to describe the wall-clutter suppression procedure. Finally, simulation results demonstrate that the proposed method is efficient in mitigating the wall returns and highlighting the targets.
2. Sisma, O., A. Gaugue, C. Liebe, and J. M. Ogier, "UWB radar: Vision through a wall," Personal Wireless Communications, Vol. 245, 241-251, 2007.
3. Baranoski, E. J., "Through wall imaging: Historical perspective and future directions," IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP, 5173-5176, 2008.
4. Borek, S. E., "An overview of through the wall surveillance for homeland security," Proceedings of the 34th Applied Imagery and Pattern Recognition Workshop (AIPR05), Vol. 6, 2005.
5. Lubecke, V. M. and A. E. Fathy, "Through-the-wall radar life detection and monitoring," IEEE Microwave Symposium, 769-772, 2007.
6. Piccardi, M., "Background substraction techniques: A review," IEEE International Conference on Systems, Man and Cybernetics, Vol. 4, 3099-3104, 2004.
7. Ahmad, F. and M. G. Amin, "Through-the-wall radar imaging experiments," IEEE Workshop on Signal Processing Applications for Public Security and Forensics, SAFE-07, 1-5, 2007.
8. Wang, G. and M. G. Amin, "Imaging through unknown walls using different standoff distances," IEEE Trans. on Signal Processing, Vol. 54, No. 10, 4015-4025, 2006.
9. Jin, T., B. Chen, and Z. Zhou, "Image-domain estimation of wall parameters for autofocusing of through-the-wall SAR imagery," IEEE Trans. on Geosci. Remote Sens., Vol. 51, No. 3, 1836-1843, 2013.
10. Ahmad, F., M. G. Amin, and S. A. Kassam, "Synthetic aperture beamformer for imaging through a dielectric wall," IEEE Trans. on Aerosp. Electron., Vol. 41, No. 1, 271-283, 2005.
11. Verma, P. K., A. N. Gaikwad, D. Singh, and M. J. Nigam, "Analysis of clutter reduction techniques for through wall imaging in UWB radar," Progress In Electromagnetics Research B, Vol. 17, 29-48, 2009.
12. Gaikwad, A. N., D. Singh, and M. J. Nigam, "Application of dielectric target behind the brick wall by stepped frequency continuous wave radar in ultra-wideband range," IET Radar Sonar and Navigation, Vol. 5, No. 4, 416-425, 2011.
13. Ahmad, F. and M. G. Amin, "Wall clutter mitigation for MIMO radar configurations in urban sensing," Signal Processing for Communication, Radar and Sonar, 1165-1170, 2012.
14. Tivive, F. H. C., A. Bouzerdoum, and M. G. Amin, "An SVD-based approach for mitigating wall reflections in through-the-wall radar imaging," Proceedings of IEEE Radar Conference, 519-524, 2011.
15. Zhang, L., B. Lu, Z. Zhou, and X. Sun, "The clutter suppression based on FA and image contrast in TWI application," Proceedings of 2013 Third IEEE International Conference on Information Science and Technology (ICIST 2013), 1498-1502, 2013.
16. Zhang, L., B. Lu, Z. Zhou, and X. Sun, "The clutter suppression based on statistical techniques in TWI application," Proceedings of 2013 IEEE International Conference on Ultra-wideband (ICUWB 2013), 130-135, 2013.
17. Yoon, Y. S. and M. G. Amin, "Spatial filtering for wall-clutter mitigation in through-the-wall radar imaging," IEEE Trans. on Geosci. Remote Sens., Vol. 47, No. 9, 3192-3208, 2009.
18. Haimovich, A. M., R. S. Blum, and L. J. Cimini, "MIMO radar with widely separated antennas," IEEE Signal Processing Magazine, Vol. 25, No. 1, 116-129, 2008.
19. Schwartz, J. L. and B. D. Steinberg, "Ultrasparse, ultrawideband arrays," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 45, No. 2, 376-393, 1998.
20. Jin, T., J. Lou, and Z. Zhou, "Extraction of landmine features using a forward-looking ground penetrating radar with MIMO array," IEEE Trans. on Geosci. Remote Sens., Vol. 50, No. 10, 4135-4144, 2012.
21. Chen, B., T. Jin, Z. Zhou, and B. Lu, "Estimation of pose angle for trihedral in ultrawideband virtual aperture radar," Progress In Electromagnetics Research, Vol. 138, 307-325, 2013.
22. McCorkle, J. W., "Focusing of synthetic aperture ultra wideband data," IEEE International Conference of Systems Engineering, 1-5, 1991.
23. Yoon, Y. S. and M. G. Amin, "Behind-the-wall target indication (BWTI)," Proc. SPIE Radar Sens. Technol. XIII Conf., 73080S1-73080S12, 2009.
24. Lu, B., Y. Zhao, X. Sun, and Z. Zhou, "Design and analysis of ultra wide band split transmit virtual aperture array for through the wall imaging," International Journal of Antennas and Propagation, 2013, Doi: 10.1155/2013/934509.
25. Wang, H., B. Lu, Z. Zhou, and Q. Song, "Through-the-wall imaging and correction based on the estimation of wall parameters," Proceedings of 2011 IEEE CIE International Conference on Radar, 1327-1330, 2011.
26. Dehmollaian, M. and K. Sarabandi, "Refocusing through building walls using synthetic aperture radar," IEEE Trans. on Geosci. Remote Sens., Vol. 46, No. 6, 1589-1599, 2008.
27. Kong, J. A., Electromagnetic Wave Theory, EMW Publishing, Cambridge, MA, 2000.
28. Sun, X., B. Lu, T. Jin, and Z. Zhou, "A fast echo construction method in through the wall simulation and analysis," Proceedings of Image Analysis Signal Processing, 208-212, 2012.
29. Keller, J. B., "Geometrical theory of diffraction," Journal of the Optical Society of America, 116-130, 1962.
30. Jackson, J. A., B. D. Rigling, and R. L. Moses, "Canonical scattering feature models for 3D and bistatic SAR," IEEE Transactions on Aerospace and Electronic Systems, Vol. 46, No. 2, 525-541, 2010.
31. Taflove, A. and S. C. Hagness, Computational Electrodynamics: The Finite-difference Time-domain, Artech House, Boston, MA, 2000.
32. Dogaru, T. and C. Le, "SAR images of rooms and buildings based on FDTD computer models," IEEE Trans. on Geosci. Remote Sens., Vol. 47, No. 5, 1388-1401, 2009.
33. Pena, D., R. Feick, H. Hristov, and W. Grote, "Measurement and modeling of propagation losses in brick and concrete walls for the 900-MHz band," IEEE Trans. on Antennas and Propag., Vol. 51, No. 1, 31-39, 2003.