The self-interference problem of linear frequency modulated continuous wave (LFMCW) radar is a known issue that limits the radar's detection range. Analog adaptive interference cancellation (AIC) technique is effective to mitigate the self-interference problem. However, we find that the phase difference between the error signal and reference signal paths may significantly deteriorate the stability of the AIC system. Therefore, in this paper, we analyze the effect of phase difference on system stability through the mathematical modeling and simulation. We find that the system is stable when the phase difference is between -90 and 90 degrees, and diverges when it is between 90 and 270 degrees. Therefore, to avoid system instability, we propose to add a phase shifter in the reference signal path to compensate the phase difference. The experiment results show that compared with the traditional delay-based compensation method, our phase compensation based method can increase interference cancellation ratio (ICR) by 15 dB for a single-antenna system and 12 dB for a dual-antenna system.
"Stability Improvement of Analog Adaptive Self-Interference Cancellation System with Phase Compensation," Progress In Electromagnetics Research C,
Vol. 95, 227-238, 2019. doi:10.2528/PIERC19071203
1. Quiroz, A. E. N. and W. Josef, "Towards a full-duplex CW radar: Development of a reflected power canceller in digital domain," ACM International Conference Proceeding Series, 21-26, Nov. 2017.
2. Wang, Q., F. He, H. Liu, K. Zhao, and J. Meng, "Adaptive spatial filtering for interference cancellation between Co-site phased arrays," IEEE 2018 Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), 451-455, Jun. 2018.
3. Nawaz, H., O. Gurbuz, and I. Tekin, "High isolation slot coupled antenna with integrated tunable self-interference cancellation circuitry," Electronics Letters, Vol. 54, No. 23, 1311-1312, Nov. 2018. doi:10.1049/el.2018.6644
4. Lin, K., Y. E. Wang, C. K. Pao, and Y. C. Shih, "A Ka-band FMCW radar front-end with adaptive leakage cancellation," IEEE Transactions on Microwave Theory & Techniques, Vol. 54, No. 12, 4041-4048, Dec. 2006. doi:10.1109/TMTT.2006.885882
5. Choi, Y. S. and H. Shirani-Mehr, "Simultaneous transmission and reception: Algorithm, design and system level performance," IEEE Transactions on Wireless Communications, Vol. 12, No. 12, 5992-6010, Dec. 2013. doi:10.1109/TWC.2013.101713.121152
6. Kim, S., Y. Jeon, G. Noh, Y. O. Park, L. Kim, and H. Shin, "A 2.59-GHz RF self-interference cancellation circuit with wide dynamic range for in-band full-duplex radio," 2016 IEEE MTT-S International Microwave Symposium (IMS), 1402-1405, Aug. 2016.
7. Lu, H., C. Huang, M. Tarantez, S. Schwarz, and S. Shao, "Quadrature down-conversion based analog self-interference cancellation for continuous wave radars," 2016 IEEE Globecom Workshops (GC Wkshps), 1-6, Feb. 2017.
8. Ponnekanti, S. and S. Sali, "Non-linear interference cancellation techniques for electromagnetically dense propagation environments," Progress In Electromagnetics Research, Vol. 18, No. 5, 209-228, Jan. 1998. doi:10.2528/PIER97032600
9. Orimoto, H. and A. Ikuta, "Signal processing for noise cancellation in actual electromagnetic environment," Progress In Electromagnetics Research, Vol. 99, 307-322, Jan. 2009. doi:10.2528/PIER09100907
10. Jiang, Y., W. Ma, and Z. Zhao, "Influence of non quadrature of phase shifter to adaptive interference cancellation system," 2009 International Conference on Intelligent Human-Machine Systems and Cybernetics, 1-5, Nov. 2009.
11. Huang, X. and Y. J. Guo, "Radio frequency self-interference cancellation with analog least mean-square loop," IEEE Transactions on Microwave Theory and Techniques, Vol. 65, No. 9, 3336-3350, Feb. 2017. doi:10.1109/TMTT.2017.2654218
12. Beasley, P. L. D., A. G. Stove, B. J. Reits, and B. As, "Solving the problems of a single antenna frequency modulated CW radar," IEEE International Radar Conference, 391-395, 1990. doi:10.1109/RADAR.1990.201197
13. Qin, H., J. Meng, F. He, and Q. Wang, "A microwave interference cancellation system based on down-conversion adaptive control," IEEE International Conference on Communication Technology, 364-368, Jan. 2019.
14. Li, W., J. Meng, J. Tang, F. He, and L. Yi, "Interference cancellation system instantaneous bandwidth and time delay problem research," 2016 Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), 1-3, Jul. 2016.
15. Chang, M. P., C. L. Lee, B. Wu, and P. R. Prucnal, "Adaptive optical self-interference cancellation using a semiconductor optical amplifier," IEEE Photonics Technology Letters, Vol. 27, No. 9, 1018-1021, Feb. 2015. doi:10.1109/LPT.2015.2405498
16. Sun, J. J., M. P. Chang, and P. R. Prucnal, "Demonstration of over-the-air RF self-interference cancellation using an optical system," IEEE Photonics Technology Letters, Vol. 29, No. 4, 397-400, Jan. 2017. doi:10.1109/LPT.2017.2651589
17. Le, A. T., L. C. Tran, X. Huang, Y. J. Guo, and J. Y. C. Vardaxoglou, "Frequency-domain characterization and performance bounds of ALMS loop for RF self-interference cancellation," IEEE Transactions on Communications, Vol. 67, No. 1, 682-692, Aug. 2018. doi:10.1109/TCOMM.2018.2867514
18. Karin, S. and G. Zeng, "The analysis of the continuous-time LMS algorithm," IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 37, No. 4, 595-597, Apr. 1989. doi:10.1109/29.17546
20. Oppenheim, A. V., Signals & Systems, 2nd Ed., 2013.
21. Xiao, H., Z. Zhao, J. Tang, Y. Li, W. Li, and C. Luo, "The influence of time delay between interference signal and reference signal to the interference cancellation system," 2011 4th IEEE International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, 1-4, Feb. 2012.