**5. Conclusions**

In this paper, we proposed a low-complexity RAB method based on INCM reconstruction via subspace projection. In this method, the component of the SOI in the SCM was eliminated by replacing the eigenvector columns in the SCM such that they could span to the signal subspace with the corresponding eigenvectors in the projection matrix.

Meanwhile, the SOI SV was estimated by employing the iterative mismatch approximation method. Since the calculation of the blocking matrix can be seen as pre-processing, the complexity of INCM reconstruction only depends on a countable number of matrices' eigen decomposition and multiplication. Both the analysis and simulation illustrate that the proposed method is robust to various types of mismatches while maintaining low complexity.

**Author Contributions:** All authors have significantly contributed to the research presented in this manuscript. Y.D. presented the main idea and wrote the manuscript. X.Y. edited the manuscript. L.M. and W.C. reviewed and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Laboratory of Science and Technology on Information Transmission and Dissemination in Communication Networks under Grant SXX19641X071.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
