  We consider a problem of unsourced random access in the quasi-static Rayleigh
fading channel. In the previous work, the authors have proposed LDPC code based
solutions based on joint and treat interference as noise in combination with
successive interference cancellation (TIN-SIC) decoder architectures. The
authors showed that TIN-SIC decoding significantly outperforms the joint
decoding approach and much simpler from the implementation point of view. In
this paper, we continue the analysis of TIN-SIC decoding. We derive a finite
length achievability bound for TIN-SIC decoder using random coding and propose
a practical polar code based TIN-SIC scheme. The latter's performance becomes
significantly better in comparison to LDPC code based solutions and close to
the finite length achievability bound.
