  In [1], the linked loop code (LLC) is presented as a promising code for the
unsourced A-channel with erasures (UACE). The UACE is an unsourced multiple
access channel in which active users' transmitted symbols are erased with a
given probability and the channel output is obtained as the union of the
non-erased symbols. In this paper, we extend the UACE channel model to the
unsourced B-channel with erasures (UBCE). The UBCE differs from the UACE in
that the channel output is the multiset union, or bag union, of the non-erased
input symbols. In other words, the UBCE preserves the symbol multiplicity of
the channel output while the UACE does not. Both the UACE and UBCE find
applications in modeling aspects of unsourced random access. The LLC from [1]
is enhanced and shown to outperform the tree code over the UBCE. Findings are
supported by numerical simulations.
