  Spatial coupling was proved to improve the belief-propagation (BP)
performance up to the maximum-a-posteriori (MAP) performance. This paper
addresses an extended class of spatially coupled (SC) systems. A potential
function is derived for characterizing a lower bound on the BP performance of
the extended SC systems, and shown to be different from the potential for the
conventional SC systems. This may imply that the BP performance for the
extended SC systems does not coincide with the MAP performance for the
corresponding uncoupled system. SC bit-interleaved coded modulation with
iterative decoding (BICM-ID) is also investigated as an application of the
extended SC systems.
