  Spatially coupled turbo-like codes (SC-TCs) have been shown to have excellent
decoding thresholds due to the threshold saturation effect. Furthermore, even
for moderate block lengths, simulation results demonstrate very good bit error
rate performance (BER) in the waterfall region. In this paper, we discuss the
effect of spatial coupling on the performance of TCs in the finite block-length
regime. We investigate the effect of coupling on the error-floor performance of
SC-TCs by establishing conditions under which spatial coupling either preserves
or improves the minimum distance of TCs. This allows us to investigate the
error-floor performance of SC-TCs by performing a weight enumerator function
(WEF) analysis of the corresponding uncoupled ensembles. While uncoupled TC
ensembles with close-to-capacity performance exhibit a high error floor, our
results show that SC-TCs can simultaneously approach capacity and achieve very
low error floor.
