  Spatially coupled low-density parity-check (SC-LDPC) codes are sparse graph
codes that have recently become of interest due to their capacity-approaching
performance on memoryless binary input channels. In this paper, we unify all
existing SC-LDPC code construction methods under a new generalized description
of SC-LDPC codes based on algebraic lifts of graphs. We present an improved
low-complexity counting method for the special case of $(3,3)$-absorbing sets
for array-based SC-LDPC codes, which we then use to optimize permutation
assignments in SC-LDPC code construction. We show that codes constructed in
this way are able to outperform previously published constructions, in terms of
the number of dominant absorbing sets and with respect to both standard and
windowed decoding.
