Upper Bounds on the Minimum Distance of Quasi-Cyclic LDPC codes   Revisited
  Two upper bounds on the minimum distance of type-1 quasi-cyclic low-density parity-check (QC LDPC) codes are derived. The necessary condition is given for the minimum code distance of such codes to grow linearly with the code length. 
Alexey Frolov and Pavel Rybin
cs.IT math.IT