Abstract:
An ensemble of codes defined by parity-check matrices composed of $M\times M$ permutation
matrices is considered. This ensemble is a subensemble of the ensemble of low-density
parity-check (LDPC) codes considered by Gallager [1]. We prove that, as $M\to\infty$, the minimum
distance of almost all codes in the ensemble grows linearly with $M$. We also show that
in several cases the asymptotic minimum-distance-to-block-length ratio for almost all codes in
the ensemble satisfies Gallager's bound [1].