1. A system for processing data, comprising: a second de-interleaver configured to de-interleave second interleaved data using a second interleaving mapping to obtain encoded data, wherein: the second interleaved data includes a copy of constrained data in the same sequence and having the same values as the constrained data; and the portion of the second interleaved data that includes the copy of the constrained data satisfies a modulation constraint associated with limiting a number of consecutive events to a maximum number of consecutive events; a decoder configured to decode the encoded data to obtain first interleaved data; and a first de-interleaver configured to de-interleave the first interleaved data using a first interleaving mapping to obtain the constrained data, a copy of which is included in the second interleaved data, wherein the constrained data satisfies the modulation constraint.