Berman Codes: A Generalization of Reed-Muller Codes that Achieve BEC Capacity

Abstract: We identify a family of binary codes whose structure is similar to Reed-Muller (RM) codes and which include RM codes as a strict subclass. The codes in this family are denoted as $C_n(r,m)$, and their duals are denoted as $B_n(r,m)$. The length of these codes is $n^m$, where $n \geq 2$, and $r$ is their `order'. When $n=2$, $C_n(r,m)$ is the RM code of order $r$ and length $2^m$. The special case of these codes corresponding to $n$ being an odd prime was studied by Berman (1967) and Blackmore and Norton (2001). Following the terminology introduced by Blackmore and Norton, we refer to $B_n(r,m)$ as the Berman code and $C_n(r,m)$ as the dual Berman code. We identify these codes using a recursive Plotkin-like construction, and we show that these codes have a rich automorphism group, they are generated by the minimum weight codewords, and that they can be decoded up to half the minimum distance efficiently. Using a result of Kumar et al. (2016), we show that these codes achieve the capacity of the binary erasure channel (BEC) under bit-MAP decoding. Furthermore, except double transitivity, they satisfy all the code properties used by Reeves and Pfister to show that RM codes achieve the capacity of binary-input memoryless symmetric channels. Finally, when $n$ is odd, we identify a large class of abelian codes that includes $B_n(r,m)$ and $C_n(r,m)$ and which achieves BEC capacity.