data storage developers

Abstract: Byrne, Gluesing-Luerssen, and Ravagnani determined the number of codewords with a prescribed nonzero support in a linear maximum sum-rank distance code whose blocks have a common number of columns. Their formula depends only on the code parameters and the support dimensions. Evaluating it for arbitrary parameters gives a family of necessary nonnegativity conditions for existence. We prove their conjecture that this family is equivalent to the condition at the vector of total dimension $d+1$ obtained by filling the longest blocks first, where $d$ is the distance parameter. The resulting explicit criterion applies over every finite field $\mathbb F_q$, for all row numbers $n_i\leqslant m$ and $1\leqslant d<N$, where $m$ is the common number of columns and $N$ is the total number of rows. It also covers the boundary cases in which this vector fills each of its nonzero blocks completely, not explicitly included in the conjecture's displayed parameter range. The proof uses a generating function and an exchange identity to reduce the problem to vectors obtained by filling the longest blocks first. We then estimate alternating sums of elementary symmetric polynomials, with a separate argument for $q=2$. The dual conditions admit the same reduction. For codes that exist, the joint condition follows from sphere-packing bounds for the code and its dual. An infinite family of parameters satisfies the joint condition but admits no such linear code.

Abstract: In this paper, we focus on decoding MDS linear block codes for insdel errors. Building on our recent work for two-dimensional Reed-Solomon codes, we present a decoding algorithm for bounded distance decoding for the general insertion-and-deletion scenario that can be used for any MDS code of rate at most half. Our algorithm employs a sliding window and has a time complexity smaller than brute-force decoding. In particular, for optimal Reed-Solomon codes, it corrects insdel errors up to the half-Singleton bound, which exceeds the scope of existing methods. Additionally, for the special cases of insertion-only and deletion-only insdel error patterns, we present two different algorithms with a time complexity smaller than our general algorithm.

Abstract: We extend the complete classifications of linear complementary dual (LCD) codes from length 15 to length 19 in the binary case, from length 10 to length 15 in the ternary case and from length 12 to length 13 in the quaternary Hermitian case. The classification rests on a reduction of the monomial equivalence of LCD codes to graph isomorphism on the coordinates, combined with canonical augmentation.

Abstract: We consider the problem of binary sequence reconstruction where a sequence is transmitted multiple times over a channel, and each undergoes substitution errors by an arbitrary error vector of Hamming weight exactly $t$. We determine $N_{\mathrm{wc}}$, the minimum number of distinct channel output observations guaranteeing unique reconstruction by an optimal decoder, and show that the bit-wise majority-vote decoder, which was proved by Levenshtein (2001) to be optimal for channels corrupting up to $t$ bits, is in fact suboptimal here. Despite this suboptimality, we prove a condition that admits a practical early-termination rule, necessary for every decoder at any number of outputs $N$, and sufficient for bit-wise majority-vote even below $N_{\mathrm{wc}}$. We evaluate the number of outputs at which this condition is triggered, numerically, and show that it frequently occurs below $N_{\mathrm{wc}}$ when the block-length $k>2t+1$. Finally, we propose an alternative algorithm aimed at guaranteeing unique reconstruction with fewer observations than bit-wise majority-vote, and demonstrate through exhaustive enumeration that it successfully decodes channel output-sets where bit-wise majority-vote fails.