Guess & Check Codes for Deletions, Insertions, and Synchronization

We consider the problem of constructing codes that can correct delta deletions occurring in an arbitrary binary string of length n bits. Varshamov-Tenengolts (VT) codes, dating back to 1965, are zero-error single deletion (delta = 1) correcting codes and have an asymptotically optimal redundancy. Finding similar codes for delta >= 2 deletions remains an open problem. In this paper, we relax the standard zero-error (i.e., worst-case) decoding requirement by assuming that the positions of the delta deletions (or insertions) are independent of the code word. Our contribution is a new family of explicit codes, that we call Guess & Check (GC) codes, that can correct with high probability up to a constant number of delta deletions (or insertions). GC codes are systematic; and have deterministic polynomial time encoding and decoding algorithms. We also describe the application of GC codes to file synchronization.