Bordered constructions of self-dual codes from group rings and new extremal binary self-dual codes

Abstract

We introduce a bordered construction over group rings for self-dual codes. We apply the constructions over the binary field and the ring F2+uF2, using groups of orders 9, 15, 21, 25, 27, 33 and 35 to find extremal binary self-dual codes of lengths 20, 32, 40, 44, 52, 56, 64, 68, 88 and best known binary self-dual codes of length 72. In particular we obtain 41 new binary extremal self-dual codes of length 68 from groups of orders 15 and 33 using neighboring and extensions. All the numerical results are tabulated throughout the paper.