Dual and self-dual negacyclic codes of even length over Z2aZ2a

In this paper, we determine the structure of negacyclic codes of even length over the ring Z2aZ2a and their dual codes. Furthermore we study self-dual negacyclic codes of even length over Z2aZ2a. A necessary and sufficient condition for the existence of nontrivial self-dual negacyclic codes is given, and the number of the self-dual negacyclic codes for a given even length is determined.