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Previously, self-dual codes have been constructed from Hadamard matrices. In this correspondence, codes constructed from weighing matrices, and in particular conference matrices are presented. A necessary condition for these codes to be self-dual is given, and examples are given for lengths up to 40. Codes constructed from all weighing matrices of order n [is less than or equal to] 13 are also considered. Index Terms--Conference matrices, self-dual codes, weighing matrices.

We study two-dimensional (2-D) arrays of fourth roots of unity which have all out-of-phase periodic autocorrelations equal to zero. Generalizing the concept of a perfect binary array, we call these arrays perfect quaternary arrays. We establish connections with combinatorial design theory and exhibit large families of such arrays. Increasing the alphabet from size two to size four greatly increases the flexibility one has in choosing the dimensions for 2-D arrays with perfect periodic autocorrelation. For example, we show that the number of entries in a 2-D perfect quaternary array may be divisible by any Mersenne prime and indeed by many other primes, whereas 2-D perfect binary arrays are only known to exist with size equal to a power of two times a power of three. Index Terms--Complex Hadamard matrices, Paley matrices, periodic autocorrelation, recursive constructions, relative difference sets.

Binary array pairs with optimal/ideal correlation values and their algebraic counterparts \difference set pairs" (DSPs) in abelian groups are studied. In addition to generalizing known 1-dimensional (sequences) examples, we provide four new recursive constructions, unifying previously obtained ones. Any further advancements in the construction of binary sequences/arrays with opti-mal/ideal correlation values (equivalently cyclic/abelian difference sets) would give rise to richer classes of DSPs (and hence binary perfect array pairs). Discrete signals arising from DSPs find applications in cryptography, CDMA systems, radar and wireless communications. [ABSTRACT FROM AUTHOR]