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A new uniquely decodable (UD) code pair for the two-user binary adder channel (BAC) is presented. This code pair leads to an improved bound for the zero-error capacity region of such a channel. The highest known rate for a UD code pair for the two-user BAC is thereby improved to (log/sub 2/240)/6/spl ap/1.3178. It is also demonstrated that the problem of(More)
— Upper and lower bounds are presented for the maximal possible size of mixed binary/ternary error-correcting codes. A table up to length 13 is included. The upper bounds are obtained by applying the linear programming bound to the product of two association schemes. The lower bounds arise from a number of different constructions.
The problem of nding the maximum radius of n non-overlapping equal circles in a unit square is considered. A computer-aided method for proving global optimality of such packings is presented. This method is based on recent results by De Groot, Monagan, Peik-ert, and WWrtz. As an example, it is shown how the method can be used to get an optimality proof for(More)
A set of points, S ⊆ P G(r, q), is said to be-saturating if, for any point x ∈ P G(r, q), there exist + 1 points in S that generate a subspace in which x lies. The cardinality of a smallest possible set S with this property is denoted by k(r, q,). We give a short survey of what is known about k(r, q, 1) and present new results for k(r, q, 2) for small(More)
Let Fn q be a vector space of dimension n over the finite field Fq . A q-analog of a Steiner system (also known as a q-Steiner system), denoted Sq(t,k,n), is a set S of k-dimensional subspaces of Fn q such that each t-dimensional subspace of Fn q is contained in exactly one element of S . Presently, q-Steiner systems are known only for t = 1, and in the(More)