Bounds on the rate of superimposed codes.

A binary code is called a superimposed cover-free $(s,\ell)$-code if the code is identified by the incidence matrix of a family of finite sets in which no intersection of $\ell$ sets is covered by the union of $s$ others. A binary code is called a superimposed list-decoding $s_L$-code if the code is identified by the incidence matrix of a family of finite sets in which the union of any $s$ sets can cover not more than $L-1$ other sets of the family. For $L=\ell=1$, both of the definitions coincide and the corresponding binary code is called a superimposed $s$-code. Our aim is to obtain new lower and upper bounds on the rate of given codes. The most interesting result is a lower bound on the rate of superimposed cover-free $(s,\ell)$-code based on the ensemble of constant-weight binary codes. If parameter $\ell\ge1$ is fixed and $s\to\infty$, then the ratio of this lower bound to the best known upper bound converges to the limit $2\,e^{-2}=0,271$. For the classical case $\ell=1$ and $s\ge2$, the given Statement means that our recurrent upper bound on the rate of superimposed $s$-codes obtained in 1982 is attained to within a constant factor $a$, $0,271\le a\le1$