A simple construction of cover-free $(s,\ell)$-code with certain   constant weight
  We give a method of constructing a cover-free $(s, \ell)$-code. For $k > s$, our construction yields a $ {{n \choose s} \choose \ell}\times {n \choose k}$ cover-free $(s, \ell)$-code with a constant column weight. 
A.G. D'yachkov, I.V. Vorobyev, N.A. Polyanskii, V.Yu. Shchukin
cs.IT math.IT