A low-rate improvement on the Elias bound
Lloyd R. Welch, Robert J. McEliece, Howard Rumsey · 1974
An upper bound on the minimum distance of binary blocks codes, which is superior to Elias' bound for R < 0.0509^+, is obtained. The new bound has the same derivative(-infty) at R = 0 as Gilbert's lower bound. (Elias' bound has derivative-ln 2 at R = 0).