I recently asked this question and got an answer from Yuval Filmus stating that we can build a solution using error-correcting codes.
More specifically, I'm looking for error correcting codes (for binary alphabet) with constant $R>0$ non-zero relative rate, and as high as possible relative distance $\delta$.
I know that using this theorem, we can achieve any $\delta < \frac{1}{2}$. As pointed out by Yuval Filmus's answer to my last question, this is the best $\delta$ we can hope for.
Where can I find a proof that states there is no binary error-correcting code with a relative distance bigger than $\frac{1}{2}$?