# Coding theory, rank metric codes

Let $S$ be a subset in $Mat_{k\times n}(\mathbb{F}_q)$ ($k\times n$ matrices with entries in $\mathbb{F}_q$) and $d(A,B)= rank(A-B)$, $dist(S)= \min\{d(A,B) \mid A,B \in S, A\neq B\}$

What is maximal size of set $S$ such that $dist(S)=d$ and $\mathbb{F}_q,k,n$ are fixed?

I tried for $k=2,n=2, \mathbb{F}_q=\mathbb{F}_2=\{0,1\}$ when $dist(S)=1$, I got maximal size of $S$ is $2$.

But is there any easy way or logic doing this for any $k$ and $n$ over $\mathbb{F}_2$?

Can anyone explain this in details please?