A basic problem for constant dimension codes is to determine the maximum possible size $A_q(n,d;k)$ of a set of $k$-dimensional subspaces in $mathbb{F}_q^n$, called codewords, such that the subspace distance satisfies $d_S(U,W):=2k-2dim(Ucap W)ge d$ for all pairs of different codewords $U$, $W$. Constant dimension codes have applications in e.g. random linear network coding, cryptography, and distributed storage. Bounds for $A_q(n,d;k)$ are the topic of many recent research papers. Providing a general framework we survey many of the latest constructions and show up the potential for further improvements. As examples we give improved constructions for the cases $A_q(10,4;5)$, $A_q(11,4;4)$, $A_q(12,6;6)$, and $A_q(15,4;4)$. We also derive general upper bounds for subcodes arising in those constructions.
تحميل البحث