On the distance distributions of single-orbit cyclic subspace codes

Abstract

{A cyclic subspace code is a union of the orbits of subspaces contained in it. In a recent paper, Gluesing-Luerssen et al. (Des. Codes Cryptogr. 89, 447-470, 2021) showed that the study of the distance distribution of a single orbit cyclic subspace code is equivalent to the study of its intersection distribution. In this paper we have proved that in the orbit of a subspace $U$ of ${\mathbb{F}}_{q^n}$ that has the stabilizer ${\mathbb{F}}_{q^t}^{\ast }(t\ne n)$, the number of codeword pairs $(U,\alpha U)$ such that $\dim (U\cap \alpha U)=i$ for any $i,0\le i<\dim (U)$, is a multiple of $q^t(q^t+1)$, if $\frac{n}{t}$ is an odd number. In the case of even $\frac{n}{t}$, if $U$ contains $\frac{q^{2tm}-1}{q^{2t}-1}(m\ge 0)$ distinct cyclic shifts of ${\mathbb{F}}_{q^{2t}}$, then the number of codeword pairs $(U,\alpha U)$ with intersection dimension $2tm$ is equal to $q^t+r{q}^t(q^t+1)$, for some non-negative integer $r$; and the number of codeword pairs $(U,\alpha U)$ with intersection dimension $i,(i\ne 2tm)$ is a multiple of $q^t(q^t+1)$. Some examples have been given to illustrate the results presented in the paper.