Bounds on subspace codes based on totally isotropic subspaces in unitary spaces

In this paper, the Sphere-packing bound, Singleton bound, Wang–Xing–Safavi-Naini bound, Johnson bound and Gilbert–Varshamov bound on the subspace codes (n,M,d,m)q based on m-dimensional totally isotropic subspaces in unitary space 𝔽q2(n) over finite fields 𝔽q2 are presented. Then, we prove that (n,M,d,m)q codes based on m-dimensional totally isotropic subspaces in unitary space 𝔽q2(n) attain the Wang–Xing–Safavi-Naini bound if and only if they are certain Steiner structures in 𝔽q2(n).