Dimensions of some LCD BCH codes

In this paper, we investigate the first few largest coset leaders modulo $\frac{q^m+1}{\lambda}$ where $\lambda\mid q+1$ and $q$ is an odd prime power, and give the dimensions of some LCD BCH codes of length $\frac{q^m+1}{\lambda}$ with large designed distances.We also determine the dimensions of some LCD BCH codes of length $n=\frac{(q^m+1)}{\lambda}$ with designed distances $2\leq \delta \leq \frac{ q^{\lfloor(m+1)/2\rfloor}}{\lambda}+1$, where $ \lambda\mid q+1$ and $1<\lambda<q+1$. The LCD BCH codes presented in this paper have a sharper lower bound on the minimum distance than the BCH bound.