3L-BC: a three-layer blockchain architecture for collaborative machine learning in secure drone communications. - Khang Wen Goh; Burhan Ul Islam Khan; Abdul Raouf Khan; Dwi Sudarno Putra; Suresh Sankaranarayanan; Md. Alamin Bhuyian (J. King Saud Univ. Comput. Inf. Sci., 2025)