  In this paper, the wireless hierarchical federated learning (HFL) is
revisited by considering physical layer security (PLS). First, we establish a
framework for this new problem. Then, we propose a practical finite blocklength
(FBL) coding scheme for the wireless HFL in the presence of PLS, which is
self-secure when the coding blocklength is lager than a certain threshold.
Finally, the study of this paper is further explained via numerical examples
and simulation results.
