  Thanks to its capability to provide a uniform service rate for the User
Equipments (UEs), Cell-free (CF) massive Multiple-Input, Multiple-Output
(mMIMO), has recently attracted considerable attention, both in academia and in
industry, and so is considered as one of the potential technologies for
beyond-5G and 6G. However, the reuse of the same pilot signals by multiple
users can create the so-called pilot contamination problem, which can hinder
the CF mMIMO from unlocking its full performance. In this paper, we address the
challenge by formulating the pilot assignment as a maximally diverse clustering
problem and propose an efficient yet straightforward repulsive clustering-based
pilot assignment scheme to mitigate the effects of pilot contamination on CF
mMIMO. The numerical results show the superiority of the proposed technique
compared to some other methods with respect to the achieved uplink per-user
rate.
