*1.1. Related Works*

Among different studies whose objectives are to minimize the pilot sequence contamination in TDD Massive MIMO systems, there is a considerable selection of methods, tools and techniques already tested, e.g., greedy and tabu search, smart pilot assignment, genetic algorithm (GA), deep learning, hybrid solutions and multi-objective approaches. To situate the contributions of this work, we present a chronological list of related work:


• The work in [22] presents different pilot allocation solutions for cell-free scenarios. The first algorithm is based on the concept of random sequential adsorption using statistical physics, while the second one is an analytical approach of the first one. The authors also describe two centralized algorithms based on clustering principles to benchmark the proposed solutions. The results show that the distributed solutions have a competitive performance compared to the centralized ones, especially when the user density is high.
