A Sequential Max K-Cut Approach for Pilot Assignment in Cell-Free Networks

This paper presents a novel sequential max k-cut approach to the pilot assignment problem in cell-free networks. In contrast to the existing max k-cut formulations that were proposed based on intuitions or qualitative analyses, we first establish a theoretical connection between pilot assignment and max k-cut, which avoids the performance degradation brought by the inaccurate max k-cut formulation. Specifically, we employ optimization techniques to equivalently transform the pilot assignment problem for uplink throughput maximization into a series of max k-cut problems with updated weights, leading to a sequential max k-cut approach. Moreover, different from the existing works that decouple pilot assignment and power control, this approach enables us to jointly optimize pilot assignment and power control with a customized scheme developed for further improvement of overall throughput and user fairness. Simulation results show the effectiveness and efficiency of the proposed approach, exhibiting significant improvement over existing methods. This sequential max k-cut approach could serve as a promising candidate for mitigating the performance deterioration resulting from severe pilot reuse in future ultra-dense cell-free networks.