Channel Estimation Enhancement in Cell-Free Massive MIMO Systems under Pilot Contamination
Mohammed Dawood Alrubay, Hayder Almosa
In this scholarly context, we delve into the realm of cell-free massive Multiple-Input Multiple-Output (MIMO) systems. These systems feature a multitude of single-antenna, low-cost, and low-power access points distributed across the coverage area. These access points are seamlessly connected to a central network controller. Notably, cell-free massive MIMO operates without the traditional constraints of cellular boundaries. Our research endeavors focus on enhancing the efficiency of cell-free massive MIMO systems. To this end, we propose a novel pilot decontamination algorithm that mitigates pilot contamination during channel estimation. This algorithm aims to address the challenge of pilot contamination, which arises when the available pilot resources are insufficient to serve all users effectively. Our approach involves judiciously sharing pilot resources among multiple users and employing dedicated algorithms in the pilot contamination domain to separate their signals. In conventional cell-free massive MIMO setups, users typically utilize unique orthogonal training signals. However, this necessitates a substantial pool of such sequences. Alternatively, in scenarios where there is a scarcity of training signals, pilot contamination phenomena come into play. Unfortunately, the reuse of pilot training signals introduces user interference due to shared resources. To mitigate this challenge and enhance the quality of channel estimation, we propose a combined approach that leverages both Principal Component Analysis (PCA) and the Least Mean Squares (LMS) algorithms. Specifically, we implement this approach for user separation within the shared pilot sequence. Our results demonstrate that this method significantly reduce the pilot contamination effect and improves the performance in compared to traditional method used.
Keywords: Cell-free massive MIMO, Pilot contamination, Channel estimation, System efficiency
