Mobile Cell-Free Massive MIMO: Challenges, Solutions, and Future Directions

Cell-free (CF) massive multiple-input multiple-output (MIMO) systems, which exploit many geographically distributed access points to coherently serve user equipment via spatial multiplexing on the same time-frequency resource, has become a vital component of the next-generation mobile communication networks. Theoretically, CF massive MIMO systems have many advantages, such as large capacity, great coverage, and high reliability, but several practical obstacles must be overcome. In this article, we study the paradigm of CF massive MIMO-aided mobile communications, including the main deployment architectures and associated application scenarios. Furthermore, we thoroughly investigate the challenges of mobile CF massive MIMO communications. We then exploit a novel predictor antenna, hierarchical cancellation, rate-splitting and dynamic clustering system for mobile CF massive MIMO. Finally, several important research directions regarding mobile CF massive MIMO communications are presented to facilitate further investigation.