Distributed Combinatorial Optimization of Downlink User Assignment in mmWave Cell-free Massive MIMO Using Graph Neural Networks. - Bile Peng; Bihan Guo; Karl-Ludwig Besser; Luca Kunz; Ramprasad Raghunath; Anke Schmeink; Eduard A. Jorswieck; Giuseppe Caire; H. Vincent Poor (GLOBECOM, 2024)