Selective Infrastructure Activation in Cell-free Massive MIMO: a Two Time-scale Approach

This paper recasts the concept of base station selective activation to the case of cell-free massive MIMO (CF-M-MIMO) networks as a means of pursuing a variety of quality and/or operational metrics. Two different mechanisms are examined that operate at two distinct time-scales. The first one relies on the users’ mobility patterns (very long time-scale) while the second one exploits the selectivity of the large-scale channel gains linking users and access points (short time-scale). A novel algorithm is proposed to conduct this latter form of adaptation that is able to drastically reduce the fronthaul requirements of the network with hardly any performance penalty. Results are presented illustrating how the two mechanisms can be synergistically combined under either centralized or distributed precoding schemes.