path-loss produced by the use of higher frequencies.

The performance of cell-free massive using conventional sub-6 GHz frequency bands and assuming infinite-capacity fronthaul links has been extensively studied in, for instance, [@Ngo17; @Nayebi17; @Nguyen17; @Ngo18]. Cell-free massive networks using capacity-constrained fronthaul links have also been considered in [@Bashar18b; @Boroujerdi18] but assuming, again, the use of fully digital precoders in conventional sub-6 GHz frequency bands. Sub-6 GHz massive systems are often assumed to implement a fully-digital baseband signal processing requiring a dedicated chain for each antenna element. The present status of technology, however, characterized by high-power consumption levels and high production costs, precludes the fully-digital implementation of massive architectures, and typically forces systems to rely on hybrid digital-analog signal processing architectures. In these hybrid transceiver architectures, a large antenna array connects to a limited number of chains via high-dimensional precoders, typically implemented using analog phase shifters and/or analog switches, and low-dimensional baseband digital precoders are then used at the output of the chains [@Ayach14; @Gao16; @Molisch17]. The network of phase shifters connecting the array of antennas to the chains determines whether the structure is fully or partially connected [@Park17TWC]. Thus, the assumptions, methods and analytical expressions in [@Ngo17; @Nayebi17; @Nguyen17; @Ngo18; 