To maximize the transmission data rate, we need to use wide-signal bandwidth. In the regulated spectrum on Earth, such wide bands are available at high RF frequencies (mm-waves). However, the free-path loss of mm-waves considerably attenuates the signals. An efficient way to compensate the attenuation is to use phased-delay arrays and beam the electro-magnetic wave only at the target direction. This approach increases the effectively the total antenna gain of the system. Moreover, there are other advantages, too.
The large transmission power is distributed among units and it is not required to be concentrated in a single place, which allows for finding an optimal power and linearity point for each parallel slice. However, one of the major advantages is the multi-beam possibilities that the digital beam forming allows. Multi-beam communication allows links with multiple users at same time and in the same frequency spectrum. This considerably improves the spectrum efficiency of the communication.
However, such an approach is possible in practice if the whole chain "DAC-Mixer-PA-Antenna" is parallelized in an array. In order to enable digital beam forming, we need a lot of parallel data converters and each of them must be power efficient and small in size!