ng "100" to a receiver that has access to the value of the field on the S curve (see Fig. 2.9). The string "1 0 0" is encoded in a current distribution J such that the field received in the three sampling positions takes on different values (amplitude and/or phase) depending on the corresponding bit. In this way it is possible to send 3 bits at the same time. From the PL point of view, we have three parallel communication sub-channels, i.e., a three-channel MIMO communication system. The maximum number of spatial communication channels is consequently limited by the NDF, or, in the spatial bandlimited approach, by the spatial bandwidth and the extension of the observation curve. This number is approximately the number of Nyquist spatial intervals on the observation curve, i.e., 2 WE/R = 2WE [34], wherein E is the extension of the observation domain measured in s, and W = W'/() is the spatial bandwidth [34]. M.D. Migliore Fig. 2.9 Each spatial sample can be associated with an independent information; up to NDFé n 2WE information can be transmitted using the space channel, each giving a potential parallel communication MIMO spatial channel at the Physical Layer level As further example, one of the emerging technologies is Massive MIMO [70], in which antennas with a large number of elements are used to connect significantly fewer users than the number of radiating elements. An important characteristic of Massive MIMO is that it is possible to obtain decorrelation among the signals on the users in non-cooperation condition. The field radiated by MU-MIMO antennas can be modeled as a wide-bandwidth spatial signal that is largely subsampled since the sample positions (i.e., the positions of the users) are placed at distances much greater than the Nyquist spatial step. In a scenario where the number of users is fixed, the greater the spatial bandwidth the greater the decorrelation between the users. It is understood that the geometrical approach outlined in this section can be extended to include scattering objects, maki