The World Beneath the Physical Layer: An Introduction to the Deep Physical Layer

In this paper a series of concepts concerning the relationships between electromagnetic theory and information transmitted in communication systems using electromagnetic waves are organized in a systematic framework through the introduction of the “Deep Physical Layer” (DPL), a layer placed under the Physical Layer (PL) of the OSI model. While the PL provides an analysis of the system at level of 'bits', the DPL regards the possible distinguishable configurations of the electromagnetic field. It is shown that the limiting performance of communication systems in terms of data throughput is fixed in this layer, while at the PL level the 'potential' offered by the DPL is expressed according to the specific communication strategy and technology. In the last part of the paper a series of solutions currently investigated in 6G, such as holographic antennas, mMIMO, smart surfaces, are discussed at the level of the Deep Physical Layer, and some comments on the antenna synthesis are reported.