Performances of LoS Holographic Radio Systems

We investigate the performances of line-of-sight (LoS) holographic transmission links. To this end, we first develop a simple channel model for LoS holographic radio systems. This model can be reduced to represent the conventional LoS multiple-input multiple-output (MIMO) channel, and further used to make a fair comparison between them. We then analytically show that, in the far-field scenario when both the transmitter and receiver are equipped with holographic surfaces to form a LoS holographic-input holographic-output (HIHO) system, the achievable power gain can be up to pi(2) times higher than the corresponding LoS MIMO system with half-wavelength spaced isotropic antenna arrays deployed in the same transmit/receive apertures. Furthermore, numerical results indicate that concurrent transmissions of multiple signal streams can be supported in both the LoS HIHO and MIMO systems at communication distances shorter than that in the far-field scenario. Specifically, by moving from isotropic antenna arrays to holographic surfaces we virtually keep the same spatial sub-channels as those of the LoS MIMO system but with notably boosted power gains.