Near-field multi-user holographic MIMO communications over Ricean fading channels

This paper investigates near-field multi-user downlink communications over Ricean fading channels underpinned by the holographic multiple-input multiple-output (HMIMO) technology. We first establish the mutual coupling and radiation efficiency models to characterize the effect of mutual coupling and then formulate the practical input-output relationship. Based on this, the achievable spectral efficiency (SE) is derived for maximum ratio transmission (MRT). By further investigating the special cases of pure line-of-sight (LoS) and Rayleigh fading, our analysis reveals that for a moderate number of antenna elements, the system's SE with mutual coupling might outperform that without mutual coupling, especially in the low transmit power regime. Moreover, the additional distance degrees-of-freedom (DoF) introduced by the near-filed channel can enable the inter-user interference mitigation, even for the worst case when the users have similar angular directions. Finally, the obtained theoretical analysis is validated through simulations.