Electromagnetic Channel Modeling and Capacity Analysis for HMIMO Communications

TL;DR

This work proposes a universal EM-compliant channel model for HMIMO/ELAA based on stochastic Green's functions, capturing near-field effects, full polarization, and mutual coupling. The model combines a coherent LoS component with an incoherent NLoS component and leverages a dyadic Green's function framework to provide physically grounded channel statistics. The authors derive theoretical capacity bounds for SISO and MISO systems and a capacity region for two users, validating the model against baselines and showing that conventional Rician or i.i.d. Rayleigh models misrepresent correlation and capacity, especially in near-field and multi-path scenarios. Simulations reveal that near-field gains and polarization diversity (notably tri-polarization) can substantially boost capacity, while practical constraints reduce some gains; the theory and results offer a robust framework for EM-aware HMIMO design and performance forecasting.

Abstract

Advancements in emerging technologies, e.g., reconfigurable intelligent surfaces and holographic MIMO (HMIMO), facilitate unprecedented manipulation of electromagnetic (EM) waves, significantly enhancing the performance of wireless communication systems. To accurately characterize the achievable performance limits of these systems, it is crucial to develop a universal EM-compliant channel model. This paper addresses this necessity by proposing a comprehensive EM channel model tailored for realistic multi-path environments, accounting for the combined effects of antenna array configurations and propagation conditions in HMIMO communications. Both polarization phenomena and spatial correlation are incorporated into this probabilistic channel model. Additionally, physical constraints of antenna configurations, such as mutual coupling effects and energy consumption, are integrated into the channel modeling framework. Simulation results validate the effectiveness of the proposed probabilistic channel model, indicating that traditional Rician and Rayleigh fading models cannot accurately depict the channel characteristics and underestimate the channel capacity. More importantly, the proposed channel model outperforms free-space Green's functions in accurately depicting both near-field gain and multi-path effects in radiative near-field regions. These gains are much more evident in tri-polarized systems, highlighting the necessity of polarization interference elimination techniques. Moreover, the theoretical analysis accurately verifies that capacity decreases with expanding communication regions of two-user communications.

Figures (9)

• Figure 1: The framework of wireless communications. (a) Conventional framework; (b) EM-domain framework.
• Figure 2: Illustration of HMIMO systems in the scattered environment.
• Figure 3: The channel correlation function vs. antenna spacing in transmitter at transceiver distance (a) $d_{\mathrm{RT}}=0.4\lambda$ and (b) $d_{\mathrm{RT}}=10\lambda$.
• Figure 4: The eigenvalues of the proposed polarized channel ($N_s=36$ and $N_r=16$) for different $K$-factors at varying transmitter-receiver distances from $2\lambda$ to $100\lambda$.
• Figure 5: The capacity of the proposed channel ($N_s=36$ and $N_r=16$) with/without practical constraints and i.i.d. Rayleigh fading model at varying distances from $2\lambda$ to $50\lambda$.