面向全息MIMO 6G通信的电磁信道建模理论与方法 = Electromagnetic channel modeling theory and approaches for holographic MIMO wireless communications

Abstract

Holographic Multiple-Input Multiple-Output (HMIMO) is an emerging technology for 6G communications. This type of array is composed of densely distributed antenna elements within a fixed aperture area. It is an extension of Massive MIMO technology under the practical constraints of antenna aperture. HMIMO systems have great potential in significantly improving wireless communication performance. However, due to the presence of closely spaced antennas, and the distane between antennas is less than half of the length, severe coupling effects are inevitable and traditional assumption of independent and identically distributed channel is invalid. Thus, designing an effective and practical channel model becomes one of the most challenging problems in HMIMO researches. To address these challenges, this paper investigates four channel modeling approaches based on electromagnetic field theory. The first approach is based on the plane Green’s function and models the integral of Green’s functions between planes with high complexity. The second and third approaches approximate the communication channel in HMIMO using plane wave expansion and spherical wave expansion, respectively, with lower complexity. The channel modeling based on plane wave expansion is relatively simple and is more suitable for far field, but would underestimate the maximum capacity of the system under strong coupling between antennas. The channel modeling based on spherical wave expansion better captures the characteristics of the electromagnetic wave channel but comes with higher complexity. Finally, a channel modeling method based on random Green’s functions is introduced, primarily describing the random characteristics of electromagnetic waves in rich scattering environments or Rayleigh channels.