Wavenumber-Domain Precoding for Sum-Rate Maximization in HMIMO Cellular Systems

Holographic MIMO (HMIMO) is a promising technology for next-generation cellular systems, wherein many antennas are arranged in a compact space at sub-wavelength spacing. We optimize the transmit precoding matrices in the downlink of an HMIMO cellular system using a channel model compliant with electromagnetic wave propagation. Exploiting the structure of the HMIMO channel matrix, we reformulate the sum-rate maximization problem in the wavenumber domain, and is solved using the weighted minimum mean squared error (WMMSE) algorithm. The proposed algorithm achieved the same sum-rate as directly applying the WMMSE algorithm but at much lower computational complexity. A statistical channel state information-based precoding algorithm is also developed. It performed poorly in isotropic scattering environments but achieved sum-rates comparable to the WMMSE algorithm in non-isotropic scattering environments. The sum-rates of all the algorithms increased as antenna spacing decreased for a fixed antenna array form factor, which demonstrates the potential of HMIMO.