Some interesting properties for zero-forcing beamforming under per-antenna power constraints in rural areas

Providing broadband services in the rural area is a challenging work. Multi-user multiple-input multiple-output (MU-MIMO) systems can be applied to increase spectral efficiency. One of the most commonly used method in MU-MIMO broadcast channel is zero-forcing beamforming (ZFBF) since it provides a good trade off between complexity and performance. In this paper, we consider the ZFBF under the per-antenna power constraints. Particularly, a deterministic line-of-sight modeling of the downlink channels is adopted. To reduce the computational complexity, we consider the problem in which all the equality constraints are eliminated. By examining the KKT optimality conditions and the properties of the channel, some interesting properties are revealed.