Degrees of Freedom of Multi-Mode-Multi-Spatial (MOMS) in Line-of-Sight Channels.

We consider multi-antenna systems carrying OAM waveforms. which are limited by the transmit power and receive antenna aperture. Under the line-of-sight (LOS) channel condition, we propose the multi-mode-multi-spatial (MOMS) solution as a low complex and flexible engineering implementation without any loss of degrees of freedom. The basic idea of MOMS is that the transmitter uses multiple OAM waveforms to carry multiple independent data streams, and the receiver uses a multiple antenna channel equalization algorithm to de-multiplex the multiple eigenchannels. Link-level and Monte Carlo simulation show that our MOMS solution has higher capacity than common unikirm linear array LOS-MIMO within the Rayleigh distance of antenna array. However, it has a lower capacity at longer distances due to the faster power intensity decrease of OAM waveforms in comparison with plane waveforms.