  Spatial division multiplexing using conventional orbital angular momentum
(OAM) has become a well-known physical layer transmission method over the past
decade. The mode-group (MG) superposed by specific single mode plane spiral OAM
(PSOAM) waves has been proved to be a flexible beamforming method to achieve
the azimuthal pattern diversity, which inherits the spiral phase distribution
of conventional OAM wave. Thus, it possesses both the beam directionality and
vorticity. In this paper, it's the first time to show and verify novel PSOAM MG
based multiple-in-multiple-out (MIMO) communication link (MG-MIMO)
experimentally in a line-of-sight (LoS) scenario. A compact multi-mode PSOAM
antenna is demonstrated experimentally to generate multiple independent
controllable PSOAM waves, which can be used for constructing MGs. After several
proof-of-principle tests, it has been verified that the beam directionality
gain of MG can improve the receiving signal-to-noise (SNR) level in an actual
system, meanwhile, the vorticity can provide another degree of freedom (DoF) to
reduce the spatial correlation of MIMO system. Furthermore, a tentative
long-distance transmission experiment operated at 10.2 GHz has been performed
successfully at a distance of 50 m with a single-way spectrum efficiency of 3.7
bits/s/Hz/stream. The proposed MG-MIMO may have potential in the long-distance
LoS back-haul scenario.
