On the capacity of an orbital angular momentum based MIMO communication system

This paper presents an orbit angular momentum (OAM) based wireless communication system combined with multi-input multi-ouput (MIMO) technique, where each MIMO branch multiplexes several OAM signals. The achievable sum-rate and array gain of the OAM-MIMO system relative to pure MIMO are analyzed. Results show that, when at near distance, e.g, the OAM beams are such collimated that each branch suffers little from crosstalk and power degradation, such an system merges the degrees of freedom (DoFs) provided by MIMO and OAM together, and thus provides higher sum-rate. However, as the transmission distance goes larger, though with more DoF, the performance advantages of OAM-MIMO disappears and may be even worse than pure MIMO due to fast power decay. Thus to enjoy the merits of incorporating MIMO into OAM entails a short distance communication scenario.