Capacity analysis of UCA-based OAM multiplexing communication system

In this paper, the capacity of a communication system based on orbital angular momentum (OAM) multiplexing is thoroughly studied and compared with the conventional multiple input multiple output (MIMO) system under different settings. In our studied OAM multiplexing communication system, both the transmitter side and the receiver side use uniform circular array (UCA) with identical or different settings. When working in the OAM mode, the transmitter radiates a radio wave carrying mulitple OAM modes while the receiver demultiplexes the wave in a spatially matched filter manner. Under this setting, we reveal that the channel capacity of the OAM system is equivalent to MIMO when the transmit and receive arrays comprise the same number of antennas and are aligned with each other perfectly, i.e., when the OAM sub-channels exhibit no crosstalk. However, when there exists a tilt angle between the two arrays or the numbers of their array elements are different, the capacity of MIMO outperforms that of OAM.