Capacity Analysis of Orbital Angular Momentum Wireless Channels

The orbital angular momentum (OAM) technology is able to provide a new degree of freedom for wireless communication systems. The energy of OAM waves is focused within a circle region surrounding the beam axis, which makes the propagation gains inside and outside the circle region different. However, in the existing literature, the propagation gains inside and outside the circle region are assumed to be the same. Therefore, the impact of OAM waves' spatial energy distribution on the capacity of OAM wireless communication systems has not been fully investigated. Considering the spatial energy distribution characteristics of OAM waves, in this paper, an OAM wireless channel model is proposed. Based on the proposed OAM wireless channel model, the capacity of OAM-based multiple-input multiple-output (MIMO) communication system is analytically derived. Simulation results indicate that the capacity of OAM-based MIMO system outperforms the capacity of conventional MIMO system when the transmission distance is larger than a specific threshold. Our results provide a basic capacity model for OAM-based MIMO communication systems.