Concentric UCAs based low-order radio vortex wireless communications with co-mode interference

To meet the rapidly capacity-growing requirements, orbital angular momentum (OAM) based Radio vOrtex Wireless COMMunications (RowComm) has received much attention in recent years. The uniform circular array (UCA) is an efficient and convenient antenna structure to transmit/receive OAM beams with multiple OAM modes simultaneously. However, for high-order OAM modes, the OAM beams are divergent with severe attenuations. Thus, it is difficult to directly utilize high-order OAM modes to achieve high capacity for wireless communications. In this paper, we transform the high-order singular UCA into the low-order concentric UCAs to increase the capacity. In particular, we propose the mode-decomposition scheme and the co-mode successive interference cancellation algorithm to mitigate co-mode interference and decode the transmit signals. Then, we formulate the capacity maximization problem and convert it into an equivalent convex optimization problem. We solve the capacity maximization problem and derive the corresponding optimal power allocation scheme. Numerical simulations are presented to validate and evaluate that our developed low-order concentric UCAs based RowComm can significantly increase the capacity as compared with the high-order singular UCA based RowComm.