javascript:void(0) In this paper, simultaneous vortex and non-vortex based transmission is proposed to enhance capacity by covering multiple users. The system model proposes a cell scenario including new and legacy user equipments (UEs) for backward compatibility and a geometrical transceiver for uniform circular array (UCA) and uniform rectangular array (URA). The proposed scenarios are divided into two different types of transmissions; vortex based, non-vortex based and a simultaneous vortex and non-vortex based. The channel model is approximated by dominant transmission distance. Moreover, modified Bessel function is proposed to derive channel model giving fair divergence effect with elevation angle. The performance of simultaneous vortex and non-vortex based transmissions is derived and simulated in terms of the average capacity (AC), outage probability (OP), and throughput.

In this paper, a novel index modulation (IM) for orbital angular momentum (OAM) communication is proposed by employing the phase offset (PO) state to enhance the capacity, called OAM-PO-IM. The uniform circular array (UCA) based OAM is exploited with PO. The UCA is divided into uniform circular sub-arrays (UCSAs) in the transmitter allocating additional index bits for the activation state of UCSA. In addition, the modified Bessel function of the first kind is used to derive the channel model for effective OAM mode combination under beam divergence. Simulation results are provided to compare with conventional schemes in terms of capacity and bit error rate (BER).

This study proposes the multiple reconfigurable intelligent surface (RIS) based index modulation (IM) called as MRB-IM, in order to improve the channel capacity by activating one or more RISs among multiple RIS (MRIS) and utilizing its number of combinations. The ergodic capacity analysis is derived to prove the validity of the simulation for the Rayleigh fading channel. Generally, MRIS suffers from inter-RIS interference (IRI) which is considered as the leverage of the secondary reflection amongst the MRIS. Despite having a larger capacity, the proposed MRB-IM has less of an impact on IRI because occurs among active MRIS. Simulation results demonstrate that the proposed system outperforms the existing MRIS in terms of capacity with and without IRI. In addition, bit error rates with different activation numbers of elements and RISs are shown. Here, the maximum likelihood on the receiver side is adopted to estimate the selected RIS index and information symbols in this study.

Divergence intensity (DI) and mode combinations are proposed for multiple orbital angular momentum (OAM) users to enhance the sum capacity