OFDM-OAM Modulation for Future Wireless Communications.

Orbital angular momentum (OAM) has attracted considerable attention as a novel solution for wireless communications because its orthogonal modes significantly increase the channel capacity without an additional frequency band. The joint multiplexing between OAM technologies and other modulation techniques has not been thoroughly investigated. In this paper, we first proposed the orthogonal frequency-division multiplexing-orbital angular momentum (OFDM-OAM) multiple-input-multiple-output (MIMO) system. The proposed OFDM-OAM MIMO based on the discrete Fourier transformation (DFT) operations achieves a very high sum-rate and spectrum efficiency (SE). However, the expensive hardware and software overheads for transmitting and receiving OAM waves lead to an unexpected cost for the OFDM-OAM MIMO scheme. A time-switched OFDM-OAM (TOO) MIMO is then proposed to reduce the computational complexity, and the procedure of OAM generations and recoveries has also explicitly been derived. The mathematical derivation shows that the proposed TOO MIMO system based on a simple switching sequence is suitable for small-scale and low-cost wireless broadband communications, and the simulation results demonstrate that the TOO MIMO scheme achieves a considerable SE and much less computational complexity than the OFDM-OAM MIMO scheme.