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The orbital angular momentum (OAM) based communication is a promising technology in the wireless communication system for its improving spectrum efficiency. However, for the OAM demultiplexing, it requires a very large aperture size in the receiving end due to the OAM beam divergence and the amplitude null in the beam center, which restricts the full development of OAM based communication. In this paper, we propose a novel partial arc sampling receiving (PASR) scheme based on the augmented dynamic mode decomposition (ADMD) to solve this issue. We explore the use of the phase delay coordinates in the conventional DMD to sort the arbitrary OAM modes with arc sampling receiving. Simulation results demonstrate the accuracy and robustness of the proposed approach in sorting both integral and fractional OAM modes with the PASR scheme. Our work offers a practical approach for demultiplexing OAM beams in radio communication systems with fewer receiving devices, especially for the long-distance transmission case. [ABSTRACT FROM AUTHOR]

The performance of the source enumeration with the uniform circular array (UCA) is deteriorated considerably by the colored noise. This effect becomes more obvious especially when the total number of the sources is lower and closed to that of the array sensors. To address this problem, this paper proposes a source enumeration modeling based on a UCA having M antennas (M-UCA). The M-UCA is operated in a narrow band far field environment with the arbitrary azimuth and elevation angles. First, the Hilbert Huang transformation is employed to derive the phase sequence of each selected intrinsic mode function (IMF) of the signal acquired by each antenna of the M-UCA. Then, the phase sequences of the selected IMFs of the signal acquired by all the antennas of the M-UCA are employed to construct an instantaneous phase covariance matrix (IPCM) among the antennas in the UCA. An IPCM is constructed for each order of the selected IMFs. After performing the eigenvalue decomposition of the all IPCMs, a set of eigenvalues carrying useful information for the estimation of the total number of the sources is acquired. This set is served as the training set. Finally, the training set is used to derive the mathematical model via the support vector machine. The trained model can be used to perform the sources number detection. Both the computer numerical simulations and the radio frequency anechoic chamber experiments validate that the source estimation accuracy of the constructed M-UCA mathematical model based on our proposed method has a high robustness to the incident angles variations, the SNR variations, and the snapshot number variations in the colored noise environment in the determined case, especially in the case of that the total number of the signal sources is only one less than the number of the antennas in the UCA. [ABSTRACT FROM AUTHOR]

Radio orbital angular momentum (OAM) provides another perspective of spatial multiplexing to improve the spectrum efficiency. However, multipath induces severe intra- and interchannel crosstalk. To solve the problem in a uniform circular array (UCA)-based OAM system, we first incorporate the effect of sign changing of OAM reflection in modeling the multipath OAM channel. Then, we propose a transceiver architecture for broadband OAM orthogonal frequency-division multiplexing (OFDM) wireless communication systems, which uses baseband digital 2-D fast Fourier transform (FFT) rather than existing radio frequency analog phase shifters to generate and receive the OAM-OFDM signal, thus reducing energy consumption and hardware cost. At last, a flexible 2-D FFT algorithm is developed. Analysis and simulation results show that compared with the traditional row–column FFT algorithm, the proposed 2-D FFT algorithm could reduce the multiplication complexity by $\frac{1}{4}MN\log _2N$ , where $N$ and $M$ are the number of UCA antenna elements and the number of subcarriers, respectively. [ABSTRACT FROM AUTHOR]