Multi-Mode OAM Radio Waves: Generation, Angle of Arrival Estimation and Reception With UCAs

Abstract

Orbital angular momentum (OAM) at radio frequency (RF) provides a novel approach of multiplexing a set of orthogonal modes on the same frequency channel to achieve high spectrum efficiencies. However, there are still big challenges in the multi-mode OAM generation, OAM antenna alignment and OAM signal reception. To solve these problems, we propose an overall scheme of the line-of-sight multi-carrier and multi-mode OAM (LoS MCMM-OAM) communication based on uniform circular arrays (UCAs). First, we verify that UCA can generate multi-mode OAM radio beam with both the RF analog synthesis method and the baseband digital synthesis method. Then, for the considered UCA-based LoS MCMM-OAM communication system, a distance and AoA estimation method is proposed based on the two-dimensional ESPRIT (2-D ESPRIT) algorithm. A salient feature of the proposed LoS MCMM-OAM and LoS MCMM-OAM-MIMO systems is that the channel matrices are completely characterized by three parameters, namely, the azimuth angle, the elevation angle and the distance, independent of the numbers of subcarriers and antennas, which significantly reduces the burden by avoiding estimating large channel matrices, as traditional MIMO-OFDM systems. After that, we propose an OAM reception scheme including the beam steering with the estimated AoA and the amplitude detection with the estimated distance. At last, the proposed methods are extended to the LoS MCMM-OAM-MIMO system equipped with uniform concentric circular arrays (UCCAs). Both mathematical analysis and simulation results validate that the proposed OAM reception scheme can eliminate the effect of the misalignment error of a practical OAM channel and approaches the performance of an ideally aligned OAM channel. Index Terms-Orbital angular momentum (OAM), uniform circular array (UCA), angle of arrival (AoA) estimation, OAM detection, multiple-input multiple-output (MIMO).

Non-Coaxial OAM: Precoding Design, Misaligned Parameter Estimation and Capacity Compensation

“…As a p d, R q d, the last term ind n,m;q,p can be neglected, and non-circulant term can be divided into those related to ψ p,m and those related to ψ q,n , indicating a simple pre-processing matrix design. Without utilizing original non-coaxial parameters [39], the pre-transmitting matrix on This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited.…”

UCA-Based OAM Non-Orthogonal Multi-Mode Multiplexing

“…It is feasible and convenient to utilize the UCA to generate, steer and receive OAM beams [14], [19], [20]. In general, the UCA-based OAM communication system requires alignment of the transmit and receive arrays [7]- [9].…”

“…Therefore, high-order and low-order integer OAM modes result in quite different received SNRs. Since not like closed-loop MIMO systems being able to perform water-filling power allocation and adaptive modulation for each sub-channel with CSIT, the orthogonal multi-mode OAM multiplexing transmission, which claims its advantage over MIMO system being low complexity due to no need of CSIT [12], [19], therefore has poor BER performance deteriorated by the higher-order OAM modes with the low received SNRs.…”

“…Especially, high-order integer OAM modes result in small received signal energy and low signal-to-noise ratio (SNR) at the receive UCA with a fixed aperture. Moreover, not like closed-loop MIMO systems being able to perform water-filling power allocation and adaptive modulation for each sub-channel with informed channel state information at the transmitter (CSIT), the orthogonal multi-mode OAM multiplexing system, which claims its advantage over MIMO system being low complexity due to no need of CSIT [12], [19], usually has poor bit error rate (BER) performance because the BER is dominated by the sub-channel with the lowest SNR, i.e., the sub-channel corresponding to the highest-order OAM mode.…”

Massive OAM‐MIMO transmission scheme for 5G networks and beyond

“…As the basis of channel matrix-based performance analysis, OAM-MIMO systems are so far mainly configured by UCA [29][30][31][32][33][34], uniform line array (ULA) [35][36][37][38], and uniform rectangular array (URA) [39]. System models of OAM-MIMO in the cases of line-of-sight (LoS) [40][41][42], non-LoS (NLoS) FIGURE 1 Uniform line array (ULA)-based massive orbital angular momentum and multiple-input multiple-output (OAM-MIMO) system in the multipath scene [38,43,44], alignment [29,45] and misalignment [33,34,44] were preliminarily analysed, which show many positive results about OAM-MIMO increasing the spectrum efficiency.…”