Electromagnetic waves carrying orbital angular momentum (OAM) can improve the spectral efficiency of communication systems by multiplexing a number of OAM modes. However, since being not able to perform water-filling power allocation and adaptive modulation for each sub-channel like closed-loop multiple-input multiple-output (MIMO) systems, the traditional orthogonal multi-mode OAM multiplexing system usually has poor bit error rate (BER) performance due to the inherent large divergence angle of high-order orthogonal OAM beams. Therefore, in this article we propose a non-orthogonal OAM (NO-OAM) multi-mode multiplexing scheme based on uniform circular array (UCA), which regulates the divergence angles of all non-orthogonal OAM beams to be the same, circumventing the problem that large beam divergence of high-order orthogonal OAM modes results in low received signal-to-noise ratio (SNR) at the receive UCA with a fixed aperture. Mathematical analysis and numerical simulations show that in contrast to the existing uniform concentric circular array (UCCA) beam adjustment scheme, the proposed NO-OAM scheme has slightly better beam adjustment effect but with only one UCA. Moreover, in contrast to the traditional orthogonal OAM multi-mode transmission, the proposed NO-OAM multi-mode multiplexing scheme has asymptotically equivalent channel capacity and much lower BER.

中文翻译：

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基于UCA的OAM非正交多模式复用

携带轨道角动量（OAM）的电磁波可以通过复用多种OAM模式来提高通信系统的频谱效率。然而，由于不能像闭环多输入多输出（MIMO）系统那样为每个子信道执行注水功率分配和自适应调制，因此传统的正交多模式OAM多路复用系统通常具有较差的误码率高阶正交OAM光束固有的大发散角，可以提高BER（速率）性能。因此，在本文中，我们提出了一种基于均匀圆形阵列（UCA）的非正交OAM（NO-OAM）多模复用方案，该方案将所有非正交OAM光束的发散角调节为相同，避免了高阶正交OAM模式的大束发散会导致固定孔径的接收UCA处的接收信噪比（SNR）低的问题。数学分析和数值模拟表明，与现有的均匀同心圆阵光束调节方案相比，提出的NO-OAM方案光束调节效果略好，但仅有一个UCA。此外，与传统的正交OAM多模式传输相比，提出的NO-OAM多模式复用方案具​​有渐近等效的信道容量和更低的BER。提出的NO-OAM方案的光束调整效果略好，但只有一个UCA。此外，与传统的正交OAM多模式传输相比，提出的NO-OAM多模式复用方案具​​有渐近等效的信道容量和更低的BER。提出的NO-OAM方案的光束调整效果略好，但只有一个UCA。此外，与传统的正交OAM多模式传输相比，提出的NO-OAM多模式复用方案具​​有渐近等效的信道容量和更低的BER。