This Letter outlines radio-over-fiber combined with radio-over-free-space optics (RoFSO) and radio frequency free-space transmission, which is of particular relevance for fifth-generation networks. Here, the frequency band of 24–26 GHz is adopted to demonstrate a low-cost, compact, and high-energy-efficient solution based on the direct intensity modulation and direct detection scheme. For our proof-of-concept demonstration, we use 64 quadrature amplitude modulation with a 100 MHz bandwidth. We assess the link performance by exposing the RoFSO section to atmospheric turbulence conditions. Further, we show that the measured minimum error vector magnitude (EVM) is 4.7% and also verify that the proposed system with the free-space-optics link span of 100 m under strong turbulence can deliver an acceptable EVM of $<9\%$ with signal-to-noise ratio levels of 22 dB and 10 dB with and without turbulence, respectively.

中文翻译：

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第五代系统的24–26 GHz光纤无线电和自由空间光学器件

该信函概述了光纤无线电与自由空间无线电技术（RoFSO）和射频自由空间传输的结合，这与第五代网络特别相关。在这里，采用24–26 GHz频带来演示基于直接强度调制和直接检测方案的低成本，紧凑且高能效的解决方案。对于我们的概念验证演示，我们使用100 MHz带宽的64个正交幅度调制。我们通过将RoFSO部分暴露在大气湍流条件下来评估链路性能。此外，我们表明测得的最小误差矢量幅度（EVM）为4.7％，并且还验证了在强湍流下具有100 m自由空间-光学链路跨度的拟议系统可以提供可接受的EVM。$<9％$ 在有和没有湍流的情况下，信噪比分别为22 dB和10 dB。