We propose and demonstrate a successful application of orthogonal frequency division multiplexing (OFDM), reflective semiconductor optical amplifier and polarization multiplexing techniques to facilitate bidirectional hybrid OFDM based integrated free-space optics and wireless transport system. The downlink 12 Gbps OFDM data-stream and 79 community antenna television (CATV) channels are transmitted over 50 km single mode fiber (SMF) as well as 12 m and 10 m free-space link, respectively. The uplink 10 Gbps/5 GHz and 5 Gbps/3.5 GHz OFDM data streams are communicated over separate 50 km SMF along with 8 m wireless links. We have used 32-quadrature amplitude modulation (QAM) and 16-QAM modulation formats for downlink and uplink, correspondingly. The performance of the system is observed by evaluating carrier-to-noise ratio (CNR), composite second-order (CSO) and composite-triple-beat (CTB) for the CATV signal, and constellations diagrams, bit error rate (BER), signal-to-noise ratio (SNR), and error vector magnitude (EVM) values for the OFDM signals. After transmission over 50 km SMF as well as 10 m free-space, the resulting CNR, CSO and CTB values are > 51 dB, < − 63 dB and < − 65 dB, respectively. The receiver sensitivity of about 4 dBm is increased for the downlink OFDM signal at BER value of $$10^{ - 9}$$ 10 - 9 using LNA and CDR, as well as EVM and average SNR are observed below 10.5% and > 23.3 dB, respectively. 4 dBm and 3.2 dBm power penalties at BER of $$10^{ - 8}$$ 10 - 8 , below 13% EVM and > 21.3 dB/ > 22.2 dB SNR values are observed for the uplink 10 Gbps/5 GHz and the 5 Gbps/3.5 GHz OFDM data signals, respectively, over 50 km SMF as well as 8 m wireless is observed.

中文翻译：

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基于双向混合OFDM的自由空间/无线光纤传输系统

我们提出并展示了正交频分复用 (OFDM)、反射式半导体光放大器和偏振复用技术的成功应用，以促进基于双向混合 OFDM 的集成自由空间光学和无线传输系统。下行链路 12 Gbps OFDM 数据流和 79 个社区天线电视 (CATV) 信道分别通过 50 km 单模光纤 (SMF) 以及 12 m 和 10 m 自由空间链路传输。上行链路 10 Gbps/5 GHz 和 5 Gbps/3.5 GHz OFDM 数据流通过单独的 50 km SMF 以及 8 m 无线链路进行通信。我们相应地为下行链路和上行链路使用了 32 正交幅度调制 (QAM) 和 16-QAM 调制格式。通过评估载噪比 (CNR) 来观察系统的性能，CATV 信号的复合二阶 (CSO) 和复合三拍子 (CTB)，以及星座图、误码率 (BER)、信噪比 (SNR) 和误差矢量幅度 (EVM) 值对于 OFDM 信号。在 50 km SMF 和 10 m 自由空间传输后，得到的 CNR、CSO 和 CTB 值分别 > 51 dB、< − 63 dB 和 < − 65 dB。使用 LNA 和 CDR 在 BER 值为 $10^{ - 9}$ 10 - 9 的情况下，下行链路 OFDM 信号的接收器灵敏度提高了约 4 dBm，并且观察到 EVM 和平均 SNR 低于 10.5% 和 > 23.3分贝，分别。对于上行链路 10 Gbps/5 GHz 和 5分别为 Gbps/3.5 GHz OFDM 数据信号，