Bi-Directional OFDM Truncated PS-4096QAM Signals Transmission in a Full-Duplex MMW-RoF System at E-Band

A bi-directional photonics-aided millimeter-wave (MMW) transmission system at E-band is proposed in this article, which can be applied in future mobile networks. Only one pair of horn antennas are adopted in the experiment to support symmetrical wireless signal transmission. The center frequency of the downlink and uplink is set as 73.5 and 83.5 GHz, respectively, to avoid the interference effect. Moreover, the probabilistic shaping (PS) technique is used to adapt transmission rate and improve system capacity under a limited SNR. The time-domain Volterra series based equalizer effectively compensates the nonlinear distortion induced by the photoelectric devices. Based on the experimental results, the proposed full-duplex MMW-RoF system can support OFDM truncated PS (TPS)-4096QAM signal transmission, whose entropy is 10 bits/symbol/Hz. We set the probability of the outermost points to zero and the generated TPS-4096QAM signal is actually a PS-1936QAM one. The system simultaneously allows 7 Gbaud TPS-4096QAM signal downlink and uplink transmission over 2 m wireless distance, satisfying the NGMI threshold at 0.83. Moreover, the bi-directional 7 Gbaud PS-1024QAM signal transmission distance can be extended to 13.4 m when we adopt a higher NGMI threshold at 0.67. So the total rate of our proposed bi-directional transmission system is achieved to 100 Gbit/s. We also investigate the BER performance with different modulation formats. Such a system is a promising solution for future high-speed backhaul networks with multiple modulation format requirements.