No abstract

For the fronthaul between the baseband unit and the remote radio unit (RRU), radio over fiber (RoF) is promising to replace the Common Public Radio Interface in beyond fifth-generation and the sixth-generation wireless communication systems. The weight, size, and power consumption of the RRU can be greatly reduced, along with easy support for the millimeter-wave band. In this paper, a dual-band RoF link is proposed, where flexible switching between high-frequency (28 GHz) and low-frequency (3.5 GHz) RF channels is realized through polarization control. Single-sideband modulation is performed on 28 GHz signals to avoid periodic power fading during long-distance fiber transmission. By adjusting the DC bias, the third-order intermodulation distortion component in the 3.5 GHz signal is suppressed, and the spur-free dynamic range (SFDR) is improved. Experimental results show a channel isolation of above 43 dB. The link gain of the 28 GHz signal channel is flat, and the SFDR of the 3.5 GHz signal channel can reach 118.6 d B ⋅ H z 4 / 5 . In the case of RF vector signal transmission, the adjacent channel power ratio of the 3.5 GHz signal channel is optimally up to 48 dB, and the error vector magnitude is 2.9%.

The in-band full-duplex (IBFD) systems can send and receive data simultaneously in the same frequency band. Although the electromagnetic interference among RF channels can be released using radio over fiber (RoF) links, the receiving antenna is susceptible to the signal leakage from adjacent transmitting antennas. Due to the electronic bottlenecks, traditional RF selfinterference cancellation (SIC) systems have some problems, such as low operating frequency, narrow transmission bandwidth, and electromagnetic interference, which seriously reduces the communication performance. In this paper, a photonic RF SIC system based on dual-phase modulation in a Sagnac loop is proposed to further increase the resistance to electromagnetic interference of the IBFD systems. Based on the principle of polarization multiplexing, the damaged received signal and local interference signal are modulated on two beams of a light wave with orthogonal polarization states. The received interference signal can be canceled by polarization adjustment. In the experiment, a single-frequency interference cancelation depth of 45 dB is achieved in the proposed photonic SIC system over the operating frequency range of 5-20 GHz. Also, a demonstration of cancellation for modulated interference with a center frequency of 10 GHz and bandwidths of 20, 30, and 50 MHz is carried out.

Microwave photonic mixing can realize the frequency conversion of microwave signals in the optical domain, breaking through the bandwidth bottleneck and electromagnetic interference problems of traditional microwave mixing methods. In the background of the hybrid macro-micro cellular system, a wideband, large dynamic range and reconfigurable microwave photonic mixer is proposed, theoretically analyzed and experimentally demonstrated in this paper. By adjusting the modulator bias voltages and matching the proper digital domain operations, a microwave photonic mixer with reconfigurable functions including single-ended dispersion immune mixing, I/Q frequency down-conversion, image rejection mixing, and double-balanced mixing are realized, respectively. Meanwhile, optimizing the electrical attenuator using convex optimization can suppress the third-order intermodulation distortion (IMD3), maximize the conversion gain, and finally improve the spur-free dynamic range (SFDR). Experimental results show that the proposed scheme can be operated with a frequency from 5 to 20 GHz, and the SFDR can achieve 118.3 dB·Hz4/5. Over the whole frequency range, I/Q frequency down-conversion can be well conducted with an amplitude imbalance below 0.7 dB and a phase imbalance below ±0.7°. After an I/Q imbalance compensation algorithm, the image rejection ratio of over 60 dB is produced. The power fading caused by fiber dispersion is also compensated successfully. For a vector signal with 16 quadrature amplitude modulation, the best error vector magnitude (EVM) reaches 3.4%.

No abstract