Microwave Photonics System with 16QAM-OFDM Based on Direct Modulation and Subcarrier Multiplexing

In view of the high cost of millimeter wave generated by the existing radio over fiber system, and the urgent need for high capacity and high bandwidth of mobile communication technology in the future, this paper proposes a microwave photonics system with 16quadrature amplitude modulation-orthogonal frequency division multiplexing (16QAM-OFDM) based on direct modulation and subcarrier multiplexing. The system adopts direct modulation technology combined with multiple subcarriers multiplexing, which includes 5G low frequency and millimeter-wave band. By transmitting multiple signals at the same time, the capacity of communication is expanded. In addition, OFDM is combined to further improve the spectral efficiency. Through simulation analysis, the results show that when the optical fiber transmission distance is 50km, the bit error rate (BER) of uplink and downlink is lower than $3.8 \times 10^{-3}$. The constellation is clear and the error vector magnitude (EVM) value meets the standard that no more than 20% specified by the standard performance evaluation organization. The system provides a reference for ROF system that can be compatible with the two application scenarios of seamless wide-area coverage and high-capacity hot-spot.