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A full-duplex radio over fiber link scheme with 16 quadrature amplitude modulation (16-QAM) 10 Gb/s downstream and 2.5 Gb/s upstream signals is proposed. In the downlink, the 60 GHz dual-tone optical millimeter-(mm-) wave signal carrier is generated by the 15 GHz local oscillator via a Mach-Zehnder modulator with frequency quadrupling. The 16-QAM 5 GHz IF signal is up-converted to 65 GHz by modulating it on one of the two tones with single-sideband (SSB) modulation at the central station. At the remote base station, the 65 GHz SSB optical mm-wave signal is detected by a high-speed photodiode. After the 60 GHz uplink dual-tone optical mm-wave carrier is abstracted by optimized filtering, the uplink 63 GHz mm-wave signal is modulated onto it to down-convert to the 3 GHz SSB optical IF signal. Since both the down-and uplink optical mm-wave signals have SSB spectra with the signal modulated on one of the two tones, they suffer little from the fiber dispersion. The simulation results show that the bidirectional signals have good performance even after being transmitted over 30 km standard single mode fiber.Index Terms-Frequency quadrupling; Full-duplex link; 16-QAM; RoF (radio over fiber).

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Communication-Based Train Control (CBTC) system is a critical signal system to ensure rail transit’s safe operation. Compared with the train-ground CBTC system, the train control system based on train-to-train (T2T) communication has the advantages of fast response speed, simple structure, and low operating cost. As the core part of the train control system based on T2T communication, the reliability of the data communication system (DCS) is of great significance to ensure the train’s safe and efficient operation. According to the T2T communication system requirements, this paper adopts Long-Term Evolution-Unlicensed (LTE-U) technology to design the DCS structure and establishes the reliability model of the communication system based on Deterministic and Stochastic Petri Nets (DSPN). Based on testing the real line’s communication performance parameters, the DSPN model is simulated and solved by π -tool, and the reliability index of the system is obtained. The research results show that the LTE-U-based T2T communication system designed in this paper meets the train control system’s needs for communication transmission. This paper’s reliability evaluation method can complete the reliability modeling of train control DCS based on T2T communication. The research in this paper will provide a strong practical and theoretical basis for the design and optimization of train control DCS based on T2T communication.