Differential encoding for unlock heterodyning millimeter-wave RoF link

Millimeter-wave base stations are expected to be deployed within the 5G cellular network to increase data rate and network capacity. The use of unlocked heterodyning of free-running optical carriers with self-homodyning receiver has shown potential due to reduced system complexity contributed by its tolerance to laser phase noise. However, direct signal detection using self-homodyning receiver for phase-modulated signal would affect signal's phase integrity. In this paper, we propose the use of differential encoding and optical baseband modulation demonstrated through an optical Differential-Phase-Shift-Keying modulated system with a modified self-homodyning receiver to overcome the aforementioned issue while maintaining bandwidth efficiency. The proposed system is evaluated through software simulations. Results reveal that the proposed system achieves BER of 10⁻⁹ at -20.5dBm optical received power while remaining phase noise-tolerant, with negligible degradation in system performance up to MHz range laser linewidth.