OFDM Baud Rate Limitations in an Optical Heterodyne Analog Fronthaul Link using Unlocked Fibre Lasers

Abstract

The phase noise (PN) of a photo-generated mmwave carrier, resulting from frequency and phase fluctuations of uncorrelated laser sources, limits the performance of heterodyne/millimeter-wave analog radio-over-fibre links. This work analyzes the effect of subcarrier baud rate and frequency offset (FO) variations on the performance of a 60 GHz OFDM signal generated using unlocked fiber lasers. Conventional digital techniques for FO and PN compensation, in a 25 km mm-wave A-RoF heterodyne system, are shown to overcome relatively large FOs and to enable the successful transmission of kHz range sub-carrier baud rates - in line with recent 5G recommendations.