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

Optical Heterodyne Analog Radio-Over-Fiber Link for Millimeter-Wave Wireless Systems

“…Also, in the recent work [23] with this DSP receiver we demonstrated the successful transmission of a 61 GHz OFDM signals with subcarrier baud rates as low as 125 kHzwhich is envisioned in the latest 5G new radio specifications. The frequency offsets of up to 140 MHz are compensated by using this digital processing without any significant performance degradation [23] indicating the suitability of this approach for future hybrid optical/mm-wave multicarrier transmission systems. The limitation of time varying frequency shift of the mm-wave signal can be eliminated by using commercially available lasers, whose frequency drift is limited within the guard bands of the wireless channels.…”

“…The digital compensation of the FO & PN at the receiver side user unit, transfers the hardware complexity of the analog mmwave receiver to the digital domain, making the DSP receiver scheme well suited for deployment in the wireless mm-wave systems. External LO induced frequency offset of up to 140 MHz can be compensated digitally [23] with this technique, showing its capabilities to compensate the FO induced by most of the commercial lasers. Our previous simulation [18] study has concluded that, for an optical heterodyne A-RoF link with independent tunable laser sources (that are frequency locked, but un-correlated in phase), the linewidths of the beating carriers should be less than ~1.5% of the subcarrier baud rate of the OFDM signal for 64-QAM modulated data.…”

“…In the DSP receiver [23] approach, the standard 'Schmidl and Cox' (S&C) [29] and decision directed least mean square (DD-LMS) algorithms are used for FO & PN compensation, respectively. The implementation of this DSP receiver will not require any additional processing as these algorithms have been traditionally implemented in the wireless systems for RF FO & PN compensation at the mobile receivers.…”

“…frequency offset (FO)) and phase noise/linewidth on the system performance. The first approach advocates the use of an analog mm-wave receiver [22]; the second approach uses the standard digital signal processing (DSP) algorithms [23], while in the third approach, the use of a photonic integrated mode locked laser (MLL) with reduced DSP compensation [24] is presented.…”

Towards a Scaleable 5G Fronthaul: Analog Radio-over-Fiber and Space Division Multiplexing

“…Phase noise plays a fundamental role in the performance of radio communication systems and limiting phase noise is one of the major concerns to be addressed before the introduction of ARoF links in fronthaul networks. While phase noise in ARoF systems has been studied [50]- [52], its impact on real-time processing of ARoF OFDM signals remains to be evaluated. Consequently, in this section the measured phase noise performance of two of the aforementioned two-tone generation schemes is discussed and simulations are presented aiming at determining the maximum acceptable level of phase noise for real-time processing with the ARoF BBU.…”