Sigma-delta PWM waveforms for optical front-hauling

Abstract

The optical links is one of the driving enablers of distributed antennas systems for future radio access networks (RAN). However, the increasing demand of the wireless band-width is a strong push toward an efficient usage of the fiber whose bandwidth is large, but not unlimited mainly if considering the electronics. Examples in the direction of bandwidth parsimony are the analog relaying of RAN signals according to the radio-over-fiber paradigm. In this paper we propose the transport of analog RAN signals by employing the pulse width modulation (PWM) as novel waveform for optical front-hauling. At transmitter the radio-signal is sampled and mapped onto the duration of on/off optical signal, at receiving end of the fiber each PW modulated sample is digitized so that the overall communication is transparent. The key contribution here stems from the noise-rejection capability of closed-loop PWM that trades some oversampling and filtering to gain in signal quality. The paper proposes a Sigma-Delta structure for PWM that is purposely designed to trade these benefits for RAN front-hauling architecture. Simulation results provide some room for discussion on pros/cons of this novel front-hauling.