Upstream and downstream analysis of an optical fronthaul system based on DSP-assisted channel aggregation

In this paper,we focus on a well-known optical fronthauling architecture based on frequency division multiplexed digital signal processing (DSP)-assisted channel aggregation, and we present new results related to the optimization of the optical setup, proposing an efficient technique for the optimization of the transmission. In particular, we report an original pre-emphasis technique to equalize the performance of the radio channels, especially focusing on the upstream (US) link that has more critical characteristics but has not typically been treated in detail in previous works on this topic. The effects of both radio and optical impairments on the error vector magnitude (EVM) are taken into account. An analytical description of our approach is provided, and then it is applied on an experimental setup (able to aggregate up to 96 20-MHz radio signals), showing the possibility of minimizing the maximum EVM at the output of the fronthauling link, for both downstream and US transmission. Additionally, a low complexity technique to practically estimate the EVM per channel by taking advantage of only the DSPaggregation/ deaggregation functionalities is proposed and, again, experimentally demonstrated.