Abstract
This article proposes an optimized version of a canonical piece-wise-linear (CPWL) digital predistorter in order to enhance the linearity of a radio-over-fiber (RoF) LTE mobile fronthaul. In this work, we propose a threshold allocation optimization process carried out by a genetic algorithm (GA) in order to optimize the CPWL model (GA-CPWL). Firstly, experiments show how the CPWL model outperforms the classical memory polynomial DPD in an intensity modulation/direct detection (IM/DD) RoF link. Then, the GA-CPWL predistorter is compared with the CPWL model in several scenarios, in order to verify that the proposed DPD offers better performance in different optical transmission conditions. Experimental results reveal that with a proper threshold allocation, the GA-CPWL predistorter offers very promising outcomes.
Highlights
Nowadays, due to the increasing demand of Information and Communication Technology (ICT) services, new architectures have been developed in order to concentrate signal processing in the same Baseband Unit (BBU), such as Cloud Radio Access Network (C-RAN) [1]
canonical piece-wise-linear (CPWL) model is compared with the proposed genetic algorithm threshold optimization model (GA-CPWL)
As the model performance depends strongly on the transmission parameters, this can be accomplished by changing the distributed feedback laser (DFB) bias intensity, the length of the link between the BBU and the Remote Radio Head (RRH) or the input signal power
Summary
Due to the increasing demand of Information and Communication Technology (ICT) services, new architectures have been developed in order to concentrate signal processing in the same Baseband Unit (BBU), such as Cloud Radio Access Network (C-RAN) [1]. RoF transmissions are analog systems, and susceptible of nonlinear distortions by electrical-to-optical and optical-to-electrical conversions, as well as the fiber dispersion [6] This issue, together with the power amplifier (PA) situated at the Remote Radio Head (RRH) side, distort the signal producing a spectral regrowth in adjacent frequency bands, known as adjacent channel interference (ACI). It is especially vulnerable to these distortions due to its high peak-to-average power ratio (PAPR) in its signal envelope Both photonic and electrical methods have been developed in order to address these RoF system distortions [8, 9], being digital predistortion (DPD) one of the most effective with high flexibility and simple operation.
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