Abstract
Digitized radio-over-fiber (D-RoF) transport schemes are being pointed as viable alternative solutions to their analog counterparts, in order to avoid distortion/dynamic range problems. Here we propose a novel D-RoF architecture that takes advantage of a bandpass sigma-delta modulator at the transmitter which subsequently permits the usage of a simpler/cheaper base station that avoids the employment of a digital to analog converter. The proposed architecture exploits the properties of the digital signal to enable the extraction of an higher carrier frequency through the employment of a bandpass filter. Furthermore, we present a comprehensive analysis regarding the impact of a low-cost electro-optic modulation on the quality of received demodulated signal. Finally, a comparison performance analysis between the conventional D-RoF and the proposed architecture is presented. We conclude that although the proposed architecture performs similarly to conventional D-RoF schemes, it is more competitive for either upgrading installed systems as well as for new deployments.
Highlights
The ever increasing demand for bandwidth in wireless mobile communications is a challenging problem
We present a comprehensive analysis regarding the impact of a low-cost vertical cavity surface emitting laser (VCSEL) based electro-optic modulation on the quality of received demodulated signals, in particular we address key design trade-offs regarding the impact of the laser bias current operating point as well as the optical modulation extinction ratio and overshoot of the modulated pulse
The paper is organized as follows: in section 2 we review the fundamentals of sigma-delta modulation; in section 3 the proposed SD based RoF concept, the experimental setup used for performance evaluation and the experimental results are presented and discussed; in section 4 we present a comparative analysis between the proposed architecture and the conventional Digitized radio-over-fiber (D-RoF); and section 5 draws the conclusions
Summary
The ever increasing demand for bandwidth in wireless mobile communications is a challenging problem. It has been shown that IMD is the main performance limiting factor in A-RoF transmissions, affecting the link dynamic range which decreases linearly with the optical fiber length due to attenuation [7, 8] This problem becomes more challenging when A-RoF is combined with the widely used orthogonal division multiplexing (OFDM) modulation, due to its inherently high vulnerability to nonlinear distortion. State-of-the-art VCSELs are currently supporting digital signal transmissions up to 10 Gbps, which is more than 5 times the 1.8 Gbps bitrate presented in this work These cost effective and still high-performance VCSEL based links are a good compromise solution for the proposed architecture. We start by analyzing low-pass prototype structures, both first and higher order, from which a bandpass structure can be derived
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