In view of the realization of short and medium range Mobile Front Haul (MFH) connections for present (LTE) and future (5G) cellular networks, a cost effective, low consumption Radio over Fiber system is proposed, based on 850 nm Single Mode Vertical Cavity Surface Emitting Lasers (VCSELs) and Standard Single Mode Fibers (SSMFs). An efficient countermeasure to possible impairments due to the bi-modal behavior of SSMFs at 850 nm allows even in critical cases to maintain at high level the quality of the received signal. The performances are evaluated with reference to the Physical Downlink Shared Channel of an entire LTE frame with 20 MHz bandwidth centered in band 20 of the standard. In terms of Error Vector Magnitude and outage probability under temperature stress the system is able to transmit 256-QAM signals in compliance with the LTE standard, which corresponds to a raw data rate transmission of 134.4 Mbit/s, up to distances of 1.5 Km.

The design and development process for the Square Kilometre Array (SKA) radio telescope’s Low Frequency Aperture Array component was progressed during the SKA pre-construction phase by an international consortium, with the goal of meeting requirements for a critical design review. As part of the development process a full-sized prototype SKA Low ‘station’ was deployed – the Aperture Array Verification System 1 (AAVS1). We provide a system overview and describe the commissioning results of AAVS1, which is a low frequency radio telescope with 256 dual-polarisation log-periodic dipole antennas working as a phased array. A detailed system description is provided, including an in-depth overview of relevant sub-systems, ranging from hardware, firmware, software, calibration, and control sub-systems. Early commissioning results cover initial bootstrapping, array calibration, stability testing, beam-forming, and on-sky sensitivity validation. Lessons learned are presented, along with future developments.

This paper investigates the possibility of implementing SiGe Hetero-junction bipolar Photo-Transistor (HPT) within low cost and low power consumption Radio-over-Fiber (RoF) systems based on Standard Single Mode Fiber (SSMF) operating in the first optical window for wireless communication networks scenarios. The SiGe HPT under study has potential lower cost compared to standard PIN photo-detectors as it is fabricated through the consolidated SiGe bipolar transistor process technologies, allowing the possible integration with Sibased circuits. Various operation modes of the photo-transistor (such as three-terminals and two-terminals) are investigated, analyzing their impact on the SSMF-based RoF link in terms of gain and noise (including modal noise fluctuations) for a frequency range up to 2.5 GHz. A 20 MHz LTE transmission is finally demonstrated as example of possible applications of the studied RoF link.

Due to their inherent capillary distribution properties, Radio over Fiber (RoF) systems are expected to play a major role within future fifth generation wireless networks. However, significant bounds on the technology usability are set by the nonlinear generation of spurious frequencies, which, in the case of RoF links exploiting Directly Modulated Lasers (DML), has the combined effect of laser chirp and optical fiber dispersion among its prevailing causes. In this paper, a signal digital predistortion system, which can lower these detrimental effects, is proposed in two different versions. A detailed description of its functional model is given, and its attractive features in terms of quality improvement of the received signal is illustrated.

The signal reception chain is an essential element for achieving the square kilometer array-low (SKA-low) system requirements in terms of high sensitivity and dynamic range. The balance between gain, linearity, and low power consumption, as well as the cost, are fundamental parameters that influence the selection of the most suitable technology for SKA-low. Further factors, such as low self-generated radio frequency (RF) interference, high reliability, robustness under extreme environment, and last but not least, the distance between the antennas and the acquisition systems, have impacts on the selection for both architecture and receiver system design. The selected technology for the SKA-low RF signal transportation is RF-over-fiber systems, where the preamplified RF signal picked up by the antennas is carried via analogue modulation over optical fiber. The rationales behind the selection are reported, along with descriptions on the development of the receiver prototypes. The prototypes were deployed and installed on the demonstrator arrays at the selected SKA-low site in Western Australian. Particular attention has been put on the thermal characterization of the receiver system under the actual operating temperature on site, especially when both transmitting part and the optical medium are subjected to external ambient temperature variations. Performance issues encountered in the demonstrator arrays are also discussed along with some proposals for future activities.