Radio Over Fiber Paves Way for Future 5G Networks

Source:Nitin Dahad
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A manufacturer of III-V photonic devices claims to have proven the feasibility of 60-GHz radio over fiber (ROF) transmission at a 1,270-nm wavelength, paving the way to potential solutions for 5G networks.

CST Global, a Scotland-based subsidiary of Sivers IMA Holdings AB in Kista, Sweden, carried out the feasibility study as part of an EU Horizon 2020 research project. The project, iBROW (innovative ultra-broadband ubiquitous wireless communications through tera-hertz transceivers), was led by the University of Glasgow and managed within CST Global by research engineer Horacio Cantu.

The company says that ROF networks are emerging as a completely new and promising communication paradigm for delivering broadband wireless access services and fronthaul at 60 GHz, relying on the synergy between fixed optical and millimeter-wave technologies. ROF technology enables RF signals to be transported over fiber across kilometers and can be engineered for unity gain RF links. Hence, it is thought that it could do a lot to ease spectrum constraints, and it can replace multiple coax cables with a single fiber-optic cable. Among several benefits, ROF could also enhance cell coverage.

ROF requires light to be modulated with radio data for optical transmission. It offers a huge bandwidth increase over existing solutions and requires no digital-to-analog conversion (DAC), resulting in a low-latency solution.

The aim of the EU's iBROW project is to develop a novel, energy-efficient, and compact ultra-broadband short-range wireless communication transceiver technology, seamlessly interfaced with optical fiber networks and capable of addressing future network needs. It's based on predictions indicating that short-range wireless data rates of tens of Gbps will be required by 2020, and currently available wireless technology cannot support these demands despite significant progress in spectrally efficient techniques.

The frequency spectrum currently in use is not expected to be suitable to accommodate these future data rate requirements. Therefore, there is a need to embrace higher-frequency bands, namely in the mmWave and THz bands above 60 GHz and up to 1 THz.

General structure of a radio-over-fiber system. Source: Helmut Schmidt University, Hamburg

General structure of a radio-over-fiber system.
Source: Helmut Schmidt University, Hamburg

"The performance characteristics of 1,270 nm, detuned, in-plane, ridge waveguide, DFB, laser diodes demonstrated it is an ideal ROF carrier wavelength," said Cantu. "We previously showed that 1,310 nm was an effective transmission wavelength. We are confident that this new technology will also be feasible at 1,550 nm, which will deliver an ultra-broadband, low-latency solution, extending transmission distances up to 25 km.”

The mmWave signal baseband is transmitted over the fiber-optic connection from an InP, mmWave transceiver, to the system core. “We are working with our sister company, Sivers IMA, to optimize a combined ROF, optical, and mmWave solution. This will offer ultra-broadband in the V-band frequencies, within the mmWave spectrum, at 60 GHz, which is one of the designated 5G network bands for telecommunication infrastructures,” added Cantu.

CST Global said in a press statement that more development is needed to establish a commercial, ultra-broadband, ROF solution that is low-cost, energy-efficient, compact, operates at room temperature, and integrates with 5G, fiber-optic network requirements.

"Although more development work is needed, I see CST Global's achievement as confirmation that we are on track to establish a commercially viable solution in this area," said Anders Storm, CEO of Sivers IMA Holding.

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