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Mobile Backhaul: How to Meet the Capacity Challenge

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VoicenData Bureau
New Update

The telecom industry is turning to optical fiber solutions as capacity demands rise aggressively

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‘Capacity’ is the new buzzword in the Indian telecom sector as the industry leaves behind a decade of unprecedented growth in voice subscribers and now looks towards data as its next big opportunity. Even as the industry waits for 4G-LTE to unfold, 3G adoption–supported by lower tariffs and cheaper devices–has been encouraging.

It is widely recognized that the bandwidth-hungry applications supported by 3G and 4G mobile broadband networks and also by fixed-line broadband networks are driving ever-increasing capacity demands throughout the network.

The Indian telecommunication industry has already witnessed capacity demand driven transmission technology migration from 10G to 40G in the core network and that upward trend is continuing with 100G systems now being deployed.

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But even as these systems are being deployed, carrier demand is growing for 400G in global capacity hotspots. At the same time, the rise in capacity demand in access networks is forcing the service providers to migrate from microwave or copper to high-speed optical fiber cabling as is evident by optical fiber enabled mobile backhaul and the evolving deployment of FTTx networks.

Innovations in Optical Fibre To ensure cost-effective operation and the ability to continuously adapt to technology evolution, fiber optic networks need to be optimized to their application. The effective operation of any fiber optic based communication system is determined largely by the ratio of the optical signal level to the level of the noise of the system measured at the receiver, or OSNR (optical signal to noise ratio).

The main sources of noise in amplified core networks are amplifier noise and non-linear effects.

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In access networks system, OSNR is more about the simple ratio of the received signal power to the inherent noise floor of the receiver. If there is any shortfall in the required system, OSNR will result in a reduction in signal quality, resulting in poor quality of service or will require a reduction in system reach to compensate.

Migration to higher data rates to meet increasing capacity needs, places further demand on a communication system in terms of increased OSNR: the basic rule of thumb is that any system migrating from 10G to 100G (in the absence of any system advances) requires an additional 10 dB of OSNR for the system to operate without any reduction in system reach or signal quality.

Recent optical system advances such as advanced modulation formats, digital signal processing (DSP), and coherent systems have proved successful in enabling 40G and 100G data rates without having to greatly increase the system OSNR, although at the cost of some reduction in system reach relative to 10G transmission: typical commercially available 100G systems are limited to 1000km.

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Nor do these advances deliver the low-cost non-coherent 100G systems required for many cost conscious regional and metro network links. There are also OSNR challenges, albeit in a simpler form, being faced in access networks that are striving to maintain a low-cost of operation while reaching out and connecting as many subscribers as possible.

However innovation in optical fiber is helping contribute significantly towards meeting the challenges associated with higher data rate in core networks and the evolution of optical fibre based access networks, enabling higher date rates with minimal compromise on reach and cost efficiency and optimised access network reach and connectivity.

The 3 key optical fiber attributes that can assist with high data rate and low-cost operation are dispersion, attenuation, and effective area.

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Low dispersion G.655 fibers have for many years provided a cost-effective solution for moderate capacity 10G networks and non-coherent 40G operation; enabling lifetime network cost savings through reduction in requirements for dispersion compensation and enabling greater use of lower cost single-stage amplifiers. G.655 fibers can also enable much lower cost 100G systems for up to 600km reach using non-coherent technology.

Increasing fiber effective area, on the other hand, provides a path to increase the power level at the transmitter. However this comes with a limitation–due to their large effective area–such fibers are not compliant with the basic G.652 and G.655 fiber standards and so are not backwards compatible, from a field installation and handling perspective. And so what fiber innovation can help with higher data rate, OSNR is another challenge for terrestrial networks.

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Optical Fiber Attenuation–Resolving the Capacity Challenge Another means of increasing the OSNR of a fiber optic system is to reduce the signal attenuation in the system such that the signal power is higher at the receiver. There are 2 main sources of signal attenuation in optical fiber, the first is transmission loss where the signal in a standard G.652 fiber is attenuated at a typical rate of 0.20 dB/km (at 1550nm) as it travels along the glass core; the second is macrobend loss (or bend loss), where light leaks out of the fiber core at the point of a bend.

Benefits for Core and Access Networks In core networks, low loss optical fibers can enable transition to a next generation network: transition to higher data rates and the deployment of optical add-drop multiplexers with minimal compromise on reach. The lower transmission loss can also be used to facilitate a lower cost network by eliminating amplifiers and regeneration stages or to deliver additional system margin: margin that can be used to facilitate repair of more cable cuts before the cable goes ‘dark’ and thus greatly extend the working lifetime of a cable before a replacement is required.

Access network system evolutions such as 10GPON are adopting operation wavelengths at the extremes of the optical fiber transmission spectrum in order to co-exist with existing systems like GPON.

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Conclusion Optical fiber is the basic foundation block of most telecom networks. As capacity demand increases relentlessly every day, potential next generation system solutions seem to be approaching a performance ceiling and the industry is turning to the optical fiber network foundation for solutions. The need of the day is to maximize reach, connectivity and high quality of service delivery while maintaining cost effective network solutions. Recent innovations in optical fiber have delivered commercially-available products that feature very low transmission loss, but also fibers with larger effective areas, both attributes that are proven to give significant signal strength and OSNR gains, resulting improved signal quality and extended system reach.

Just as a best in class sports car will be unable to reach its top speed without a smooth road to drive on, next generation networks will not be able to achieve high capacity core transmission or cost-effective reliable broadband access services without an advanced fiber infrastructure to transmit over.

As any optical fiber cable deployed today is generally expected to have an operation lifetime upwards of 20 years, it is important to deploy advanced fiber today in order to enable the advanced networks needed for tomorrow.

The author is regional marketing manager,India and EMEA,Corning

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