Optical Connections Magazine Autumn 2018

ANDY EXTANCE FUTURE NETWORKS

WDM via Infinera’s mux/ demux (MDU) device allows fibre to be used for many purposes.

adds. ‘Link requirements may increase in bandwidth too, because of trac aggregation from more towers.’

Ericsson, which will be speaking at ECOC2017 in Gothenburg, Sweden, in September, also oers active and passive WDM fronthaul architectures depending on the situation. ‘It is all about performance versus total cost of ownership,’ echoes Sanguineti. Infinera is working on autotunable optical technology that might help as mobile networks evolve to 5G. ‘The first generation WDM-PON-based autotunable technology was limited to 1Gbit/s and around 20km, but that isn’t what operators need in the longer term,’ Baldry explains. His company and others are therefore developing longer reach, 10Gbit/s capabilities. ‘That will enable simplification of optics that go to the remote end of the networks,’ Baldry says. ‘You don’t need someone to tune optics during installation or manage lots of spares.’ The company will demonstrate advanced technology in this space at ECOC 2017. Autotunability might help in long fronthaul links, as in C-RAN, Centralised or Cloud Radio Access Networks. First- generation centralised-RAN, pioneered by China Mobile, locates many BBUs in a vault within 20 kilometres of their RRHs, so providers can operate them more easily together. This doesn’t require much optical innovation, but next generation cloud-RAN being trialled by China Mobile, NTT, AT&T and others would, says Lively. Then, when BBUs become software running in a data centre, the distance to the server could be distinctly longer, he

As 5G looms, alternatives to CPRI are being considered, as implementing it on architectures used for 4G could increase needed data rates from 12Gbit/s to over 100Gbit/s. Estimates suggest that a new, Ethernet-based Next Generation Fronthaul Interface that eliminates CPRI would reduce required data rates by around an order of magnitude. This would enable o-the-shelf Ethernet optics to connect the BBU and RRU. The result could combine fronthaul and backhaul, meaning that WDM ‘may not be needed so much even for 5G’, Lively suggests. If WDM is used in such 5G ‘crosshaul’ networks, it will mainly be in cities with high bandwidth needs and limited ability to deploy new fibre, he says. But in those settings microwave wireless technologies could also fulfil crosshaul needs. Infinera’s fronthaul solutions work with its EMXP mobile backhaul products that today support pre-5G test networks. These solutions will evolve as 5G standards are ratified, with passive and active WDM fronthaul options suiting dierent customers, Baldry says. He cites an example where a US operator chose active technologies to avoid putting coloured WDM optics in RRHs. Though more expensive to buy, active technologies can avoid replacing the existing ‘grey’ RRH optics. ‘It was cheaper overall to put active gear at the bottom of the tower than pay people to go up the tower to swap out optics,’ Baldry says.

It is all about performance versus total cost of ownership.

This makes fibre-optic technology a key player, Sanguineti emphasises. The entire network will need more bandwidth, flexibility and manageability. Assigning and managing dierent functions in network elements depending on requirements like latency and bandwidth will benefit from flexibility provided by features like tuneable optics and, in the future, low cost reconfigurable optical add-drop multiplexers (ROADMs). Such increased optical versatility could combine wireless networks with other access networks, Lively says. ‘A lot more people are publicly supporting the idea that by the time 5G is widely deployed, operators could use multi-service access networks,’ he says. Therefore, 5G cell-site crosshaul may be carried by fibre-to-the- home (FTTH) PON networks instead of dedicated fronthaul networks. Pluggable optics already in commercial use to terminate FTTH systems might then be deployed in RRHs. With so many possibilities, Lively is looking forward to clarification. The first step is in September 2017, when a re-engineered CPRI standard should emerge and help evaluate future bandwidth needs. ‘Until 5G is clarified, fronthaul is not going to be,’ Lively stresses.

Today most fronthaul links use one fibre pair to connect each remote radio head (RRH) to the baseband unit (BBU).

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ISSUE 10 | Q3 2017

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