When choosing between fibre and wireless backhaul for urban small cells, an important factor concerns the installation time, specialist skillset and durability. A new “plug and play” approach for fibre connections offers to speed up and improve the process.

Trade-off between fibre and wireless backhaul

While it might be everybody’s technical first choice, fibre simply isn’t available everywhere, it can be costly and may involve considerable effort and lapsed time to install. There can be trenches to dig, ducting to lay, fibre to blow through and splicing of connections. Wireless backhaul offers a simpler and flexible approach and is capable of data rates adequate for independent small cells.

However the very high bandwidth of fibre supports all forms of small cells in their broadest definition, especially outdoor DAS radios and remote radio heads in addition to independent small cells. Their very high bandwidth is futureproof, and should meet any foreseen demand including 5G.

Ultimately we will see a mix of both, where regional differences and local preferences determine the split between the two.

If the cost of fibre deployment can be reduced, it would become more attractive.

Typical fibre commissioning procedure

When installing a new site, sometimes there may be ducts in place that can be reused, but often additional trenching is required to extend the route. Underground moles and other mechanical methods can expedite the process. Roadways or sidewalks may need to be closed (which may require advance notice) or work conducted during offpeak hours (at higher cost).

The picture below shows a sealed fibre interconnect point used for wireline broadband service. The cylindrical enclosure contains a rack of splicing trays used to connect up fibres buried below street level.

At the small cell site, incoming fibres are spliced onsite and attached to standard LC duplex connectors inside a weatherproof box. Separate fibres are then run from the distribution box to each remote radio, antenna or small cell. These are also spliced with LC connectors into the distribution box.

The site is tested and commissioned.

Sometimes pre-formed LC connectors are already attached to the shorter fibre cables connecting local equipment, avoiding the need to splice that onsite.

Splicing outside in the open environment is a demanding task – any small specks of dust can affect the quality and durability of the connection.

Wide variety of weatherproof fibre connectors

While the LC connector is an industry standard for fibre termination of indoor equipment – you’ll find this on most routers and hubs – there is as yet no global standard for an outdoor weatherproof format. HUBER+SUHNER strongly supports the need for a common standard for outdoor fiber connectivity and is promoting their Q-ODC as the preferred solution.

As with mobile phone chargers, basestation vendors seem to have adopted a variety of proprietary formats for fibre connectors used in harsh environments. Ericsson has branded theirs FullAXS while Nokia and Huawei don’t seem to have a specific branding.

HUBER+SUHNER have developed Q-ODC (Quick Outdoor Connector) providing “plug and play” connections for two separate fibres (i.e. uplink and downlink).

Using a pre-manufactured cable assembly with standard connectors saves time and avoids the need for specialist technician skills.

Separate vs shared fibres

Where there are two or more small cells at the same site, either belonging to different network operators or simply handling multiple sectors, it is possible to provide individual fibres which handle traffic separately for each radio and/or operator.

Alternatively, a single fibre pair could make use of WDM (Wave Division Multiplexing) to aggregate the traffic. Up to 18 wavelengths can be used with each endpoint getting the full duplex bandwidth. This is achieved using distribution modules which split and combine their assigned wavelength.

You could think of this in a similar way to RF splitter/combiners used when multiple basestations share the same antenna on a site.

Daisy Chaining

One topology involves connecting several units positioned along a roadway or street. There may be one or more small cells at each of the dropoff points.

A daisychain can be used where 18 fibres are connected to the first hub, which splits off three pairs. The remaining 12 fibres connect the second hub, which also splits off a further three pairs. The final hub consumes the remaining three sets.

Because these are pre-formed in the factory, quality is very high. This leads to long durability, resilience and lower long term maintenance issues.

Neutral host

Fibre backhaul is not the preserve of the mobile network operator directly. We have seen tower companies (such as Crown Castle), wholesale transmission companies, Cable TV (MSOs) and others provide fibre termination and backhaul as a managed service.

These support the variety of outdoor DAS, Remote Radio Head and independent Small Cell architectures.

Diverse Applications for Smart Cities

Shared sites on the streets may be used by other non-telco applications, such as Advertising, CCTV etc. In the future, street furniture may be pre-assembled in the factory with equipment for cellular, CCTV, Advertising and other applications already built in.

It would simply be a case of dropping this into place and connecting to power and backhaul to light it up. Bus shelters and advertising hoardings spring to mind as easy wins.

Summary

Fast, reliable deployment for all types of urban small cells is critical to their viability and long term success.

Fibre will be an important backhaul option in many cities, alongside wireless.

Pre-formed, standardised plug-and-play connectors ensure rapid deployment requiring less skilled technicians.

Deployment cost relates not just to technician time but indirect costs where street/lane/sidewalks have to be closed.

For more details of the HUBER+SUHNER Small Cell Solution, visit their website