Most mobile operators agree that they will need to deploy outdoor small cells at some point. Generally they are needed to densify networks to meet demand in areas where macro cells either cannot supply enough capacity or are needed to infill coverage not-spots. Other applications include rural deployments.
In urban areas these deployments at street level are also likely to require a variety of other small cells to provide wireless backhaul solutions where it is physically difficult or not cost-effective to run fibre connections.
However, aside from trials, such deployments are still in their infancy. ‘We are seeing operators start to deploy outdoor small cells,’ says Alan Law, Chair of the Small Cells Forum. ‘There have been some good recent developments from the likes of AT&T in the US. The latest ABI Research report forecasts revenue growth of 33% year-on-year.’
Mike Schabel, VP Small Cells Business at Alcatel-Lucent, says deployment depends on the region. ‘What I’m seeing is that operators who made an early and aggressive move to LTE now have the capacity to justify deploying small cells in both urban and rural areas.’
Law acknowledges that many other operators are still concentrating investment in their macro networks, but he warns: ‘They need to be ready to deploy small cells in large numbers when the time comes, so they need a very good grasp of what is required in terms of site acquisition, installation, commissioning, management and investment costs.’
Small cell architectures
What kinds of small cell architectures will prove to be most popular still remains to be seen. David Chambers, founder and senior analyst at ThinkSmallCell and a Cambridge Wireless Small Cells Special Interest Group (SIG) champion, says: ‘I think operators generally want to use 4G LTE small cells rather than 3G in the urban space, but with outdoor small cells you have to integrate and co-ordinate them a lot more seamlessly with the macro cells than you do with indoor small cells.’
Chambers says that it is widely accepted that a lot more radio transmitters will be needed for 4G small cells. ‘You can have totally standalone 4G cells, or something more like a remote radio head architecture, or even a DAS (distributed antenna system) with dark fibre to the small cell site.’
Chambers points out that the advantage of the small cell approach is that it places less technical stringency on the backhaul link, while other solutions may well require fibre or even dark fibre to each small cell site. ‘So, small cells give you a lot more flexibility as to where and how many small cells you deploy.’
However, he notes that each approach still faces a common set of problems in terms of finding and securing sites, finding a power supply and providing a suitable backhaul solution. Identifying sites at street level is far more of a headache than finding rooftop locations for macro cells given the greater number of third parties involved.
Law says: ‘Operators are appreciating the need to work with people that have a significant portfolio of infrastructure assets for mounting small cells, including councils, bus operators and big advertising companies such as JC Decaux.
‘Operators are looking to have access to a spread of different street furniture assets, but negotiating with individual landlords would be horrendous,’ notes Law. ‘However, councils are starting to appreciate that a better connected city is a more efficient and successful city, generating more GDP and consuming less energy.’
Alcatel-Lucent has been really proactive in this field by putting together its Metro Cell Express Site Certification Program. Schabel says: ‘Our strategy was quite simple. As an industry we have industrialised macro cell installation on rooftops. Installing metro small cells is the same but new, in that it requires different partners and it mostly pertains to public spaces rather than rooftops where people don’t usually go.
‘We said to these new partners; we’ll train you, but we need to understand the assets you have. You then pull together people with site or backhaul assets and sit with the operator and design a network – and give them the option to negotiate optimum pricing,’ says Schabel, who adds: ‘If you want to be a leader in this new market you have to help create programmes that benefit the whole market.’
One area being watched with some anxiety is small cell interoperability. At a Cambridge Wireless Small Cell SIG event in London in October 2014, Nick Johnson, CTO at small cell vendor ip.access, expressed concern at the ambiguity of some aspects of the S1, and in particular the X.2 interface specifications (which connect small cells to the macro network).
He argued that this was leading too many vendors to create proprietary extensions, meaning they could not interoperate within a multi-vendor HetNet environment. This might lead operators to opt for single vendor supply chains creating vendor lock-in.
However, Schabel says: ‘I think the standards community did a great job really thinking through how to make HetNets work. There was a heck of a lot of innovation involved in leveraging the standard from theoretical to real deployment to make it work operationally.
Law agrees: ‘Multi-vendor interoperability is in the interest of every operator. We need a highly responsive ecosystem with flexibility and product choice, so we can have the right product for the right environment.’
He adds that the Small Cell Forum and the standards bodies are trying to identify any gaps in the standards. The SCF holds ‘Plug Fests’ where vendors can test innovations and the interoperability of their equipment with other vendors’ products.
‘Our job is to try to accelerate the introduction of small cells into the market,’ asserts Law. ‘We understand the changes that may or may not be required, come up with solutions and then act as a liaison to bring these solutions to the standards bodies such as 3GPP.
Many rural areas have long been notorious for poor cellular voice coverage and the same pattern has repeated itself for access to broadband services. Law says the Small Cell Forum will be unveiling its guidance on small cells for rural coverage at Mobile World Congress in March.
Various vendors have been arguing for some time that small cells can be a cost-effective way of providing rural coverage. However, in December 2014, UK operator EE surprised the market by announcing a deal with the little-known Parallel Wireless to bring connectivity to villages.
The all-in-one solution meshes several small cells together and connects them back to an EE
macro cell with one of the small cells acting as an integrated wireless backhaul node.
‘They are talking about covering 1,500 sites within three years, which will fill in a lot of the rural not-spots,’ says Chambers. ‘You don’t just get basic 2G voice services, but quite respectable data rates too. Because it is such a big deal it means it must make sense commercially for EE.’
2015 and beyond
Two other key areas for exploration going forward are the impact of network functions virtualisation (NFV) technology and cloud or centralised RAN (C-RAN) on small cells and the place Wi-Fi small cells have to play in mobile networks.
But what seems clear is that outdoor small cells and wireless backhaul solutions are needed now, so operators are able to cater to the latent demand that is building up.
Box: Small cells for wireless backhaul
Operators will always use fibre connections where possible, but a number of mostly independent vendors have come up with ingenious solutions for wireless backhaul alternatives.
Products are available in everything from sub-6GHz (including unlicensed spectrum), point-to-point microwave (6-38GHz), point-to-multipoint microwave (24-32GHz); Q-band (40.5-43.5GHz), V-band (60GHz) millimetre wave; and E-band (70-80GHz) millimetre wave.
At present sub-6GHz and V-band solutions are attracting the most attention, but the others may well find their place. ‘It is difficult to consolidate in the backhaul space because operators have access to different spectrum that can be used in one market but not in another,’ says Law.
‘I look at it this way: operators are in a fortunate position that there is this spread of backhaul choice, so they are able to use different wireless and fixed asset solutions to solve backhaul issues.’
Many operators favour the ‘toolkit’ approach of having a variety of backhaul solutions available, but as Chambers says: ‘At some point the operator has to make the hard choice of what is in that toolkit and it can’t be too large. They’ve got to have volume, so that means maybe three technologies; that way the vendors can crank up the volume and pass on cost benefits.’