5G must succeed indoors where 4G failed, and neutral hosts will be key

Despite the hype about 5G, many MNOs are clear that LTE still has considerable headroom, and a mature ecosystem. For many applications, including those requiring wide area coverage and affordable gigabit data rates, they will continue to enhance their 4G networks, adding new spectrum and smaller cells to boost capacity. However, there is one area in which 4G – or rather, the way MNOs have deployed it – has failed, and that is in deep indoor coverage.

High quality indoor mobile signals remain elusive and in many industries, in-building coverage is scandalously low. This severely limits the extent to which enterprises can support basic applications like unbroken voice calls, let alone think about ultra-reliable IoT services or other 5G-class activities. That, in turn, has driven most indoor enterprise wireless traffic onto WiFi, which has some drawbacks for highly mobile or QoS-sensitive applications, but at least can be controlled and optimized by the organization for its own particular requirements.

If 5G is to succeed in the enterprise and IoT services which are its main commercial raison d’etre, it must be better deployed indoors by the MNOs, or alternatively, by enterprise specialists, private network operators and neutral hosts, which will have a more compelling commercial case for investing in enterprise networks (rather than bickering about who pays the bill – cited in a Rethink survey as a top three reason for poor progress on deploying enterprise small cells).

One example of the emerging breed of neutral host providers – which will support multi-operator small cell networks, often with edge compute integrated – comes from the UK, where tower operator Arqiva is working with independent fiber provider CityFibre.

The companies have agreed a new partnership to create wholesale, 5G-ready small cell infrastructure, combining sites and backhaul, for a London borough (Hammersmith & Fulham, London’s fifth most densely populated district). If this is successful, it could be a blueprint for other boroughs or cities.

“This pilot network is a massive step forward for mobile and fixed wireless connectivity in London,” said David Crawford, managing director of telecoms & M2M (machine-to-machine) at Arqiva. “We are showing that ubiquitous high speed connections using dark fiber and small cells are possible and we are delighted to be leading the way with our pilot in Hammersmith & Fulham.”

He pointed out that densification using street furniture and small cells is critical to the 5G model, both indoors and outdoors.

CityFibre is part of a wave of companies installing fibre to buildings and cities in the UK, in response to operator fears that OpenReach – the wholesale fiber arm of the BT Group – is too dominant to create healthy price competition, and too close to BT’s mobile arm EE (though regulator Ofcom has taken successive steps to separate them). CityFibre has certainly benefited from the appetite for new providers, forming an alliance with Vodafone under which the pair will co-invest in fiber for home connectivity and small cell backhaul, with the MNO acting as the anchor tenant.

Under this latest alliance, CityFibre will install a 15-kilometer high density fiber network, which will be able to support multiple operators, in the borough. The idea will be to support Cloud-RAN and small cell roll-outs by MNOs, though the neutral host aspect of the platform means it could support alternative operators too, especially when 5G small cells start to appear in shared spectrum. Any operator will be able to deploy small cells quickly on the ready-to-go infrastructure and backhaul.

Arqiva was awarded a concession contract with Hammersmith & Fulham in 2014, allowing it to use the borough’s street furniture to install communications equipment, which would then improve the district’s wireless facilities. The company has similar contracts in a further 13 of London’s 32 boroughs (Barnet, Brent, Camden, Haringey, Harrow, Hounslow, Islington, Kingston-Upon-Thames, Lambeth, Merton, Richmond upon Thames, Waltham Forest and Wandsworth).

Rob Hamlin, commercial director at CityFibre, adde: “5G networks will only work on fiber and a new modern infrastructure is needed at scale to support them. With our £2.5bn roll-out of full fiber infrastructure to 5m homes already underway, we are creating a 5G-ready network platform nationwide that will provide the best network at the best economics for MNOs.”

The model will need to be stretched further in future, to support the full requirements of enterprises indoors, and smart cities outdoors. It will be important for infrastructure providers to support non-MNO deployers, especially as some of these start to harness shared spectrum (like CBRS in the USA) or acquire their own (for instance, the German auto industry is lobbying the regulator to set aside some 5G airwaves for a neutral host network for the car makers).

And the neutral hosts will need to start considering the inclusion of active radio equipment along with the passive sites and the backhaul facilities. This would support a truly neutral host system in which many virtual service providers could access specific slices of bandwidth, either by static contracts or on-demand, to enable their particular enterprise sectors or applications.

Some towercos are considering this transition, and the initiative is likely to come from Crown Castle in the USA, the most advanced major neutral host to venture into small cells. Small cell siting now accounts for about one-quarter of its business, harnessing its string of recent investments in fiber as well as a new set of small cell sites, and it is working with edge compute specialists like to add edge capabilities to its platform. The company has agreed that to add multi-operator small cells would be a logical next step to adding more value to its infrastructure, and taking a larger share of the densification and enterprise mobile segments – though it does involve a towerco in some unfamiliar activities such as active network optimization.

The US cable operators are also showing high interest in the potential to attach small cells to their indoor and outdoor fiber networks, to support their own cellular networks in shared or licensed spectrum, and to build a neutral host platform for home or enterprise service providers – and for MNOs, in areas, such as indoor or remote industrial environments, where the mobile carriers find it hard to make a business case to deploy themselves.

CableLabs, the R&D arm of the US cable industry, has carried out extensive research in small cells, shared spectrum and cellular backhaul. Its distinguished wireless technologist, Joey Padden, recently wrote on a blog post that cablecos should start considering deployment of indoor small cells for homes and enterprises, to relieve congestion on outdoor networks, and place indoor data under the control of the cable operator and its gateway or controller.

“When selectively deployed alongside WiFi hotspots, indoor femtocells give the converged operator the chance to capture the majority of indoor traffic with an indoor radio, freeing the outdoor radio to better serve outdoor traffic,” wrote Padden.

He believes that some of CableLabs’ work on new small cell form factors will address some shortcomings in the market. “With the new technologies developed by CableLabs, for the first time, they can be done right,” he boasted. “Gone are the days of failed GPS lock, poor handover performance and interference issues … From a spectral and economic viewpoint, femtocells over DOCSIS are poised to be the most efficient deployment model for 4G evolution and 5G cellular densification.”

Interestingly, the CableLabs small cell designs have emerged from its participation in Facebook’s Telecom Infra Project (TIP), and particularly the vRAN Fronthaul project, which aims to establish open interfaces between centralized basebands and remote radio heads (see earlier item), in macro or small cell RANs. One aspect of that project is examining fronthaul and backhaul over ‘non-ideal’ (i.e. non-fiber) technologies, which could include some cable DOCSIS links.

Last month, Aricent, Benetel, Phluido and Tech Mahindra announced a virtualized LTE RAN reference solution “under the guidance of CableLabs”, which promised to address some vRAN-over-DOCSIS challenges.

The reference design primarily targets dense urban networks, which have commercial potential for non-MNOs to deploy, especially in shared spectrum such as the USA’s CBRS band. Just as public WiFi vendors like Ruckus prospered on the heavy investment by cablecos in non-MNO city infrastructure, so companies like Aricent will hope to do the same as the cable firms move towards LTE and 5G.

Aricent said: “A cable network with DOCSIS is susceptible to variations in delay and throughput in the data path. Enhancements to RAN Layer 1 and Layer 2 implementations from Phluido and Aricent allows cable operators to overcome common challenges with DOCSIS, such as latency, jitter, and limited capacity to make it an effective means for fronthaul transport.  In this way, cable operators can benefit from RAN virtualization and centralization, while reusing existing DOCSIS network infrastructure as transport.”

The solution is based on a general purpose processor (GPP) and running LTE. In the design, the lower part of LTE Layer 1 is hosted on a remote radio unit, while upper Layer 1 and Layers 2/3 are on the GPP-based central unit, with eCPRI or Ethernet fronthaul connections between the two. This conforms to 3GPP’s Option 7 functional split specification.

It combines Aricent’s LTE vRAN software framework, at LTE Layers 2 and 3, with  Phluido’s virtualized Layer 1 and Benetel’s RRU (which could also be 5G).

Alan Barbieri, Phluido’s CEO, said in a statement: “We strongly believe that virtualization, disaggregation, and open interfaces are finally disrupting the traditional approach to deploy radio networks, and the live reference design showcased at the TIP Summit demonstrates such an advanced approach in a very challenging environment, with fronthaul over DOCSIS networks”.

The small cell ecosystem has been more diverse and open than that of the macro RAN, with a group of start-ups – such as Parallel Wireless and IP.access – playing alongside the big vendors, and some DAS providers which have made small cell acquisitions (CommScope of Airvana, for example, and Corning of Spidercloud).

The latest entrant is Fujitsu, which has announced a four-user mini-base station with a single antenna panel, capable of delivering up to 10Gbps. This will not be commercial until 2021, but shows the drive to innovate more and more quickly in ultra-compact, highly efficient form factors as 5G becomes real (Vodafone announced a small cell embedded in a manhole cover this week, for instance).

This would be used in dense environments like stadiums, transport hubs and malls and Fujitsu says this is the most compact small cell available, able to allow simultaneous communications to four users with a single antenna panel, at 5G speeds, in the 28 GHz band. Conventional 5G systems require an antenna panel for each terminal when simultaneously transmitting to multiple terminals.

Fujitsu Laboratories has succeeded in suppressing the interference between these simultaneous signals by controlling, with high accuracy, the phase or angle of signals separately emitted from 128 antenna elements. The ability to shift the antennas horizontally or vertically also improves the coverage area, though the vendor envisages these tiny access points being deployed every 10-20 meters in a dense environment. The components fit on a single 13 square-centimeter circuit board.

Fujitsu Laboratories developed a phased array chip using a technology that can regulate the phase of a signal propagated from an antenna element with accuracy of one degree or less, and built into the panel one phased array chip per eight antenna elements. The company also uses circuitry that detects the differences in phase between phased array chips, which enables highly accurate phase control for any size antenna panel that has between 64 and 256 antenna elements.

As a result, by holding the difference in undesired emissions intruding between one radio wave communicating with a device and another radio wave with another device to 20dB or more, it makes it possible for a single antenna panel to carry out communications of 10Gbps or more.

Detecting the phase differences from the signals produced by each antenna element and controlling the phase with high accuracy to concentrate the signal in the desired direction, these technologies successfully led to compact equipment that transmits to four users simultaneously with just one antenna panel. The compact equipment propagates radio waves on two axes, including horizontal and vertical directions, enabling wide area communications with users, said Fujitsu.

The company is aiming for commercialization around 2021.


Indoor small cells will be the high growth RAN segment in the coming years:

Rethink’s most recent small cell forecasts indicate that 5G will drive acceleration of the roll-out of indoor enterprise cellular networks, whether these are actually 5G, or are mixed zones of 4G and 5G cells to densify a macro network and support 5G-class services. By 2025, we expect the installed base of indoor small cells to be about 5.7 million worldwide (excluding residential), more than twice the size of the outdoor base.

In a recent report, ABI Research analysts went a step further and predicted that RAN revenue growth between 2019 and 2023 will almost entirely come from indoor deployments, whether small cells or DAS (distributed antenna system). Today, indoor equipment accounts for 27% of total RAN sales, but this segment will grow at a CAGR of 15.5% over the next five years to reach 42% of the total in 2023, said research director Nick Marshall.

Verizon said recently that 62% of its wireless deployments in 2017 were small cells, “a figure that will only grow larger as we deploy 5G in 2018 and beyond … Small cells are needed to meet exploding consumer demand for data, drive innovation, create new jobs, and fuel new services and capabilities such as smart communities, connected cars, smart farming, and the IoT.”



ADVA signifies revival of interest in small cell backhaul:

As small cells come into their own at last, there should be a revival for companies providing backhaul for these dense networks. A decade ago, there was a mini-bubble around small cell backhaul, especially using wireless technologies in high frequency spectrum. Now, there is greater focus on getting fiber to as many cells as possible, to support 5G traffic levels, though in very dense zones, it is likely that a few master cells will be fiber-linked, with others connected using wireless mesh or an enhanced copper technology like

The wireline, optical and backhaul players are starting to revive their interest in this segment, as illustrated by ADVA’s claim to have developed the smallest small cell backhaul device in the industry. About the size of two or three cigarette packets, the

ADVA FSP 150-GO102Pro Series draws on the Ethernet expertise ADVA acquired with the purchase of Overture and MRV.

The product supports Layer 2 and Layer 3 services, highly precise time and frequency synchronization, plus automated testing and in-service monitoring to get close to a plug-and-play system. For outdoor use, it is ruggedized and hardened against temperature changes.

ADVA is also looking ahead to the future need for bandwidth slicing in dense networks. Ulrich Kohn, director of technical marketing, said: “Service providers with 5G are going to virtualize the complete network, with network slices with specific capabilities, characteristics and performance parameters for special customer groups. They are also going to want to virtualize the connectivity network and this is why we have implemented programmatic interfaces for SDN control to completely segment virtual connectivity slices.”