5G Faces Indoor Coverage Challenge

Article By : John Walko

Some 5G frequencies have completely different characteristics from 4G and 3G, making indoor coverage a particular challenge...

According to a widely cited statistic, some 80% of all mobile calls and data traffic is accessed indoors, either in homes or commercial buildings. This is likely to change as operators begin in earnest rolling out 5G networks, however.

This is in part because current generations of cellular have focused on simply maximizing the potential of voice and data services. With 5G we will see a significant shift, with many operators, and companies operating their own private networks, offering or using cellular networks for a very diverse range of applications and use cases.

Some of the earliest of these use cases will include the widely discussed Internet of things (IoT) and the industrial Internet of things (IIoT) serving end user sectors such as agriculture, healthcare, education and manufacturing, making the most of 5G’s ultra-low latency capabilities and deploying different chunks of the spectrum.

Most operators will need to significantly alter the core layer of their networks to meet these challenging demands for good indoor coverage in all the low, mid-range and millimeter wave (mmWave) frequencies.  Compounding the challenge is that many of the higher-frequency bands suffer from poor propagation and will struggle to work in indoor environments.

And yet operators cannot afford to ignore indoor customers — after all, as we noted, the majority of cellular traffic will continue to be used indoors. Ericsson’s latest Mobility Report suggests that for smartphones in just North America, average monthly use will likely increase from about 8.5 GB last year to nearer 45 GB per month by 2025.

Even if, as seems likely, some of this increased demand will be offloaded to Wi-Fi connections, and even though the latest iterations of Wi-Fi, such as WiFi-6 and 6E, are on the way, there will still be increased strain on the performance of 5G cellular.

Poorer propagation means more antennas

Operators will need to respond by significantly densifying their networks with more access points than were necessary for 3G and 4G. This will be a hugely expensive operation, and the returns are by no means guaranteed.

5G indoor coverage, notably where mmWave frequencies are involved, will require the highest number of antennas, with the exact configuration depending on the type of enterprise environment.

Currently, indoor coverage mostly relies mainly on distributed antenna systems (DAS) that were first deployed in large stadiums, shopping malls and airports, where vast numbers of subscribers used their handsets at the same time. They were needed since outdoor signals just could not reach to all parts of such facilities, and the cost of installing all these systems largely had to be borne by the operators.

A DAS is basically a network where a base station is connected by fiber to a group of antennas placed indoors or outdoors.

Several solutions also exist that rely on small cell technologies, though the industry has only just started on defining industry standards for what are essentially easily deployable compact antennas.

DAS and small cell solutions provide similar power output and coverage capabilities with a small form factor, but they work in different ways. In essence DAS networks share and receive signals with remote nodes simultaneously, while small cells typically operate independently of each other.

“This has become a significant and urgent issue for the whole sector. Enterprises seem to be willing to pay for Wi-Fi, but to date not at all readily for indoor cellular coverage. It’s a real stale-mate on the business side,” Caroline Gabriel, co-founder and research director of Rethink Research and a principal consultant at Analysis Mason told EE Times.

Business versus technology

“The operators are coming up with different business models so that they can monetize 5G indoors. That must include ways of sharing up-front costs with the owners of enterprises and buildings”.

“Some operators are of course more enterprise focused than others, but the industry as a whole will have to come up with solutions. The network providers just can’t pay for all the infrastructure inside office complexes, large venues or warehouses, as well, in addition to the huge costs incurred in buying all the necessary spectrum,” Gabriel added.

One of the major issues is that today’s DAS systems, operating on low-band spectrum that propagates well, just won’t cut it in the 5G world, especially when it comes to the mmWave bands. These just can’t penetrate glass, doors or go around corners so, as noted above, will likely need a host of antennas to achieve good indoor coverage.

We are now seeing the emergence of what are described as ‘5G-Ready’ digital distributed radio systems (DRS). These can overcome many of the disadvantages of traditional DAS systems. Most incorporate technologies such as massive MIMO, so allow indoor networks to be planned and deployed in parallel with outdoor 5G networks.

Ericsson’s indoor cell.

In a recent research note by Gabriel for Analysis Mason, she notes that such a holistic and optimized approach has some challenges. “Indoor cellular systems need to behave in different ways to those outdoors. They have different power limitations and backhaul requirements. They also often need to support more people and devices per square meter and they may need to integrate with other IT systems such as LANs or edge computing.

“Technologies have been evolving to meet these indoor needs, but each solution had its shortcomings in earlier network generations, and there was very limited alignment with outdoor networks.”

In any case “it’s much less of a technology issue than a commercial one, Gabriel suggests.

The key to achieving optimal cellular coverage indoors, according to many in the industry, is the importance of bringing together all interested parties,  the owners (and in greenfield projects the potential tenants), the small cell suppliers and the operators. Which is just as well since it is clear that indoor solutions will need to come in a variety of form factors that could be combined to achieve the optimal balance between cost, capacity and coverage for both users and the operators.

Not surprisingly, none of this has stopped the big RAN vendors from coming up with their own and thus proprietary solutions.

Ericsson has started testing its 5G small cells solution — dubbed the 5G Radio Dot — with several operators, so that they can re-use some of their existing indoor network infrastructure as they upgrade from 4G.

Building on its Radio Dot System architecture, the Swedish group suggests operators and owners of premises can easily upgrade and complement existing networks.

Nokia’s AirScale mmWave Radio, mounted in a stadium setting.

Nokia is promoting its Smart Node range of base stations for use in both enterprises and residential networks, and says the portfolio complements its 5G Small Cells line up such as the AirScale Micro Remote Radio Head and the AirScale Indoor Radio.

Using the Qualcomm 5G RAN platform for small cells, the Smart Node range is expected to be available from Q1 next year. The Finnish group claims the portfolio will enable indoor deployment for 5G “at a significantly lower price point and smaller form factor than other solutions.”

The modular design 5G Smart Node, incorporating Qualcomm’s FSM 100xx software defined small cell, will be deployable in a variety of ways, including on walls, ceilings and even table-tops, Nokia says.

Soon after Qualcomm identified the 5G indoor sector as a significant opportunity, it published a blog that lays out the significant challenges and potential solutions. In this it even argued that the propagation characteristic of 5G in mm Wave spectrum could actually be a benefit rather than a drawback.

The author suggested “the fact that mm Wave does not propagate well from the outside to inside is beneficial for deploying mm Wave indoors as well, since the same mm Wave spectrum can be reused indoors with limited coordination with the outdoor deployment.”

Samsung recently revealed its Link Cell mmWave cell for indoor use also uses Qualcomm’s 5G Ran platform and that Verizon will be the first operator to deploy it, within its 5G Ultra Wideband Network. The companies are targeting enterprises, manufacturing and warehousing facilities, corporate offices, shopping centres and public venues such as stadiums.

The first version of the Link Cell will support 28 GHz and be capable of supporting four 100 MHz bandwidth of frequencies. The compact box design will incorporate a radio, antenna and digital unit, and with less than 4 liters in volume, is said to be the one of the smallest thus far targeting this market.

Samsung is readying low and mid-band versions of its indoor portfolio. The Link Hub range will focus on venues with existing DAS set-ups, while the Link HubPro is designed as an active antenna system and incorporates a hub and indoor radios for mid-to-large enterprises and offer a wide range of spectrum options. Both are expected to begin commercial roll-out in the first quarter of next year.

Verizon has also been trialing and field testing 5G mm Wave in-building solutions from Corning which the operator says will be a very important step towards private 5G networks. The total system will combine a private core, and indoor cell site and a Mobile Edge Computing (MEC) platform within a facility. The whole set-up is expected to be available by early next year.

Corning is also involved in a long-term partnership with Qualcomm that combines the former’s small cell expertise with Qualcomm’s in 5G mm Wave technology. One project involves deploying Qualcomm’s 5G RAN platform in a 5G NSA (Non Stand Alone) mm Wave design specifically targeting enterprises’ and public venues’ indoor coverage needs. The aim is a solution that will be cost-effective, easily deployable and scalable.

The inside scoop

Separately, Verizon has also been working with Movandi and NXP Semiconductors on repeaters that will amplify mmWave coverage in public spaces and buildings as well as chipsets for a variety of customer equipment

Meanwhile SK Telecom has teamed with Deutsche Telekom to develop solutions for 5G in–building use. The project builds on an on-going development of a 5G/LTE dual-mode repeater from SKT that the German operator has been trialing for indoor coverage in several cities in Germany.

Huawei has a wide portfolio of DAS and DRS solutions ranging from top-end MIMO and metro and campus needs to what it calls Light Suite models targeting smaller premises. The range also includes LampSite Sharing, a multi-operator solution for locations such as shopping centres and campuses where users of several MNOs will be using the network.

There are of course other smaller and more focused companies in the sector including Boingo, Cobham Wireless, StrattoOpencell, iWireless Solutions and Zinwave.

“Our DAS systems, which we have been supplying for indoor cellular coverage for many years, has the significant advantage that it can work with all the network operators’ systems,” Derek Paton, president of international operations at Zinwave told EE Times.

“The motto is one box, all frequency options. So upgrading from the current 4G version is just an evolution for us with the architecture we deploy. And the latest architecture iteration will also be suitable for mm Wave and thus ideal for 5G.”

Zinwave is headquartered in Dallas, TX but has much of its R&D and assembly facilities in Cambridge, UK.

Zinwave’s Primary Hub provides the interface to the RF sources and converts RF signals to optical and connects via fiber to either additional Hubs or Remotes.

Paton stressed the company is constantly refreshing and refining its portfolio. “For instance we are well advanced with a system that would plug simply into a cloud infrastructure network.”

He also suggested that most of the small cell based options are fine for small buildings and areas, “but they just don scale well.”

On the business side of the equation Paton welcomes the timely and positive moves by owners of venues and large buildings to take some responsibility for the costs of ensuring good indoor coverage when it come to the next generation of cellular.

Network operators are alive to this and starting to offer novel solutions. T- Mobile, for instance, is promoting what it terms BYOC, for Bring Your Own Coverage, an initiative where the operator provides network coverage reviews, approvals and its signal source to the building or venue owners.

To date T-Mobile has been the most aggressive carrier with such a scheme –and can point to numerous commercial and residential premises, stadiums, campuses and malls  that it has supported—but other operators are known to be offering or working on similar schemes.

Perhaps inevitably, there are some regulatory issues involved here that are slowing progress. For instance, and specifically for 5G when deployed using mm Wave frequencies, as has been noted,   there are often numerous antennas needed. That means that in many cases, there will need to be a ‘neutral host’ design so that users will be able to share a building’s 5G network without the owner having to install antennae for each network provider.

But to date there are standards for such as neutral host model. Other technologies that could solve the problem, for instance a 3GPP standard Multi Operator Core Network, are no-where near ready to be deployed.

A detailed explanation of the issues involved were discussed in a white paper from the US-focused Alliance for Telecoms Industry Solutions (ATIS).

Let’s leave the final observation to Caroline Gabriel, who stresses “the indoor quality of experience must no longer take a back seat in the 5G era if enterprise requirements are to be satisfied.”

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