Telefonica and Ericsson have conducted the latest live demonstration of LTE-Unlicensed, bringing the technology closer to commercial implementation even outside the US and Korea. And with another 5 GHz LTE technology, LTE-LAA (Licensed Assisted Access) due to be standardized in 3GPP Release 13 this year, there is intense focus on these new options for mobile operators.
Some of the debates, as the platforms near reality, concern use cases and the way these systems will be sold and managed, especially in the enterprise, which will be the first major opportunity. But others revolve around the same old issues – whether LTE-U and LTE-LAA really can be a good neighbor to other 5 GHz residents, notably WiFi. This still hotly disputed, with Broadcom the latest to weigh in against unlicensed LTE, against old enemy Qualcomm. One outcome of the rows is likely to be an enhanced role for ETSI, which is working on new coexistence rules and likely to take the lead in 5 GHz LTE, rather than regulators like the FCC.
The Telefonica demo indicates that eager European operators could implement LTE-U (already standardized) rather than waiting for LTE-LAA. That has previously not been an option because Europe and many other regions, unlike the US and Korea, insist on listen before talk (LBT) anti-interference mechanisms in 5 GHz, and these are not included in the LTE-U specifications.
However, Ericsson has introduced LBT mechanisms on top of the standard LTE-U features to comply with this requirement – though regulators would still need to approve them. Telefonica’s director of radio and core networks, Angel Blazquez, insisted that there was harmony in the band, saying in a statement: “This demonstration proves that multiple technologies will coexist for best use of all spectrum and to support all deployment scenarios, widening the LTE ecosystem using the aggregation with licensed spectrum to provide the best performance experience.”
Ericsson also announced other enhancements to its LTE-U network software – as well as LBT support, it claims improved performance, and full coexistence between LTE-U and LTE-LAA on the same LAA carrier, which could encourage operators to introduce LTE-U, with the reassurance of a smooth migration to the more advanced LAA in future. That would effectively address one of the main obstacles to LTE in 5 GHz outside the US – the timing, with operators having to wait at least another year for fully standardized and tested LAA gear, at a time when they are under pressure from WiFi-oriented providers such as cablecos, armed with a WiFi platform which is itself improving all the time in terms of capacity and efficiency.
The over-the-air test used an RBS 6402 indoor picocell from Ericsson which supports 10 frequency bands and up to 300Mbps of aggregated LTE spectrum. The unlicensed band was used in conjunction with licensed frequencies. LTE-U and LTE-LAA require an anchor LTE network in a licensed band, keeping the unlicensed portion under the control of the MNO (even though the 5 GHz small cells might be owned or deployed by a third party via an MVNO deal).
A third set of technologies – LTE-LWA (LTE WiFi Aggregation) and Qualcomm’s MuLTEfire – allow LTE to run in unlicensed spectrum without a licensed-band host, and so could potentially be highly disruptive by placing LTE technologies in the hands of non-spectrum owners, as an alternative to WiFi for certain use cases.
Eric Parsons, Ericsson’s head of mobile broadband 4G/5G radio access, said the demo was a “milestone in the development of LTE-U”, adding: “With global data traffic growing exponentially, spectrum has become one of the world’s most valuable resources. By enabling the use of unlicensed 5 GHz spectrum to boost peak data rates and capacity, LTE-U helps operators extract maximum value from their spectrum investments while bringing high quality experiences to mobile broadband users everywhere.”
Like the rest of the Ericsson/Telefonica releases, there was no specific mention of WiFi at all, but while the 3GPP community may wish to forget the fact, WiFi is, of course, the incumbent technology in 5 GHz, and has a huge and powerful ecosystem to fight against any dilution of its position. Some of that fight has centered on claims of interference, while others will be centered on commercial deployment norms.
On the interference side, Broadcom weighed in again earlier this month, claiming LTE-U in its current form would be a disaster for WiFi, while LAA (or any other co-channel implementation) would significantly reduce WiFi’s range. In a presentation to the FCC, the chip company said various tests and simulations had convinced it that WiFi connections will be degraded by neighboring LTE-U or LTE-LAA. The company’s director of product marketing and government affairs, Christopher Szymanski, discussed the results of these lab tests with advisers to the FCC chairman and commissioners.
Broadcom conducted the tests based on a draft test plan devised by the WiFi Alliance, which has taken the lead in creating a coexistence test regime for LTE-U and WiFi, to the consternation of some cellular players. The firm said it wanted to steer clear of purely technical debates, or of framing the discussion in terms of market competition (MNOs versus WiFi-first cablecos, for instance). Instead, it focused on end user experience and on “ensuring this public resource, the unlicensed spectrum, isn’t a race to the bottom” and to far worse interference levels than with WiFi alone, Szymanski told FierceWirelessTech recently. The goal, he said, is to create a “library type of environment [in 5 GHz] – quieter and more polite rather than a noisy bar room environment.”
According to Szymanski’s presentation to the FCC, the biggest risk to a good user experience will be on WiFi signal strengths below -62 dBm, the vast majority. Measurements in the field for enterprise and outdoor deployments have demonstrated that about 90% of WiFi links are below -62 dBm. Broadcom recommends a mandatory neighbor detection level of at least -82 dBm, consistent with WiFi preamble detect levels.
Meanwhile, Qualcomm continues to push the positives of multiple technologies living happily in 5 GHz. Its most recent set of tests was carried out with the Korean research institute ETRI, in an over-the-air demonstration of LTE-U coexistence with large numbers of Cisco WiFi access points and Samsung WiFi stations, all sharing the same 20 MHz channel in 5 GHz.
Qualcomm said that various tests were conducted. One was to verify that LTE-U’s CSAT (Carrier Sensing Adaptive Transmission) used a fair share of the resources – the result was that CSAT limited LTE-U utilization of the channel to one-eighth of the time when sharing with seven APs.
The partners also claim that levels of interference did not get worse when WiFi APs were replaced by LTE-U neighbors within a group of 15; and that total network throughput increased, the more of the 15 nodes were replaced with LTE-U. This, said Qualcomm’s report, was “thanks to LTE’s better spectral efficiency but also its ability to operate with a reuse of 1 – simultaneous transmission of the LTE-U eNB small cells and efficient interference management at the LTE-U UE”.
The pros and cons of these arguments will not be agreed easily, and purely technical cases are inevitably colored by commercial interests. However, there is widespread consensus that LAA will be a more robust solution – for MNOs as well as for WiFi protection – than LTE-U. Enhancements such as LBT support for LTE-U provide a near term stopgap, but many carriers will still be happy to wait for LAA. It is not just the new standard which justifies patience – it is also the ongoing work to ensure that LAA satisfies the regulatory rules of ETSI. Most regulators round the world base their regimes in 5 GHz and other unlicensed bands either on FCC or ETSI frameworks, but the former’s 5 GHz approach is, as Aruba engineer Peter Thornycroft put it in a recent blog post, “so thin that unmodified LTE in the 5 GHz band would be completely legal by the letter of existing FCC regulations”.
ETSI is far more prescriptive, and in this contentious area, its leadership will be more valuable to creating a working solution for LTE/WiFi coexistence – partly because, unlike the FCC, it will not be told that it is going beyond its remit if it comments on how individual technologies work in 5 GHz, and partly because its starting point is the most advanced LAA, not the compromised LTE-U. ETSI is in the midst of a series of hearings to establish explicit rules for all transmitters in 5 GHz, which will apply to any technologies (including LTE-U). If these are adopted by the US, LTE-U’s window will shrink and it will make sense for it to converge with LAA. And with the FCC largely leaving it to the industry to sort out its differences, ETSI’s role is being enhanced – it will be the chief influence over 3GPP work on LAA coexistence mechanisms, rather than the FCC, the traditional arbiter of unlicensed technologies; and its regulations will doubtless be adapted in future for other technologies and bands, as unlicensed, shared and flexible spectrum become the most important way to boost wireless capacity at affordable cost.
While standards and regulations still have a way to go, there are other obstacles in the path of mass deployment of LTE in 5 GHz. One is that, for most stakeholders, the strongest business case for LTE-U and LTE-LAA rests on the challenge of improving in-building wireless coverage and capacity, an urgent necessity for many enterprises and public venues as they increasingly dump landlines and go wireless-first. High frequency 5 GHz spectrum is well suited to high capacity and short range, and so could improve the economics of boosting in-building wireless via small cells. Combining the low cost and high capacity of 5 GHz with the mobility and wide area roaming of a macro anchor network is a highly logical architecture for MNOs, whether the small cells are deployed directly or by a partner, such as an enterprise integrator, a cableco or an MVNO (which could manage the 5 GHz cells and pay the MNO for rights to the anchor network).
Some MNOs will hope to run the whole enterprise deployment, and associated revenues, themselves, but others will welcome partners to target business venues, especially smaller ones, if they do not have the channels and integration partners to support large numbers of contracts and to work with IT departments.
But is this approach as logical for the enterprises? Arguably, many of their needs could be met by enhancements to WiFi, such as WiFi Calling for decent quality voice (when the unlicensed network can be properly optimized and managed, as inside an enterprise); or Passpoint for seamless hand-off to the mobile network. However, as recent research for the Small Cell Forum by enterprise research firm Nemertes demonstrated, the vast majority of organizations see the benefit of having high quality cellular coverage alongside WiFi – indeed, in a survey of 500 enterprises round the world, those who considered themselves to have the best WLANs were also most interested in small cells.
This is a hopeful indicator for LTE in 5 GHz, provided it can indeed live happily alongside those WLANs. But because it is inherently based on small cells, it will also have to address some of the issues which face small cells in licensed bands, notably the channels to market, and the support for multi-operator and neutral host models. These are important reasons for WiFi’s success in the business environment – it can be deployed and managed by any qualified entity, not just an operator, and so can be integrated with the corporate IT systems in areas like access control; it has a very open ecosystem with many choices of equipment with different levels of sophistication and cost; and it has evolved to support multiple service providers with minimum complexity for the enterprise or end user.
These issues are high on the agenda of the Small Cell Forum and many of its members in 2016 and will be essential to the enterprise success of LTE-U and LTE-LAA. These 4G small cells will have to be as easy to deploy – by all kinds of entities from IT departments to integrators – as WiFi, and they will have to support all users and visitors, regardless of their MNO home network. And MNOs, after years of chasing enterprise markets, are still poorly equipped, in most cases, to sell more than bundles of minutes and megabytes. They generally lack sales and support teams which understand IT departments, integration with LANs and WLANs, and long sales cycles.
Meanwhile, WiFi vendors are questioning whether their own sales teams and distributors will be eager to add a new set of products – with new expertise required – to their portfolios. Thornycroft wrote on the IDG Contributors’ Network: “Operators and small cell vendors will explore relationships with enterprise networking vendors and their channel partners: they know how to sell sophisticated networking equipment to enterprises. But networking vendors already have WiFi offerings as established, core products in their portfolios. It will be hard to make room for a new set of products that require considerable expertise to plan, install and support, and that have at least some competitive overlap.”
As with so many technologies before, these practical considerations will prove more important than the technical debates to the level of adoption, once deployment moves beyond a few flag-waving early adopters (and equivalent naysayers). When the arguments shift from religion to practical cost and benefit, unlicensed LTE will have to make a strong case to find its place in the established enterprise connectivity market.
The answer must lie in greater support for flexible, on-demand platforms which enable a new generation of managed service models. There is currently a rise in providers and tools for running enterprise and hotspot WiFi from the cloud, which will allow organizations to offload the task of running WLANs, and to pay just for the capacity they require at any given time. These need to spread quickly to embrace cellular small cells, and combinations of WiFi, small cells, LTE in 5 GHz and even DAS. Then, rather than forcing enterprises to make a stark choice, they can get the best of all worlds, according to their requirements, with a ‘network as a service’ platform that can mix and match the different options according to need. Tools to do this, such as those from Interdigital spin-out XCellAir, are evolving quickly, as are even more flexible bandwidth on-demand and capacity trading platforms. For LTE-LAA, it will be essential that MNOs cast aside their competitive qualms and accept this new market structure, as their best chance to get inside the enterprise IT market.