LTE in 5 GHz – too good a chance for small cells to miss

By Caroline Gabriel, Research Director, Rethink Technology Research

LTE in unlicensed spectrum – killer of the free spirit of WiFi, or enabler of new services and quality of experience in the 5 GHz band?

The question was probably the most hotly debated one at the recent Small Cells World Summit in London, though the viewpoints varied markedly if one wandered from that largely cellular-oriented conference to its co-located event, the Carrier WiFi World Summit. And anyone who feared unlicensed LTE fatigue might have set in by Friday, when the Small Cell Forum held a workshop on the topic, need not have worried – especially as Qualcomm announced its MuLTEfire implementation, which does not require an anchor network in licensed bands, that morning.

The implications of the emerging technology for the small cell ecosystem were clearly a deeply important issue for operators and vendors, as seen in the number of questions fired at the panel of experts assembled to discuss the issue at the workshop. This is understandable. Whether you are talking about using LTE in 5 GHz as a supplemental downlink for an anchor network in licensed spectrum (LTE-LAA); as a standalone technology in unlicensed bands (LTE-LWA or MuLTEfire); or a combination of the two (Alcatel-Lucent’s WiFi Boost, for instance), the technology is dependent on small cells.

The three main factors which create synergies between small cells and LTE-LAA are:

  • Small cells are designed to operate at the power levels mandated in the 5GHz band
  • Small cells have inherently short range, and so work well with the propagation characteristics of high frequency spectrum as well as reducing interference risk
  • There is ongoing work on cooperation and integration with WiFi access points in 5GHz, which will be a valuable contribution to ensuring that the band works well for everyone.

In addition, there is a strong argument that LTE-LAA will deliver the optimum benefits when small cells are deployed in the primary licensed band as well as the supplemental unlicensed spectrum, creating a harmonized pool of capacity with maximum quality of experience, which could greatly improve the LTE business case.

So, arguably for the first time, a key cellular standard is emerging which has to be driven by the small cell community, in order to become workable.

If operators are truly enthusiastic about LTE-LAA, that will be a catalyst to invest in small cells on both sides of the licensed/unlicensed divide, reducing the cost of deploying dense capacity. For some, that will save them having to venture too far into the Wild West of WiFi. For others, the key will be to integrate WiFi and cellular at any level from OSS/BSS to access point, to get the best of both, as outlined by panellist Mark Grayson of Cisco.

There are two big (and interrelated) clouds on this sunny horizon (for the cellular community at least). One is timing and the other is the device ecosystem, both areas in which WiFi has a clear advantage.

Of course, advocates of LTE-LAA try not to talk in terms of competition, and it is certainly possible to envisage a world where WiFi and LTE coexist harmoniously – in technical terms and in service providers’ business models, combining to enable better overall user experiences and range of applications. But for now, there are companies which make their money out of either cellular or WiFi, not both, and need their preferred technology to dominate. And there isn’t unlimited capacity in 5 GHz, LTE-LAA’s primary target band – some WiFi providers see it becoming congested within just three years. Panel expert Simon Saunders of RealWireless put a strong case for harmony, but acknowledged ruefully that its best hope might lie in the high capacity of licence-exempt 60 GHz spectrum.

That is where the timing factor comes in. With LTE-LAA due to be ratified in 3GPP Release 13, it will not be in standards-based equipment until 2016. In that timeframe, whatever LAA’s technical superiorities, WiFi will have caught up with many of them, and some operators will have invested so much in integrating carrier-class WiFi into their HetNets that LTE-LAA will have become an unnecessary distraction.

A few carriers will go pre-standard, but most want the most mainstream solution available in order to reduce cost and risk – which brings us to the second cloud, the device ecosystem. Lack of full-blown support from the device makers has killed more promising wireless technologies than it has enabled, as panel expert Monica Paolini of SenzaFili Consulting outlined. If that ecosystem is too worried by the timelags, it may prefer to stick with the certainties of WiFi (with its installed base of 176m access points, as Nick Johnson, CTO of ip.access, pointed out).

It will be important to convince key device makers, especially those outside the handset base (where cellular technologies have struggled far more than WiFi to make an impact). The case for LTE-U in smartphones may be clear, but growth for vendors and service providers will increasingly lie in ‘post-PC’ gadgets and the Internet of Things. This, then, is where the Small Cell Forum and its members have an important role to play. The Forum has a track record of bringing together different players from across an ecosystem and creating business cases which appeal to all of them. If it can successfully do that for LTE in unlicensed spectrum, it may prove one of the most significant catalysts so far for small cell adoption in general.