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Wi-Fi and Small cells dominate future capacity growth for mobile networks

Cell Tower AntennaFew new macrocell towers are being built these days. In some countries it's quite the opposite, with site sharing agreements driving consolidation and decommissioning of duplicate adjacent sites. Some are being added to satisfy pockets of poor coverage, especially in rural areas. There are a few regions of the world where further macrocell rollout continues makes good business sense. A further complication is regulatory restrictions on total cellsite RF emission levels, which in at least one country renders the majority of cellsites unsuitable for 4G rollout.

Over the last year or so, we've seen heavy investment to upgrade and expand capacity at selected existing sites where traffic levels require it. Quite a lot of the oldest macrocell basestation kit has been swapped for the latest Single RAN equipment. For example, Huawei's standard radio modules are now completely remotely software configurable between 2G, 3G, FDD-LTE and TD-LTE. Andy Sutton told us how UK operator EE has been splitting sectors in these upgraded cellsites, with 6 sectors being common in the most demanding locations.

But there are limits on how far a strategy limited to macrocell sites can go. From a technical viewpoint, not all of the frequencies are as useful as others. In-building penetration using 2.6GHz is far less effective than at (say) 800MHz. The size and number of antenna which can be fitted to each cellsite may be restricted by planning or landlord consent, limiting the use of MIMO techniques that require multiple antenna per sector.

Regulatory constraints on macrocell site growth

Further restrictions apply on a national or state-wide basis.

This Indian state High Court decision ordered the removal of all cell towers from the vicinity of schools, colleges, hospitals and playgrounds because of radiation "hazardous to life." This could be counter productive because it results in mobile phone users being connected through more distant basestations, requiring higher RF power to be radiated from their handsets.

Some countries, specifically Belgium, France, Italy, Lithuania and Poland, place very tight restrictions on the total level of RF radiation emitted from any cellsite. The international level of EMF radiation agreed by the INCIRP is 41V/m. These countries specify 5 to 7V/m, which makes 64% of existing antenna sites in Italy unsuitable for 4G rollout, according to this GSMA study report.

Meanwhile, the public attitude is much more accepting towards Wi-Fi service. The very low RF power levels – typically even less than used by domestic cordless phones - are visibly demonstrated by the limited range especially through (brick) walls.

Growing investment in Wi-Fi

ABI research recently forecast that 22% of all new cellular data capacity installed during 2014 will come through Wi-Fi offload. 

My interpretation of the forecast is that this offload may not all require additional Wi-Fi hotspots, and some will come from more proactive use of existing Wi-Fi assets.

Operators have had a tremendous return from the relatively small investment of mandating Wi-Fi in the smartphones they subsidise and support. More than half of all smartphone data is already sent using Wi-Fi, although as many as a third of users never switch this feature on. Several vendors promote solutions which offer a "quick win" by proactively and remotely turning on Wi-Fi for use at home or in the office. For example, Devicescape recently signed a deal with Virgin Media that gives Virgin customers easy access to over 20 million hotspots in their curated database.

ABI's latest report indicates 4.2 million Carrier Wi-Fi hotspots are now in use worldwide, quoting China Mobile's 400,000 being overtaken by Oi Brazil's 500,000. It's clear that several operators now have public Wi-Fi presence scaled into 100Ks of sites, typically at least an order of magnitude more than the number of cellular sites. This total is less than the number of cellular cellsites or femtocells deployed today. However, these figures exclude residential Wi-Fi access points, which are sometimes shared through schemes such as FON. China Mobile's 2013 Annual Report states 4.29 million Wi-Fi access points, somewhat at odds with the figure above, presumably because of differing definitions and scope.

A concern of this "blind handoff" approach is that performance, service quality and battery life might suffer. A few solutions are already available which actively monitor the QoS when connected via Wi-Fi and automatically revert back to cellular where appropriate. This needs to be done intelligently, so that streaming audio and similar services aren't disrupted. End user preferences also need to be taken into account to allow the more technical users to exert control.

A larger offload opportunity through Small Cells with integrated Wi-Fi in the longer term

Perhaps a surprising aspect of the ABI forecast is that by 2018, a further 21 percent will come from small cells with integrated Wi-Fi. This is in addition to, and exceeds, the 20% predicted from Wi-Fi only hotspots.

Caroline Gabriel, Research Director, Maravedis-Rethink, speaking at a recent conference predicted 16% of traffic being offloaded to Wi-Fi during 2014. Looking ahead to 2018, the additional capacity contributed by Wi-Fi would drop to 9%, with public access Small Cells growing to 24%.

Conclusion

What this tells us is that the industry is on the cusp of making a major transition from the traditional macrocell architecture to one that encompasses both Wi-Fi and Small Cells. This will be most visible in the dense urban areas where capacity demand is strongest and existing cellsites are close to maximum throughput.

Significant financial investment will continue in the installed base of macrocells, with LTE-Advanced. But additional capacity will primarily come from spectral reuse in all its forms – Small Cells, Wi-Fi, DAS, Remote Radio Heads and Cloud RAN.

We can expect to find many more antennas installed in the coming years. Some will be highly visible on those large cell towers, but the vast majority will be hidden inside small, discrete Small Cells and other types of access point.

As a result, the surprising and somewhat counter intuitive result will be lower RF emission levels and higher throughput per user because we will all be much closer to the access point/basestation being used.

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