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Femtocells at tipping point: Don't want to become also-RANs

From the Macro, to the femto, to the metro, to the micro...

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The femtocell industry gathered for its fourth annual world summit this week, and it was clear that significant progress had been made since the last London-based gathering. In June 2010, the tiny base stations had achieved wide acceptance as carrier controlled devices to improve indoor coverage and support offload.

However, actual wide scale deployments remained limited; the talk of new applications and services enabled by femtos had not really borne commercial fruit, and the idea of stretching femto concepts into other areas such as public access metrozones was just that, an idea.

One year on – following a Mobile World Congress in February whose dominant new theme was the ultra-small 3G or 4G cell – the "grown-up femtocell", or metrocell, was also the talk of the London conference, and traditional wireless infrastructure players including Texas Instruments were there with product plans to back up the words.

As they seek to prevent the outdoor RAN falling into the hands of femto specialists, those early movers – firms like Picochip and Ubiquisys – are starting to announce public access products too, bringing a new set of economics to the carrier network.

And in their established territory, the indoor femto is close to the tipping point that should make it a truly mass market product from 2012, while attention has refocused on apps again, as emphasized by Intel's maiden appearance at the show, with its notion of an "edge cloud" of tiny base stations containing significant apps horse-power.

The rise of the metrocell

The Femto Forum announced that femtocells now outnumber conventional 3G base stations, marking the acceptance that small cells have entered the mainstream as indoor devices.

According to research by Informa, there are now 2.3m 3G femtocells deployed worldwide, compared to 1.6 million 3G macrocells and microcells. Operator roll-outs were up by 60 per cent in the last quarter, the fastest growth rate seen to date, numbering 31 deployments. Commercial support is seen at eight of the top 10 global cellcos by revenue.

The research group forecasts that 48 million femtocell access points will be in use by 2014 as the technology expands into the enterprise and the public network. Another interesting result is that 60 per cent of operators surveyed responded that small cells would be more important than macrocells in LTE.

Dr Shahram Niri, director of global LTE/SAE strategy and solutions at NEC, believes the shrinking of cells is inevitable, and less of a culture shock to carriers than some suspect. Indeed, it is already underway with 3G because the only way to increase capacity has been to reuse spectrum.

"Even today, 3G cells are down to a few hundred meters or even a hundred meters in some cases, when it was supposed to be kilometers," he said. "That's because we're learned that of all the techniques we've come up with to increase capacity and the spectral efficiency, the biggest gains we're had was from reusing the frequency, which means we can reuse the same frequency everywhere, but that means smaller cells."

While some vendors and carriers are focusing on femtocells and picocells to infill macrocells to boost capacity, Niri believes that, especially where operators have high frequency spectrum such as 2.6GHz, the best route will be to do LTE with small cells only.

"We're telling customers to not to do macro any more," he said. The new architectures: Metrocells for the public access network have been a key R&D driver for the specialist players for the past year or more.

Picochip makes silicon pay

Picochip, the leading provider of femto silicon, set the ball rolling last fall when it unveiled its picoXcell PC333 system-on-chip, which supports 32 voice/data channels (or 64 in cascade mode) with range of over 2km and handover at 120km per hour.

This indicated the way that consumer grade economics could be applied to a product for the main RAN, but also the additional functionality that would be necessary, such as receive diversity (not always included in residential femtos, but essential to mitigate interference with larger user numbers), and smart signalling.

The metrocell, then, needs to be more robust and complex than its indoor cousin, and will inevitably be far more expensive than the $50 or less targeted for those devices – most carriers are mainly interested in the lower opex associated with features like commodity backhaul and simple installation, rather than in a huge capex reduction.

But it can benefit from the experience in the home market, claim the femto specialists, though there is debate about how far a common architecture is desirable across the different categories.

Picochip's platform is very consistent in supporting residential, enterprise and outdoor base stations with pin and code compatibility, and CTO Doug Pulley says the metrocells use so many of the elements of their residential cousins that they significantly reduce cost and support strong scalability.

"Some day, all base stations will be made like this," Pulley said. "Femto technology will soon be in every base station. With the PC333 we have extended the parameters of femtocell performance to levels that would traditionally have been considered as 'picocell' or even 'microcell'. This high performance coupled with zero-touch provisioning means carriers can routinely deploy femtocells as part of their wide area network roll-outs."

However, others are less interested in the common platform and think the most important crossover from the residential market lies in software or management techniques.

Ubiquisys, for instance, has chosen Texas Instruments' newly unveiled small cell SoCs for its public access product, while relying on Broadcom (via its acquisition of Percello) for its residential offerings.

Both chip providers have steered clear of spanning as wide a range as that of Picochip. TI has said in the past that it could not make the economics of the low-end femto chip work, and now confirms that it will not drill down into the home space but will extend its existing base station architecture for very small cells.

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