This week's Small Cell Global Congress in Berlin attracted some 150 delegates, and is a smaller event than the similarly titled Small Cell World Summit in London. The major focus was on metrocells, but there were contrasting views on the urgency of the need for adoption. We also heard case studies about residential femtocells, 2G off-grid rural small cells in Indonesia and new commercial models for wholesale metrocell hosting. Backhaul for the last mile (or few hundred metres) to connect public access metrocells was also a hot topic for debate. There were lots of questions asked, many viewpoints presented, and several areas where there wasn't a clear consensus answer.

A contrast in urgency

Vodafone have been champions of femtocells and small cells for many years. Alan Law, recently appointed European Vice-Chairman of the Small Cell Forum, enthused not only about their recent Femtoplug – a compact residential femtocell embedded into a mains power plug, which was recently launched in the Netherlands and soon to be available in other countries worldwide – but about their extensive testing of 3G metrocells.

3 UK, positioned as the data-centric UK network operator, and who carry some 40% of UK total mobile data traffic, have also been trialling outdoor small cells. Since their existing RAN equipment supplier can't offer them any product today, they've run a trial with a competitor's small cell and found they work rather well. Despite having access to 4G/LTE 1800 spectrum and announcing a new vendor (Samsung) for their LTE network, they still see the need to expand 3G data capacity significantly and are looking at small cells as an essential component of their solution.

Deutche Telekom (who own T-Mobile) on the other hand, suggested that the macrocell network wouldn't run out of capacity until 2020. While agreeing that small cells were essential in the long term, there didn't seem to be the same sense of urgency as with other operators. They've done a lot of cost modelling with an example showing that 100% capacity gain could be achieved for 25% of the cost of a macrocell. One specific case showed 200% gain for the same 25% cost.

A common theme was that the location of each small cell is critical. This requires both analysis tools which determine the ideal position to within a few metres, and the practical deployment as close to that location as possible – which is not always feasible. Although the location and size of capacity hotspots might change over time, several operators in the panel session were confident that they knew where their traffic hotspots were and that they didn't expect every one to be 100% optimal – they would measure the success of a cluster rather than each individual one.

Richard Swinford of Arthur D Little, told me that European operators have several major CAPEX programs in progress at the moment. Concerns about a lack of network capacity last year have changed – operators think that the extra spectrum of LTE should allow them to cope with forecast demand for the next 2-3 years, but (large scale) small cell deployments will be essential by that time to serve forecast demand.

Outsourcing the solution

We heard the three common difficulties for deployment of metrocells are site acquisition, backhaul and power. Virgin Media offered to resolve these through their small cell hosting service, where they would provide fibre connections to a hub and install an operator's small cells and wireless "last mile". Since the company already provides backhaul to UK network operators, it seems a logical extension. COLT, another UK fixed network operator, was also touting a similar service but I understand could be even more of a managed service where they would buy rather than just host the small cell.

Remote Rural Areas

For those of us already used to good 3G or 4G mobile data, Indosat reminded us of the large numbers of people who have never had any access to basic voice telephony. They explained their case study of bringing 2G GSM service to remote outposts of Indonesia, which required a cost saving of 80% over traditional methods. A standard 2 transceiver GSM cellsite consuming less than 150 Watts, powered by solar panels and linked through satellite backhaul has been developed which can be quickly and cheaply be deployed. It only needs at most 2 site visit per year for maintenance (which can each cost 3,000 to 5,000 dollars), but is otherwise self sustaining.

Optimisations include local routing of voice calls, which are switched within the cellsite and avoid the satellite backhaul and the use of highly compressed voice codec. Indosat believes that they will have first mover advantage with their solution, because it wouldn't be commercially viable for a second operator to deploy subsequently in these remote and sparsely populated areas – leaving them with 100% of the traffic.

Mosaic, a small network operator based in Wisconsin, USA, exaplined their success with residential femtocells to bring voice cellular coverage to remote parts of the countryside which already had wireline service. Unlike many other networks, they don't have capacity or data issues – it's down to straightforward cellular voice service.

Backhaul

There was a separate stream on small cell backhaul which I wasn't able to attend. From the plenary session, it was clear that operators are evaluating many options including Non-Line-of-Sight (I heard one vendor claim their solution could scale to 250Mbit/s), microwave, millimetre wave (60GHz, 70 to 80GHz) and an optical solution from SkyFiber was also on show. Typical range requirements are between 160 and 600metres.

This is becoming a crowded marketplace, with small numbers of deployments of some of these new types of products. Sprint explained a long "laundry list" of factors which need to be considered, all the way down to the impact of sway and twist of the transceiver mounted on a lamppost. They are at a mature stage of evaluation and are trialling many types of backhaul throughout their Kansas HQ campus, with a view to working with vendors to improve and perfect these products. This should put them in a good position to make good selection when they want to scale up their small cell deployments.

One delegate commented to me that the industry would benefit from making some clear choices in order to enable the massive cost savings achieved through high volume. I heard that one large multi-national European operator has issued an RFP with this in mind.

Inside-Out or Outside-In

With so much wireless traffic consumed indoors, the question arises whether outdoor metrocells can service this demand. Virgin Media had run a trial with LTE metrocells at 2.6GHz, and were pleasantly surprised at just how much indoor coverage was achieved. Qualcom proposed a contrary view, suggesting that indoor small cells could be used to provide coverage in the street areas outside. The advantage being the lower TCO of indoor cells – with less need for weatherproofing or wireless backhaul etc. I think it would be fair to say there was strong disagreement between these views between delegates. For me, it seemed more likely that both outdoor metrocells and indoor small cells will be needed.

Small Cells surpass Macrocells worldwide

Informa's Julian Bright presented their latest quarterly market update, confirming the day's earlier press release that the number of small cells now exceeded the number of macrocells worldwide. This is helped by Sprint's 1 million residential femtocells, while AT&T are thought to have a similar number, and several European operators are in the hundreds of thousands. They predict market growth to over 90 million small cells by 2016, based on linear growth, of which the vast majority (more than 90%) will be residential.

Major Vendors have the complete solution...but not quite yet

Huawei and Ericsson positioned themselves as being able to offer a complete HetNet solution, with a range of small and large cell products that work closely together to give optimal performance. However, it seems that their small cell products are not yet as mature as those of the dedicated small cell vendors. They appear to be squeezing a bit more mileage out of their macrocells and delay the small cell rollout.

For example, Huawei described how their macrocells could be expanded to provide wider service. They believe that DAS (Distributed Antenna System) isn't good enough for inbuilding anymore, and that a new solution are required. They propose connecting a nearby macrocell to power a cluster of radio nodes embedded inside neighbouring tower blocks. This required fiber transmission capacity to connect these nodes back to the basestation, which may not always be available.

Huawei later mentioned they are actively trialling a Carrier Wi-Fi solution in China where their cellsites incorporate a Wi-Fi hotspot, which identifies if the basestation being used by a customer is equipped with Wi-Fi. If so, it can remotely turn on the Wi-Fi in the customer's smartphone and hand over. Quality of service is monitored and the session returns to cellular if degraded.

I asked the panel session if "Wi-Fi offload" seems a strange term to use for carrier controlled/operated service, and there seemed general agreement. One comment was that there have been problems with the recent iPhone launch which drove a lot of Wi-Fi traffic over the cellular network – a decision made by the phone itself, and which consumed a lot of unexpected cellular data allowance. Network operators thought they could control the traffic better themselves.

The above is a subset of the wider range of material presented and discussed during the event. My apologies for omitting many valuable contributions and side conversations.

Some side snippets:

• Telecom Italia: "For small cells, the time is coming"
• NSN: "Average mobile data traffic of 1 Gbyte per user per day by 2020"
• EE: "See 3G small cells as cost effective solution to capacity needs in areas of high demand"
• Deutsche Telekom: "The 3 principle use cases for small cells are (1) Extending macro coverage (2) Improving data rates at the edge of the macro and (3) cost efficient capacity extension."
• Deutch Telekom: "Small cells can provide at least 100% capacity gain of a macrocell for 25% of the cost"