Telephone briefings and conference presentations are very useful learning opportunities, but nothing quite beats a site visit where the practical issues can be explained and discussed. I walked around several city centre areas of London with Andy Sutton, Principal Network Architect for EE. He showed me their current physical installations, explained how they will evolve and pointed out enormous range of potential sites for future urban small cells. In this first of two articles, we look at the macro, micro and small cell sites that will make up the dense urban HetNet of the future.
Three stage evolution strategy
Andy, a popular speaker in the conference circuit, is nothing if not consistent. He's been saying for some time that EE would make full use of their existing assets (spectrum and sites) before densifying with an additional layer of small cells. He outlined a three stage evolution plan:
a) Expanding existing macrocell sites on city centre rooftops with additional sectors and full complement of 2G, 3G and 4G technologies. This includes the 2600 MHz FDD LTE band that is now supported by the latest smartphones, and may expand to 4, 5 or sometimes even 6 sectors as macro sites evolve.
b) Expanding existing street level microcells, again with the full complement of 2G, 3G and 4G. These can often reuse the same small antenna already in place and may be single sector, sometimes two or even three.
c) Installing a new underlay of urban small cells, which would be 4G only and capable of Carrier Aggregation.
Andy was keen to point out that in central urban areas, there are plenty of rooftop macrocells. These so-called "super macros" have a lot of capacity but are usually deliberately operating at reduced RF power to reduce interference with adjacent cells. Many are shared with 3 UK; many sites are also shared with other UK operators. He showed me one on the rooftop of the QE Conference Centre opposite Big Ben and the Houses of Parliament that hosts all four operators, suggesting this was probably the busiest and most complex site in the capital.
To be honest, some of these rooftop sites are pretty ugly with an assortment of antenna, microwave links and supporting metalwork. In many cases, antenna can be shared but these more complex sites may need multiple antennas to avoid excessive combining losses or PIM (Passive Inter-modulation) issues. One rooftop installation had a long run of RF feeder cable down into the building. This all adds cost because of signal attenuation, requiring more powerful RF to compensate.
Looking around Trafalgar Square and Leicester Square, it was difficult to spot the macrocells from ground level. Walk a street further back and they became much more visible. This is often due to local planning laws, where local council views have to be taken into account – nobody wants to see these ugly monstrosities.
To circumvent that, antennas have been designed to merge into the architecture. Opposite Downing Street, Andy pointed out what looked to me like a flagpole (see photo below). Elsewhere, another grey non-descript concrete building had a couple of matching grey non-descript panel antennas that easily blended into the cityscape.
Moving down to street level
Figure above - No need for site rental for this standalone street microcell
We walked along a city street to a microcell installation which has been there for almost 20 years, first for GSM only and later upgraded with 3G. They'll shortly be adding LTE too, which involves plugging some cards into the rack. There were three street cabinets, one for 3G, one for 2G/4G and a third for power and backhaul. The antenna was mounted on a dedicated street pole, about 8m high, that didn't look out of place amongst the other street lights. I thought the street cabinets were fairly bulky. The street itself had been redesigned since the site was first installed, with a parking bay being carved out of the pavement. Cities constantly evolve and develop, meaning that what works one year may not be the best choice at a future time - planners have to constantly monitor and re-evaluate – but this seemed like a very useful site.
Another microcell site was outside St James Park underground station, with the street cabinets on the pavement driving a small lamppost mounted antenna.
EE share many but not all of their cellsites with 3 UK. After consolidation, some 18,000 sites will be shared with a further 3,000 EE only sites giving them a competitive advantage.
What I didn't realise was that as an approved telecommunications operator, EE can install their own equipment in the street (including street poles, cabinets etc.) without having to pay any site rental. They may need planning consent from the local council. If they used existing street lights, then they'd probably have to pay some rental to the council. If they used an advertising hoarding or a street sign, bus shelter etc., then another organisation may be due a fee.
The small size of antenna makes them unobtrusive, about the same size as an alarm box. The tell-take sign are the two bulky RF cables feeding the box. Just some 30 metres down the street was another site with the antenna mounted on the outside wall of a pub, serving both the street outside and the buildings nearby. It wasn't really intended to serve customers inside the pub itself, although some of the signal might bounce back from the stone walled building opposite and anyway; the number of sites in the area ensured good in-building coverage. The microcell was installed inside the building. These antennas are cross polarised, so can provide the MIMO benefits regardless of their orientation. They support 2G, 3G and 4G technologies. Some may need to be upgraded to cope with the 2.6GHz band, but otherwise 4G can be added by base station cards only.
[The antenna is white rectangular to the right and above the red alarm bell box, with two RF coax cables running down and inside the building]
Depending on the construction of the buildings, these signals are transmitted at a height suitable for penetrating into nearby buildings. Some of the older, heavy stone architecture can be as difficult to penetrate as the latest LEED compliant glass showcases. Planners would need to take account of that when predicting coverage deeper inside buildings.
The third step of urban small cells
Once the capacity expansion options in these existing sites have been exhausted, Andy would expect a further layer of urban small cells to be rolled out. He thinks these would be LTE only, dual-carrier and capable of Carrier Aggregation. EE are clearly trialling and testing a range of products so they will be well placed when the time is right.
Proof of the pudding
Although very unscientific, I couldn't resist comparing performance between EE and 3 UK. Andy's speedtest won hands down in two locations, first with 30Mbps compared to my 10Mbps and later 20Mbps compared to just 1.7Mbps. To be fair, EE benefits from their 20MHz LTE bandwidth vs 10MHz, but even so this is very impressive.
3 UK's LTE speeds are impressive (left), but EE seems to go that much faster (right, results emailed from Andy's phone after I witnessed the test) .
In both networks, the LTE uplink speeds were very fast and sometimes beat the downlink performance. It's much faster than most wireline ADSL broadband connections. And all this is before carrier aggregation with 2.6GHz band is added, which should double the performance for compatible devices.
Where would these new 4G urban small cells be positioned?
Perhaps I've been reading too many Jason Bourne books lately, where the hero constantly assesses the sight lines for potential assassins every time he enters a room. Andy seems to do the same thing for mobile coverage opportunities, constantly spotting potential new opportunities for small cell deployments. These included (in no particular order):
- Street lights, such as the new park lights in the centre of busy Leicester Square. Antennas could easily have been integrated into them and even made into a feature.
- Signage. EE already build antennas into the signage above some of their storefronts. Many other stores have signs projecting out into the street which could be used. They can also be hidden behind canvas or plastic signage without significant impact on the RF signal.
- Advertising hoardings: There was a huge one above the dual carriageway on Marylebone Road which could easily serve the slow moving traffic driving past.
I asked Andy if he was concerned about competitors snapping up potential small cell sites in these dense urban areas, in effect a landgrab that could lock them out of the best locations. He's not concerned, explaining that there are more than enough potential opportunities for all four operators. Beam-forming will be an important attribute for these small cells because it will allow greater flexibility of choice of sites, adapting the coverage footprint to match the location chosen without interfering so much with nearby macro and microcells.
While this approach to outdoor deployment is clearly where most of their investment is going, Andy confirmed that EE also invest in in-building systems where appropriate. These include both DAS systems for larger buildings, shared with other operators, and their own dedicated residential and enterprise small cells as required.
In part 2, we share a discussion about small cell backhaul. EE have some surprising views on fibre/wired vs wireless as well as how to achieve small cell synchronisation.