Wembley Stadium in London is one of the UK’s most prestigious (and challenging) venues for wireless service. EE sponsor the site and operate the DAS system shared by other operators. Andy Sutton and Kin Wan gave me a full tour of their facility, sharing not just the technical specifications but also the reasoning behind their choices.
A huge site
The stadium itself has 92,000 seats and is best known for football and other major sporting events. Teams from America’s NFL will be playing a few matches next month here too. But it also hosts concerts where tens of thousands of people will stand on the pitch (for which they remove the grass temporarily). The building has extensive indoor facilities, catering, meeting rooms, entertainment boxes and lots of behind the scenes admin and support areas.
Unlike some stadiums elsewhere, such as in the US where NFL games are often a full day’s entertainment, many events here are fairly short and can be over in a couple of hours.
Central equipment room
An older 2G/3G DAS system was replaced in February 2014 with an active DAS from Axell Wireless. This takes in raw RF from racks of macrocell basestations which it converts and combines onto optical fibre cables piped around the stadium. RF heads close to the antennas re-convert the signal back into RF form.
The machine room, buried deep inside the building, consists of several locked cages interconnected with large bundles of thick RF coax. One cage holds the DAS system, others are dedicated for each operator and host their respective basestations. The EE cage had a rack of eight shiny new Huawei 2G/4G three sector macrocells alongside their 3G Nokia Flexi kit.
The stadium power supply has its own UPS and generators. Extractor fans increase air circulation to deal with the heat generated from the basestations and attenuators.
Backhaul is supplied by two different fixed operators, each providing 2 x 1Gbps Carrier Ethernet service. A third backhaul supplier is to be connected up soon, expanding the 4Gbps significantly and adding a further layer of diversity/redundancy with 10Gbps capacity in the future plan. That’s a lot more than many other stadiums that I’ve heard are running on 1Gbps today.
At its simplest, the machine room took in a number of optical fibres for EE’s backhaul and outputs RF through separate bundles of optical fibres for distribution around the site. There was an awful lot of kit involved in translating the backhaul into RF signals and a heck of a lot of energy used.
Huge frequency spectrum assets available
EE benefits from considerable spectrum assets at 800MHz, 1800MHz, 2100MHz and 2600MHz. The 800Mhz band isn’t used at Wembley and probably never will be, because it’s more suitable for wider area/longer range than high capacity.
Currently active are
- - 2G GSM 1800MHz
- - 20MHz LTE FDD at 1800MHz
- - 4 x 5MHz 3G at 2100MHz
- - 20MHz LTE FDD at 2600MHz
Still to be deployed
- - 1 x 15MHz LTE FDD at 2600MHz
LTE MIMO is not yet fully deployed everywhere but will be ready for next season (early 2016). It’s already installed in the main bowl and using Carrier Aggregation can achieve peak speeds of 300Mbps. The additional 15MHz band will increase that to around 410Mbps. These headline rates are theoretical maximums, but can deliver as much as 150Mbps with a Cat 6 device such as the new iPhone 6S. In a packed stadium no one user is ever going to get that kind of throughput, but there’s up to 300Mbps to go around so this is more about capacity. In an empty stadium during my tour, a quick speedtest on a Cat 4 device achieved 83Mbps down and 47 Mbps up – I’d be very happy to have those speeds on my fixed broadband at home.
Three other mobile operators share the DAS system, but only one for 4G, and also deploy their own spectrum assets and backhaul, achieving high throughput per sector – I’d estimate anything up to 1Gbps and today probably limited more by backhaul constraints.
Antennas around the stadium are grouped into 24 active sectors. The stadium is segmented vertically like an orange, with each sector covering both a segment of the main bowl and the indoor area behind and underneath. EE undertook the radio planning and the same sectorisation is shared with all operators. Andy and Kin pointed out the antenna to me, with some of the older rectangular DAS antennas also still visible.
The main bowl uses very large stadium flat panel antennas from Commscope with each one very precisely aligned. Very large means 1.3 metres by 0.8 metres and each weighs 37kg. They’re wind resistant to 99mph so not going anywhere fast.
28 antennas are installed because it’s difficult to isolate the end areas that have no roof, with four sectors having duplicate antenna. A laser sight was attached during the commissioning phase to identify the specific seat they were centralised on. Some measurements and calculations were made, then the alignment adjusted by moving the focus to the relevant nearby seat. This made the setup much faster than the trial and error method sometimes used elsewhere. Once installed, it’s difficult and impractical to access the antennas outside pre-scheduled maintenance windows months ahead. The roll-off (RF radiation pattern at the edge of coverage) is very tight, only 2-3 degrees, which reduces inter sector interference.
The central area of the pitch is covered by just four antennas at the ends, relevant when the stadium is used for concerts.
Elsewhere in the building we saw a variety of different antenna types, uni-directional and rectangular, discretely providing coverage throughout the heavy concrete structure. There are around eight antennas of different types per sector, totalling over 200 antennas in all.
Why such a major upgrade?
I asked Andy Sutton why they chose to make such a significant replacement to the DAS system rather than an incremental upgrade, and whether a small cell solution was considered.
“The older DAS system wasn’t compatible with the new frequency bands for LTE and didn’t support MIMO. It could handle LTE at 1800 but we needed to accommodate the frequencies allocated to other operators. Adding support for the 2600 band would have been expensive.
“For large changes like this every participant needs to agree including all other operators and the venue owner. Real Wireless have acted as consultants for the stadium to facilitate common agreement. EE have selected the equipment and designed the solution. We’ve planned on at least a 5 year lifetime, taking full account of the TCO (Total Cost of Ownership).It is however anticipated that this solution will last significantly longer.
“We are considering small cell solutions such as Airvana’s OneCell for medium/large Enterprise deployments and are interested in those kinds of new technology. Introducing a new vendor into the RAN is a major undertaking involving everything from testing, configuration management, staff training, logistics to spare parts. For a shared venue like this, all operators would need to agree to support a common system which none of us have yet introduced, so at this stage it’s not feasible. That might be different elsewhere.”
Aren’t all those high power macrocells wasting a lot of energy?
I noted that the macrocells all deliver full 20 Watts RF power which is then attenuated before being converted into an optical signal. Couldn’t you directly connect to the DAS using CPRI, bypassing the RF modulation/demodulation stages? Or could a lower power small cell be used instead?
“Operationally, we dimension and configure our network with as few variants as possible. We’re down to a handful of different standard macrocell configurations. If we set these to unusual values, we might find that risks a technician inadvertently resetting them to defaults, resulting in sub optimal performance. If we used different parts, we’d need to hold spares, train technicians to use them, perhaps even have different procedures for maintenance and upgrade cycles. There’s a lot involved when introducing new variants that can easily be overlooked, and these aspects often override the more visible power inefficiencies.
“Having said that, if there was a lower power direct connection to the DAS, we’d certainly consider it. At the moment, I’m unaware of any small cell that could match the performance of these macrocells and could cope with the mix of 2G/3G and LTE radio technologies.”
What’s the typical traffic throughput during a major event?
“As a trend, data traffic has consistently increased event by event. The biggest leap was in early 2015 when we added 2.6GHz spectrum. 4G traffic is now split 1:2 between the 1800MHz and 2600MHz spectrum because we prioritise the higher frequency. We tend to see around 3.5x more traffic on LTE than 3G, with music events driving higher consumption. Ed Sheeran’s third concert is our top performer with over 700Gbytes of traffic. Music events drive ~40% higher uplink traffic than sporting events with again Ed Sheeran’s concert exceeding 200Gbytes. NFL games have a reputation for the top traffic levels of any sporting event worldwide, so we expect to see new peaks for this season’s three NFL games to be played at Wembley.”
Why no Wi-Fi in the stadium bowl?
Figures from the Superbowl and similar events show that around half the total data traffic in those stadiums uses Wi-Fi rather than cellular. As wireless communication lead at Wembley, why haven’t EE installed a stadium Wi-Fi network?
“EE have invested in large spectrum assets which can handle huge amounts of traffic. We position ourselves as an “onload” rather than “offload” network and want to carry as much traffic as possible. LTE gives us better control and management of the service delivered. LTE penetration is growing at a phenomenal rate and we find many of our customers prefer to use it because of the performance and quality it provides.
“And there are question marks over the capability of WiFi to meet the demand of huge crowds in the way that LTE can. However, WiFi remains a consideration for the future so long as it can deliver the right experience, and there are already several smaller systems installed in some areas to meet specific needs. If we did deploy across the bowl, this would need to be a completely separate system from the DAS with a large number of separate antennas, possibly with some fitted underneath the seats.”
Would you consider LAA useful in this environment?
“While LAA could provide some additional spectrum, this is only relevant once you’ve already deployed all available licenced spectrum and made full use of a small cell layer. So I wouldn’t expect that to be used in this context for quite some time.”
Have you tested any other technology features here?
Kin Wan explained they had run a trial of eMBMS (also known as LTE broadcast) using the Huawei kit. Multiple video streams were used to send several different camera angles for spectators to see the action from. This required phase sync which they sourced using GPS, but they also have SyncE (Synchronous Ethernet) with IEEE 1588v2 from both fixed network suppliers as a backup. Read more about the trial here.
Would you want to reconfigure the sectors for different events?
Dr Kin Wan explained: “We want this to be as low maintenance as possible, and have installed enough capacity to meet demand. Even when the stadium is used as a concert venue, we wouldn’t want to reconfigure the sector assignments. I visit this venue approximately every two to three weeks at the moment, supervising the ongoing upgrades and expansion. We don’t have permanent staff based here and want to keep the operational side as straightforward as possible.”
EE’s Wembley Stadium DAS solution an impressive installation which can deliver a huge amount of data traffic to those in and around the stadium. It also supports 2G/3G preserving voice and text services. The active DAS system allows each operator to continue to use their own equipment vendor, staff and configuration. The new LTE frequencies (and need to support MIMO) were a major factor in driving such a large new investment.
DAS systems aren’t inexpensive but costs can be shared between participating operators. Where only one operator wants to make a larger investment, say for LTE, then perhaps there would be an opportunity for a standalone overlay small cell solution such as we discussed recently.
It was also a surprise not to see any significant Wi-Fi investment. EE is one operator who has positively chosen to excel using LTE, onloading rather than offloading traffic from their network, and has assembled the spectrum assets to realise that objective.
My thanks to Andy Sutton and Kin Wan for taking the time to show me around and answer my questions. My ticket for the NFL game next month should allow me to try out the system under pressure. As I left, I noticed they've even named a street outside after them...