Large outdoor environments face the challenge of handling thousands of simultaneous users while maintaining decent throughput speeds for uploading and downloading data.
However, many are temporary and therefore need to be set up rapidly without interfering with whatever is already in place. They also need to be cost-effective at the same time as delivering the necessary scalability.
‘The basic problem with large outdoor environments that are well populated is that you get a lot of people trying to use the network at once,’ says Steven Glapa, senior director of marketing at Ruckus Wireless. ‘We’ve provided Wi-Fi for the WOMAD Festival, for example, and everybody’s got this expectation that mobile operators will give them a Wi-Fi network wherever they go. Whether it’s 3G or Wi-Fi, fundamental physics continues to apply.’
Clearly distinct channels
There’s only so much spectrum available in a given location at a specific time, and much of that is occupied by previously licensed service providers.
In addition, a service such as Wi-Fi needs to operate in clearly distinct channels that are separate from each other in order to avoid interference.
‘You can’t use bandwidth from another chunk of spectrum until you are far enough away from the first chunk,’ says Glapa.
‘In Wi-Fi you have 2.4GHz and 5GHz [bands] but most [capacity is] useless because nearly all mobile clients in use today don’t support 5GHz, so you’re stuck with 2.4GHz,’ Glapa explains. ‘That means there are only about three channels to work with. The challenge then is to isolate the access points from each other, so you can get enough density down to the level of a stand full of seats.’
That has led to the need for more intelligent antennas and repeaters that can adapt on the fly to changing situations and shifting levels of demand. Glapa says there are several different approaches that can be taken to mitigate the limited number of channels available.
‘To address the limited spectrum availability, one option is to build outdoor access points that have a range of coverage patterns or have a basic platform that gives you omni-directional capability. It’s a little bit like the shape of a bullhorn. Another option is to narrow down to a 30x30m pattern with smart antennas inside that [to steer or shape the signal],’ says Glapa.
Channel adaptation technology isn’t new but it has been limited in its efficiency. For example, switching from channel one to channel six is only worthwhile if you know that the performance of channel six is better. Many current systems aren’t able to do that efficiently. They may listen to the channel they plan to move to and then switch over but the time involved in that process may mean the conditions have already changed. This really needs to happen in near real-time for maximised efficiency.
‘Lots of Wi-Fi vendors have call channel adaptation available but if you’re going from channel one to channel six you have to know if it is better,’ adds Glapa. ‘We have a new autonomous adaptive channel management tool that addresses changes in demand. For instance, if everybody gets up to get a beer at once, demand in a specific area changes radically.’
In terms of the challenges that Wi-Fi providers face in deploying large outdoor systems, there are several issues to consider. ‘We are supporting a couple of operators in London [to cope with the influx of visitors to the 2012 Olympics, although not in the Olympic Park itself,] and there are a couple of different elements in play,’ says Glapa.
‘The first issue is to pick the right [approach to] Wi-Fi. There’s a certain amount of learning by doing in deploying Wi-Fi for high demand environments, so pick a team that has done it before and take advantage of the inherent nature of the environment to deploy the best Wi-Fi service possible. Good Wi-Fi has the advantage of meshing, so you need to be good at adopting mesh technology and changes within meshes. People deploy using their best guess at the outset then turn up the outer access point and mesh.’
Glapa continues: ‘The company that does WOMAD with our equipment has a lot of practical deployment experience built up around the cell on wheels concept – they have an access point on wheels deployment – so they can extend a pole, put a battery up and mesh back to other access points on wheels.’
Could the capacity limitations of Wi-Fi be offset by handing off traffic to cellular networks or vice versa depending on which technology has the best experience available at a given location? Yes, in theory, says Glapa, but the practicalities are not so straightforward.
‘As far as radio [signals] are concerned, all we need to ensure is that we’re not interfering with each other. It is also possible to integrate with the mobile core and back end but there is a limited amount of that happening so far,’ he says. ‘[But mobile network] operators tend to act relatively cautiously – you don’t just walk in and plug in new [equipment to their networks and systems].
‘However, we have already demonstrated in one of the operators in the UK that you can take mobile traffic. Operators have been selling Wi-Fi-enabled handsets with an FSID configured on the device to do the EAP-SIM (Extensible Authentication Protocol Method for GSM Subscriber Identity Module) authentication. It is as seamless and secure as anything on 3G.’
There is, therefore, a move towards integrating Wi-Fi more closely with cellular technologies, according to Glapa. However, the emergence of tablet devices has seen the landscape shift again and SIM-based devices may no longer be the terminals of choice for users of outdoor wireless capacity.
‘One thing coming up more and more is that the last two years have been all about automatic authentication work for SIM-based devices, then along comes the iPad and its imitators and few are used with the cellular interface. That poses another round of challenges. How do you get the same sort of seamless user experience?’