The new LAN is deliberately designed to slice up Wi-Fi coverage as narrowly as possible, keeping cells small to control the number of concurrent users and reduce their contention for the wireless medium.
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Ruckus Wireless, which won the contract for the new network over incumbent Aruba Networks and others, designed a new access point antenna, dubbed Thunderbolt, specifically for this deployment, and is already using it other stadium-like deployments. The antenna radiates in 30-degree sectors, instead of the more conventional 360-degree and 120-degree sector. The narrower radio swaths help keep media contention low and signal strength high, allowing more users to access clear channels.
The arena area has about 120 Ruckus' ZoneFlex access points, both , many of them mounted overhead in catwalks and scaffolding (see photo at right), as well as under seats, VIP suites, offices and locker rooms, and outside the arena. In the main seating bowl, the WLAN uses the outdoor ZoneFlex 7762 units.
Time Warner Cable provides the fiber ring surrounding the arena, connecting to PoE switches in wiring closets. Gigabit Ethernet copper links the switches to the Ruckus access points. All Wi-Fi traffic from the arena routes to a Ruckus ZoneDirector 5000 controller based at TWC's Herndon Data Center, along with the vendor's FlexMaster WLAN management application.
The upgrade to 11n was pushed by the arena's main tenant, the Charlotte Bobcats basketball team, which wanted to support the growing number of Wi-Fi and tablets with reliable bandwidth, and offer fans new wireless services. These mobile devices are . Time Warner Cable, besides having the name rights, also supplied the arena's fiber infrastructure. The cable company worked Ruckus and the WLAN vendor's Georgia-based broadband communications integrator, Arris, to design and install the new WLAN.
The network is designed assuming that 28% of the nearly 20,000 attendees, at full capacity, would be using Wi-Fi, mainly for uploading photos or short video clips, and for sharing with friends via social media sites like Facebook and , according to Lou Lazzaro, vice president of wireless for Time Warner Cable East Region. For non-sports events, like the Democratic National Convention, the center court is covered for stages and additional seating. The only network change for the DNC was adding another handful of access points for this central sector.
The access points can balance the load, so users can be shifted to another access point as needed, says Doug Sabo, product manager for Wi-Fi with Time Warner East Region. "We don't anticipate folks will have a lot of downtime," he says. "In our initial testing, it's fared pretty well. We haven't seen that capacity max out."
The companies ran a detailed site survey initially, and then began running extensive simulations that mimicked real-world performance arena attendees to determine the optimal access point deployment. It was this work that led to the new antenna design, according to Ruckus co-founder and CTO Bill Kish.
"The main problem [in high density deployments] is radio congestion -- the RF gets saturated," says Kish. "The spectrum is highly utilized at a fairly high power level. So there are very few 'windows' for a client to jump onto the RF link. You have to give as good a link as possible to each client, so they can get on and off quickly."
If links degrade, Wi-Fi access points automatically drop down to lower data rates to improve link quality. But that change slows the network down for all clients.
The Ruckus access points in the arena run in both the 2.4GHz and 5GHz bands. In an unusual move, the WLAN uses all 11 available 2.4GHz channels, instead of the conventional three non-overlapping channels. The reason is the way in which the 802.11 standard handles the initial signaling -- it uses a preamble to start each 802.11 transmission. The preamble is sort of like yelling at the top of your voice in a crowded room to get someone's attention, according to Kish. But this low-energy yell can be heard by a lot of access points, and when they hear it, they drop what they're doing and try to focus on the receiving process for this "shout," according to Kish.
"You want to avoid this [reaction] in a high-density environment," he says. "If someone is transmitting at a low level, you want the access points to 'not hear' that transmission," he says. "Staggering these [11] channels is one way to accomplish this." The new, narrow-sector antenna aids in this.
This additional spectrum reuse in the 2.4 band is important, says Kish, because "we're seeing now only about 10% of the Wi-Fi clients supporting 5GHz." Ruckus' built-in "band-steering" can direct clients that do support 5GHz to connect on that frequency.
The WLAN supports several VLANS/SSIDs to support separate such as public access, arena staff, the food and beverage services and on-site ticket scanners.
John Cox covers wireless networking and mobile computing for Network World. Twitter: http://twitter.com/johnwcoxnww Email: john_cox@nww.com Blog RSS feed: http://www.networkworld.com/community/blog/2989/feed
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