Guest post: Can Wi-Fi for stadiums really work?

Getting Wi-Fi to work at home or at work is one thing, but trying to connect 20,000 screaming fans trying to post their experiences to Instagram all at the same time is, well, nothing less than a daunting task.

Yet this is what stadiums and other high capacity venues around the world are rushing to do.

Event-goers are now coming to stadiums and large public venues armed with one or more Wi-Fi-enabled mobile devices, with the expectation that reliable connectivity will just be there. But in these environments, delivering even a usable, let alone quality Wi-Fi experience to tens of thousands of users, is a tall order.

Wi-Fi in stadiums: challenges and opportunities

Although the emergence of smartphones is the catalyst for expanding Wi-Fi access in venues, there are myriad challenges in supporting critical back-office users and a potentially overwhelming number of fans eager for more compelling content. For example, operating multiple (competing) Wi-Fi networks in the same area results in higher deployment costs and degraded network performance. Instead, the preferred approach is to provide a unified and converged Wi-Fi network capable of supporting all venue services, each with its own Wi-Fi security and performance requirements.

It is equally important to protect critical back-office applications such as ticketing and point-of-sales (POS) applications from fan access. A variety of tools can be used to meet these challenges by separating, protecting, and prioritizing Wi-Fi traffic, including the advertisement of different Wi-Fi networks, the use of different security schemes, and segregating and prioritizing traffic network traffic using VLANs. In addition there are physical challenges to providing adequate coverage and capacity in the venue “bowl.”

Standard Wi-Fi deployments cannot address these challenges. Careful placement of the access points, use of special high gain antennas, and unique radio frequency tuning are essential.

Stadiums, public venues, and their owners understand that delivering such services can not only improve their fans’ overall experience, they can also enable new services while creating additional revenue streams.

Wi-Fi enabled mobile devices open the door for these venues to directly engage an unprecedented number of fans at a personal, real-time level. New applications allow fans to order drinks, download club statistics, watch replays, and even match wits with other fans via trivia quiz games.

Historically, wireless communication within stadiums and large public venues such as train stations, concert halls, and convention centers, has been the domain of expensive distributed antenna systems (DAS). But this is changing as new and smarter forms of Wi-Fi reach the market.

A distributed antenna system (DAS) is a shared-infrastructure or neutral host approach to offering multiple wireless technologies within a facility via a shared passive cabling system. Wi-Fi APs and cellular base stations are connected into the RF distribution channel, but the data processing is still performed by the AP or base station. Conceived and developed primarily for extending cellular signals indoors where “outside-in” coverage is challenging, some 802.11 Wi-Fi features, such as multiple input/multiple output (MIMO) may not work as designed over a DAS.

Meanwhile, technical advances in Wi-Fi technology have been developed for high capacity environments that leverage sophisticated narrow-beam adaptive antenna arrays. These innovations are creating new opportunities for venue owners to deliver higher capacity and higher-speed Wi-Fi services to data-starved fans.

Originally conceived and developed for consumer use at home where users and devices are sparse, Wi-Fi has always been ideal. The goal in these environments is to blanket Wi-Fi signals everywhere using the fewest number of access points possible. In stadiums and public venues, however, where there are thousands or tens of thousands of users and orders of magnitude of more space, the opposite approach to deploying Wi-Fi is required.

How to optimize Wi-Fi in stadiums

In these ultra high-density environments, the key to good Wi-Fi performance that counters conventional Wi-Fi wisdom is to contain, as much as possible, Wi-Fi signals to a physical area. This helps limit the number of users who can connect to a given access point. More importantly, it provides better signal separation to minimize co-channel interference that occurs when the signals from access points bleed into each other and further degrade Wi-Fi capacity.

The need for signal separation is analogous to a very large conference room with thousands of attendees. If the noise from each area of the conference room could be isolated to a small physical area, more simultaneous conversations could occur. In stadiums, thoughtful AP mounting gets us started with the signal isolation problem, but additional technology enhancements are needed to provide sufficient separation for very high capacity networks—or in other words, networks that can satisfy user expectations in these kinds of environments.

One such technique is akin to shining an RF spotlight on a group of people, and then extending this concept across the venue with many discrete spotlights. With Wi-Fi, this strategy is achieved using special directional antenna arrays that keep signals strong and tight within a given area—and avoid sending signals where they are not needed or wanted. This signal focus towards users is particularly important given the diversity of low-powered client devices like mobile phones that tend to transmit and receive signals poorly—compared to higher-powered laptops used indoors—requiring stronger signals to keep data rates high and connections stable.

New high-density 30 degree and 120 degree sectorized antenna arrays are useful for this purpose, allowing Wi-Fi signals to cover a bank of seats, for example, keeping Wi-Fi contention low and throughput high. Unlike most Wi-Fi deployments in places like hotels and schools, where the goal is to use the fewest number of access points to cover the greatest area possible, within high density venues such as stadiums, the opposite goal is desired. In this case, more access points (as long as signals can be properly isolated) equates to better performance for fans because each AP supports fewer users. However this creates another potential problem: cl-channel interference. This is where signals from access points sharing the same channel can hear each other. To solve this problem, better signal separation and intelligent controls that automatically pick the best channels as the RF environment constantly changes is imperative for successful stadium Wi-Fi deployments.

Wi-Fi uses a contention-based protocol within a shared, unlicensed RF medium that operates at half duplex so users access the network on a first-come first-served basis. Any interference or physical obstacles that impede signals during transmission or reception cause packets to be retransmitted, creating further delays and congestion for those waiting to get online.

This problem can be effectively avoided or at least mitigated with systems capable of focusing Wi-Fi energy only where it is needed while dynamically selecting the best available signal path that will yield the highest data rates for any given client. By getting clients on and off the shared radio frequencies more quickly, the network access wait time can be minimized, thereby increasing the overall network capacity. This is an absolutely essential, but often overlooked, aspect of Wi-Fi deployments within high-density environments.

Beyond physically focusing Wi-Fi signals to reduce airtime contention, “smart” Wi-Fi systems can help ease pains for high-capacity environments by combining a number of new techniques such as dynamic channel assignment, band balancing, and client load balancing. Advanced channel selection mechanisms that use statistical methods can be used to learn the available capacity of any given channel across the band, influencing clients to use those channels known to yield the highest throughput.

Band balancing influences client devices to use the channel-rich 5 GHz band by withholding probe and authentication responses. A properly designed band-balancing algorithm can optimally spread clients across both 2.4 and 5 GHz bands according to capacity.

Client load balancing also helps in these environments by limiting the number of clients that can connect to a given AP and automatically distributing clients between neighboring APs to help optimize overall performance of the system. On the wired side of the network, a useful technique consists of dynamically assigning VLANs through a pool of available VLANs. This helps to limit traffic within a broadcast domain and allows VLANs to be defined with specific traffic thresholds and traffic parameters. Don’t forget, no matter where a problem or bottleneck occurs, Wi-Fi will be blamed first.

Another major issue for Wi-Fi within high-density environments is calculating the capacity needed for each user. This is becoming more of an art and less of a science, requiring venues to make educated guesses about what percentage of fans will have devices that can access the network, what kinds of applications will be accessed, and how much bandwidth those applications could potentially consume. Key considerations include estimating the total number of Wi-Fi client devices, and the average number of active client devices and the peak number of active devices at any given time. As one can imagine, these estimates can vary widely from venue to venue, and the target changes along with new technologies and device adoption.

Another key consideration is backhaul capacity. Because access points must be connected to the network and most users want to use cloud-based applications, adequate backhaul capacity is critical to the success of any Wi-Fi deployment. If backhaul speeds are slow, Wi-Fi network performance will suffer and users will blame the Wi-Fi network. Any stadium Wi-Fi deployment must address, as early as possible in the design process, a number of areas including:

• Client capabilities;
• Required applications and their behavior;
• Minimum bandwidth required for each client;
• Average and maximum devices per AP;
• Maximum latency tolerated;
• Number and density of APs;
• Client capabilities;
• Clients per AP;
• Environmental RF conditions;
• AP mounting and location;
• Network backhaul; and
• Network service provisioning.

Summary

Distinctly different than conventional wireless deployments, a good stadium Wi-Fi deployment requires relentless site surveys and RF planning coupled with industrial-strength Wi-Fi products and technologies that give IT staff better control over the management of shared radio frequencies. The keys to success include reducing media contention by limiting Wi-Fi cell sizes and the deployment of lots of access points that serve a fixed amount of users within a given area. Finally the use of advanced Wi-Fi techniques such as band steering, client load balancing intelligent, dynamic channel selection and airtime fairness should be employed to help smooth traffic load to ensure the sports fans have a fair shot at a winning Wi-Fi connection.

Tackling these issues, combined with lots of testing and tuning at small events prior to the big show, will only help to ensure success and a much-improved online experience for fans.

Author: David Callisch, VP of Corporate Marketing, Ruckus Wireless