LARRY ESTRIN /
12.01.2011 12:00 PM
Taming the 2.4GHz band
Plug-and-play devices need coordination to avoid interference.

In recent years, there has been an explosion in license-free devices using the Wi-Fi 2.4GHz spectrum. These devices have been billed as “plug-and-play,” resulting in a serious misconception about the need for frequency coordination throughout the production industry. That misconception hinges on the flawed belief that the absence of a license means interference is impossible. Simply put, that belief is dead-wrong!

While it is true that a specific license to use the product is not required, there are a significant and growing number of instances where there may be upward of 50-plus 2.4GHz devices operating in relatively close proximity to one another. These locations include almost all motion picture, television production and news studios, college and professional sporting venues, as well as live performance theaters. One of the best ways to combat this issue isn't through a technical solution. It is communication between all parties involved in the broadcast or event that ensures frequency channels do not interfere with one another.

Rampant devices

The 2.4GHz spectrum is used for hundreds of devices, including portable billing devices, surveillance systems, restaurant and service facilities, and more. Of course, every user believes he or she has the most optimal use of the spectrum. A primary purpose of coordination is to allow the maximum use of as many devices as possible without interference. Most of these devices have multiple channel settings within the 2.4GHz spectrum. Coordination in advance allows for all the devices to work without conflict or disruption.

That said, no production is immune to interference. Sometimes, however, it is at larger events where frequency coordination is paramount. An example of this came when technicians were coordinating wireless devices for the most recent telecast of the NFL draft.

“At the NFL draft at Radio City Music Hall, a 2.4GHz wireless intercom system was fired up,” said Ralph Beaver, manager of the NFL game day coordinators. “Immediately, the NFL IT people were trying to find out why more than half of their many, many laptops in use in the hall had slowed or stopped. CP Communications technicians on-site immediately recognized the problem and very quickly changed the settings on the wireless intercom system so as not to occupy that much of the Wi-Fi band.

“At the same event, a 2.5GHz wireless camera was turned on in the theater. The camera wreaked havoc with the other wireless devices until it was adjusted so that it would not conflict with the 2.4GHz devices.”

Human element is key

Michael Mason, president of CP Communications, believes that one of the best ways to work through this issue is simple communication.

“The fundamental principles of coordination are cooperation and the sharing of information,” Mason said. “There is no difference if you are using 500MHz or 2.4GHz. All parties using RF need to communicate with each other so a plan can be put together to ensure a successful show.

“The challenge with the 2.4GHz band, as well as all other license-free bands, is the lack of understanding that license-free does not mean coordination free. In large venue events, such as NFL's Super Bowl or the MLB All-Star Game, great expense (both time and money) is put forth on frequency coordination. Unfortunately, tens of thousands of handheld devices and/or smartphones come into these venues that we have no control over. These can and will adversely affect the spectrum.

“While they may not be permitted to access the Internet through the Wi-Fi systems in the venues, they are constantly pinging them, looking for access. This constant chatter alone raises the noise floor tremendously. Taking this into consideration, it is critical that the users who do have control over their equipment coordinate with each other by sharing information and steering their equipment toward usable parts of the spectrum.”

Henry Cohen, of Production Radio Rentals — a supplier and integrator of communication devices for special events, believes that along with communication, preplanning needs to be a part of frequency coordination.

“Coordinating the unlicensed bands (generally 900MHz to 928MHz in the United States, 1.92GHz to 1.93GHz, 2.405GHz to 2.485GHz, and the 5GHz U-NII sub-bands) have become an absolute requirement in most special and high profile events,” Cohen said. “Many bad experiences have managed to get the attention of management. A significant element of coordination is to clearly communicate the policies governing equipment operations to all event vendors, participants, venue administration and, in particular, IT departments during the planning phase(s).

“As this remains a somewhat new concept to most entities involved in productions, time is generally required to find and contact the appropriate technical individuals and educate them so they can acquire the proper equipment needed to manage spectrum coordination.”

Most IT department technicians have little concept of, or experience with, the production world and the dynamically growing requirement for RF communications to support ever-increasing levels of production. IT technicians' training and experience rarely goes beyond the plug-and-play concept, or the use of non-overlapping channels and possibly transmission power levels. They generally believe that latency is not a problem; just send the information packet again and again.

Aid from technological advances

In addition to resolving this issue via communication, manufacturers are developing products to help with frequency coordination. Many companies have built in various channel configurations in their 2.4GHz products. One company, for example, has reached out to some of the wireless DMX receiver/transmitter manufacturers in order to coordinate the channel configuration schemes between manufacturers.

It is also appropriate to mention that other spectrums that are license-free, such as Digital Enhanced Cordless Telecommunications (DECT) wireless telephone systems, can and will interfere with each other as well as other services. Some production communications manufacturers have designed wireless stage management systems using the DECT platform, further exacerbating the problem of license-free without frequency coordination.

Frequency coordination is the most effective way to guarantee the proper operation of all devices at a particular event, whether it is the Super Bowl or a church service. Taking the time to plan the use of the available spectrum will yield positive results for everyone. A good reason to do so is that if everyone coordinates at a particular event, then everyone can be protected by the frequency coordinator.

Larry Estrin is strategic technology consultant for Clear-Com.



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