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April 13, 2009
Is it the right time to add a wireless network to your system?
No pulling cables, fewer AV source devices, fast connections, and a clutter-free environment. What’s not to like about wireless transmission? Not much, says Chuck Pheterson, vice president of product marketing for Sunrise, FL-based wireless vendor Avocent. “There are many reasons people select wireless,” says Pheterson. “Wireless reduces installation costs in challenging environments that require connectivity under concrete or marble flooring, across barriers such as railroad tracks, and inside historical buildings where you can’t drill holes.”
Avocent senior vice president and general manager Mitch Friend adds that installing cable can be highly disruptive. “False ceiling installation is less so, but integrators and customers
say that when deploying a digital signage network in a store, for example, pulling cable disrupts the environment. There are also situations where building codes are going to make cable installation very expensive. Along with that, there are EPA concerns, such as going into a ceiling where there is asbestos. Or consider going into the ceiling over a restaurant and dropping dirt. What does that cleanup situation look like? Wireless can make these processes easy.”
Wireless networking is as attractive to audiovisual as it is in any data delivery application. But although wireless networking in the home is commonplace, and while commercial wireless internet access is exploding, audiovisual professionals have been hesitant to accept wireless audiovisual delivery. The evolution of wireless helps explain why.
HISTORY OF WIRELESS NETWORKS
An early model of wireless AV used Bluetooth. Bluetooth-enabled projectors were limited to around 30 feet with bandwidth of 720 Kbps. These appeared in the late 1990s and early 2000s. Bluetooth was quickly quashed with Wi-Fi’s entry into the wireless space with 802.11.
The first 802.11 spec to garner attention was the 802.11b, which was 10 times faster than Bluetooth and could be used with Ethernet LANs. 802.11b uses the 2.4 GHz band and supports up to 11 Mbps, or about the same as traditional Ethernet. 802.11a, on the other hand, uses the higher 5.3 and 5.8 GHz bands and supports up to 54 Mbps. The speed of 802.11a was more appealing, but range was compromised — the higher frequency has more difficulty penetrating obstructions. 802.11a devices were also more expensive. Neither 802.11a nor 802.11b solved all wireless challenges.
802.11g was developed to make up for the shortcomings of a/b. Using 2.4 GHz band and yielding up to 54 Mbps, 802.11g combined the best of what 802.11a and 802.11b had to offer — lower frequency for better range and the higher bit rate. Importantly, 802.11g is backwards compatible.
The IEEE began work on 802.11n in 2003, and it was so hard to get consensus on it
that more than 30 different proposals made the rounds. In 2005, a network industry consortium banded together to help speed up the process. This group drafted its own proposal, which was accepted in 2006 by the IEEE. In 2007, major network equipment companies began to release products, partly assisted by the Wi-Fi Alliance’s certification program, which ensured interoperability
“A year ago, my recommendation would be to stay away from 802.11n,” says Joe Bardwell, president and chief scientist at Connect802. Bardwell’s San Ramon, CA-based company is a wireless network design, sales, installation, and support company. “But now 75 percent of the standard is locked in, and all the major LAN manufacturers are providing “n” standardized to the Draft 2.0, so they’re all interoperable. We’ve been using them. It’s great.”
802.11n operates on either the 2.4 GHz or 5.0 GHz band, making design and installation more flexible and interference-free, and at 100 Mbps or more (Connect802 is seeing up to 200 Mbps in some scenarios), compared to 54 Mbps for 802.11g and 802.11a, and 11 Mbps for 802.11b. It’s generally believed that 802.11n handles wireless multimedia applications better than the other 802.11 standards. Also nice is the backwards compatibility, so an infrastructure can support all protocols.
The most significant advance, however, is the Multiple Input Multiple Output (MIMO) technology in the 802.11n spec. MIMO uses multiple antennas on the same channel. Each antenna transmits different spatial characteristics, and every receiver listens for signals from each transmit antenna. The result is a multipath configuration that takes advantage of signal reflection and diffusion.
The Spatial Division Multiplexing (SDM) technology further enhances the signals with different encoding sent via different antennas and a receiving process that de-multiplexes the signal to use the information.
“Reflections that result in ‘dead spots’ for b/g/a networks are actually beneficial to 802.11n networks,” says Bardwell.
WIRELESS ALTERNATIVES
Bluetooth, designed for handheld devices, and WiMAX (IEEE 802.16), designed for “metropolitan area networks,” are not considered competing wireless technologies to 802.11.
Ultra wideband (UWB), however, can be a viable alternative. Hagai Gefen, president and CEO of Gefen Inc., explains that UWB is a radio frequency for short distance, high-bandwidth requirements that are well suited to AV signal transmission. Distances of around 30 feet between sender and receiver allow for a transmission of 1080p/24 fps resolutions, he says.
“The 802.11n technology at 5 GHz offers similar advantages,” says Gefen, “but can transmit longer distances and through walls. Its disadvantages are that it uses a narrower bandwidth, so lesser amounts of data are transmitted, and it is vulnerable to adjacent 802.11n channels interference.
“Currently, our Wireless for HDMI UWB Extender can be used for line-of-sight distances within the room. For large venues, or applications where the signal must transmit through a wall, we do not recommended UWB unless the distance is short and line of sight is available.”
Another alternative uses a radio broadcast model to deliver wireless AV signals. Madison, AL-based AvaLAN offers long-range wireless Ethernet products for industrial or commercial applications, including digital signage and IP surveillance video networks. According to the company, AvaLAN products are designed to provide maximum range (up to 30 miles line-ofsight at 5.8 GHz) at modest data rates, compared to 802.11 technologies that offer higher data rates, but shorter range. To achieve maximum range, AvaLAN systems employ a highpower RF amplifier and a high-gain, low-noise receive preamplifier. The receiver is optimized for range by minimizing the occupied bandwidth compared to Wi-Fi products.
“AvaLAN has established itself by succeeding where Wi-Fi fails,” says company president and CEO Matt Nelson. “We operate in extreme temperature ranges, from -40- to +80-degree Celsius. Because we use 900 MHz, we can penetrate through walls and dense trees. We operate at higher power and have better receiver sensitivity, giving us much further reach both indoors and outdoors. We use a simple direct sequence protocol, which requires less overhead than traditional Wi-Fi.”
With UWB, 802.11a/b/g/n, and AvaLAN’s technology as examples, the bandwidth and speed are there, as well as enough diversity to choose the best technology for specific applications. Multimedia PowerPoint presentations and wireless video no longer have to jitter and lag. Test results by research company Burton Group indicated that 802.11n’s range of latency and jitter was quite acceptable for most applications. It took demanding uses, such as graphic design, CAD, and video production, to noticeably affect performance of the wireless network.
As for HD, a 50 Mbps Blu-ray video bit rate is no problem for wireless extenders capable of 110 Mbps streaming. HD wireless transmission has definitely arrived. The customers are there — users and integrators are asking for wireless. And the reasons to implement are many.
Projectors with built-in wireless capabilities are highly practical and becoming more commonplace. With wireless, multiple presenters can easily connect their laptops to a ceilingmounted projector without having to “pass the cable” or move to where the cable happens to be located.
Wireless signal transmission has also driven much of the growth of the
digital signage market — and vice versa. Wireless connectivity enables content delivery to locations that were previously difficult to reach with cable — especially in retrofit installations. For example, a growing application for digital signage is gas station pump-top displays. Without wireless transmission, getting the AV signal to these displays would require cutting troughs through concrete.
Wireless also provides an elegant solution for installations with multiple screens. Because multi-point wireless extenders serve the dual function of extension and distribution, they simplify the process of synchronizing audio and video across multiple displays. “When many displays within eyeshot or earshot are all are several seconds to a minute apart from each other, you get a chaotic environment,” says Pheterson. “But with one media player, a wireless transmitter and receivers, they stay in step with each other. That is a compelling reason to go wireless.”
Sometimes, wireless solves problems a cabledconnection just can’t handle. Oil and gas exploration company Anadarko had trouble installing employee messaging systems into elevators in their new 30-story office in The Woodlands, TX
“Cables kept breaking, and the single, central player couldn’t keep up with increasing demand,” says Michael Bialas, senior ITS administrator at Anadarko. A wireless solution using AxisTV from visual communications company Visix did the trick. Using 802.11b and g, they mounted dedicated transmitters above the four elevator shafts, and directional antennas atop each of the 16 cars. Access points are configured with an access control list, preventing unauthorized devices from accessing the rest of the network.
A screen in the elevator wirelessly receives the signal and displays internal news such as the stock price and employee notices at 10-second intervals. “We know people get the message from the water cooler talk about that day’s stock price, the advertised United Way campaign, and so on,” says Bialas. “I have actually seen people stay in the elevator to finish reading the news and bonus program slides.”
CHALLENGES AND TRADE-OFFS
Even as 802.11n and other alternatives gain popularity, they aren’t the only, or the perfect, solutions. The 802.11n spec hasn’t even been finalized yet (most believe it’s close enough). 802.11n needs multiple antennas to generate exceptional data rates. If one breaks, then these rates reduce to normal levels. 802.11n is also more expensive.
802.11n systems are fully backward compatible with 802.11a/b/g, so your install can support all three. But the performance actually depends on that of the legacy system, so you may not get maximum benefits of 802.11n. And don’t leave the other 802.11 protocols on the bench. Avocent’s 802.11a or g products, for example, provide video rates of 20 Mbps — quite adequate for typical retail digital signage applications. UWB allows short distance transmission of HD content, but is limited to line-of-sight links. And AvaLAN trades extra long distance in difficult applications for lower data rates.
One question to consider when deciding which technology to use: Is my application mission- critical? An ad node in a mall isn’t. A live presentation, classroom, telemedicine, or courtroom proceeding may be. “With situations requiring critical viewing, it makes sense to use higher bandwidth with 802.11n,” says Pheterson.
And with any wireless deployment, frequency allocation planning is important. If your wireless AV install is on the 2.4 GHz band, you need to select non-overlapping channels to avoid interference from Wi-Fi network infrastructures. 802.11a’s 5 GHz channels are unaffected by traffic on 2.4 GHz channels and are all non-overlapping. Nonetheless, planning is required to avoid simultaneous use of the same channel. As with wireless networks, proper planning is the key to success.
You’ll also want to consider these other questions your AV integrator may ask:
Will your signal need to travel 1,000 feet?
Will it need to travel from indoors to outdoors?
Can you manage and service it remotely?
Will you need IR or serial device control?
Is security adequate? Will you need HDCP-compliance for your high definition video?
More technologies will surely emerge over the coming years, and the IEEE 802.11 team continues to develop new specs. Most professionals agree, though, that selecting any of the popular commercial wireless technologies today will still give that network a long and useful life.
“We are at the beginning of the curve for wireless AV,” says Connect802’s Bardwell. “Now that most quality issues have been resolved, demand should only go up from here.”
Denise Harrison, a writer and marketing communications consultant, has managed publications in a variety of industries, including commercial and consumer audiovisual.
Got a comment? Contact us at AVT@nbmedia.com, and type the title of this article into the subject header.
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