Ruckus readies draft 802.11n streaming video demo

Smart-N gateway transmits and manages high-definition MPEG-2 video streams wirelessly

The Consumer Electronics Show in Las Vegas in January promises to showcase wireless LAN products implementing the draft version of the 802.11n standard.

Expect to see a range of prototype demonstrations like the one planned by Ruckus Wireless, a California-based company that sells systems to reliably transmit multimedia streams over a residential WLAN, carrying the signal through multiple floors and walls.

At CES, Ruckus' prototype Smart-N gateway, using the Atheros Communications chipset based on the draft 802.11n standard, will transmit and manage three high-definition MPEG-2 video streams. Each stream will run over an 11n link to a companion Ruckus adapter that's plugged into a Motorola set top box, which is cabled to a high-definition TV set.

Using current silicon, the so-called "pre-11n" equipment offers throughput of about 70Mbps, compared to about 21-24Mbps for 802.11a/g, according to Ruckus executives. The 11n prototype gateway will stream three 19.2Mbps video streams to the adapters on the three set top boxes.

By contrast, a companion demonstration, with the existing 802.11a/g Ruckus MediaFlex router and adapters, will beam simultaneously two or three MPEG-4 high definition IPTV streams, each about 4Mbps or somewhat higher.

The company's existing MediaFlex products were designed to sustain consistent wireless throughput for video and audio traffic over longer distances than is possible with conventional WLAN equipment.

To do so, Ruckus combined a sophisticated, adjustable multiple input multiple output (MIMO) antenna array at both ends of the link, with software that analyzes and classifies each packet and then sets up the optimal data rate and signal path.

Ruckus engineers have been marrying this technology with 802.11n, which also uses MIMO to achieve much higher levels of throughput, and to sustain them over longer distances, than is possible with today's WLANs.

For example, the 802.11 WLAN standard mandates a series of changes to lower the data rate in preset steps, as the distance between access point and client device increases or as the connection degrades due to interference. The idea is to maintain the connection with a somewhat predictable, usable, though lower, data rate.

But whereas 11g has 12 such data rate steps, managed by a set of rate adaptation algorithms, 11n has 88 such steps, according to Ruckus Vice President of Engineering Steve Martin. In addition, Martin says that Ruckus' tests found that the existing algorithms will step down automatically, but with multiple traffic streams, these lower rates sometimes perform worse than the higher rates.

Ruckus is writing code that works with the rate adaptation algorithms, to make them smarter about which data rate to select, in conjunction with the self-adjusting Ruckus antenna technology. "As you shift rates, we [then] pick the one that gives the best possible throughput, and it's not obvious [ahead of time] what that rate should be in any given case," Martin says.

The 11n standard may result in WLAN products that could support up to 600Mbps, depending on the number of antennas on each end of the link, the use of 40 MHz instead of 20 MHz channels, the distance between devices, and other variables. In Ruckus' case, some of those variables include the number of video streams, and their resolution. Martin estimates the Ruckus 11n products, due out later in 2007, will deliver about 150-160Mbps.

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John Cox

Network World
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