The New Wi-Fi Speed: 90Mbps

By Eric Griffith

April 30, 2003

Atheros says its Super G and Super A/G capabilities can push wireless LAN throughput to 90 Megabits per second in real-world use using a mixture of packet burst mode, compression, dual-channel use and modulation tricks.

First, some history.

Atheros, one of the primary providers of 802.11a chips for the 5GHz WLAN product market, has long provided a "Turbo mode" on it's products to boost the standard 802.11a speed of 54 Megabits per second (Mbps) up to 72Mbps in its first generation, and later 108Mbps.

The problem with Turbo mode was and is that, like most theoretical speeds for any network, it didn't even come close to 108Mbps -- usually only around 35Mbps. That's still nice and fast compared to 802.11b, but if an 802.11a access point was in Turbo mode, it had to physically be reset to normal mode before non-Atheros based 802.11a clients could connect to it. And that's just annoying.

Now Atheros is ready to show off its 802.11g chips and multimode 802.11abg chips -- in fact, at this week's Networld+Interop, they're demonstrating products from retail companies like D-Link, Linksys, SMC, and Netgear using Atheros-based 11abg. With those new chips comes a new speed boost Atheros is calling "Super G" (for their 802.11g single band chip, the AR5001G) and "Super A/G" (for the dual-mode AR5001X+chip).

Atheros says Super speeds can again reach a 108Mbps data rate, but -- when mixing the various solutions used to get the boost and depending on the network environment -- the actual TCP/IP throughput in real-world use could go as high as 90Mbps.

Rival chipmaker Intersil recently announced a software upgrade called Nitro for its own 802.11g chips (the single mode PRISM GT and the dual-mode 802.11a/g PRISM Duette) that uses burst mode to push speeds to 30Mbps in real-world use.

Atheros says they've done much more.

According to Atheros vice chairman Rich Redelfs, the first thing they did was to take customer requests to heart and made sure that the Super G and Super A/G speeds are "dynamic and interoperate," meaning an access point using Super G speed will "talk to any client with our chips in turbo speed, but will jump out of that if needed," such as when an non-Atheros 802.11g client wants to log on. No more manually resetting the access point to normal speeds.

So how do they get the top speeds they claim? It takes a mixture of things, including a burst mode similar to what Intersil's Nitro does. The burst is based on functions that will come soon in other WLAN specifications such as 802.11e, which will handle quality of service (QoS) for multimedia transmissions.

"Instead of sending a packet and waiting your turn...you can send 3 or 4 packets at a time," says Redelfs. This depends, of course, on the overall network traffic, and he adds that since it's based on a QoS specification, multimedia traffic will get priority.

Couple the bursts with hardware-based compression, using two-channels instead of just one for transmitting and receiving, and some proprietary optimization of the modulation schemes, and you've got Super speed. Atheros apparently has a chart that shows the steps to Super speed thusly:

1) Mixed 802.11b/g environments get between 9 to 14 Mbps throughput

2) Pure 802.11g can go as high as 24Mbps

3) If you add the double channel turbo mode, it jumps to 42Mpbs

4) Bursting + turbo brings the speed to 65Mbps

5) Bursting + turbo + compression (all in pure 802.11g environment) = 90Mbps.

The use of the features is not only dynamic so to be backwards compatible, but also configurable. Redelfs says the features that provide the speed boost can be turned off if desired.

Of course, "actual results may vary depending on conditions." Meaning, don't get your hopes too high of maintaining 90Mbps depending on your mix of clients, access points, duct work, cement walls, microwaves in the kitchen, and the alignment of the stars.

There's a new group that might be forming with the 802.11 Working Group of the IEEE (those responsible for the specifications on which wireless LANs are based) that some have termed 802.11n. It's expected to have the sole purpose of increasing WLAN speed by focusing on a new modulation scheme that could push speeds to 108 or as much as 320Mbps.

802.11 Planet Conference Did you even know dual-mode products are now readily available? Or have you given up on 802.11a as an option? Join us at the 802.11 Planet Conference & Expo, June 25 - 27, 2003 at the World Trade Center Boston in Boston, MA. You might not be alone, and you can find out what the expert think as they sit on the panel that answers the question Competing Technologies: Will 802.11a Survive?



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