Technology tussle

Round One: Number of channels

In the U.S., 802.11a offers eight nonoverlapping channels vs. three channels shared by 802.11b and 802.11g. If the company or department next door (or upstairs or downstairs) has an 802.11a network, more channels makes it easier to configure your 802.11a network to avoid interference.

In dense installations, extra channels can make 802.11a networks up to 14 times faster than 802.11b networks, says Rich Redelfs, CEO of Atheros, currently the only chip maker shipping 802.11a chipsets.

However, the U.K. and the Netherlands, the first two countries to approve 802.11a in Europe, have approved only four channels. Other countries in Europe might approve different channels and different numbers of channels.

"By the time you get to pan-European approval, you might be down to three channels, which is no different than [802.11]b," says Tom Dowd, principal product manager of wireless computers and terminals, for Intermec.

If 802.11a fails in Europe, you'll see 802.11g succeeding there in the long term, Dowd predicts.

Then again, regulation can work against 802.11b, too. For instance, in Japan, 802.11b can only use one channel.

A dual 802.11a/b or 802.11a/g network gives you 11 channels in the U.S., for instance. Anywhere in the world, a dual system will give you more channels than a nondual system.

Winner: Dual-mode 802.11a/b or 802.11a/g
Second: 802.11a
Third: 802.11b

Round Two: Bandwidth

What you care about is not theoretical bandwidth, but real throughput, which can vary tremendously with distance, obstacles and interference, not to mention the nature of the application. The theoretical difference of 43M bit/sec (54M bit/sec minus 11M bit/sec) between 802.11a and 802.11b is actually more like 30M bit/sec (36M bit/sec minus 6M bit/sec).

The ABGs of wireless LANs
802.11 insecurity

Furthermore, to the extent that 802.11b has better range and penetration, its throughput will degrade less with the same distance and obstacles, narrowing the gap still further.

"There have been instances where companies tried to use 802.11a to bridge across the street, and discovered they can only get an effective throughput of 6M bit/sec," says Matthew Wheeler, chief wireless architect at consulting firm Blue Modal.

In some instances, 802.11g could provide better throughput than 802.11a. This could occur in situations where density is modest (and therefore extra channels don't matter) but obstacles or distances are significant (and therefore lower frequencies do better).

If you're considering bandwidth for an individual client, most clients today can't even stress an 802.11b pipe. In fact, says Allen Nogee, senior analyst for

Cahners Instat/MDR, throughput in excess of what 802.11b offers is needed only for very specialized applications.

Finally, if you look at the bandwidth of the entire network, the dual-mode 802.11a/b or 802.11a/g systems come out on top, because they combine the throughputs of both technologies.

Winner: Dual-mode 802.11a/b or 802.11a/g
Second: 802.11a
Third: 802.11b

Round Three: Interference

There is very little operating in the 5.2-GHz band used by 802.11a, while the 2.4-GHz band used by 802.11b and 802.11g is getting more crowded every day, with devices such as cell phones, microwave ovens and Bluetooth peripherals for PDAs. To the extent that higher-frequency signals have shorter range and more limited ability to penetrate barriers, 5.2-GHz systems will tend to interfere less with one another than 2.4-GHz systems.

However, the 2.4-GHz and the 5.2-GHz bands are unlicensed and fair game for whoever wants to use them. The 5.2-GHz band also may fill up over time. Ultimately, interference is a sign of popularity. Redelfs says that analysts are "dramatically underestimating" how fast 802.11a is moving. Perhaps they also are dramatically underestimating the amount of interference that users ultimately will experience in this band.

Proponents of 802.11a say that subsequent generations will have better range and penetration characteristics. That should increase interference, too.

In short, the better it gets, the worse it gets.

There's also the fact that 802.11a is less of a known quantity when it comes to interference.

"Hospitals have stacks of data on how 2.4 GHz doesn't interfere with their systems," Wheeler says. For now, they are likely to stick with 802.11b technology that is working well for them, rather than taking the chance of going to something that is theoretically better, he says.

The same thinking should make 802.11g attractive, because its interference characteristics should be identical to 802.11b.

Finally, for interference, too, the best system is a dual system, which opens the possibility of selecting the band that avoids whatever interference you encounter. This is particularly important for mobile devices that might encounter various types of interference in their travels.

Winner: Dual-mode
Second: 802.11a
Third: 802.11b

Round Four: Power consumption

Equipment operating at a higher frequency generally consumes more power than similar equipment running at a lower frequency.

However, the modulation scheme also plays a significant role in determining power consumption. 802.11g uses the same modulation schemes as 802.11a, Orthogonal Frequency Division Multiplexing (OFDM). In contrast, 802.11b uses the less power-hungry complimentary code keying.

OFDM radios, whether operating at 5GHz or 2.4GHz, consume significant power because of the high peak-to-average power ratio (PAPR) of OFDM signals, notes Tyler Burns, product marketing manager for IceFyre Semiconductor. High PAPR results in inefficient power amplification, increasing power consumption, Burns says.

Winner: 802.11b
Second: 802.11g
Third: 802.11a

Round Five: Range/penetration

A higher frequency signal will have shorter range and worse penetration than a lower frequency signal. This is based on the laws of physics. Nevertheless, chipset and system manufactures can find ways to mitigate these effects.

Redelfs says the disparities seen so far are because a first-generation 802.11a product is being compared with a fourth- or fifth-generation 802.11b product. The next generation of 802.11a, he says, will have a longer range than 802.11b at any throughput.

Another thing to consider is if you're worried about eavesdropping, signals not traversing walls too easily might be a good thing.

Winner: 802.11b
Second: 802.11a
Third: 802.11g

And the winner is

The three most important technical advantages of 802.11a over 802.11b are more channels, more bandwidth and less interference. While each of these is arguable to some extent, 802.11a is better. Bring 802.11g into the mix and the balance begins to tip away from 802.11a, although still not decisively.

Multimode products, however, are clearly superior to any of the other options on all three fronts. The biggest problem is that early multimode products will likely be pricey.

Technology tussle

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