4. 802.11a

Updated April 2003

This standard debuted in late 2001. Its main attractions are that it operates in the presently uncrowded 5 GHz frequency band, and has a maximum data rate of 54Mbps. It also has thirteen non-interfering channels - 8 lowband and 5 highband (though not every card supports the highband channels) vs. three for 802.11b, making it easier to set up large, multi AP installations.

As attractive as those features are, there are disadvantages that have slowed 802.11a's acceptance. First, 802.11a equipment will not interoperate with 802.11b products, i.e. there's no backward compatibility.

Second, the higher frequency band may make it more difficult to get good indoor coverage, since 5 GHz signals have a harder time getting through typical residential construction materials. Note that you'll encounter plenty of conflicting claims on this issue. 802.11a manufacturers generally say that although 802.11a signals have a harder time with residential construction, you still get faster speed than you will for 802.11b products at equivalent distances. Our testing of products seems to support this assertion, but performance under weaker signal conditions can be "bursty" in nature, with short periods of high speed, followed by periods of virtually no signal transmission.

On the brighter side, it looks like second-generation 802.11a products have significantly improved indoor range. See our Second-generation 802.11a NTK for more info.

Note also that the advertised 2X or Turbo modes are good only under strong-signal conditions, and using them under weak-signal conditions usually results in slower throughput than you'd get without the Turbo mode enabled. In addition, Turbo is an all-or-nothing proposition for a network, since 802.11a APs can't simultaneously support Turbo and non-Turbo clients.

Third, 802.11a products are more expensive than 802.11b, although prices especially on dual-band (a/b) products have come down significantly since their introduction.

Finally, the lack of adapters in USB and PC Card formats is making it difficult to add desktops and PDAs to 802.11a networks. Desktops must use PCI-based adapters, which get the job done, but require opening the computer's case... something that many users want to avoid. The lack of a 16 bit PC Card format (802.11a PCMCIA cards use the 32 bit CardBus) is probably moot, since the increased drain on a PocketPC's battery would probably limit an 802.11a adapter's usefulness any way.

The 11a-only product market has essentially been replaced by dual-band (a/b) products. This new generation tends to be lower-priced and have much-improved performance.

Recommendation: 11a products can help avoid interference from 2.4 GHz cordless phones, microwave ovens, and neighboring wireless LANs. Definitely worth considering if any of these problems are bothering you, but make sure you choose only second-generation dual-band products.