Software defined radios and 802.11n

* Tunable APs become consideration for 802.11n networks

Software-defined radios, or SDRs, persevere as a lively topic of discussion. An SDR enables a given radio to tune to variable frequencies to meet the specifications of different applications and country-by-country regulations. SDR capabilities are emerging as a consideration for 802.11n, which relies heavily on the 5GHz band for optimum throughput - a band that is subject to regulation around the world.

Cisco Wi-Fi access points (AP), including its Aironet 1250 802.11n AP, have long been the only APs certified by the FCC as an SDR. Today, Aruba Networks intends to announce that its 5GHz-capable products have been FCC SDR-certified, too, and also certified for dynamic frequency selection (DFS).

Formal SDR certification is important as it relates to transmissions using the 5.25GHz to 5.35GHz and 5.47GHz to 5.725GHz bands and DFS. Products that transmit across these bands, which play a prominent role in helping 802.11n networks achieve their high speeds, are required by the FCC to support DFS. The reason is that these bands are also used for military and weather radar: DFS detects the existence of radar in channels and quickly changes channels to get out of the way.

SDR and DFS are intertwined in the following way: The FCC doesn’t allow 802.11 infrastructure vendors to upgrade their products to support DFS or to amend their DFS implementations to work on relevant channels as they change over time unless those products have also been FCC-certified as an SDR. Until today, Cisco was the sole vendor to have achieved that status.

Said Chris Kozup, Cisco senior manager, mobility solutions, in an interview in July:

“From a regulatory perspective, SDR allows us to make adjustments effectively and easily, even in other countries. Let’s say Japan comes up with a regulation change. Assuming the change can be handled in software, we are in the position to incorporate those changes through software, where any other vendor would have to swap out their hardware for that country” and potentially disrupt its customers’ networks.

In other words, you can look at SDR certification from Cisco, Aruba and, perhaps, others still to come as important investment protection against changing regulatory rules surrounding frequency use.

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Copyright © 2008 IDG Communications, Inc.

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