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Analysis: Fixed Wireless: Page 5 of 11

Licensed microwave systems, available from companies like Alcatel, BridgeWave, Ceragon Networks, DragonWave, Gigabeam and Harris Stratex Networks, operate in frequencies that range from 11 GHz to 95 GHz with licenses from the FCC. Fortunately, because of the low power and limited propagation of a typical fixed wireless installation, the licensing process is relatively painless, albeit not speedy. Depending on frequency, a license could be approved within 48 hours of submission; however, it takes 30 days before it can be used for your organization. During this waiting period the FCC issues a "Prior Coordination Notice" that gives other license holders in your area a chance to contest issuance based on overlap. Once approved, licenses are renewable and good for 10 years.

Licensed systems, though expensive, offer some of the best fixed wireless data performance, with throughput ranging from 50 Mbps to 10 Gbps. And, because your organization "owns" the spectrum for that installation, you're immune from interference posed by other installations. On the downside, if you need a link up within a week, the lengthy licensing process will be a roadblock.

FSO (Free Space Optical) systems are available from Canon USA, LaserBit Communications, LightPointe Communications and other vendors. Whereas fixed microwave installations operate in various parts of the traditional RF spectrum, FSO uses infrared or visible light for communications. FSO can offer high performance (up to 1.25 Gbps) over short distances (generally under one mile), and these links are extremely hard to intercept and thus very secure. However, FSO can be adversely affected by heavy fog or other atmospheric conditions.

Finally, license-free microwave systems run the gamut in range, price and quality. In the United States, the FCC has set aside numerous frequency bands for fixed wireless, including the 2.4-GHz and 5-GHz ISM bands, most often associated with Wi-Fi, as well as the 24-GHz and 60-GHz bands. These higher bands are relatively immune to interference compared with the 2.4-GHz and 5-GHz bands, which are becoming increasingly cluttered.

A 24-GHz system, like those available from DragonWave, offer up to 500 Mbps of throughput, while 60 GHz, or millimeter microwave, can provide speeds of 1 Gbps to 1.5 Gbps and are available from vendors like Terabeam and Ceragon. These 60-GHz links are unique in that radio signals are actually absorbed by oxygen in the atmosphere, which attenuates the signal. This offers advantages and disadvantages: On one hand, 60-GHz links are better isolated from interference because absorption by oxygen keeps the signal from straying. However, this also limits the distance a 60-GHz link can cover. Moreover, 60-GHz systems can be negatively impacted by rain. Depending on your geographic location, expect maximum distances of .5 to 1.5 miles.