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Chapter 2, Spectrum Bands: Different Frequencies

There are three major frequency bands available for WISPs to provide coverage to customers, and a fourth that is gaining acceptance for large trunk links. Spectrum bands are described in terms of their frequency range; the ranges stay the same in most regions, while details such as channel availability vary widely between jurisdictions. Learn about 2.4 Ghz, 5.8 Ghz, 900 Mhz and 24 Ghz spectrum bands.

There are three major frequency bands available for WISPs to provide coverage to customers, and a fourth that is gaining acceptance for large trunk links. Spectrum bands are described in terms of their frequency range; the ranges stay the same in most regions, while details such as channel availability vary widely between jurisdictions.

The 900 mhz band is commonly used by old cordless telephones, industrial SCADA (Supervisory Control and Data Acquisition; used in industrial processes), and by WISPs to provide “last-mile” links to hard-to-reach customers. In some areas it can be heavily congested, but sometimes it provides the only option to reach a customer. Unlike higher frequencies, it does a reasonably good job of penetrating foliage, and sometimes it can clear low obstacles. The available 900mhz band is relatively small, so it is of limited use for high-bandwidth links, or for servicing large numbers of customers from a single site.

The 2.4 ghz band is commonly used by Wi-Fi. It offers some foliage penetration potential, and can sometimes reach clients through limited obstacles. However, it is also frequently quite noisy because of home and business wireless access points. 2.4ghz can be a good solution for medium-bandwidth links, and for providing service to end-users, when it is available.

The 5.8 ghz band is commonly used by WISPs, some Wi-Fi systems, and also by Doppler radar. It barely penetrates any foliage, and is typically stopped by walls and even some coated windows. There is a large (and expanding) band of spectrum available, and because of the non-penetrating aspects of the band it is often relatively free of noise and congestion. This makes it the most popular spectrum choice for WISPs, both for high-bandwidth point-to-point links and for point-to-multipoint links to the customer. 5.8ghz should be considered to require a good line-of-sight.

The 24 ghz band is available for high-speed point-to-point links. Over relatively short (up to 5 miles), unlicensed microwave units can provide very high speed (1.5 gigabit-per-second) links, usually with very little noise. 24 Ghz signals do not penetrate any obstacle reliably: perfect line-of-sight is an absolute requirement. Additionally, 24ghz is quite susceptible to “rain fade” - the droplets of water in heavy rain can considerably reduce the quality of a link.

Most WISPs start with 5.8 Ghz links between sites, and either 5.8ghz or 2.4ghz links to customers.

Band Advantages Disadvantages
900 Mhz Good penetration of obstacles. Often noisy, small band available.
2.4 Ghz OK penetration of obstacles. Often very noisy, medium band available.
5.8 Ghz Often quite clean, large band available. Poor penetration of obstacles.
24 Ghz Generally very clean. No penetration of obstacles.
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