Chapter 2, Spectrum Bands: Licensed vs. Unlicensed
This chapter discusses some of the more common spectrum bands available for use by a WISP, and their relative advantages and disadvantages. The majority of WISPs operate in what is called “unlicensed spectrum”; that is, spectrum that is made freely available by their country's regulatory bodies for anyone to use. Other options exist; this section examines these options.
The majority of WISPs operate in what is called “unlicensed spectrum”; that is, spectrum that is made freely available by their country's regulatory bodies for anyone to use. There are a number of advantages to using unlicensed spectrum:
- There are no fees associated with using it.
- Equipment for the popular unlicensed spectrum bands is widely available, at a reasonable cost.
- There is considerable practical knowledge to be found on the properties of unlicensed spectrum, because of its widespread use.
There are, of course, also disadvantages to utilizing unlicensed spectrum. These include:
- Congestion. Some frequency bands are heavily utilized, particularly in cities, and may be rendered useless by other wireless operators. This is particularly true of the 2.4ghz spectrum band, which is commonly used by home and business Wi-Fi. There are, however, a number of tools available to help you make use of this spectrum even in crowded areas – and with proper insight, planning and monitoring it is entirely possible to co-exist with other systems.
- Regulatory Limits. Many frequency bands operate under regulatory limits on effective radiated power (“EIRP” - Effective Isotropic Radiated Power). It is necessary to be aware of the regulations affecting your region, and to comply with these restrictions.
There are also a number of “licensed frequencies” available. Licenses can be obtained from your region's regulatory body (for example the FCC), and most of the licensed equipment vendors will assist in obtaining a spectrum license for your link (most licenses are per-link; per-area licenses are typically very expensive, if they are available at all – the major cellphone companies own the majority of the licensed spectrum for wide-area coverage). The advantages to using licensed spectrum include:
- No Congestion. If you have a license, then the spectrum covered by the license is yours. If interference appears on your link, you have the right to involve the authorities in removing the interfering parties from your licensed area.
- Performance. Many licensed links out-perform unlicensed links, mostly because of the lack of congestion (above), but also because some of the “better” frequencies are only available with a license.
There are also significant disadvantages to using licensed spectrum:
- Equipment Cost. Equipment for licensed spectrum is often several orders of magnitude more expensive than equipment for unlicensed spectrum. The majority of the buyers are large, so there is no impetus for equipment vendors to aggressively reduce pricing.
- License Cost. Purchasing licenses can be expensive, especially if your network is large and requires many licensed links. Additionally, maintaining spectrum licenses can require FCC attorney assistance (or your regional equivalent), which can be a very large expense in and of itself.
Most start-up WISPs operate entirely in unlicensed frequencies. As they grow, licensed options can become attractive for heavily utilized “backhaul” [trunk routes between towers] sites. It is therefore recommended that WISPs remain mindful of licensed options for the future, but start out in unlicensed territory to reduce start-up costs.
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