Availability of spectrum is key to making a fixed wireless network deployment work. Cellular and 4g data operators like Clear have purchased the rights to huge chunks of “licensed” spectrum, which is set aside for their use and free of any interference from competing devices. This is the common deployment methodology used by the telcos. Being able to control the RF environment is very important to the integrity of a mobile wireless network, because of the small antennas used.
Unfortunately, in many rural areas the main advantage of owning spectrum is to prevent competition. It is costly to purchase even tiny slivers of spectrum for exclusive use, but well funded telcos and cellcos have a large inventory of spectrum that is booked as an asset on their accounting but lies fallow or only maintains the bare minimum of equipment installed to meet the buildout requirements. The way that the spectrum borders are determined also puts rural areas at a substantial disadvantage. From the perspective of a single town, or even a county, licensed spectrum is not going to be an option, due to the high costs.
In recent years, a new alternative to licensed spectrum has emerged – unlicensed. Once considered to be “junk” spectrum, unlicensed has become very commonplace and is used for cordless phones, baby monitors, wireless video transceivers and even for lighting purposes. The most common use of unlicensed spectrum is for indoor wireless networks, with the most common type being the WiFi standard. WiFi uses spread spectrum modulation, which lowers the capacity that it can carry but makes it much more tolerant of interference from other devices in the same spectrum. Outdoor deployments using unlicensed spectrum are capable of delivering broadband speeds as long as they are done with equipment that synchronizes the transmit and receive time slices (GPS Sync) or are laid out carefully to minimize the amount of potential interference between nodes.
There are three band of unlicensed spectrum in commonplace use today: the 900mhz band (902mhz to 928mhz), 2.4ghz (2400 to 2483mhz) and 5ghz (three sub bands – 5.25-5.35ghz, 5.47-5.725ghz and 5.72-5.825ghz. Typically, 900mhz is used for situations where penetration of foliage and buildings is required, 5ghz is used for backhaul and point-to-multipoint when there are no trees, and 2.4ghz is normally used for point-to-multipoint access. Unlicensed spectrum devices can be deployed anywhere, as long as they follow specifications for power, antenna size and modulation schemes. They are also required to accept interference from other devices, in accordance with the Part-15 rules laid out by the FCC.
Unlicensed spectrum has several disadvantages. Many common consumer devices use the same spectrum, and it is quite common for devices to interfere with each other. Baby monitors and cordless phones cause a substantial amount of noise. WiFi access points in the 2.4ghz spectrum are another source of noise for fixed wireless broadband deployments, and this issue has been exacerbated to a certain degree by the high power, on-by-default wireless access points built into new DSL and cable modems. If multiple broadband providers are using the same spectrum, there is also the possibility of interference between providers. GPS sync technology will remedy this if all of the providers are using the same type of equipment, but most of the low cost, outdoor broadband equipment does not use this feature. Spectrum coordination between fixed wireless broadband providers is critical to system integrity.
Unlicensed spectrum has many important advantages that make it very useful, in spite of its other shortcomings. There are no licensing requirements, so equipment can be deployed at any time, and in any location desired. This is a sharp contrast to the geographic restrictions on regular spectrum licenses and the wait times involved when trying to coordinate and plan deployments. Unlicensed equipment is also substantially cheaper than licensed gear. This is partially due to the huge volumes of consumer devices that run in unlicensed spectrum. Almost every make and model of unlicensed fixed wireless broadband equipment uses the same chipsets and basic components as consumer equipment, so costs are lower and the rate of innovation is higher than what is seen in licensed gear. The necessity of dealing with interference has also lead to equipment that is more robust and capable of dealing with adverse RF environments. As long as a good signal to noise ratio is maintained, unlicensed radios can deliver good performance, offsetting one of the biggest perceived advantages of licensed spectrum.
One of the most overlooked advantages of unlicensed spectrum is that is unlocks the entrepreneurial ability of the smaller business to generate competition. This is what enabled the WISP (Wireless Internet Service Provider) industry to develop. There are at least 2000 documented WISPs in the United States, and most likely many more. Many of the independent ISPs that grew disillusioned with the inability to make money in dialup or DSL turned to wireless and recreated themselves. Being able to build their own networks makes it possible for a WISP to be profitable, even with very small customer counts. When it is possible to overcome the hurdles of high equipment costs, spectrum licenses and middle-mile connectivity, there is more room for competition in other aspects of the business. Customer service, specialized deployments and innovative uses of the technology allow WISPs to create profitable businesses, even while serving areas that are unprofitable for the telcos despite the large subsidies that they receive.
Armed with low cost, unlicensed equipment and an entrepreneurial spirit, WISPs have been able to take the “guerilla” approach to building out broadband networks. Often found in places where cable and dsl networks will not go, WISPs have been building out broadband in unserved and underserved areas across the US for over ten years. For a town like Medicine Bow – ignored by the incumbent telephone company, sitting next to a fiber network that they cannot connect to and isolated from any other population centers – this looked like the only way to get broadband in the foreseeable future.