05/06

This paper will briefly discuss some questions that come up concerning the use of licensed frequency bands for broadband wireless access (BWA). The intent is to provide simple answers to these questions without too much technical detail.

By far the most prevalent form of wireless broadband is unlicensed. The FCC has set aside several frequency bands for use with products that don’t require a license to operate from the FCC. These bands are known as the Industrial, Scientific and Medical (ISM) bands. In addition, the 5 GHz bands overlap with another unlicensed service known as the Unlicensed National Information Infrastructure (UNII) bands. UNII bands were intended to foster the growth of information networks on a national level.

Band Standard

These are the most common bands in use. There are several other unlicensed bands that are seeing product offerings as well. Some of these bands are much higher in frequency and have a much higher data carrying capacity but are shorter in range.

3.65 GHz to 3.70 GHz
24.05 GHz to 24.25 GHz
57.05 GHz to 64 GHz

The higher frequency bands are used almost exclusively for point to point (PTP) and point to multipoint (PTMP) bridging of high speed backbone links, usually 155Mbps and higher.

By far the most prevalent reason for using unlicensed is the fact they don’t require a license to operate from the FCC. The entire spectrum of a particular band is open for use rather than a specific frequency. The gear tends to be less expensive. Also there is generally a wider selection of antennas. Many of which are lower in cost.

There are a few drawbacks to unlicensed operation however. All of the below items can be countered or thwarted with a professional site survey from a certified WAV technician.

No coordination of frequencies means the potential for interference from another system can be considerable. The FCC will not help resolve conflicts with other users. This is particularly evident in highly populated metropolitan areas.

Other products such as cordless phones, medical equipment, security systems, RFID systems, telemetry systems and microwave ovens use the very same frequency bands. So operation of these devices in close proximity of a broadband system can cause degradation of the system or cause it to shut down completely.

Output power is more restricted with unlicensed products meaning the potential for shorter distances and less coverage.

Many municipalities have avoided using unlicensed bands for public safety based systems. These systems many times are used for health, welfare and safety traffic and the potential for an outage due to interference from another system is unacceptable.

For these reasons the move to licensed frequencies has become more evident. The FCC has made the licensing process easier and less costly. In the past licensing could take many weeks and cost several thousand dollars. The licenses also needed to be renewed more frequently, sometimes every year.

Now, the licenses are more in the range of a few thousand dollars and run for as long as 5 to 10 years depending on the band.

The most common licensed bands are:

Band Service
2.305 GHz to 2.320 GHz Wireless Comm. Svc (WCS)
2.345 GHz to 2.360 GHz Wireless Comm. Svc (WCS)
2.5 GHz to 2.7 GHz Multipoint Distribution (MMDS)
3.3 GHz to 3.8 GHz Possible WiMax
5.9 GHz to 6.9 GHz Possible WiMax
10.7 GHz to 11.7 GHz Possible WiMax
17.7 GHz to 20.2 GHz
21.2 GHz to 23.6 GHz
27.5 GHz to 31.2 GHz Local Multipoint Dist. (LMDS)
38.6 GHz to 40 GHz

There are other bands but these are the ones where BWA has been discussed.

The benefits of licensed operation include:

Exclusive assignment of a specific frequency, which can eliminate co-channel or co-system interference.

Higher power output rules which allow for longer distances.

Higher frequencies allow for higher data rates.

There are a few drawbacks though. Not all bands have frequencies available. For example, Sprint and Clearwire “own” approximately 85% of the 2.5GHz MMDS band. The remaining 15% is owned by several educational and religious groups. In order to obtain a frequency in this band one must attempt to lease a frequency from one of these organizations.

All licensed bands usually require the services of a Frequency Coordinator. An FC is a person or organization that has agreed to take on the task of assigning frequencies in a geographic area. They look up the existing assignments and will find a clear frequency for you. Frequency Coordinators are not a part of the FCC and their services are fee based.

Most manufactures of licensed products can put a customer in touch with a Frequency Coordinator for their particular area.

Most Licensed BWA products now seem to be appearing in the 11 GHz,18 GHz, 3.6 GHz, 23GHz, 24GHz and 39GHz bands. With some in the lower 2.3GHz as well.

The time period to obtain a license can vary from a week or so to several weeks. So this isn’t a product that can be installed quickly.