5GHz

drew · #1 05-21-2007, 02:45 PM

Introduction

This spectrum was originally allocated as part of the National Information Infrastructure (NII) in the US. When the IEEE began pushing the 802.11a standard around the world, many other countries allocated blocks of this spectrum for unlicenced use. As such, the available frequencies vary from country to country.
This band allows high-bandwidth networking devices to move out of the crowded 2.4GHz ISM band, allowing more of these devices to cooexist with one another. As wireless technologies become more commonplace, the need for this additional bandwidth is increasingly important. To further aide this objective, the UNII bands are reserved for high-speed digital communications so fewer devices are permitted to share it.
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Available Spectrum

The U-NII block is actually divided into three 100MHz sub-bands, providing more than 3X the bandwidth of the 2.4GHz ISM band. The low band (UNII-1) spans from 5150-5250MHz, the mid band (UNII-2) from 5250-5350MHz and the high band (UNII-3) from 5725-5825MHz. The following chart illustrates the location of these bands relative to a number of other common services:

Each of these sub-bands may have different regulations governing their use, so it is important for users to check the rules in their local jurisdiction. For instance, in the United States each of the three bands has it's own set of power limits and restrictions on where the networks can be installed (eg. UNII-1 can only be used indoors).
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5470-5725MHz Band

While not part of the official 802.11a standard, this band was originally added by European regulators and is slowly being adopted in other jurisdictions. This provides an additional 254MHz of bandwidth, allowing the use of 10 additional non-overlapping channels. Support for this band is currently limited, however as more countries allocate the spectrum it may become more common.
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5.8GHz ISM Band

Partially confusing the issue is that in some jurisdictions a 5.8GHz ISM band (5725-5850MHz) overlaps the upper band of the UNII spectrum. The use of this ISM band is regulated by a seperate set of rules (similar to those governing 2.4GHz) and allows a much wider range of devices (eg cordless phones) to make use of it. As such, the upper UNII band does carry with it some additional complications.
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Applications

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IEEE 802.11a

The standard that pushed worldwide adoption of this spectrum, 802.11a provides high speed wireless networks with a wide swath of spectrum. Thanks to the wider band, 802.11a networks have access to up to twelve non-overlapping channels. As such, wireless networks using this protocol are better able to deal with other devices in the vicinity. The channel arangement for these networks is illustrated below:

Note that some countries have not allocated all three bands, so in some jurisdictions users may only have a subset of these channels available to them.
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Power Limits

Each jurisdiction has their own set of rules governing the use of this spectrum. The following sections highlight the regulations in several major markets. Note that rules do change over time, so users verify the limitations in their jurisdiction before pushing the limits.
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North America

Band	Low (UNII-1)	Mid (UNII-2)	High (UNII-3)
Usage	Indoor Only	Indoor or Outdoor	Indoor or Outdoor
Removable Antenna	N	Y
Transmit Power	50mW	250mW	1W
Antenna Gain (Omni)	6dBi
Antenna Gain (Directional)	6dBi		23dBi