Wireless frequency band information for networks, devices, and countries - Stay connected anywhere in the world. 802.11 WLAN Frequency Bands - five distinct frequency ranges: 2.4 GHz, 3.6 GHz, 4.9. European standard EN 301 893 covers 5.15–5.725 GHz operation,.

Because I have been in the Wi-Fi industry for 12+ years, I sometimes forget that the technology is still a young technology. To this day I find that many people are just getting introduced to the basic concepts of 802.11 wireless networking. Therefore, I wanted to write a quick Wi-Fi back-to-basics blog about channel reuse patterns in the 2.4 GHz frequency band. This blog is not intended for all of you Wi-Fi veterans but is instead targeted to Wi-Fi newbies.

802.11b/g/n Wi-Fi radios can transmit in the 2.4 GHz band with a total of fourteen available channels. In the US only eleven of those channels are legally available and only 13 are available in Europe. Figure 1 depicts a spectrum analyzer view of the frequency space occupied by these fourteen channels. Please note that within the 2.4 GHz band, only three channels have non-overlapping frequency space: channels one, six and eleven.

_{Figure 1}

When designing a wireless LAN (WLAN), overlapping RF cell coverage is necessary to provide for seamless roaming. However, the overlapping coverage cells should not have overlapping frequency space. In the United States, there are only three channels (1, 6 and 11) that do not share frequency space. RF is a half-duplex medium that allows for the transmission of only a single radio on any frequency channel, therefore when three or more 2.4 GHz APs are needed to cover an enterprise facility, only the non-overlapping Figure 1channels of one, six and eleven should be used. Figure 2 shows a floor plan using six APs to provide coverage. Note that only the non-overlapping channels of 1, 6 and 11 are used. This cell design is often referred to as a channel reuse pattern. A 1-6-11 channel reuse pattern in always the proper design in North America.

_{Figure 2}

Figure 3 shows an improper channel design using the same six APs. Note that channels 1-7 are used and all the channels share overlapping frequency space. The improper channel reuse design depicted in Figure 3 causes what is often known as adjacent cell interference. Data corruption is caused by your own APs transmitting at the same time over shared frequency space. The end result is decreased throughput and increased latency. Adjacent cell interference is simply RF interference caused by your own APs due to improper channel design.

_{Figure 3}

One of the most common mistakes many businesses make when first deploying a WLAN is to configure multiple access points all on the same channel as depicted in Figure 4. If all of the APs are on the same channel, unnecessary medium contention overhead occurs. Wi-Fi uses a listen-before -you-talk technology called the clear channel assessment (CCA) to ensure that only one radio can transmit on the same channel at any given time.

If an AP on channel 1 is transmitting, all nearby access points and clients on the same channel will defer transmissions. The result is that throughput is adversely affected: Nearby APs and clients have to wait much longer to transmit because they have to take their turn. The unnecessary medium contention overhead that occurs because all the APs are on the same channel is called co-channel interference (CCI).

In reality, the 802.11 radios are operating exactly as defined by the CCA mechanisms, and this behavior should really be called co-channel cooperation. The unnecessary medium contention overhead caused by co-channel interference is a result of improper channel reuse design.

_{Figure 4}

It should be noted that it is impossible to avoid all instances of co-channel interference/cooperation when using a three-channel reuse pattern at 2.4 GHz, because there is always a certain amount of bleed over between channels on the same channel. If only three channels are available for a channel reuse pattern, it is pretty much a given that there will be access points on the same channel within hearing distance of each other. One of the advantages of using the 5 GHz frequency band is that there are many more channels. Co-channel interference/cooperation can be completely avoided with a proper 5 GHz channel reuse pattern. (That’s a topic for my next blog.)

Please understand that client station transmissions also result in the medium contention performance downgrade known as co-channel interference/cooperation. As shown in Figure 5, if a client is at the outer edges of a coverage cell, the client’s transmissions may propagate into another cell using the same channel. All of the radios in the other cell will defer if they hear the original client’s transmissions from a different cell but on the same channel.

_{Figure 5}

In Europe, a 2.4 GHz four-channel reuse pattern of channels 1, 5, 9 and 13 is sometimes deployed as shown in Figure 6. Although there is a small amount of frequency overlap between those four channels, the performance might in some cases be better if the medium contention overhead of co-channel cooperation can be reduced because there is less channel bleed over.

_{Figure 6}

I am personally not a big believer of the four-channel plan, even in Europe. The four-channel plan has disadvantages. If a nearby business has APs deployed using the traditional 1-6-11 plan, the neighboring business’s APs will cause severe adjacent channel interference with your APs deployed with a 1-5-9-13 plan. Also, all North American Wi-Fi radios are restricted by firmware and cannot transmit on channel 13. Any visiting customer or employee with a laptop, iPad, or other mobile device that was purchased in North America will not be able to connect to a European access point transmitting on channel 13.

Consumer Alert for Wireless Microphone Purchases

Anyone selling or leasing a wireless microphone or other device designed to operate in the 617-652 MHz and 663-698 MHz frequencies must provide the following disclosure to consumers:

'This particular wireless microphone device operates in portions of the 617-652 MHz or 663-698 MHz frequencies. Beginning in 2017, these frequencies are being transitioned by the Federal Communications Commission (FCC) to the 600 MHz service to meet increasing demand for wireless broadband services. Users of this device must cease operating on these frequencies no later than July 13, 2020. In addition, users of this device may be required to cease operations earlier than that date if their operations could cause harmful interference to a 600 MHz service licensee's wireless operations on these frequencies. For more information, visit the FCC's wireless microphone website at www.fcc.gov/wireless-microphones-guide or call the FCC at 1-888-CALL-FCC (TTY: 1-888-TELL-FCC).'

New rules now in effect for operating wireless microphones and similar devices will restrict their use in certain bands of the spectrum currently used for television broadcast. As a result, some equipment changes may be needed for local theaters, churches, schools, conference centers, sports stadiums and other users of such devices.

Wireless mics and similar devices are designed to tune and operate on certain frequencies known as 'spectrum bands.' Most wireless mics today operate in the various unused portions of the broadcast television bands, including both VHF and UHF channels. They can be operated on either on a licensed basis, for qualifying users, or on an unlicensed basis, open to all who use the appropriate equipment, provided that users follow the applicable rules for operation on designated spectrum bands.

Changes to operations on frequencies in the 600 MHz service band

To meet increasing demand for wireless broadband services nationwide, the FCC recently auctioned spectrum that had been licensed to broadcast television stations operating on TV Channels 38-51. The results of the auction (completed in April 2017) will affect the availability of spectrum for wireless microphone operation on the 600 MHz frequencies that correspond to these TV channels, specifically the 614-698 MHz frequencies. Most of these 600 MHz frequencies have been repurposed for new 600 MHz service wireless operations (specifically, the 617-652 MHz and 663-698 MHz frequencies).

Transition operations

The FCC has established a time period to help smooth the transition of wireless microphone operations out of the 600 MHz service band to other available frequencies. Specifically, the FCC allows users to continue operations on the 600 MHz service band under certain conditions until July 13, 2020. However, users must not cause harmful interference, either to the existing broadcast television operations or to the 600 MHz service wireless licensees' operations in the band. In addition, users are not entitled to any interference protection from broadcast television and 600 MHz service licensees.

Available frequencies following the transition

Many frequencies in the TV bands that had been available for wireless microphone use prior to the auction will continue to be available after the transition period. These include:

• VHF and UHF frequencies on TV channels 2-36, which fall below 608 MHz.
• Certain frequencies in the 600 MHz guard band: 614-616 MHz.
• Certain frequencies in the 600 MHz duplex gap: 653-657 MHz for licensed use or 657-663 MHz for unlicensed use.

Additional frequencies outside of the TV bands also are available for wireless microphone use. Unlicensed wireless microphone use is permitted on the 902-928 MHz band, the 1920-1930 MHz, and on portions of the 2.4 GHz and 5 GHz bands under specified power levels and rules for operation for each of those bands. Licensed wireless microphone use is permitted on several other spectrum bands, including on portions of the 900 MHz band, the 1435-1525 MHz band, and the 6875-7125 GHz band.

What specific wireless mics are affected by the transition?

To determine whether the transition affects the continued use of particular wireless mics, operators will need to know the specific frequencies that are used by their mics. Contacting the manufacturer may be the most effective way of determining whether a particular wireless mic is affected by the transition and may need to be modified or replaced. Additionally, information on the frequencies used maybe be provided in the user manual of the particular model.

Power restrictions for unlicensed mics

Unlicensed wireless mics must not be operated at a power level in excess of 50 milliwatts when operating in the TV bands, and no more than 20 milliwatts when operating in the 600 MHz guard band or duplex gap. Users are advised to consult their owner's manual or other materials provided by the manufacturer or distributor to determine the output power of their wireless mics.

Devices 'similar' to a wireless mic

Wireless devices similar to wireless mics include 'low power auxiliary station' equipment, which typically can transmit over distances of 100 meters. Examples include wireless intercoms, wireless in-ear monitors, wireless audio instrument links and wireless cueing equipment. Operators of such unlicensed devices should follow the same rules for frequency use as wireless microphone users.

Licensed operations

Under FCC rules, certain specified entities can obtain a license to operate under specified rules and interference protections. Such entities include licensees of AM, FM or TV stations, broadcast networks and cable-television system operators, and venue owners/operators and professional sound companies that routinely operate 50 or more wireless mics for events and productions at large venues such as large sports stadiums and arenas, music centers, or major theaters.

Part 74 licensees

Licensees under the Commission's Part 74 rules may operate in the spectrum bands identified in their licenses. The changes going into effect will require anyone operating in the spectrum that is now licensed for the 600 MHz service (most of the spectrum that was used for TV channels 38-51) to cease operation in those bands and move to other portions of the TV bands (TV channels 2-36) or to other spectrum bands authorized for wireless microphone use.

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Prohibition on use of the 700 MHz band

In 2010, the FCC prohibited the use of wireless mics and devices on unused broadcast channels on the 600 MHz service band and on the 700 MHz band – specifically the frequencies between 698 and 806 MHz. It did so because such use could cause harmful interference that disrupts or degrades communications in the spectrum bands that had been repurposed for use by public-safety networks and licensed commercial wireless services.

Reporting interference

Failure to comply with FCC rules by unlawfully operating wireless mics or devices in the 600 and 700 spectrum bands may result in fines or additional criminal penalties.

Public safety licensees may contact the FCC Operations Center 24 hours a day, seven days a week, at (202) 418-1122, or FCCOperationCenter@fcc.gov to report interference. They may also contact the FCC's Public Safety Support Center at https://www.fcc.gov/general/public-safety-support-center.

Consumers may report interference with devices operating on licensed spectrum by filing a complaint with the FCC.

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Operation of Wireless Microphones (pdf)