802.11a Channels

What are channels in 802.11a?

Channels in 802.11a refer to specific frequency ranges in the 5 GHz band on which wireless devices communicate.

How many channels are available in 802.11a?

802.11a supports up to 12 or more non-overlapping channels depending on the regulatory domain.

What is a frequency band in wireless communication?

A frequency band is a specific range of frequencies within the radio spectrum used for communication.

Which frequency band does 802.11a operate in?

802.11a operates in the 5 GHz frequency band, specifically between 5.15 GHz and 5.825 GHz.

What are UNII bands in 802.11a?

UNII (Unlicensed National Information Infrastructure) bands are subsets of the 5 GHz spectrum used by 802.11a.

What are UNII-1, UNII-2, and UNII-3 bands?

They are regulatory frequency ranges within the 5 GHz spectrum, each with specific usage rules and channel allocations.

What is channel width in 802.11a?

Channel width refers to the size of the frequency band used to transmit data. In 802.11a, it is 20 MHz.

Why does 802.11a use 20 MHz channels?

20 MHz channels strike a balance between data rate and resistance to interference, standardizing operation across devices.

Are 802.11a channels overlapping?

No, 802.11a channels are non-overlapping due to their spacing and 20 MHz width, reducing interference.

What determines the number of usable channels?

The country’s regulatory rules and allowed UNII bands determine how many 802.11a channels can be used.

What is Dynamic Frequency Selection (DFS)?

DFS allows access points to detect radar signals and switch channels to avoid interference, often required in UNII-2 bands.

What is Transmit Power Control (TPC)?

TPC adjusts transmission power based on link conditions, reducing interference in 802.11a networks.

Can 802.11a use 40 MHz or 80 MHz channels?

No, 802.11a only supports 20 MHz channels. Wider channels are introduced in later standards like 802.11n/ac.

Why is channel planning important in 802.11a?

Proper channel planning minimizes co-channel interference and maximizes network performance.

Are all 5 GHz channels available globally?

No, channel availability varies by country due to local spectrum regulations.

Can devices auto-select 802.11a channels?

Yes, modern devices often auto-select channels based on congestion and interference levels.

How do clients know which channel to use?

Clients scan for available channels and connect to an access point broadcasting a beacon on a valid channel.

What is the channel center frequency?

It is the midpoint frequency of a wireless channel. For example, Channel 36 has a center frequency of 5.180 GHz.

How are 802.11a channels numbered?

Channels are typically numbered as 36, 40, 44, etc., with 20 MHz spacing between adjacent channels.

What are the typical channel numbers for 802.11a?

Common channels include 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, etc.

How far apart are 802.11a channels spaced?

Channels are spaced 20 MHz apart to ensure non-overlapping operation.

What is co-channel interference?

It occurs when multiple access points use the same channel, leading to performance degradation due to contention.

How can co-channel interference be avoided in 802.11a?

By assigning non-overlapping channels to nearby access points during deployment.

Does weather affect 5 GHz channel performance?

Rain and walls can attenuate 5 GHz signals more than 2.4 GHz, but weather effects are generally minimal indoors.

Why is 5 GHz considered less congested than 2.4 GHz?

Fewer devices and more channels in 5 GHz make it less prone to interference compared to the crowded 2.4 GHz band.

What is the typical range of 802.11a channels?

Due to higher frequency, 802.11a range is shorter—typically 30–50 meters indoors depending on obstacles.

Can 802.11a channels be used outdoors?

Yes, but only specific channels and under regulatory rules—especially with DFS and TPC enabled.

What happens if two APs use the same channel?

They must share the medium, causing contention and possibly reducing performance.

What tools help with 802.11a channel planning?

Spectrum analyzers, Wi-Fi scanners, and controller

Topics in this section,

Channel Number (MHz)

Center Frequency (MHz)

Frequency Range

DFS Required

36

5180

5170 – 5190

No

40

5200

5190 – 5210

No

44

5220

5210 – 5230

No

48

5240

5230 – 5250

No

52

5260

5250 – 5270

Yes

56

5280

5270 – 5290

Yes

60

5300

5290 – 5310

Yes

64

5320

5310 – 5330

Yes

100

5500

5490 – 5510

Yes

104

5520

5510 – 5530

Yes

108

5540

5530 – 5550

Yes

112

5560

5550 – 5570

Yes

116

5580

5570 – 5590

Yes

120

5600

5590 – 5610

Yes

124

5620

5610 – 5630

Yes

128

5640

5630 – 5650

Yes

132

5660

5650 – 5670

Yes

136

5680

5670 – 5690

Yes

140

5700

5690 – 5710

Yes

144

5720

5710 – 5730

Yes

149

5745

5735 – 5755

No

153

5765

5755 – 5775

No

157

5785

5775 – 5795

No

161

5805

5795 – 5815

No

165

5825

5815 – 5835

No

  • channel widths

Band Name

Frequency Range (GHz)

Frequency Range (MHz)

Channels

UNII-1

5.150 – 5.250

5150 – 5250

36, 40, 44, 48

UNII-2 (DFS)

5.250 – 5.350

5250 – 5350

52, 56, 60, 64

UNII-2 Extended (DFS)

5.470 – 5.725

5470 – 5725

100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144

UNII-3

5.725 – 5.825

5725 – 5825

149, 153, 157, 161, 165

  • Reference links