802.11h Channels

What is 802.11h?

IEEE 802.11h is an amendment to 802.11a that adds Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to meet European regulations in the 5 GHz band.

Which frequency band does 802.11h operate in?

802.11h operates in the 5 GHz band, specifically within UNII frequency ranges to avoid interference with radar systems.

What is Dynamic Frequency Selection (DFS) in 802.11h?

DFS detects radar signals on a channel and automatically switches to another channel to avoid interference.

What is Transmit Power Control (TPC) in 802.11h?

TPC adjusts the transmission power to the minimum necessary level to maintain communication, reducing interference and conserving energy.

How many channels does 802.11h support?

802.11h supports multiple 20 MHz channels in the 5 GHz band, overlapping with 802.11a channel assignments but with DFS/TPC enforcement.

Are 802.11h channels non-overlapping?

Yes, 802.11h channels use 20 MHz bandwidth and are spaced to avoid overlap and minimize interference.

What regulatory domains require 802.11h?

Primarily the European Union, to comply with ETSI regulations governing 5 GHz spectrum usage.

How does DFS impact channel availability in 802.11h?

Channels where radar is detected must be vacated, temporarily reducing the number of usable channels until the radar clears.

What happens when radar is detected on an 802.11h channel?

The access point must switch to a different channel and notify clients of the change to avoid interference.

Does 802.11h support wider channel widths like 40 MHz?

No, 802.11h channels are 20 MHz wide, similar to 802.11a.

How does Transmit Power Control improve network performance?

By reducing unnecessary power, TPC minimizes interference with neighboring networks and extends device battery life.

Are 802.11h features mandatory for all 5 GHz devices?

In regions with DFS/TPC regulatory requirements, yes; devices must implement these features for legal operation.

How do 802.11h devices detect radar signals?

Devices monitor specific radar pulse patterns on channels and use detection thresholds defined by regulations.

Does 802.11h affect latency during channel switching?

Yes, DFS-triggered channel switches introduce a short delay while devices re-synchronize on the new channel.

Can 802.11h coexist with 802.11a networks?

Yes, 802.11h is an extension of 802.11a PHY with added regulatory compliance, so devices are compatible.

How do clients know which channels are available with 802.11h?

Access points broadcast allowed channel lists and handle DFS scans, guiding clients during association.

What is the typical range of 802.11h channels?

Similar to 802.11a, range is typically 30–50 meters indoors due to 5 GHz propagation characteristics.

Is 802.11h still relevant today?

Yes, its DFS and TPC mechanisms form the basis for regulatory compliance in many modern 5 GHz Wi-Fi devices.

What tools help with 802.11h channel planning?

Spectrum analyzers and Wi-Fi scanners that detect radar signals and monitor DFS status assist network design.

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