802.11h Channels ====================== .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Are 802.11h channels non-overlapping?** Yes, 802.11h channels use 20 MHz bandwidth and are spaced to avoid overlap and minimize interference. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **What regulatory domains require 802.11h?** Primarily the European Union, to comply with ETSI regulations governing 5 GHz spectrum usage. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **Does 802.11h support wider channel widths like 40 MHz?** No, 802.11h channels are 20 MHz wide, similar to 802.11a. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How does Transmit Power Control improve network performance?** By reducing unnecessary power, TPC minimizes interference with neighboring networks and extends device battery life. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **How do 802.11h devices detect radar signals?** Devices monitor specific radar pulse patterns on channels and use detection thresholds defined by regulations. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow **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. .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: shadow Topics in this section, * :ref:`List of channels ` * :ref:`List of channel widths ` * :ref:`List of Bands ` * :ref:`Reference links ` .. _channels_80211h_step4: .. tab-set:: .. tab-item:: List of 802.11h channels ===================== ======================= ====================== ============== 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 ===================== ======================= ====================== ============== .. _channels_80211h_step5: .. tab-set:: .. tab-item:: List of channel widths * channel widths .. _channels_80211h_step6: .. tab-set:: .. tab-item:: List of Bands ======================= ====================== ====================== ============================================================ 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 ======================= ====================== ====================== ============================================================ .. _channels_80211h_step17: .. tab-set:: .. tab-item:: Reference links * Reference links